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Simultaneous determination of dissolved organic carbon and phosphorus in waters using flame ionization and photometric detectors
Water Res. Vol. 18. No. 5. pp. 555-559. 1984 Printed in Great Britain. All rights reserved
0043-135484 53.00---0.00 Copyri.mlat ~ 1984Pergamon Press Ltd
SIMULTANEOUS D E T E R M I N A T I O N OF DISSOLVED O R G A N I C CARBON A N D PHOSPHORUS IN WATERS USING FLAME IONIZATION AND PHOTOMETRIC DETECTORS KUNIO NAKAJIMA Government Industrial Research Institute, Nagoya, Hirate-cho, Kita-ku, Nagoya-city. 462 Japan (Received August 1983)
Abstract--An apparatus with flame ionization and photometric detectors was assembled for the simultaneous determination of dissolved organic carbon (DOC) and phosphorus (DP) in waters. The optimum operating conditions were described. The long-term precision (relative standard deviation) is 5.8% for DOC and 5.2% for DP. The detection limits are 0.09/~gml -l for DOC and 0.03 ,ugml -~ for DP. The responses for various DOC and DP compounds agreed almost with those obtained by combustion-infrared and persulfate digestion-colorimetric methods, respectively.DOC and DP in several water samples were determined by this method and other methods, and the results obtained by those methods were discussed. Key words--simultaneous determination, dissolved organic carbon and phosphorus, waters, FID and
FPD INTRODUCTION As one of the evaluation of water qualities in environmental research and in optimization of wastewater treatment process, the measurement of total organic carbon (TOC) and phosphorous and nitrogeous substances concerned especially with eutrophicational factors have been the focus of this study. It is understood as the principle for TOC measurement that the CO~ o r CH 4 as the result of an oxidatative or reductive combustion of organic substances has been determined by non-dispersive infrared photometry (Van Hall and Stenger, 1967; Menzel and Vaccaro, 1964; Nakajima, 1978) of flame ionization method (Dobbs et al., 1967; Lysyj and Nelson, 1968; Eggertsen and Stross, 1972), respectively. Phosphorus in various waters have been determined by colorimetry after the various forms of phosphorus have been converted to orthophosphate (APHA, 1975). Digestion methods for the conversion of all the phosphorus to orthophosphate are time-consuming. Flame photometry has been studied by several investigators to determine phosphorus in various waters (Bowman and Beroza, 1968; Aldous et al., 1970; Prager and Seitz, 1975; Julin et al., 1975; Patterson et al., 1978; Chester, 1980; Miyagi et al., 1976). Both organic carbon (OC) and phosphorus (P) have been separately determined in water by the above investigators. For the rapid evaluation of OC and P in waters, the simultaneous determination was used. Frostling (1973) used a modified flame ionization detector (FID) instrument with a flame photometric detector (FPD) for the detection of phosphorylated hydrocarbons in gaseous or aerosol form. Further555
more, a combined F I D - F P D is well established in gas chromatography. There is a possibility that OC and P in waters are simultaneously determined with the combined F I D - F P D . Aldous et al. (1970) and Julin et al. (1975) have recognized that the emission response of phosphorus has been interfered with by several cations in water. Therefore, a means must be devised to eliminate this interference. In this work, a cation exchange resin was used for the elimination of the cation interference, and an ultrasonic nebulizer was used for the introduction of sample aerosol into the FID-FPD. Because of using the cation exchange resin in sample introduction pass, the determination of particulate organic carbon and phosphorus in waters could not be performed. Consequently, only dissolved organic carbon (DOC) and dissolved phosphorus (DP) were determined in this work. This paper describes the signal responses of DOC and DP compounds, the analytical curves, the detection limits, the analytical results of several water samples, etc. EXPERIMENTAL Apparatus
Table 1 shows the instrument and operating conditions used in this work. Figure 1 shows the schematic diagram of the apparatus set up with the instrument listed in Table I. In this burner system, FPD in a Hitachi 163 gas chromatograph was reconstructed to detect flame ionization current. Sample solution was introduced into the nebulization cell through the ion-exchangecolumn with the peristaltic pump. The ion-exchange column was used to eliminate the interference of cations such as Na ÷, K-, etc. on the phosphorus molecular emission at 526 nm. Sample aerosol was introduced into the FID--FPD by the flow of N., carrier gas and
556
Kvyto NAKAJIMA 8
--
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Sample Fig. I. Schematic diagram of the apparatus. (I) peristaltic pump; (2) cation-exchange resin column; (3) nebulization cell; (4) cyclic pump; (5) thermostat (5°C); (6) heater (I ]0°C); (7) FPD; (8) FID; (9) high voltage source; (I0) amplifier; (I I) integrator; (12) recorder (2 pens); (13) nebulizer.
interacted with N2-O,-H 2 flame. DOC and DP were detected with the FID-FPD, respectively, and the signals from the detectors were amplified• Because the direct tracings of signals for DOC and P were unstable (Fig. 2), the signals were integrated for a constant time (5 s) with the integrators. The integrated values were recorded with the two-pen strip chart recorder.
Reagents The standard solutions of DOC (1000/~g ml -~) and DP ( 1000 # g ml - i) were prepared by dissolving glucose (reagent grade) and potassium dihydrogen phosphate (reagent grade) in distilled water, respectively. Other DOC and DP compounds used were prepared freshly for every experiment to minimize the hydrolysis of the compounds to orthophosphate• All other chemicals used were reagent grade•
In order to get the o p t i m u m flow rate of N2-O2-H,. flame, the flow rates of N2, 02 a n d H, were investigated. Figure 3 shows the effect of N2 flow rate on the F I D and F P D responses. The flow rate of N 2 varied between 70-130 ml m i n - ~. Those of 02 and H 2 were held at 40 a n d 100 ml m i n - ' , respectively. The highest F I D signal intensity was o b t a i n e d at the N, flow rate o f 7 0 m l m i n -~. Similarly, the signal-tobackground intensity ratio was highest at 7 0 m l m i n - L The b a c k g r o u n d intensity was determ i n e d from the F I D response o b t a i n e d with distilled water. A n increasing N2 flow rate increased the rate of sample i n t r o d u c t i o n into the burner. However, the F I D signal intensity decreased with increasing N_,
RESULTS AND DISCUSSION ] /.ig rnl-I ; phosphorus
Operating conditions In the F I D - F P D system, the gas flow rates of N2, 02 a n d H2 are i m p o r t a n t p a r a m e t e r s affecting the responses o f O C a n d P. O p t i m u m o p e r a t i n g conditions for the d e t e r m i n a t i o n o f D O C a n d D P were established using a sample solution c o n t a i n i n g each 10 p g m l - ' o f D O C a n d DP.
Table 1. Instruments and operating conditions FPD: HTV R-628 photomultiptier; photomul, applied voltage 750V; interference filter 526 am FID: Hitachi 163 Gas chromatograph; applied potential 90V Burner: All quartz, 10(o.d.)x 50(H)mm Nebulization cell: Pyrex glass, 25 (o.d.) x 300 (H) mm Ultrasonic nebulizer: Devilbiss model 35B, 1.3 MHz Rate of sample introduction into the burner: 40 ~ulrainSample uptake: Tokyo Rikakikai model MP. peristaltic pump Sample uptake rate: 3.5 ml rain -t Sample feeding tube: Teflon, 2.0 (o.d.)x 1.0(i.d.)mm Cation-exchange resin: Dowex 50W-X8, 200-400 mesh Volume of cation-exchange column: 4 ml Gas controller: Hitachi 163 Gas chromatograph Gas flow rate: 80mlN~min -I, 40mlO~ rain-', 100ml H:min -~ Integrator: Rikadenki Kosyo model COMP. UNIT Recorder: National model UP-654A (2 pens)
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Fig. 2. Direct tracings of signals for DOC and DP.
Simultaneous determination of DOC and DP in waters
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Fig. 3. The effect of Nz flow rate on the FID and FPD response. (C)) FID; (Q) FPD. flow rate. It was understood that the flame temperature decreased with increasing N2 flow rate, and the sensitivity of the FID response lowered. The FPD signal intensity showed a maximum at a N,_ flow rate of 9 0 m l m i n - L The signal-tobackground intensity ratio was also highest at 9 0 m l m i n - L From the results mentioned above, it was found that optimum N2 flow rates for the FID were different from that of FPD. Therefore, in this work, the N 2 flow rate of 80 ml min- ~was used as an optimum operating conditions for the FID--FPD. At the flow rate of 8 0 m l m i n -t, the rate of sample introduction into the burner was 40 yl min-L Sample introduction volume was about 1.I~ of sample uptake volume. Figure 4 shows the effect of 02 and H2 flow rates on the FPD response. The flow rates of 02 and H 2 varied between 35-50 and 80-120mlmin -t, respectively. N2 flow rate was held at 80 ml min- m.The FPD response was highest at the flow rates of 40 ml O., min -~ and 120 ml H2 min -~. However, the signal-to-background intensity ratio was highest at
557
40 ml 02 min -~ and 100 ml H., min -~. Although the FID response was highest at 45 mlOzmin -t and 100 ml H, min-~, the signal-to-background intensity ratio was highest at 40 ml O: min- ~ and 100 ml H, min-L Therefore, the optimum flow rates of N 2, 02 and H, were 80, 40 and 100mlmin -I, respectively. The operating conditions are summarized in Table 1. Precision
A solution containing 10/~gDOCmI-~ and l # g D P m l -~ was repeatedly measured at 10min intervals. Short-term stability was evaluated from precision (relative standard deviation) on 6 replicate measurements for l b . The precision was 1.7~o for DOC and 0.6~ for DP. Long-term stability was evaluated from precision on repeated measurements over 10 h (60 times measurements). The precision was 5.8~ for DOC and 5.2~o for DP. From these results, short-term precision was better than long-term precision. It is considered that the signal drift occurs over a period of 10 h.
Analytical curves
The analytical curves for DOC and DP were constructed in the concentration ranges of 0.5-300 and 0.05-30pgml -~, respectively. The curves for DOC and DP were linear in the ranges of 1-300 and 0.1-30/~g ml -~, respectively. The concentrations over 300/~g DOC ml -~ and 30/.zg DP ml -~ could not be measured owing to the limitations of the functions of the apparatus used in this work. Therefore, it was necessary to dilute sample solutions for determining concentrations above 300pg DOC ml-t and/or 30pg D P m I - L Detection limits
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The detection limits of DOC and DP were determined using a solution containing 10/~g DOC ml -~ and 1 yg DP ml-L The detection limit was defined as the concentration which gives a signal intensity equal to twice the standard deviation of the background intensity. The signal intensity obtained with distilled water was used as the background intensity. The detection limits obtained were 0.09 yg ml-~ for DOC and 0.03/~gml -t for DP. This value for DOC was lower than obtained by Eggertsen and Stross (1972). However, the detection limit of DP obtained in this work was higher than those obtained by other investigators (Bowman and Beroza, 1968; Aldous et al., 1970; Julin et al., 1975). This must be due to the difference in the rates of sample introduction into the burner. Sample solutions were introduced into the burners at the rates of 2-10ml min-t; however, the author introduced the sample solution into the burner at the rate of 40#1 min -I. As the purpose of this work was to determine simultaneously DOC and DP in water, a small burner system with FID and
558
KUNIO NAKAJIMA
FPD was constructed. Judging from the detection limits of DOC and DP obtained in this work, the apparatus must be practically usable for the simultaneous determination of DOC and DP in waters.
Responses of DOC and DP for ~'arious DOC and DP compounds The responses per unit DOC and DP were examined for various kinds of DOC and DP compounds and the results are listed in Table 2. A solution containing glucose and potassium dihydrogen phosphate was used as standard response for DOC and DP, respectively. The found values shown in Table 2 were expressed as values to be relative to the standards. Each found value in Table 2 was the average of five measurements. To compare the values obtained by this method with those obtained by other methods, the DOC and DP compounds were also measured with a OIC 524 TOC analyzer (combustion-infrared method, Method I) and a Technicon Auto Analyzer II (persulfate digestion-colorimetric method, Method II), respectively. The values obtained by Method I and II are also shown in Table 2. DOC and DP in waters are present as various organic or inorganic compounds. From the viewpoint of DOC and DP determination, the same responses per unit carbon and phosphorus should be obtained for all compounds. Perkins et al. (1962) have reported that a variety of functional groups in organic compounds affects the response of OC in a FID; hydrocarbons give higher response than organic compounds with the groups containing oxygen, nitrogen or halogens. As shown in Table 2, the difference in
responses of 8 organic compounds was small. All the compounds tested in this study contain oxygen, nitrogen or halogens. Though the compounds containing oxygen, nitrogen or halogens give a lower degree of effect of oxygen, nitrogen or halogens than hydrocarbons, the responses of DOC in FID may be low. Therefore, the found values for DOC must agree well with theoretical values and the values obtained by Method I. When water samples containing hydrocarbons are analyzed by this method, the higher response of hydrocarbons must be considered. The found values for DP agreed well with the theoretical values except for sodium pyrophosphate. The found value of DP for sodium pyrophosphate was somewhat higher than the theoretical value. However, the found value agreed well with the value obtained by Method II. Since a part of the reagent used in this work probably differed from sodium pyrophosphate, the results mentioned above might be obtained.
Analysis of practical water samples DOC and DP in water samples were determined by this method. Each sample was filtered through a 0.45-~m membrane filter in a Swinny holder, and the filtrates were introduced into the nebulizer cell with peristaltic pump. Table 3 shows the analytical results for DOC and DP in the samples. The values of DOC and DP obtained by Method I and II are also shown in Table 3. The values for DC obtained by this method agreed approximately with those obtained by Method II. Patterson et al. (1978) have mentioned that the FPD selectivity ratio of P:S is high at the low concentrations of sulfur; the FPD response of P is
Table 2. Responses of DOC and DP for various compounds containing DOC and DP Found (/2gml -t) Theoretical (/~gml -I) This work Method 1" MethodIIt Compound DOC DP DOC DP DOC DP Glucose, C6Htz06 Fluoroacetamide, C2H4ONF Acetic acid, CzH40z Sodium oxalate, NazC204 Potassium dihydrogen phosphate, KH2PO4 Sodium hypophosphate, NaHzPO2- HzO Sodium phosphate, dibasic, Na2HPO3. 5HzO Sodium tripolyphosphate, NasPjOi0 Sodium pyrophosphate, Na4P20 ~. 10H20 Sodium metaphosphate, (NaPOj), Glucose phosphate, dipotassium salt, C6HtIK2OgP.2HzO Disodium phenyl phosphate, C6HsNa2PO,.2H20 Adenosine triphosphate, disodium salt, C10Hi4NsOtjP3Na2.3H,.O Sodium glycerophosphate, CjHTOsPNa2- 5.5H20 *Combustion-infrared method. tPersulfate digestion-colorimetric method.
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Simultaneous determination of DOC and DP in waters
559
Table 3. Analytical results (in/~g mt-~) of practical water samples This work Method [+ Method 11.~ Sample DOC DP DOC DP Raw municipal wastewater 120 4.2 130 z.5 Water treated by activated sludge process 25 1.4 29 1.5 Water treated by flocculation-sedimentation process 13 0.4 9 0.4 Water treated by flocculation-sedimentation process 9 1.6 7 1.6 *Each sample was taken from the effluent of flocculation-sedimentation process for industrial v,astewaters containing phosphate; samples (I-2) were withdrawn at different times. ~'Combustion-infrared method. ~Persulfate digestion-colorimetric method.
little affected by $2 molecular emission. As the conc e n t r a t i o n s o f sulfate ion in the practical samples were low, the interference o f sulfur on the F P D response was little observed. However, the a g r e e m e n t between the values for D O C o b t a i n e d by this M e t h o d I was less satisfactory. In the case of sample Nos 1 and 2, the values o b t a i n e d by this m e t h o d were lower t h a n those o b t a i n e d by M e t h o d I. This m a y be due to the difference in the degree of a d s o r p t i o n o f glucose used as a s t a n d a r d solution of D O C a n d organic c o m p o u n d s present in the practical waters on the cation-exchange resin column. In the case o f sample Nos 3 a n d 4, those o b t a i n e d by this m e t h o d were higher t h a n those o b t a i n e d M e t h o d I. Sample Nos 3 a n d 4 m a y contain small a m o u n t s og hydrocarbons. A l t h o u g h the d e t e r m i n a t i o n of D O C a n d D P in a sea water was examined, the d e t e r m i n a t i o n was impossible because the exchange capacity of the c o l u m n in the a p p a r a t u s was too small to a d s o r b the total a m o u n t s of cations in a 1 0 m i n run o f water. T h e increase of the c o l u m n volume m a y be able to determine D O C a n d D P of sea water. C o n c o m i t a n t l y , since the time taken to introduce the sea water into the b u r n e r is prolonged, this m e t h o d becomes timeconsuming. Therefore, this m e t h o d seems to be suitable for the analysis of water samples with low salinity such as river water, lake water, municipal water a n d some of industrial wastewater.
Acknowledgements--The author is pleased to acknowledge Professor Hiroshi Sunahara, Department of Environmental Science, Faculty of Engineering, Hiroshima University. His interest, help and enthusiasm were responsible for this investigation. Thanks are due to Dr Toshio Ishizuka, Government Industrial Research Institute Nagoya, for his critical reading of the manuscript.
REFERENCES
Aldous K. M., Dagnall R. M. and West T. S. (1970) The flame-spectroscopic determination of sulfur and phosphorus in organic and aqueous matrices by using a simple filter photometer. Analyst 95, 417-424.
APHA (1975) Standard Methods for Examination of Water and Wastewater, 14th Edition. American Public Health Association, Washington. DC. Bowman M. C. and Beroza M. (1968) Gas chromatographic detector for simultaneous sensing of phosphorus- and sulfur-containing compounds by flame photometry. Anal. Chem. 40, 1448-1452. Chester T. L. (1980) Flame geometry effects on the flame photometric measurement of phosphorus in aqueous/organic liquids. Anal. Chem. 52, 638-642. Dobbs R. A., Wise R. H. and Dean R. B. (1967) Measurements of organic carbon in water using the hydrogenflame ionization detector. Anal. Chem. 39, 1255-1258. Eggertsen F. T. and Stross F. H. (1972) Flame detection method for determining organic carbon in water. Anal. Chem. 44, 709-714. Frostling H. (1973) Continuous detection of vapours and aerosols of organophosphorus compounds by flame ionization-flame emission. J. Phys. E: Scient. Instr. 6, 863-867. Julin B. G., Vandenvorn H. W. and Kirkland J. J. (1975) Selective flame emission detection of phosphorus and sulfur in high-performance liquid chromatography. J. Chromat. 112, 443--453. Lysyj I. and Nelson K. H. (1968) Direct gas chromatographic method for nonvolatile organics in aqueous solutions. J. Gas Chromat. 6, 106-109. Menzel D. W. and Vaccaro R. F. (1964) The measurement of dissolved organic and particulate carbon in sea water. Limnol. Oceanog. 9, 138-142. Miyagi H., Kawazoe K., Takata Y., Kamo T. and Arikawa Y. (1976) Determination of phosphate in water using flame photometry (Japanese). Paper Presented at 34th National Meeting of the Japan Chemical Society, 4T19, Tokyo. Nakajima K. (1978) Determination of organic carbon in water by chemical oxidation method (Japanese). Bunseki Kagaku 27, 48-52. Patterson P. L., Howe R. L. and Abu-Shumays A. (1978) Dual-flame photometric detector for sulfur and phosphorus compounds in gas chromatograph effluents. Anal. Chem. 50, 339-344. Perkins G. Jr, Rouayheb G. M. and Lively L. D. (1962) Response of the gas chromatographic flame ionization detector to different functional groups. In Gas Chromatography (Edited by Brenner N., Callen J. E. and Weiss M. D.), pp. 269-285. Academic Press, New York. Prager M. J. and Seitz W. R. (1975) Flame emission photometer for determining phosphorus in air and natural waters. Anal. Chem. 47, 148-151. Van Hall C. E. and Stenger V. A. (1967) An instrumental method for rapid determination of carbonate and total carbon in solutions. Anal. Chem. 39, 503-507.
0043-135484 53.00---0.00 Copyri.mlat ~ 1984Pergamon Press Ltd
SIMULTANEOUS D E T E R M I N A T I O N OF DISSOLVED O R G A N I C CARBON A N D PHOSPHORUS IN WATERS USING FLAME IONIZATION AND PHOTOMETRIC DETECTORS KUNIO NAKAJIMA Government Industrial Research Institute, Nagoya, Hirate-cho, Kita-ku, Nagoya-city. 462 Japan (Received August 1983)
Abstract--An apparatus with flame ionization and photometric detectors was assembled for the simultaneous determination of dissolved organic carbon (DOC) and phosphorus (DP) in waters. The optimum operating conditions were described. The long-term precision (relative standard deviation) is 5.8% for DOC and 5.2% for DP. The detection limits are 0.09/~gml -l for DOC and 0.03 ,ugml -~ for DP. The responses for various DOC and DP compounds agreed almost with those obtained by combustion-infrared and persulfate digestion-colorimetric methods, respectively.DOC and DP in several water samples were determined by this method and other methods, and the results obtained by those methods were discussed. Key words--simultaneous determination, dissolved organic carbon and phosphorus, waters, FID and
FPD INTRODUCTION As one of the evaluation of water qualities in environmental research and in optimization of wastewater treatment process, the measurement of total organic carbon (TOC) and phosphorous and nitrogeous substances concerned especially with eutrophicational factors have been the focus of this study. It is understood as the principle for TOC measurement that the CO~ o r CH 4 as the result of an oxidatative or reductive combustion of organic substances has been determined by non-dispersive infrared photometry (Van Hall and Stenger, 1967; Menzel and Vaccaro, 1964; Nakajima, 1978) of flame ionization method (Dobbs et al., 1967; Lysyj and Nelson, 1968; Eggertsen and Stross, 1972), respectively. Phosphorus in various waters have been determined by colorimetry after the various forms of phosphorus have been converted to orthophosphate (APHA, 1975). Digestion methods for the conversion of all the phosphorus to orthophosphate are time-consuming. Flame photometry has been studied by several investigators to determine phosphorus in various waters (Bowman and Beroza, 1968; Aldous et al., 1970; Prager and Seitz, 1975; Julin et al., 1975; Patterson et al., 1978; Chester, 1980; Miyagi et al., 1976). Both organic carbon (OC) and phosphorus (P) have been separately determined in water by the above investigators. For the rapid evaluation of OC and P in waters, the simultaneous determination was used. Frostling (1973) used a modified flame ionization detector (FID) instrument with a flame photometric detector (FPD) for the detection of phosphorylated hydrocarbons in gaseous or aerosol form. Further555
more, a combined F I D - F P D is well established in gas chromatography. There is a possibility that OC and P in waters are simultaneously determined with the combined F I D - F P D . Aldous et al. (1970) and Julin et al. (1975) have recognized that the emission response of phosphorus has been interfered with by several cations in water. Therefore, a means must be devised to eliminate this interference. In this work, a cation exchange resin was used for the elimination of the cation interference, and an ultrasonic nebulizer was used for the introduction of sample aerosol into the FID-FPD. Because of using the cation exchange resin in sample introduction pass, the determination of particulate organic carbon and phosphorus in waters could not be performed. Consequently, only dissolved organic carbon (DOC) and dissolved phosphorus (DP) were determined in this work. This paper describes the signal responses of DOC and DP compounds, the analytical curves, the detection limits, the analytical results of several water samples, etc. EXPERIMENTAL Apparatus
Table 1 shows the instrument and operating conditions used in this work. Figure 1 shows the schematic diagram of the apparatus set up with the instrument listed in Table I. In this burner system, FPD in a Hitachi 163 gas chromatograph was reconstructed to detect flame ionization current. Sample solution was introduced into the nebulization cell through the ion-exchangecolumn with the peristaltic pump. The ion-exchange column was used to eliminate the interference of cations such as Na ÷, K-, etc. on the phosphorus molecular emission at 526 nm. Sample aerosol was introduced into the FID--FPD by the flow of N., carrier gas and
556
Kvyto NAKAJIMA 8
--
3 :::..,.
2
'
FI2
o
[ -i'i--]
Drain
Sample Fig. I. Schematic diagram of the apparatus. (I) peristaltic pump; (2) cation-exchange resin column; (3) nebulization cell; (4) cyclic pump; (5) thermostat (5°C); (6) heater (I ]0°C); (7) FPD; (8) FID; (9) high voltage source; (I0) amplifier; (I I) integrator; (12) recorder (2 pens); (13) nebulizer.
interacted with N2-O,-H 2 flame. DOC and DP were detected with the FID-FPD, respectively, and the signals from the detectors were amplified• Because the direct tracings of signals for DOC and P were unstable (Fig. 2), the signals were integrated for a constant time (5 s) with the integrators. The integrated values were recorded with the two-pen strip chart recorder.
Reagents The standard solutions of DOC (1000/~g ml -~) and DP ( 1000 # g ml - i) were prepared by dissolving glucose (reagent grade) and potassium dihydrogen phosphate (reagent grade) in distilled water, respectively. Other DOC and DP compounds used were prepared freshly for every experiment to minimize the hydrolysis of the compounds to orthophosphate• All other chemicals used were reagent grade•
In order to get the o p t i m u m flow rate of N2-O2-H,. flame, the flow rates of N2, 02 a n d H, were investigated. Figure 3 shows the effect of N2 flow rate on the F I D and F P D responses. The flow rate of N 2 varied between 70-130 ml m i n - ~. Those of 02 and H 2 were held at 40 a n d 100 ml m i n - ' , respectively. The highest F I D signal intensity was o b t a i n e d at the N, flow rate o f 7 0 m l m i n -~. Similarly, the signal-tobackground intensity ratio was highest at 7 0 m l m i n - L The b a c k g r o u n d intensity was determ i n e d from the F I D response o b t a i n e d with distilled water. A n increasing N2 flow rate increased the rate of sample i n t r o d u c t i o n into the burner. However, the F I D signal intensity decreased with increasing N_,
RESULTS AND DISCUSSION ] /.ig rnl-I ; phosphorus
Operating conditions In the F I D - F P D system, the gas flow rates of N2, 02 a n d H2 are i m p o r t a n t p a r a m e t e r s affecting the responses o f O C a n d P. O p t i m u m o p e r a t i n g conditions for the d e t e r m i n a t i o n o f D O C a n d D P were established using a sample solution c o n t a i n i n g each 10 p g m l - ' o f D O C a n d DP.
Table 1. Instruments and operating conditions FPD: HTV R-628 photomultiptier; photomul, applied voltage 750V; interference filter 526 am FID: Hitachi 163 Gas chromatograph; applied potential 90V Burner: All quartz, 10(o.d.)x 50(H)mm Nebulization cell: Pyrex glass, 25 (o.d.) x 300 (H) mm Ultrasonic nebulizer: Devilbiss model 35B, 1.3 MHz Rate of sample introduction into the burner: 40 ~ulrainSample uptake: Tokyo Rikakikai model MP. peristaltic pump Sample uptake rate: 3.5 ml rain -t Sample feeding tube: Teflon, 2.0 (o.d.)x 1.0(i.d.)mm Cation-exchange resin: Dowex 50W-X8, 200-400 mesh Volume of cation-exchange column: 4 ml Gas controller: Hitachi 163 Gas chromatograph Gas flow rate: 80mlN~min -I, 40mlO~ rain-', 100ml H:min -~ Integrator: Rikadenki Kosyo model COMP. UNIT Recorder: National model UP-654A (2 pens)
50 k~g mL- I cordon
: Sornple anjechon
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d
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÷ I
iO
. . . .
I
5
. . . .
I
O
Time (rain)
Fig. 2. Direct tracings of signals for DOC and DP.
Simultaneous determination of DOC and DP in waters
8 ~n "~ 40
-\
g
\
Q,,
_o
,
3 ~ o~ 2 ~'
'N 2C
g
/
,,
fO
co
I
l
?'0
90 N~
flow
I I I0
rate
(ml
l
co
130
rain -~)
Fig. 3. The effect of Nz flow rate on the FID and FPD response. (C)) FID; (Q) FPD. flow rate. It was understood that the flame temperature decreased with increasing N2 flow rate, and the sensitivity of the FID response lowered. The FPD signal intensity showed a maximum at a N,_ flow rate of 9 0 m l m i n - L The signal-tobackground intensity ratio was also highest at 9 0 m l m i n - L From the results mentioned above, it was found that optimum N2 flow rates for the FID were different from that of FPD. Therefore, in this work, the N 2 flow rate of 80 ml min- ~was used as an optimum operating conditions for the FID--FPD. At the flow rate of 8 0 m l m i n -t, the rate of sample introduction into the burner was 40 yl min-L Sample introduction volume was about 1.I~ of sample uptake volume. Figure 4 shows the effect of 02 and H2 flow rates on the FPD response. The flow rates of 02 and H 2 varied between 35-50 and 80-120mlmin -t, respectively. N2 flow rate was held at 80 ml min- m.The FPD response was highest at the flow rates of 40 ml O., min -~ and 120 ml H2 min -~. However, the signal-to-background intensity ratio was highest at
557
40 ml 02 min -~ and 100 ml H., min -~. Although the FID response was highest at 45 mlOzmin -t and 100 ml H, min-~, the signal-to-background intensity ratio was highest at 40 ml O: min- ~ and 100 ml H, min-L Therefore, the optimum flow rates of N 2, 02 and H, were 80, 40 and 100mlmin -I, respectively. The operating conditions are summarized in Table 1. Precision
A solution containing 10/~gDOCmI-~ and l # g D P m l -~ was repeatedly measured at 10min intervals. Short-term stability was evaluated from precision (relative standard deviation) on 6 replicate measurements for l b . The precision was 1.7~o for DOC and 0.6~ for DP. Long-term stability was evaluated from precision on repeated measurements over 10 h (60 times measurements). The precision was 5.8~ for DOC and 5.2~o for DP. From these results, short-term precision was better than long-term precision. It is considered that the signal drift occurs over a period of 10 h.
Analytical curves
The analytical curves for DOC and DP were constructed in the concentration ranges of 0.5-300 and 0.05-30pgml -~, respectively. The curves for DOC and DP were linear in the ranges of 1-300 and 0.1-30/~g ml -~, respectively. The concentrations over 300/~g DOC ml -~ and 30/.zg DP ml -~ could not be measured owing to the limitations of the functions of the apparatus used in this work. Therefore, it was necessary to dilute sample solutions for determining concentrations above 300pg DOC ml-t and/or 30pg D P m I - L Detection limits
//
3
I
\ •
n"
II I
%
..%
",
/
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/
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iI i /
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5
2
50 co
f
~o
1 35 02
e~
I 40 flow
rate
o ~ e
I 4,5
o~
I .50
( m L rain - I )
Fig. 4. The effect of 02 and H2 flow rates on the FPD response. (O) 80 ml H2min-t; (A) 100 ml H2min-Z; ( n ) 120 m l H., min- t. W.P.. 18~5~D
The detection limits of DOC and DP were determined using a solution containing 10/~g DOC ml -~ and 1 yg DP ml-L The detection limit was defined as the concentration which gives a signal intensity equal to twice the standard deviation of the background intensity. The signal intensity obtained with distilled water was used as the background intensity. The detection limits obtained were 0.09 yg ml-~ for DOC and 0.03/~gml -t for DP. This value for DOC was lower than obtained by Eggertsen and Stross (1972). However, the detection limit of DP obtained in this work was higher than those obtained by other investigators (Bowman and Beroza, 1968; Aldous et al., 1970; Julin et al., 1975). This must be due to the difference in the rates of sample introduction into the burner. Sample solutions were introduced into the burners at the rates of 2-10ml min-t; however, the author introduced the sample solution into the burner at the rate of 40#1 min -I. As the purpose of this work was to determine simultaneously DOC and DP in water, a small burner system with FID and
558
KUNIO NAKAJIMA
FPD was constructed. Judging from the detection limits of DOC and DP obtained in this work, the apparatus must be practically usable for the simultaneous determination of DOC and DP in waters.
Responses of DOC and DP for ~'arious DOC and DP compounds The responses per unit DOC and DP were examined for various kinds of DOC and DP compounds and the results are listed in Table 2. A solution containing glucose and potassium dihydrogen phosphate was used as standard response for DOC and DP, respectively. The found values shown in Table 2 were expressed as values to be relative to the standards. Each found value in Table 2 was the average of five measurements. To compare the values obtained by this method with those obtained by other methods, the DOC and DP compounds were also measured with a OIC 524 TOC analyzer (combustion-infrared method, Method I) and a Technicon Auto Analyzer II (persulfate digestion-colorimetric method, Method II), respectively. The values obtained by Method I and II are also shown in Table 2. DOC and DP in waters are present as various organic or inorganic compounds. From the viewpoint of DOC and DP determination, the same responses per unit carbon and phosphorus should be obtained for all compounds. Perkins et al. (1962) have reported that a variety of functional groups in organic compounds affects the response of OC in a FID; hydrocarbons give higher response than organic compounds with the groups containing oxygen, nitrogen or halogens. As shown in Table 2, the difference in
responses of 8 organic compounds was small. All the compounds tested in this study contain oxygen, nitrogen or halogens. Though the compounds containing oxygen, nitrogen or halogens give a lower degree of effect of oxygen, nitrogen or halogens than hydrocarbons, the responses of DOC in FID may be low. Therefore, the found values for DOC must agree well with theoretical values and the values obtained by Method I. When water samples containing hydrocarbons are analyzed by this method, the higher response of hydrocarbons must be considered. The found values for DP agreed well with the theoretical values except for sodium pyrophosphate. The found value of DP for sodium pyrophosphate was somewhat higher than the theoretical value. However, the found value agreed well with the value obtained by Method II. Since a part of the reagent used in this work probably differed from sodium pyrophosphate, the results mentioned above might be obtained.
Analysis of practical water samples DOC and DP in water samples were determined by this method. Each sample was filtered through a 0.45-~m membrane filter in a Swinny holder, and the filtrates were introduced into the nebulizer cell with peristaltic pump. Table 3 shows the analytical results for DOC and DP in the samples. The values of DOC and DP obtained by Method I and II are also shown in Table 3. The values for DC obtained by this method agreed approximately with those obtained by Method II. Patterson et al. (1978) have mentioned that the FPD selectivity ratio of P:S is high at the low concentrations of sulfur; the FPD response of P is
Table 2. Responses of DOC and DP for various compounds containing DOC and DP Found (/2gml -t) Theoretical (/~gml -I) This work Method 1" MethodIIt Compound DOC DP DOC DP DOC DP Glucose, C6Htz06 Fluoroacetamide, C2H4ONF Acetic acid, CzH40z Sodium oxalate, NazC204 Potassium dihydrogen phosphate, KH2PO4 Sodium hypophosphate, NaHzPO2- HzO Sodium phosphate, dibasic, Na2HPO3. 5HzO Sodium tripolyphosphate, NasPjOi0 Sodium pyrophosphate, Na4P20 ~. 10H20 Sodium metaphosphate, (NaPOj), Glucose phosphate, dipotassium salt, C6HtIK2OgP.2HzO Disodium phenyl phosphate, C6HsNa2PO,.2H20 Adenosine triphosphate, disodium salt, C10Hi4NsOtjP3Na2.3H,.O Sodium glycerophosphate, CjHTOsPNa2- 5.5H20 *Combustion-infrared method. tPersulfate digestion-colorimetric method.
10.0 10.0 10.0 10.0
0 0 0 0
10.0 9.7 10.0 10.0
0 0 0 0
10.0 10.1 10.0 9.8
0 0 0 0
0
10.0
0
10,0
0
10.0
0
10.0
0
10.0
0
10.7
0
10.0
0
9.7
0
10.3
0
10.0
0
9.8
0
10.3
0
10.0
0
10.5
0
10.6
0
10.0
0
10.0
0
9.8
23.3
10.0
23.2
10.4
22.5
10.2
23.3
10.0
22.5
10.4
24.2
t0.5
12.9
10.0
13.0
9.7
13.0
9.9
11.6
10.0
12.0
10.0
10.8
10.8
Simultaneous determination of DOC and DP in waters
559
Table 3. Analytical results (in/~g mt-~) of practical water samples This work Method [+ Method 11.~ Sample DOC DP DOC DP Raw municipal wastewater 120 4.2 130 z.5 Water treated by activated sludge process 25 1.4 29 1.5 Water treated by flocculation-sedimentation process 13 0.4 9 0.4 Water treated by flocculation-sedimentation process 9 1.6 7 1.6 *Each sample was taken from the effluent of flocculation-sedimentation process for industrial v,astewaters containing phosphate; samples (I-2) were withdrawn at different times. ~'Combustion-infrared method. ~Persulfate digestion-colorimetric method.
little affected by $2 molecular emission. As the conc e n t r a t i o n s o f sulfate ion in the practical samples were low, the interference o f sulfur on the F P D response was little observed. However, the a g r e e m e n t between the values for D O C o b t a i n e d by this M e t h o d I was less satisfactory. In the case of sample Nos 1 and 2, the values o b t a i n e d by this m e t h o d were lower t h a n those o b t a i n e d by M e t h o d I. This m a y be due to the difference in the degree of a d s o r p t i o n o f glucose used as a s t a n d a r d solution of D O C a n d organic c o m p o u n d s present in the practical waters on the cation-exchange resin column. In the case o f sample Nos 3 a n d 4, those o b t a i n e d by this m e t h o d were higher t h a n those o b t a i n e d M e t h o d I. Sample Nos 3 a n d 4 m a y contain small a m o u n t s og hydrocarbons. A l t h o u g h the d e t e r m i n a t i o n of D O C a n d D P in a sea water was examined, the d e t e r m i n a t i o n was impossible because the exchange capacity of the c o l u m n in the a p p a r a t u s was too small to a d s o r b the total a m o u n t s of cations in a 1 0 m i n run o f water. T h e increase of the c o l u m n volume m a y be able to determine D O C a n d D P of sea water. C o n c o m i t a n t l y , since the time taken to introduce the sea water into the b u r n e r is prolonged, this m e t h o d becomes timeconsuming. Therefore, this m e t h o d seems to be suitable for the analysis of water samples with low salinity such as river water, lake water, municipal water a n d some of industrial wastewater.
Acknowledgements--The author is pleased to acknowledge Professor Hiroshi Sunahara, Department of Environmental Science, Faculty of Engineering, Hiroshima University. His interest, help and enthusiasm were responsible for this investigation. Thanks are due to Dr Toshio Ishizuka, Government Industrial Research Institute Nagoya, for his critical reading of the manuscript.
REFERENCES
Aldous K. M., Dagnall R. M. and West T. S. (1970) The flame-spectroscopic determination of sulfur and phosphorus in organic and aqueous matrices by using a simple filter photometer. Analyst 95, 417-424.
APHA (1975) Standard Methods for Examination of Water and Wastewater, 14th Edition. American Public Health Association, Washington. DC. Bowman M. C. and Beroza M. (1968) Gas chromatographic detector for simultaneous sensing of phosphorus- and sulfur-containing compounds by flame photometry. Anal. Chem. 40, 1448-1452. Chester T. L. (1980) Flame geometry effects on the flame photometric measurement of phosphorus in aqueous/organic liquids. Anal. Chem. 52, 638-642. Dobbs R. A., Wise R. H. and Dean R. B. (1967) Measurements of organic carbon in water using the hydrogenflame ionization detector. Anal. Chem. 39, 1255-1258. Eggertsen F. T. and Stross F. H. (1972) Flame detection method for determining organic carbon in water. Anal. Chem. 44, 709-714. Frostling H. (1973) Continuous detection of vapours and aerosols of organophosphorus compounds by flame ionization-flame emission. J. Phys. E: Scient. Instr. 6, 863-867. Julin B. G., Vandenvorn H. W. and Kirkland J. J. (1975) Selective flame emission detection of phosphorus and sulfur in high-performance liquid chromatography. J. Chromat. 112, 443--453. Lysyj I. and Nelson K. H. (1968) Direct gas chromatographic method for nonvolatile organics in aqueous solutions. J. Gas Chromat. 6, 106-109. Menzel D. W. and Vaccaro R. F. (1964) The measurement of dissolved organic and particulate carbon in sea water. Limnol. Oceanog. 9, 138-142. Miyagi H., Kawazoe K., Takata Y., Kamo T. and Arikawa Y. (1976) Determination of phosphate in water using flame photometry (Japanese). Paper Presented at 34th National Meeting of the Japan Chemical Society, 4T19, Tokyo. Nakajima K. (1978) Determination of organic carbon in water by chemical oxidation method (Japanese). Bunseki Kagaku 27, 48-52. Patterson P. L., Howe R. L. and Abu-Shumays A. (1978) Dual-flame photometric detector for sulfur and phosphorus compounds in gas chromatograph effluents. Anal. Chem. 50, 339-344. Perkins G. Jr, Rouayheb G. M. and Lively L. D. (1962) Response of the gas chromatographic flame ionization detector to different functional groups. In Gas Chromatography (Edited by Brenner N., Callen J. E. and Weiss M. D.), pp. 269-285. Academic Press, New York. Prager M. J. and Seitz W. R. (1975) Flame emission photometer for determining phosphorus in air and natural waters. Anal. Chem. 47, 148-151. Van Hall C. E. and Stenger V. A. (1967) An instrumental method for rapid determination of carbonate and total carbon in solutions. Anal. Chem. 39, 503-507.