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A simple equipment and colorimetric method for determination of chloroform in water
Analytica Chimica Acta xxx (xxxx) xxx
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A simple equipment and colorimetric method for determination of chloroform in water Masoud Shariati-Rad*, Fariba Fattahi Department of Analytical Chemistry, Faculty of Chemistry, Razi University, Kermanshah, Iran
h i g h l i g h t s
g r a p h i c a l a b s t r a c t
A simple device was designed for analysis of THMs in water. Trapping and analysis were performed in a single step. The analysis method is based on colorimetry. Water samples were analyzed by the method successfully.
a r t i c l e i n f o
a b s t r a c t
Article history: Received 14 October 2019 Received in revised form 23 November 2019 Accepted 26 November 2019 Available online xxx
Chlorination is a common and successful method for disinfection of water all around the world, especially in developing countries. However, this process can produce trihalomethanes (THMs) byproducts which are carcinogen. The major THM occurring in this process is chloroform. The purpose of this study was to design a simple equipment for colorimetric determination of chloroform in various water samples. The method is based on the colorimetric reaction of chloroform with resorcinol in strong basic medium on a filter paper. Response surface methodology (RSM) was employed to optimize the determination condition. The reagents were immobilized on filter paper and the color change was followed to quantify chloroform without using any analytical instrument. Detection limit and linear range of the proposed method were 0.007 mg/L and 0.011e1.192 mg/L, respectively for analysis of samples with volume of 2.0 L. The method was successfully applied to determine chloroform in different water samples and compared with GC-MS as a standard method. Employing the designed device, purge, trap and analysis steps were performed in a single run which can reduce the uncertainties originated by excessive steps of the analysis. © 2019 Published by Elsevier B.V.
Keywords: Colorimetric method Resorcinol Chloroform Response surface methodology Water
1. Introduction Formation of chlorinated compounds especially trihalomethanes (THMs) in disinfection of water by chlorine reduces
* Corresponding author. E-mail address: [email protected] (M. Shariati-Rad).
water quality because of carcinogenic effect of these compounds [1]. The maximum allowed concentration level of THMs in drinking water based on the recommendation of United State environmental protection agency (USEPA) is 0.080 mg/L. Chloroform is the main product of chlorination of water with harmful effects as mentioned for THMs. Therefore, most of the studies about determination of chlorination byproducts in water focus on determination of chloroform.
https://doi.org/10.1016/j.aca.2019.11.066 0003-2670/© 2019 Published by Elsevier B.V.
Please cite this article as: M. Shariati-Rad, F. Fattahi, A simple equipment and colorimetric method for determination of chloroform in water, Analytica Chimica Acta, https://doi.org/10.1016/j.aca.2019.11.066
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Different analytical methods have been applied to analysis THMs in water samples like chromatography [2,3], liquideliquid extraction (LLE) [4], headspace (HS) technique [5,6], purge and trap (P&T) technique [7,8], liquid-phase microextraction (LPME) [9,10] and solid phase microextraction (SPME) techniques [11e13]. In chromatography, problems such as column stability and critical temperatures for column and injector can be mentioned. In extraction techniques like LLE, HS, P&T, LPME and SPME, for improving sensitivity and selectivity, they are followed by a chromatographic method like GC or GC-MS [14]. In most cases, methods based on purge and trap also need a chromatographic step. On the other hand, colorimetric and spectrophotometric methods mainly based on Fujiwara reaction for determination of THMs have been introduced [15]. The method in most cases does not need any complex instrument and spectrophotometer can be employed for recording the absorbances. Several modifications of the method have been introduced [16e20]. Pyridine used in Fujiwara reaction is a hazardous material. Moreover, the system is biphasic because of the insolubility of alkaline solution of NaOH or KOH in pyridine. Purge and trap techniques which adsorb volatile THM and then desorb it into a GC column are common in the analysis of THMs [4,8,21,22]. Though the technique is very sensitive, the required devices are expensive and need considerable expertise and knowledge of purge and trap, chromatography and MS and the level of the skill of the analyst should be high. In extraction techniques [12,23], the analysis is made in two separate steps. The gap between two steps is where the loss of the analyte may occur. Therefore, in analyzing volatile compounds like THMs, it is desired to shorten the time between extraction and desorption steps. Here, a colorimetric method for chloroform determination is introduced using simple colorimetry in a single step.
1.0 mL of the mixture of resorcinol and sodium hydroxide with optimal concentrations (resorcinol 1.8 M and sodium hydroxide 3.6 M). ASF Thomas DC 12 V Air pump with capacity up to 12 L/min was employed for air purging. A Foodie Puppies aquarium air stone line diffuser (3 inch) was used to distribute the purge gas through the water sample. After purging for in the optimal conditions, the image of the filter paper was taken and R (red), G (green) and B (blue) value of them were extracted by GetData Graph Digitizer software for the analysis and employed as analytical signal. The images were taken by camera of a J7 Samsung Galaxy cellphone with resolution of 13 megapixel. In order to fix conditions for taking different images, paper sensor was set at a fixed position in a box which had been lightened by LED lamps.
2. Experimental
2.4. Real samples
2.1. Materials and solutions
Water samples from swimming pool of Razi University and Khayyam suburban in Kermanshah city were analyzed by the proposed method. Samples were collected in different positions in each case and mixed and homogenized before analysis. Sampling of pool water was performed at 30 cm depth of the pool. However, until performing analysis, samples were contained in air tight glass containers and stored at 4 C before analysis.
Resorcinol (purity 99.5, Merck, Darmstadt, Germany), sodium hydroxide (NaOH), chloroform (purity 99e99.4, Merck, Darmstadt, Germany), dimethyl sulfoxide (DMSO), water (doubly distilled water), and Whatman filter paper No. 4.0 were used in the experiments. A chloroform stock standard solution was prepared with concentration of 14800 mg/L in DMSO and stored at 4 C. Because of the insolubility of the analyte in water, DMSO was chosen for preparing standard solutions of chloroform. Other standard solutions of chloroform were prepared by diluting the stock solution with DMSO. For calibration, working standards were prepared at the different concentration levels by spiking known volumes of the standard in DMSO into doubly distilled water. 2.2. Instrumentation and software The analysis was designed in such a way that it has no need to instrument. For this purpose, a simple device was designed. A sample container of 2.0 L volume was equipped with purge system. The purge system includes an air inlet pipe equipped with a bubble making device and an air outlet pipe (Fig. 1). For the bottle, with cork stopper, two apertures were prepared for purging of air and exit the air containing the analyte. In order to avoid the gas leakage, the place of the apertures were then sealed with glue. In the reaction zone, filter paper which has been cut circularly with diameter of 1.0 cm was inserted. The filter paper was of 4.0 Whatman type. Filter paper was ready for the analysis by impregnation in
2.3. Procedure Calibration was performed by adding different concentrations of chloroform diluted with DMSO to the sample container of the designed device containing 2.0 L of doubly distilled water. Then, the purge system was turned on for 40.0 min, which strips the analyte in the water sample to the reaction zone in the Whatman filter paper impregnated with the reagent (resorcinol 1.8 M and sodium hydroxide 3.6 M). After 40.0 min, the image of the filter paper was taken and digitized to R (red), G (green) and B (blue) indices using Getdata Graph Digitizer. R index was employed in optimization of the factors and to construct the calibration curve. R color index of the images were used as response because of its higher changes during the experiments. For analysis of real samples, the same procedure was used except that 2.0 L of the real water sample was initially placed in the sample container.
3. Results and discussion Variables such as purging time, concentration of resorcinol and concentration of sodium hydroxide should firstly be optimized. These variables are the most influencing factors in the studied system. The flow rate of the purge system was constant at about 12.0 L/min. The reaction between resorcinol and chloroform in the presence of concentrated sodium hydroxide can be shown as: Scheme 1. In the first step, the reported Reimer-Tiemann is performed and 2,4-dihydroxybenzaldehyde is produced [24]. However, in the presence of the excess of resorcinol, a molecule of resorcinol is added to the resulted aldehyde and the final mentioned product is obtained in a reaction called Seliwanoff’s reaction [25]. Due to the large conjugation, this last product is expected to be a dye and in practice, a deep green color on the paper sensor is observed. 3.1. Optimization of time Because of the independency of the purge time with the two other factors, it was decided to optimize time in one at a time
Please cite this article as: M. Shariati-Rad, F. Fattahi, A simple equipment and colorimetric method for determination of chloroform in water, Analytica Chimica Acta, https://doi.org/10.1016/j.aca.2019.11.066
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Fig. 1. Purge and analysis device designed for analysis of water samples for chloroform.
Scheme 1. Reaction between chloroform and resorcinol in the presence of concentrated sodium hydroxide.
approach. For this purpose, the Whatman filter paper No. 4.0 impregnated with resorcinol and NaOH with concentrations of 2.25 and 5.0 M, respectively was placed in its position in the designed device (see Fig. 1). As can be seen in Fig. 2, with the examined times (0, 5, 10, 20, 30 and 40 min), the color intensity of the impregnated Whatman filter paper increases with time. However, the variation in the amount of the color intensity in the higher times slowdowns. Moreover, in order to prevent the prolonging of the analysis time, the experiments were performed at 40.0 min as optimal purging time. 3.2. Response surface methodology (RSM) in optimization of sodium hydroxide and resorcinol concentration
Fig. 2. Optimization of purging time. Conditions: water containing chloroform 0.50 mg/L and impregnated Whatman filter paper with resorcinol 2.25 M and NaOH 5.0 M. Error bars have been calculated for each experiment by three replicates.
To optimize the concentration of sodium hydroxide and resorcinol, RSM was employed [26]. Thirteen experiments with central composite design were designed (Table 1). High (þ1) and low level (1) of concentration of sodium hydroxide were set at 1.0 and 3.0 M, respectively and those for concentration of resorcinol were
set at 0.5 and 2.0 M, respectively. Whatman filter paper was impregnated with different concentrations of sodium hydroxide and resorcinol as indicated in Table 1 and placed in its position in the designed device. After 40 min purging, the image of the
Please cite this article as: M. Shariati-Rad, F. Fattahi, A simple equipment and colorimetric method for determination of chloroform in water, Analytica Chimica Acta, https://doi.org/10.1016/j.aca.2019.11.066
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Table 1 Experiments designed for optimization of resorcinol and sodium hydroxide concentration. For concentration of resorcinol lower and higher levels are 0.5 and 2.0 M, respectively and corresponding levels for concentration of sodium hydroxide are 1.0 and 5.0 M, respectively. The purging time in all experiments is 40.0 min. Experiment No.
NaOH concentration (M) (A)
Resorcinol concentration (M) (B)
Response (R index)
1 2 3 4 5 6 7 8 9 10 11 12 13
3.0 5.0 5.0 1.0 3.0 5.6 0.4 3.0 1.0 3.0 3.0 3.0 3.0
1.25 2.00 0.50 2.00 1.25 1.25 1.25 1.25 0.50 1.25 1.25 2.20 0.30
171.27 164.00 158.89 180.88 175.66 208.25 175.66 192.57 170.76 174.35 154.86 151.27 193.70
Whatman filter paper was taken and digitized to R, G and B indices. In all experiments, chloroform concentration was 0.050 mg/L and temperature was 25.0 ± 0.5 C. Escape of chloroform into the headspace of the container isn’t a matter because it is swiped to the reaction zone. The method is such that this cannot destroy the work. 3.3. Analysis of variance (ANOVA) for elucidation of the factor relationships and relative importance Results of ANOVA have been collected in Table 2. Statistical parameter p shows the significance of the examined factors. Concentration of resorcinol (B) is highly important factor in the studied system in 90% significance level (p < 0.1). Although seems that the concentration of NaOH (A) is not as important as concentration of resorcinol (B), its square term is highly significant (A A). This means that the effect of this factor (A) on the response depends on its level. From the ANOVA results collected in Table 2, it can also be concluded that the examined factors do not interact with each other (p value for the A B term is large, 0.557). Moreover, Pareto chart (Fig. 3) which shows the significance of the factors and corresponding combinations, represents the results collected in Table 2. In Fig. 4, response surface of the studied system has been shown. Curvature in the response surface with variation of concentration of NaOH (A) is clearly observed. Steepness of the response in direction of concentration of resorcinol (B) implies that this factor has significant effects on the response. In all experiments performed, response (R, G and B indices) decreases with increasing the color intensity of the Whatman filter paper. Therefore, condition which reduces the response (R index) is desired. Therefore, in response optimization the purpose was to find conditions in which the response (R index) is lower. Response optimization in such a conditions showed that the response at level of factors A and B equal to 3.6 and 1.8 M, respectively is the lowest.
Fig. 3. Pareto chart of the ANOVA of the experiments of Table 1. The factors are concentration of sodium hydroxide (A) and concentration of resorcinol (B).
Fig. 4. Response surface obtained by the results of ANOVA for the studied system.
Table 2 Results of ANOVA for the designed experiments (Table 1). Term
Coefficient
p-Value
Constant
155.5
0.002
28.9 54.8 80.9 39.8 25.9
0.317 0.084 0.020 0.172 0.557
Concentration Concentration Concentration Concentration Concentration
of of of of of
NaOH (A) Resorcinol (B) NaOH Concentration of NaOH (A A) Resorcinol Concentration of Resorcinol (B B) NaOH Concentration of Resorcinol (A B)
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Table 3 Statistical parameters of the calibration curve obtained by the designed device.
Fig. 5. Calibration curve obtained by the designed device for chloroform in water. Conditions: concentration of resorcinol is 1.80 M and for sodium hydroxide is 3.60 M. Error bars have been calculated for each concentration by three replicates.
Statistics
Value
Slope Intercept R2 Detection limit (mg/L) Linear range (mg/L) F-statistics
234.8 (±2.0) 149.6 (±4.22) 0.9892 0.007 0.011e1.195 1257.1
proposed method can occur with 1,2-dichloroethane. However, it does not a matter of concern because, the main goal of the proposed method is the detection and determination of chlorinated hydrocarbons formed during chlorination of water. On the other hand, the concentration level of the chlorinated hydrocarbons other than chloroform is usually very small. The paper is impregnated by resorcinol and sodium hydroxide. The color of the blank is due to this mixture.
3.4. Calibration
3.6. Analysis of real water samples
In order to find the relation between chloroform concentration and the signal (R index), R index of the images of the impregnated Whatman filter paper after contact with the stream of purge gas containing chloroform was plotted against different standard chloroform concentrations in the sample container of the designed device. In Fig. 5, corresponding images of the filter paper taken for calibration samples along with the calibration curve have been shown. Statistical parameters of the calibration curve have been collected in Table 3. Detection limit (DL) was calculated based on the relation 3Sb/m, where Sb is the standard deviation of the blank determination and m is the slope of the calibration curve. It is clear from data in Table 3 that the analysis based of the designed device resulted in a relatively high sensitivity (low value of DL and relatively high value of the slope). The sensitivity of the method can be attributed to simultaneous preconcentration and reaction of the analyte with the reagents immobilized on the Whatman filter paper. In order to further evaluate the responsibility of the sensor at low concentrations, analysis of a sample containing 0.05 mg/L chloroform was performed three times. The image of the paper along with the blank have been shown in Fig. 6. Moreover, standard deviation of analysis of this sample was calculated. An evident color change can be observed between paper sensor resulted by blank and sample. The color analyses showed that the difference between the mean R index of blank and sample is 30.47 ± 0.68. Sensitivity and precision of the method clearly is observed from these results and Fig. 6. Another important characteristics of the results based on the proposed method is a relatively wide linear range which extends to two orders of magnitude which enables its application to samples with different chloroform content. The robust and the correct linear relationship of the calibration curve was confirmed by the high value of the F statistics of the obtained linear model.
For investigation about the applicability of the chloroform analysis based on the designed device, two real water samples were analyzed. Pool water sample was used in the analysis since for its disinfection chlorination is employed. The results have been reported in Table 5. It was not detected any chloroform in the analyzed samples. Samples were also spiked with known amount of chloroform (0.797 mg/L). For evaluation of the reproducibility of the analysis based on the designed device, three independent analyses were performed. Precision based on the reproducibility were all satisfactory (RSD values in Table 5). The spiked amounts of chloroform were all recovered with low relative errors. This can be related to the selectivity of the proposed method. The recovered amounts of the chloroform are below the spiked ones (relative errors are negative) due to the volatility of chloroform. The analyses were performed on site without any time delay. Moreover, the analysis is based on the evaporation, therefore this problem does not interfere in the work. In order to further evaluate the method, the same water samples without spiking of chloroform were also analyzed by standard chromatographic method of GC-MS after liquid-liquid extraction. The results have also been included in Table 5 for three replicates. In the tap water samples, similar to the proposed method, it was not detected any THM by GC-MS. However, in the swimming pool water, two methods detect THM. Considering the amount determined by GC-MS as the true one, it is concluded that the proposed method performs satisfactory for determination of THMs with relative percent error of 20.8%. Though the error seems that is relatively high, it can be noted that the concentration is very low and lies in the initial parts of the calibration range.
3.5. Interference study In order to examine the selectivity of the proposed method in determination of chloroform, an interference study was performed. Some chlorinated hydrocarbons which probably are produced in chlorination of water along with chloroform, were tested in similar manner as worked for chloroform determination. The results have been collected in Table 4. As the results collected in Table 4 show, the highest interference in determination of chloroform by the
Fig. 6. Images of the paper sensor after three times contact with purge gas stream of blank (b1, b2 and b3) and three times contact with sample containing 0.05 mg/L chloroform (s1, s2 and s3) in optimal conditions (resorcinol 1.8 M and sodium hydroxide 3.6 M).
Please cite this article as: M. Shariati-Rad, F. Fattahi, A simple equipment and colorimetric method for determination of chloroform in water, Analytica Chimica Acta, https://doi.org/10.1016/j.aca.2019.11.066
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Table 4 Interference study of the proposed method for determination of chloroform in water samples. Concentration of chloroforms and interferents are 0.573 mg/L. Image of the filter paper without the chlorinated hydrocarbon (blank)
Compound
Image of the filter paper with the chlorinated hydrocarbon Variation in R color (sample) index
Chloroform
109
Bromoform
Carbon tetrachloride
27
1,2Dichloroethane
106
Dichloromethane
12
Table 5 Results of the analysis of water samples using designed device. Real sample
Spiked (mg/L)
Founda (mg/L)
Standard method (GC-MS, EPA 501.2)a
RSD (%)
Percent relative error
Tap water
0.000 0.797
Not detected 0.679 (10.3)
0.002>
e 10.3
14.8
0.000 0.797
0.029 (5.8) 0.736 (10.7)
0.024 (9.6)
e 5.8 10.7
Swimming pool water
a
6.1
Values in the parentheses are the percent relative standard deviations estimated for three replications.
Table 6 Results of the comparison of determination of chloroform by the designed device and published works based on spectroscopy. Detection Sample limit (mg/L) volume
Total amount of the analyte detected (mg)
Concentration range (mg/L)
Measurement method
Raw material
e
200 mL 2L
e e
14.5 0.17
85 mL 500 mL
1.23 0.085
2.77
200 mL
0.554
0.19
500 mL
0.095
e
Not e mentioned
Spectrophotometry Optical sensor based on Fujiwara reaction Spectrofluorimetry Host-guest complex formation with bcyclodextrin e Spectrophotometry Aggregation of capped AuNPs 0.17e0.98 Spectrophotometry Chloroform, carbon tetrachloride, n-Bu4NOH, 4,4-Dipyridyl 5e500 Optical sensor Tetra-n-butyl ammonium hydroxide, 2,20 dipyridyl, tetraethoxysilane, ethyl cellulose Spectrophotometry Ultrasonic oxidation decolorization of methyl 0.4e20 (CCl4) orange 0.008e0.250 (for total Colorimetry (Image Colorimetric sensor based on Fujiwara reaction trihalomethanes) analysis)
0.007
2.0 L
0.011e1.195
0.014
0.19e1.48
Colorimetry (Image H2O, resorcinol, CHCl3 analysis)
3.7. Comparison with the published works for chloroform determination In order to further evaluate the significance of the analysis of water samples for chloroform based on the designed device, analytical characteristics of spectroscopic methods for determination of chlorinated hydrocarbons were compared with those of the proposed method (Table 6). All of the analysis methods reported in Table 6 require instrument for completing the analysis. However, without any instrumentation, water can be analyzed for chloroform
References [16] [28] [29] [17] [16] [30] [31] Sensors and Actuators B 223 (2016) 1e8 proposed method
in a simple approach and even on site by the current designed device. Since the maximum contaminant level (MCL) for THMs in drinking water is 0.08 mg/L (or 0.05 mg/L for CHCl3) [27], analysis of the water samples for chloroform based on the designed device is recommended. Other reported methods in Table 6 do not have this ability. Therefore, contamination of water with chloroform can simply be detected using the designed device, precisely. Relative to the sensor developed by ref. 31, our sensor is as sensitive as it and requires no heating.
Please cite this article as: M. Shariati-Rad, F. Fattahi, A simple equipment and colorimetric method for determination of chloroform in water, Analytica Chimica Acta, https://doi.org/10.1016/j.aca.2019.11.066
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4. Conclusions The analysis based on the designed device provides a precise, accurate, relatively fast, and low-cost method for determination of chloroform in water. Sensitivity, simplicity and low cost of the analysis based on the proposed method were confirmed upon comparison by spectroscopic methods for determination of chloroform. Based simplicity and low cost of the analysis, the method is superior over chromatographic methods like GC-MS which are routinely used for chloroform analysis. For increasing sensitivity, a purge and trap step was included in the determination process. The method is also recommended for determination of chlorinated hydrocarbons in air samples. Author contributions Masoud Shariati-Rad: Conceptualization, Methodology, Experimental design, Validation, Editing Fariba Fattahi: Data curation, Writing- Original draft preparation. Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper. Appendix A. Supplementary data Supplementary data to this article can be found online at https://doi.org/10.1016/j.aca.2019.11.066. References [1] A.A. Stevens, C.J. Slocum, D.R. Seeger, G.G. Robeck, Chlorination of organics in drinking water, J. Am. Water Work. Assoc. 68 (1976) 615e620. ski, D. Gorlo, B. Makuch, W. Janicki, [2] M. Biziulk, J. Namiesnik, J. Czerwin Z. Polkowska, L. Wolska, Occurrence and determination of organic pollutants sk district, J. Chromatogr., A 733 (1996) in tap and surface waters of the Gdan 171e183. [3] L. Wolska, C. Olszewska, M. Turska, B. Zygmunt, J. Namiesnik, Volatile and semivolatile Organo halogen traces analysis in surface water by direct aqueous injection GC-ECD, Chemosphere 37 (1998) 2645e2651. [4] A.D. Nikolaou, T.D. Lekkas, S.K. Golfinopoulos, M.N. Kostopoulou, Application of different analytical methods for determination of volatile chlorination byproducts in drinking water, Talanta 56 (2002) 717e726. [5] S.K. Golfinopoulos, T.D. Lekkas, A.D. Nokolaou, Comparison of methods for determination of volatile organic compounds in drinking water, Chemosphere 45 (2001) 275e284. [6] J. Kuivinen, H. Johnsson, Determination of trihalomethanes and some chlorinated solvents in drinking water by headspace technique with capillary column gas chromatography, Water Res. 33 (1999) 1201e1208. [7] L. Zoccolillo, L. Amendola, C. Cafaro, S. Insogna, Improved analysis of volatile halogenated hydrocarbons in water by purge-and-trap with gas chromatography and mass spectrometric detection, J. Chromatogr. A 1077 (2005) 181e187. [8] A.S. Allonier, M. Khalanski, A. Bermond, V. Camel, Determination of trihalomethanes in chlorinated sea water samples using a purge-and-trap system coupled to gas chromatography, Talanta 51 (2000) 467e477.
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[9] R.S. Zhao, W.J. Lao, X.B. Xu, Headspace liquid-phase microextraction of trihalomethanes in drinking water and their gas chromatographic determination, Talanta 62 (2004) 751e756. [10] A. Tor, M.E. Aydin, Application of liquid-phase microextraction to the analysis of trihalomethanes in water, Anal. Chim. Acta 575 (2006) 138e143. [11] M.A. Stack, G. Fitzgerald, S. O’Connell, K.J. James, Measurement of trihalomethanes in potable and recreational waters using solid phase micro extraction with gas chromatography-mass spectrometry, Chemosphere 41 (2000) 1821e1826. [12] D.-H. Cho, S.-H. Kong, S.G. Oh, Analysis of trihalomethanes in drinking water using Headspace SPME technique with gas chromatography, Water Res. 37 (2003) 402e408. [13] P.M. San Juan, J.D. Carrillo, M.T. Tena, Fiber selection based on an overall analytical feature comparison for the solid phase microextraction of trihalomethanes from drinking water, J. Chromatogr. A 1139 (2007) 27e35. [14] M.L. Di Gioia, A. Leggio, A. Le Pera, A. Liguori, A. Napoli, C. Siciliano, SPEeGCeMS analysis of chloroform in drinking water, Chromatographia 60 (2004) 319e322. [15] G.A. Lugg, Fujiwara reaction and determination of carbon tetrachloride, chloroform, tetrachloroethane, and trichloroethylene in air, Anal. Chem. 38 (1966) 1532e1536. [16] J.K. Fong, J.K. Pena, Z.-L. Xue, M.M. Alam, U. Sampathkumaran, K. Goswami, Optical sensors for the detection of trace chloroform, Anal. Chem. 87 (2015) 1569e1574. [17] D.L. Rodman, N.A. Carrington, H. Qiu, K. Goswami, Z.-L. Xue, Spectroscopic detection of halocarbons using modified Fujiwara reactions, Anal. Chim. Acta 548 (2005) 143e147. [18] N.A. Carrington, D.L. Rodman, K. Goswami, Z.-L. Xue, Controlled-release polymers for delivery of dipyridyls and tetraalkyl ammonium hydroxide, J. Appl. Polym. Sci. 104 (2007) 1043e1048. [19] M. Bhattacharjee, L. Cherian, V.K. Gupta, Modified Fujiwara reaction for the determination of trichloroacetic acid, Microchem. J. 43 (1991) 109e111. [20] F.P. Milanovich, S.B. Brown, B.W. Colston Jr., P.F. Daley, K.C. Langry, A fiberoptic sensor system for monitoring chlorinated hydrocarbon pollutants, Talanta 41 (1994) 2189e2194. [21] B. Zygmunt, Determination of trihalomethanes in aqueous samples by means of a purge and-trap system with on-sorbent focusing coupled to gas chromatography WithElectron-capture detection, J. Chromatogr. A 725 (1996) 157e163. [22] T.-C. Chen, G.-R. Her, On-line monitoring of trihalomethanes in drinking water using continuous-flow purge and cryofocusing gas chromatography-mass spectrometry, J. Chromatogr. A 927 (2001) 229e235. [23] M.-L. Chen, I.-F. Mao, C.-C. Hsu, Determination of trihalomethanes in drinking water by solid-phase microextraction and gas chromatography with electron capture detection, Toxicol. Environ. Chem. 60 (1997) 39e45. [24] H. Wynberg, The Reimer-Tiemann reaction, Chem. Rev. 60 (1960) 169e184. [25] R. Katoch, Analytical Techniques in Biochemistry and Molecular Biology, Springer ScienceþBusiness Media, LLC, 233 Spring Street, New York, NY 10013, USA, 2011. [26] S.N. Deming, S.L. Morgan, Experimental Design. A Chemometric Approach, second ed., vol. 11, 1993. [27] Trihalomethanes in Drinking-Water, World Health Organization, 2004, p. 30, 2014, http://www.who.int/water_sanitation_health/dwq/chemicals/en/ trihalomethanes. [28] P. Ncube, R.W.M. Krause, B.B. Mamba, Detection of chloroform in water using an azo dye-modified b-cyclodextrin e epichlorohydrin copolymer as a fluorescent probe, Phys. Chem. Earth, Parts A/B/C 67e69 (2014) 79e85. [29] H. Jia, X. Leng, P. Huang, N. Zhao, J. An, H. Wu, Y. Song, Y. Zhu, H. Zhou, A sensitive and selective sensor for the detection of chloroform using biosurfactant ethoxylated phytosterol-capped gold nanoparticles, Mater. Chem. Phys. 202 (2017) 285e288. [30] W. Luo, Z. Chen, L. Zhu, L. Wang, H. Tang, A sensitive spectrophotometric method for determination of carbon tetrachloride with the aid of ultrasonic decolorization of methyl orange, Anal. Chim. Acta 588 (2007) 117e122. [31] E.K. Wujcik, S.E. Duirk, G.G. Chase, C.N. Monty, A visible colorimetric sensor based on nanoporous polypropylene fiber membranes for the determination of trihalomethanes in treated drinking water, Sens. Actuators B 223 (2016) 1e8.
Please cite this article as: M. Shariati-Rad, F. Fattahi, A simple equipment and colorimetric method for determination of chloroform in water, Analytica Chimica Acta, https://doi.org/10.1016/j.aca.2019.11.066
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A simple equipment and colorimetric method for determination of chloroform in water Masoud Shariati-Rad*, Fariba Fattahi Department of Analytical Chemistry, Faculty of Chemistry, Razi University, Kermanshah, Iran
h i g h l i g h t s
g r a p h i c a l a b s t r a c t
A simple device was designed for analysis of THMs in water. Trapping and analysis were performed in a single step. The analysis method is based on colorimetry. Water samples were analyzed by the method successfully.
a r t i c l e i n f o
a b s t r a c t
Article history: Received 14 October 2019 Received in revised form 23 November 2019 Accepted 26 November 2019 Available online xxx
Chlorination is a common and successful method for disinfection of water all around the world, especially in developing countries. However, this process can produce trihalomethanes (THMs) byproducts which are carcinogen. The major THM occurring in this process is chloroform. The purpose of this study was to design a simple equipment for colorimetric determination of chloroform in various water samples. The method is based on the colorimetric reaction of chloroform with resorcinol in strong basic medium on a filter paper. Response surface methodology (RSM) was employed to optimize the determination condition. The reagents were immobilized on filter paper and the color change was followed to quantify chloroform without using any analytical instrument. Detection limit and linear range of the proposed method were 0.007 mg/L and 0.011e1.192 mg/L, respectively for analysis of samples with volume of 2.0 L. The method was successfully applied to determine chloroform in different water samples and compared with GC-MS as a standard method. Employing the designed device, purge, trap and analysis steps were performed in a single run which can reduce the uncertainties originated by excessive steps of the analysis. © 2019 Published by Elsevier B.V.
Keywords: Colorimetric method Resorcinol Chloroform Response surface methodology Water
1. Introduction Formation of chlorinated compounds especially trihalomethanes (THMs) in disinfection of water by chlorine reduces
* Corresponding author. E-mail address: [email protected] (M. Shariati-Rad).
water quality because of carcinogenic effect of these compounds [1]. The maximum allowed concentration level of THMs in drinking water based on the recommendation of United State environmental protection agency (USEPA) is 0.080 mg/L. Chloroform is the main product of chlorination of water with harmful effects as mentioned for THMs. Therefore, most of the studies about determination of chlorination byproducts in water focus on determination of chloroform.
https://doi.org/10.1016/j.aca.2019.11.066 0003-2670/© 2019 Published by Elsevier B.V.
Please cite this article as: M. Shariati-Rad, F. Fattahi, A simple equipment and colorimetric method for determination of chloroform in water, Analytica Chimica Acta, https://doi.org/10.1016/j.aca.2019.11.066
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Different analytical methods have been applied to analysis THMs in water samples like chromatography [2,3], liquideliquid extraction (LLE) [4], headspace (HS) technique [5,6], purge and trap (P&T) technique [7,8], liquid-phase microextraction (LPME) [9,10] and solid phase microextraction (SPME) techniques [11e13]. In chromatography, problems such as column stability and critical temperatures for column and injector can be mentioned. In extraction techniques like LLE, HS, P&T, LPME and SPME, for improving sensitivity and selectivity, they are followed by a chromatographic method like GC or GC-MS [14]. In most cases, methods based on purge and trap also need a chromatographic step. On the other hand, colorimetric and spectrophotometric methods mainly based on Fujiwara reaction for determination of THMs have been introduced [15]. The method in most cases does not need any complex instrument and spectrophotometer can be employed for recording the absorbances. Several modifications of the method have been introduced [16e20]. Pyridine used in Fujiwara reaction is a hazardous material. Moreover, the system is biphasic because of the insolubility of alkaline solution of NaOH or KOH in pyridine. Purge and trap techniques which adsorb volatile THM and then desorb it into a GC column are common in the analysis of THMs [4,8,21,22]. Though the technique is very sensitive, the required devices are expensive and need considerable expertise and knowledge of purge and trap, chromatography and MS and the level of the skill of the analyst should be high. In extraction techniques [12,23], the analysis is made in two separate steps. The gap between two steps is where the loss of the analyte may occur. Therefore, in analyzing volatile compounds like THMs, it is desired to shorten the time between extraction and desorption steps. Here, a colorimetric method for chloroform determination is introduced using simple colorimetry in a single step.
1.0 mL of the mixture of resorcinol and sodium hydroxide with optimal concentrations (resorcinol 1.8 M and sodium hydroxide 3.6 M). ASF Thomas DC 12 V Air pump with capacity up to 12 L/min was employed for air purging. A Foodie Puppies aquarium air stone line diffuser (3 inch) was used to distribute the purge gas through the water sample. After purging for in the optimal conditions, the image of the filter paper was taken and R (red), G (green) and B (blue) value of them were extracted by GetData Graph Digitizer software for the analysis and employed as analytical signal. The images were taken by camera of a J7 Samsung Galaxy cellphone with resolution of 13 megapixel. In order to fix conditions for taking different images, paper sensor was set at a fixed position in a box which had been lightened by LED lamps.
2. Experimental
2.4. Real samples
2.1. Materials and solutions
Water samples from swimming pool of Razi University and Khayyam suburban in Kermanshah city were analyzed by the proposed method. Samples were collected in different positions in each case and mixed and homogenized before analysis. Sampling of pool water was performed at 30 cm depth of the pool. However, until performing analysis, samples were contained in air tight glass containers and stored at 4 C before analysis.
Resorcinol (purity 99.5, Merck, Darmstadt, Germany), sodium hydroxide (NaOH), chloroform (purity 99e99.4, Merck, Darmstadt, Germany), dimethyl sulfoxide (DMSO), water (doubly distilled water), and Whatman filter paper No. 4.0 were used in the experiments. A chloroform stock standard solution was prepared with concentration of 14800 mg/L in DMSO and stored at 4 C. Because of the insolubility of the analyte in water, DMSO was chosen for preparing standard solutions of chloroform. Other standard solutions of chloroform were prepared by diluting the stock solution with DMSO. For calibration, working standards were prepared at the different concentration levels by spiking known volumes of the standard in DMSO into doubly distilled water. 2.2. Instrumentation and software The analysis was designed in such a way that it has no need to instrument. For this purpose, a simple device was designed. A sample container of 2.0 L volume was equipped with purge system. The purge system includes an air inlet pipe equipped with a bubble making device and an air outlet pipe (Fig. 1). For the bottle, with cork stopper, two apertures were prepared for purging of air and exit the air containing the analyte. In order to avoid the gas leakage, the place of the apertures were then sealed with glue. In the reaction zone, filter paper which has been cut circularly with diameter of 1.0 cm was inserted. The filter paper was of 4.0 Whatman type. Filter paper was ready for the analysis by impregnation in
2.3. Procedure Calibration was performed by adding different concentrations of chloroform diluted with DMSO to the sample container of the designed device containing 2.0 L of doubly distilled water. Then, the purge system was turned on for 40.0 min, which strips the analyte in the water sample to the reaction zone in the Whatman filter paper impregnated with the reagent (resorcinol 1.8 M and sodium hydroxide 3.6 M). After 40.0 min, the image of the filter paper was taken and digitized to R (red), G (green) and B (blue) indices using Getdata Graph Digitizer. R index was employed in optimization of the factors and to construct the calibration curve. R color index of the images were used as response because of its higher changes during the experiments. For analysis of real samples, the same procedure was used except that 2.0 L of the real water sample was initially placed in the sample container.
3. Results and discussion Variables such as purging time, concentration of resorcinol and concentration of sodium hydroxide should firstly be optimized. These variables are the most influencing factors in the studied system. The flow rate of the purge system was constant at about 12.0 L/min. The reaction between resorcinol and chloroform in the presence of concentrated sodium hydroxide can be shown as: Scheme 1. In the first step, the reported Reimer-Tiemann is performed and 2,4-dihydroxybenzaldehyde is produced [24]. However, in the presence of the excess of resorcinol, a molecule of resorcinol is added to the resulted aldehyde and the final mentioned product is obtained in a reaction called Seliwanoff’s reaction [25]. Due to the large conjugation, this last product is expected to be a dye and in practice, a deep green color on the paper sensor is observed. 3.1. Optimization of time Because of the independency of the purge time with the two other factors, it was decided to optimize time in one at a time
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Fig. 1. Purge and analysis device designed for analysis of water samples for chloroform.
Scheme 1. Reaction between chloroform and resorcinol in the presence of concentrated sodium hydroxide.
approach. For this purpose, the Whatman filter paper No. 4.0 impregnated with resorcinol and NaOH with concentrations of 2.25 and 5.0 M, respectively was placed in its position in the designed device (see Fig. 1). As can be seen in Fig. 2, with the examined times (0, 5, 10, 20, 30 and 40 min), the color intensity of the impregnated Whatman filter paper increases with time. However, the variation in the amount of the color intensity in the higher times slowdowns. Moreover, in order to prevent the prolonging of the analysis time, the experiments were performed at 40.0 min as optimal purging time. 3.2. Response surface methodology (RSM) in optimization of sodium hydroxide and resorcinol concentration
Fig. 2. Optimization of purging time. Conditions: water containing chloroform 0.50 mg/L and impregnated Whatman filter paper with resorcinol 2.25 M and NaOH 5.0 M. Error bars have been calculated for each experiment by three replicates.
To optimize the concentration of sodium hydroxide and resorcinol, RSM was employed [26]. Thirteen experiments with central composite design were designed (Table 1). High (þ1) and low level (1) of concentration of sodium hydroxide were set at 1.0 and 3.0 M, respectively and those for concentration of resorcinol were
set at 0.5 and 2.0 M, respectively. Whatman filter paper was impregnated with different concentrations of sodium hydroxide and resorcinol as indicated in Table 1 and placed in its position in the designed device. After 40 min purging, the image of the
Please cite this article as: M. Shariati-Rad, F. Fattahi, A simple equipment and colorimetric method for determination of chloroform in water, Analytica Chimica Acta, https://doi.org/10.1016/j.aca.2019.11.066
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Table 1 Experiments designed for optimization of resorcinol and sodium hydroxide concentration. For concentration of resorcinol lower and higher levels are 0.5 and 2.0 M, respectively and corresponding levels for concentration of sodium hydroxide are 1.0 and 5.0 M, respectively. The purging time in all experiments is 40.0 min. Experiment No.
NaOH concentration (M) (A)
Resorcinol concentration (M) (B)
Response (R index)
1 2 3 4 5 6 7 8 9 10 11 12 13
3.0 5.0 5.0 1.0 3.0 5.6 0.4 3.0 1.0 3.0 3.0 3.0 3.0
1.25 2.00 0.50 2.00 1.25 1.25 1.25 1.25 0.50 1.25 1.25 2.20 0.30
171.27 164.00 158.89 180.88 175.66 208.25 175.66 192.57 170.76 174.35 154.86 151.27 193.70
Whatman filter paper was taken and digitized to R, G and B indices. In all experiments, chloroform concentration was 0.050 mg/L and temperature was 25.0 ± 0.5 C. Escape of chloroform into the headspace of the container isn’t a matter because it is swiped to the reaction zone. The method is such that this cannot destroy the work. 3.3. Analysis of variance (ANOVA) for elucidation of the factor relationships and relative importance Results of ANOVA have been collected in Table 2. Statistical parameter p shows the significance of the examined factors. Concentration of resorcinol (B) is highly important factor in the studied system in 90% significance level (p < 0.1). Although seems that the concentration of NaOH (A) is not as important as concentration of resorcinol (B), its square term is highly significant (A A). This means that the effect of this factor (A) on the response depends on its level. From the ANOVA results collected in Table 2, it can also be concluded that the examined factors do not interact with each other (p value for the A B term is large, 0.557). Moreover, Pareto chart (Fig. 3) which shows the significance of the factors and corresponding combinations, represents the results collected in Table 2. In Fig. 4, response surface of the studied system has been shown. Curvature in the response surface with variation of concentration of NaOH (A) is clearly observed. Steepness of the response in direction of concentration of resorcinol (B) implies that this factor has significant effects on the response. In all experiments performed, response (R, G and B indices) decreases with increasing the color intensity of the Whatman filter paper. Therefore, condition which reduces the response (R index) is desired. Therefore, in response optimization the purpose was to find conditions in which the response (R index) is lower. Response optimization in such a conditions showed that the response at level of factors A and B equal to 3.6 and 1.8 M, respectively is the lowest.
Fig. 3. Pareto chart of the ANOVA of the experiments of Table 1. The factors are concentration of sodium hydroxide (A) and concentration of resorcinol (B).
Fig. 4. Response surface obtained by the results of ANOVA for the studied system.
Table 2 Results of ANOVA for the designed experiments (Table 1). Term
Coefficient
p-Value
Constant
155.5
0.002
28.9 54.8 80.9 39.8 25.9
0.317 0.084 0.020 0.172 0.557
Concentration Concentration Concentration Concentration Concentration
of of of of of
NaOH (A) Resorcinol (B) NaOH Concentration of NaOH (A A) Resorcinol Concentration of Resorcinol (B B) NaOH Concentration of Resorcinol (A B)
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Table 3 Statistical parameters of the calibration curve obtained by the designed device.
Fig. 5. Calibration curve obtained by the designed device for chloroform in water. Conditions: concentration of resorcinol is 1.80 M and for sodium hydroxide is 3.60 M. Error bars have been calculated for each concentration by three replicates.
Statistics
Value
Slope Intercept R2 Detection limit (mg/L) Linear range (mg/L) F-statistics
234.8 (±2.0) 149.6 (±4.22) 0.9892 0.007 0.011e1.195 1257.1
proposed method can occur with 1,2-dichloroethane. However, it does not a matter of concern because, the main goal of the proposed method is the detection and determination of chlorinated hydrocarbons formed during chlorination of water. On the other hand, the concentration level of the chlorinated hydrocarbons other than chloroform is usually very small. The paper is impregnated by resorcinol and sodium hydroxide. The color of the blank is due to this mixture.
3.4. Calibration
3.6. Analysis of real water samples
In order to find the relation between chloroform concentration and the signal (R index), R index of the images of the impregnated Whatman filter paper after contact with the stream of purge gas containing chloroform was plotted against different standard chloroform concentrations in the sample container of the designed device. In Fig. 5, corresponding images of the filter paper taken for calibration samples along with the calibration curve have been shown. Statistical parameters of the calibration curve have been collected in Table 3. Detection limit (DL) was calculated based on the relation 3Sb/m, where Sb is the standard deviation of the blank determination and m is the slope of the calibration curve. It is clear from data in Table 3 that the analysis based of the designed device resulted in a relatively high sensitivity (low value of DL and relatively high value of the slope). The sensitivity of the method can be attributed to simultaneous preconcentration and reaction of the analyte with the reagents immobilized on the Whatman filter paper. In order to further evaluate the responsibility of the sensor at low concentrations, analysis of a sample containing 0.05 mg/L chloroform was performed three times. The image of the paper along with the blank have been shown in Fig. 6. Moreover, standard deviation of analysis of this sample was calculated. An evident color change can be observed between paper sensor resulted by blank and sample. The color analyses showed that the difference between the mean R index of blank and sample is 30.47 ± 0.68. Sensitivity and precision of the method clearly is observed from these results and Fig. 6. Another important characteristics of the results based on the proposed method is a relatively wide linear range which extends to two orders of magnitude which enables its application to samples with different chloroform content. The robust and the correct linear relationship of the calibration curve was confirmed by the high value of the F statistics of the obtained linear model.
For investigation about the applicability of the chloroform analysis based on the designed device, two real water samples were analyzed. Pool water sample was used in the analysis since for its disinfection chlorination is employed. The results have been reported in Table 5. It was not detected any chloroform in the analyzed samples. Samples were also spiked with known amount of chloroform (0.797 mg/L). For evaluation of the reproducibility of the analysis based on the designed device, three independent analyses were performed. Precision based on the reproducibility were all satisfactory (RSD values in Table 5). The spiked amounts of chloroform were all recovered with low relative errors. This can be related to the selectivity of the proposed method. The recovered amounts of the chloroform are below the spiked ones (relative errors are negative) due to the volatility of chloroform. The analyses were performed on site without any time delay. Moreover, the analysis is based on the evaporation, therefore this problem does not interfere in the work. In order to further evaluate the method, the same water samples without spiking of chloroform were also analyzed by standard chromatographic method of GC-MS after liquid-liquid extraction. The results have also been included in Table 5 for three replicates. In the tap water samples, similar to the proposed method, it was not detected any THM by GC-MS. However, in the swimming pool water, two methods detect THM. Considering the amount determined by GC-MS as the true one, it is concluded that the proposed method performs satisfactory for determination of THMs with relative percent error of 20.8%. Though the error seems that is relatively high, it can be noted that the concentration is very low and lies in the initial parts of the calibration range.
3.5. Interference study In order to examine the selectivity of the proposed method in determination of chloroform, an interference study was performed. Some chlorinated hydrocarbons which probably are produced in chlorination of water along with chloroform, were tested in similar manner as worked for chloroform determination. The results have been collected in Table 4. As the results collected in Table 4 show, the highest interference in determination of chloroform by the
Fig. 6. Images of the paper sensor after three times contact with purge gas stream of blank (b1, b2 and b3) and three times contact with sample containing 0.05 mg/L chloroform (s1, s2 and s3) in optimal conditions (resorcinol 1.8 M and sodium hydroxide 3.6 M).
Please cite this article as: M. Shariati-Rad, F. Fattahi, A simple equipment and colorimetric method for determination of chloroform in water, Analytica Chimica Acta, https://doi.org/10.1016/j.aca.2019.11.066
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Table 4 Interference study of the proposed method for determination of chloroform in water samples. Concentration of chloroforms and interferents are 0.573 mg/L. Image of the filter paper without the chlorinated hydrocarbon (blank)
Compound
Image of the filter paper with the chlorinated hydrocarbon Variation in R color (sample) index
Chloroform
109
Bromoform
Carbon tetrachloride
27
1,2Dichloroethane
106
Dichloromethane
12
Table 5 Results of the analysis of water samples using designed device. Real sample
Spiked (mg/L)
Founda (mg/L)
Standard method (GC-MS, EPA 501.2)a
RSD (%)
Percent relative error
Tap water
0.000 0.797
Not detected 0.679 (10.3)
0.002>
e 10.3
14.8
0.000 0.797
0.029 (5.8) 0.736 (10.7)
0.024 (9.6)
e 5.8 10.7
Swimming pool water
a
6.1
Values in the parentheses are the percent relative standard deviations estimated for three replications.
Table 6 Results of the comparison of determination of chloroform by the designed device and published works based on spectroscopy. Detection Sample limit (mg/L) volume
Total amount of the analyte detected (mg)
Concentration range (mg/L)
Measurement method
Raw material
e
200 mL 2L
e e
14.5 0.17
85 mL 500 mL
1.23 0.085
2.77
200 mL
0.554
0.19
500 mL
0.095
e
Not e mentioned
Spectrophotometry Optical sensor based on Fujiwara reaction Spectrofluorimetry Host-guest complex formation with bcyclodextrin e Spectrophotometry Aggregation of capped AuNPs 0.17e0.98 Spectrophotometry Chloroform, carbon tetrachloride, n-Bu4NOH, 4,4-Dipyridyl 5e500 Optical sensor Tetra-n-butyl ammonium hydroxide, 2,20 dipyridyl, tetraethoxysilane, ethyl cellulose Spectrophotometry Ultrasonic oxidation decolorization of methyl 0.4e20 (CCl4) orange 0.008e0.250 (for total Colorimetry (Image Colorimetric sensor based on Fujiwara reaction trihalomethanes) analysis)
0.007
2.0 L
0.011e1.195
0.014
0.19e1.48
Colorimetry (Image H2O, resorcinol, CHCl3 analysis)
3.7. Comparison with the published works for chloroform determination In order to further evaluate the significance of the analysis of water samples for chloroform based on the designed device, analytical characteristics of spectroscopic methods for determination of chlorinated hydrocarbons were compared with those of the proposed method (Table 6). All of the analysis methods reported in Table 6 require instrument for completing the analysis. However, without any instrumentation, water can be analyzed for chloroform
References [16] [28] [29] [17] [16] [30] [31] Sensors and Actuators B 223 (2016) 1e8 proposed method
in a simple approach and even on site by the current designed device. Since the maximum contaminant level (MCL) for THMs in drinking water is 0.08 mg/L (or 0.05 mg/L for CHCl3) [27], analysis of the water samples for chloroform based on the designed device is recommended. Other reported methods in Table 6 do not have this ability. Therefore, contamination of water with chloroform can simply be detected using the designed device, precisely. Relative to the sensor developed by ref. 31, our sensor is as sensitive as it and requires no heating.
Please cite this article as: M. Shariati-Rad, F. Fattahi, A simple equipment and colorimetric method for determination of chloroform in water, Analytica Chimica Acta, https://doi.org/10.1016/j.aca.2019.11.066
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4. Conclusions The analysis based on the designed device provides a precise, accurate, relatively fast, and low-cost method for determination of chloroform in water. Sensitivity, simplicity and low cost of the analysis based on the proposed method were confirmed upon comparison by spectroscopic methods for determination of chloroform. Based simplicity and low cost of the analysis, the method is superior over chromatographic methods like GC-MS which are routinely used for chloroform analysis. For increasing sensitivity, a purge and trap step was included in the determination process. The method is also recommended for determination of chlorinated hydrocarbons in air samples. Author contributions Masoud Shariati-Rad: Conceptualization, Methodology, Experimental design, Validation, Editing Fariba Fattahi: Data curation, Writing- Original draft preparation. Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper. Appendix A. Supplementary data Supplementary data to this article can be found online at https://doi.org/10.1016/j.aca.2019.11.066. References [1] A.A. Stevens, C.J. Slocum, D.R. Seeger, G.G. Robeck, Chlorination of organics in drinking water, J. Am. Water Work. Assoc. 68 (1976) 615e620. ski, D. Gorlo, B. Makuch, W. Janicki, [2] M. Biziulk, J. Namiesnik, J. Czerwin Z. Polkowska, L. Wolska, Occurrence and determination of organic pollutants sk district, J. Chromatogr., A 733 (1996) in tap and surface waters of the Gdan 171e183. [3] L. Wolska, C. Olszewska, M. Turska, B. Zygmunt, J. Namiesnik, Volatile and semivolatile Organo halogen traces analysis in surface water by direct aqueous injection GC-ECD, Chemosphere 37 (1998) 2645e2651. [4] A.D. Nikolaou, T.D. Lekkas, S.K. Golfinopoulos, M.N. Kostopoulou, Application of different analytical methods for determination of volatile chlorination byproducts in drinking water, Talanta 56 (2002) 717e726. [5] S.K. Golfinopoulos, T.D. Lekkas, A.D. Nokolaou, Comparison of methods for determination of volatile organic compounds in drinking water, Chemosphere 45 (2001) 275e284. [6] J. Kuivinen, H. Johnsson, Determination of trihalomethanes and some chlorinated solvents in drinking water by headspace technique with capillary column gas chromatography, Water Res. 33 (1999) 1201e1208. [7] L. Zoccolillo, L. Amendola, C. Cafaro, S. Insogna, Improved analysis of volatile halogenated hydrocarbons in water by purge-and-trap with gas chromatography and mass spectrometric detection, J. Chromatogr. A 1077 (2005) 181e187. [8] A.S. Allonier, M. Khalanski, A. Bermond, V. Camel, Determination of trihalomethanes in chlorinated sea water samples using a purge-and-trap system coupled to gas chromatography, Talanta 51 (2000) 467e477.
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Please cite this article as: M. Shariati-Rad, F. Fattahi, A simple equipment and colorimetric method for determination of chloroform in water, Analytica Chimica Acta, https://doi.org/10.1016/j.aca.2019.11.066