- Email: [email protected]
Flow injection-chemiluminescence determination of ascorbic acid based on luminol–ferricyanide–gold nanoparticles system
Journal of Luminescence 154 (2014) 350–355
Contents lists available at ScienceDirect
Journal of Luminescence journal homepage: www.elsevier.com/locate/jlumin
Flow injection-chemiluminescence determination of ascorbic acid based on luminol–ferricyanide–gold nanoparticles system Yong Ping Dong a,n, Ting Ting Gao a, Xiang Feng Chu a, Jun Chen a, Cheng Ming Wang b,n a b
School of chemistry and chemical engineering, Anhui University of Technology, Maanshan, China, 243002 Hefei National Laboratory for Physical Science at the Microscale, University of Science and Technology of China, Hefei, China, 230026
art ic l e i nf o
a b s t r a c t
Article history: Received 29 September 2013 Received in revised form 9 May 2014 Accepted 11 May 2014 Available online 20 May 2014
A novel flow-injection chemiluminescence (CL) method for the determination of ascorbic acid (AA) is proposed, based upon its enhancing effect on the CL reaction of luminol with ferricyanide catalyzed by gold nanoparticles in alkaline solution. Different sizes gold nanoparticles exhibited different catalyzing effect towards luminol CL and 38 nm gold nanoparticles exhibited the best enhancing effect. Under the optimal experimental conditions, a linear relationship was obtained between the CL intensity and the concentration of ascorbic acid in the range of 1.0 10 10–1.0 10 6 mol L 1. The detection limit was 2.0 10–11 mol 1 and the relative standard deviation for 1.0 10 6 mol L 1 ascorbic acid was 0.71% (n ¼10). This method has been successfully applied in the determination of ascorbic acid in several real samples. & 2014 Elsevier B.V. All rights reserved.
Keywords: Chemiluminescence Ascorbic acid Gold nanoparticles Luminol Ferricyanide
1. Introduction Ascorbic acid, also known as vitamin C, plays an essential role in biological metabolism and its determination has attracted great attention in bioanalysis [1]. Meanwhile, recent advancement in food and pharmaceutical industries also requires a simple and sensitive method for ascorbic acid evaluation [2]. Numerous methods, such as titrimetry [3], fluorimetry [4], spectrometry [5], chromatography [6], electrochemistry [7,8], and chemiluminescence (CL) [9–11], have been employed in the detection of ascorbic acid. Among these techniques, the CL method has the advantage of simple equipment and produces low back ground signals for the emission of CL coming from the chemical reaction. Coupling with flow injection analysis (FIA), the classical CL systems, such as luminol, lucigenin, peroxalate, potassium permanganate and Ce (IV) have been widely developed and employed to applications. For example, ascorbic acid has been detected with cerium (IV)–rhodamine B CL system [9], hydrogen peroxide–sodium hydrogen carbonate–CdSe/CdS quantum dot CL system [10], and luminol–Fe3 þ –hydrogen peroxide CL system [11]. However, the CL intensity of traditional system is weak, as a result, the detection sensitivity is limited. Therefore, it is necessary to find some new substances to enhance the CL intensity.
n
Corresponding authors. Tel.: þ 86 555 2311807, 86 551 63606447. E-mail addresses: [email protected] (Y.P. Dong), [email protected] (C.M. Wang). http://dx.doi.org/10.1016/j.jlumin.2014.05.011 0022-2313/& 2014 Elsevier B.V. All rights reserved.
Recently, metal nanoparticles which can participate in CL reactions as catalyst, reductant, luminophore or energy accepter have been under intense investigation [12–14]. Among these metal nanoparticles, gold nanoparticles (GNPs) are the most famous and have been explored in various CL systems. For example, Cui et al. reported that GNPs could catalyze CL reactions of luminol–H2O2 system, bis (2, 4, 6-trichlorophenyl) oxalate–H2O2 system, KIO4– NaOH–Na2CO3, and luminol–K3Fe(CN)6 system [15–18]. Li et al. found gold nanoparticles could enhance CL signal of luminol–KIO4 system in alkaline solution and polyphenols could be detected sensitively based on their inhibiting effect [19]. It was reported in the above result that small size gold nanoparticles could inhibit CL of luminol–ferricyanide system, whereas large scale gold nanoparticles could enhance this CL. The enhancement of large size gold nanoparticles was ascribed to the catalysis of gold nanoparticles in the electron-transfer process during the luminol CL reaction and the relatively low quenching efficiency of the luminolphor by gold nanoparticles [18]. Although the enhancing effect of gold nanoparticles on luminol–ferricyanide CL system has already been found, however, the analytical application of luminol–ferricyanide CL system catalyzed by gold nanoparticles in the detection of ascorbic acid has not been reported. In this paper, it was found that ascorbic acid could enhance CL signal of the luminol–ferricyanide–gold nanoparticles and the CL intensity is dependent on ascorbic acid concentration. Based on this phenomenon, a new, simple, and sensitive method is proposed for the determination of ascorbic acid, which has been successfully used to detect ascorbic acid in real samples with satisfactory results.
Y.P. Dong et al. / Journal of Luminescence 154 (2014) 350–355
351
used for determining the ascorbic acid content by the proposed FIA–CL method.
2. Experimental section 2.1. Chemicals and solutions A 1.0 10 2 mol L 1 stock solution of luminol was prepared by dissolving luminol (Sigma) in 0.1 mol L 1 sodium hydroxide solution without further purification. Working solutions of luminol were prepared by diluting the stock solution in 0.1 mol L 1 Na2CO3– NaHCO3 buffer solution (CBS). A 1.0 g L 1 HAuCl4 stock solution was prepared by dissolving 1 g of HAuCl4 in 1 L of redistilled water and stored at 4 1C. All of other reagents were of analytical grade, and redistilled water was used throughout. 2.2. Synthesis of gold nanoparticles Colloidal solutions of 16-, 25-, 38-, 68-, 99-diameter gold nanoparticles were synthesized by the citrate reduction method according to the Ref. 17 A typical synthesis procedure is as follows: A 50 mL portion of HAuCl4 (10 2%, w/w) solution was heated to boil. While stirring vigorously, different amount of 1% trisodium citrate was added rapidly. The solution was maintained at the boiling point for 15 min, during which time a color change from gray to blue to purple was observed. The heating source was removed and the colloid was kept at room temperature for 15 min and stored at 4 1C. 2.3. CL measurements
3.1. CL between luminol and gold nanoparticles It has been already proven that gold nanoparticles could catalyze different CL systems. For example, gold nanoparticles of different sizes could enhance the CL of luminol–H2O2 system, and the most intensive CL signals were obtained with 38-nm-diameter gold nanoparticles [16]. Gold nanoparticles could react with a potassium periodate–sodium hydroxide–carbonate system to generate chemiluminescence and the light intensity increased linearly with the concentration of the gold nanoparticles [17]. However, the application of gold nanoparticles catalyzed CL system is seldom reported. In the present work, different sizes gold nanoparticles are synthesized and characterized by UV–vis absorption spectra as shown in Fig. 2. The results revealed that the maximum surface plasma resonance (SPR) absorption band was evidently red-shifted with the increase of diameter of gold nanoparticles. The SPR absorption intensity of the gold nanoparticles increased with increasing gold nanoparticles size, reached the maximum at 38 nm gold colloids, and then decreased with further increase of the particle size. In order to investigate the influence of gold nanoparticles on luminol CL, gold nanoparticles were mixed with luminol in pH 9.6 CBS. As shown in Fig. 3 that extremely weak CL emission could be found in alkaline solution, suggesting that OH could react with luminol to generate light emission in the presence of dissolved oxygen, which was also reported by other work [20]. When different sizes of gold nanoparticles were added in alkaline luminol solution, CL signal was apparently enhanced. With the increase of gold nanoparticles size, the CL intensity increased and reached the maximum at 38 nm. With further increase gold nanoparticles size, the CL intensity began to decrease. It was suggested that when gold nanoparticles get larger than 38 nm, the active surface areas of gold nanoparticles decrease with increasing particle size, and the catalytic efficiency of the gold nanoparticles decreased accordingly. When the size of gold nanoparticles is smaller than 38 nm, its active surface area will increase and its catalytic efficiency will also increase. However, it could be found from the UV–vis spectra that SPR absorption intensity of the gold nanopartilces decrease with the decreasing size below 38 nm in diameter, reached the maximum with 38 nm gold nanoparticles, and then decreased once again with further increase of the particle size. SPR absorption intensity is considered to be an indicator of
0.10
Absorption
The CL measurements were conducted on a model MPI-F flowinjection CL analysis system. The diagram of CL measurement is shown in Fig. 1. PTFE tubing (0.8 mm i.d.) was used to connect all components in the flow system. Two peristaltic pumps were used to deliver all solution. In flow injection analysis system, the flow rates of luminol, K3Fe(CN)6, GNPs, and CBS were 3.0 mL min 1. Ascorbic acid standard solution or sample solution was injected into the CBS stream by a loop valve injector, which mixed with GNPs solution through a three-way piece. Luminol is mixed with K3Fe (CN)6 by another three-way piece. The solutions from two threeway piece were mixed in a spiral flow CL cell, which was placed in front of the photomultiplier tube. The CL intensity was recorded as the peak height. The net CL intensity ΔI¼ Is I0 was used for the quantitative determination, where Is and I0 were the CL intensity of sample and blank solutions, respectively. The high voltage applied to the photomultiplier tube was maintained at 600 V throughout. A known amount of the powders of vitamin C tablets was weighted and dissolved to the required volume with 0.1 mol L 1 carbonate buffer solution. Fruit juice was extracted and centrifuged until a clear liquid was obtained. Weighed amounts of these liquids were diluted to a known volume with 0.1 mol L 1 carbonate buffer solution. The known amount of ascorbic acid standard solution was added in the samples and the final solutions were
3. Results and discussion
luminol K3Fe(CN)6
0.05
GNPs MPI-F
CBS/AA
Peristaltic pump
waste
Fig. 1. Schematic diagram of flow-injection chemiluminescence detection system.
0.00 300
16nm 25nm 38nm 68nm 99nm
400
500
600
700
800
Wavelength/nm Fig. 2. UV–vis absorption spectra of different size gold nanoparticles.
352
Y.P. Dong et al. / Journal of Luminescence 154 (2014) 350–355
180
3000
160
luminol luminol-99nm GNP luminol-25nm GNP luminol-16nm GNP luminol-68nm GNP luminol-38nm GNP
CL intensity/a.u.
120 100 80 60
luminol luminol-k3Fe(CN)6
2500
luminol-K3Fe(CN)6-16nmGNP CL intensity/a.u.
140
luminol-K3Fe(CN)6-25nmGNP
2000
luminol-K3Fe(CN)6-38nmGNP luminol-K3Fe(CN)6-68nmGNP
1500
luminol-K3Fe(CN)6-99nmGNP 1000
40
500
20 0
0
-20 0
5
10
15
20
25
0
30
5
10
Time/s
3.2. Gold nanoparticles catalyzed luminol and K3Fe(CN)6 CL system Despite gold nanoparticles could enhance CL with luminol, the CL intensity is too weak to be applied. Therefore, different CL systems, such as luminol–H2O2, luminol–KMnO4, luminol–KIO3, luminol–K3Fe(CN)6, were selected to investigate the influence of gold nanoparticles on traditional CL systems. It was found that gold nanoparticles could significantly enhance CL signals of these systems. However, the obtained CL emission of luminol–K3Fe(CN)6 system is most stable and the enhancing effect of gold nanoparticles on luminol–K3Fe(CN)6 CL system was most significantly. Therefore, luminol–K3Fe(CN)6 system was used as a model to investigate the effect of gold nanoparticles on traditional CL emission. The effect of different size gold nanoparticles on luminol–K3Fe (CN)6 CL is investigated and shown in Fig. 4. It could be found that 38 nm gold nanoparticles exhibited the best enhancing effect, which is also in accordance with the results of Ref. [17]. It was reported that some reducing agents could decrease or increase luminol CL in alkaline solution [22]. Therefore, in the present study, some reducing reagents, such as citric acid, ascorbic acid, and cysteine, were added into luminol–K3Fe(CN)6–gold nanoparticles CL system to investigate their effects on CL signal. Fig. 5shows that cysteine can decrease CL signal while ascorbic acid and citric acid can enhance CL signal. Though citric acid could also enhance luminol CL, the enhancing effect of ascorbic acid is more significantly than that of citric acid, suggesting that citric acid might not influence the detection of ascorbic acid with the present luminol CL system. In order to support this assumption, the CL intensity was recorded by adding citric acid into ascorbic acid solution. The results revealed that only 3.4% increase in CL intensity was obtained after citric acid was added. Therefore, the interference from citric acid in the detection of ascorbic acid is not very serious. The possibility of using luminol–K3Fe(CN)6–gold nanoparticles CL system to detect ascorbic acid was investigated in the following text. Fig. 6 shows that ascorbic acid can enhance luminol–K3Fe(CN)6 CL signal. However, the enhancing effect of ascorbic acid to luminol–K3Fe (CN)6 CL was more significant in the presence of 38 nm gold nanoparticles, which suggested that the detection of ascorbic acid using luminol–K3Fe(CN)6–gold nanoparticles CL system will be more sensitive.
25
9000 8000
CL intensity/a.u.
the electron density in the conduction bands of nanoparticles, which is very important for the catalytic effect of gold nanoparticles [21]. Therefore, the catalytic effects also decreased with decreasing size below 38 nm in diameter due to the decrease in electron density with the decreasing particle size. These results reveal that gold nanoparticles could catalyze luminol CL.
20
Fig. 4. Enhancing effect of different sizes of gold nanoparticles on luminol–K3Fe (CN)6 CL system. luminol, 1.0 10 4 mol L 1; K3Fe(CN)6, 1.0 10 3 mol L 1; pH, 9.6; CBS, 0.1 mol L 1.
7000
luminol-K3Fe(CN)6-GNP-ascorbic acid
6000
luminol-K3Fe(CN)6-GNP-citric acid
5000
luminol-K3Fe(CN)6-GNP-cysteine
4000
luminol-K3Fe(CN)6-GNP
3000 2000 1000 0 -1000 -2
0
2
4
6
8
10
12
14
16
18
20
22
24
Time/s
Fig. 5. Effects of different reducing reagents on luminol–K3Fe(CN)6 CL catalyzed by 38 nm gold nanoparticles. luminol, 1.0 10 4 mol L 1; K3Fe(CN)6, 1.0 10 3 mol L 1; pH, 9.6; CBS, 0.1 mol L 1; ascorbic acid, 1.0 10 6 mol L 1; citric acid, 1.0 10 6 mol L 1; cysteine, 1.0 10 6 mol L 1.
9000
luminol-K3Fe(CN)6
8000
luminol-K3Fe(CN)6−AA
7000 CL intensity/a.u.
Fig. 3. Chemiluminescence of luminol catalyzed by different sizes of gold nanoparticles in alkaline aqueous solution. luminol, 1.0 10 4 mol L 1; pH, 9.6; CBS, 0.1 mol L 1.
15 Time/s
luminol-K3Fe(CN)6-38nmGNP
6000
luminol-K3Fe(CN)6-38nmGNP−AA
5000 4000 3000 2000 1000 0 0
5
10
15
20
25
30
Time/s Fig. 6. Enhancing effect of ascorbic acid on luminol–K3Fe(CN)6 CL system in the absence and presence of 38 nm gold nanoparticles. luminol, 1.0 10 4 mol L 1; K3Fe(CN)6, 1.0 10 3 mol L 1; pH, 9.6; CBS, 0.1 mol L 1; ascorbic acid, 1.0 10 6 mol L 1.
3.3. Effect of media and pH It is well known that luminol CL occurs in alkaline mediums. Various buffer solutions, such as NaH2PO4–Na2HPO4, Na2CO3– NaHCO3, NaOH–Na2B4O7 at 0.1 mol L 1 were examined and the strongest CL signal was obtained in Na2CO3–NaHCO3 medium.
Y.P. Dong et al. / Journal of Luminescence 154 (2014) 350–355
The effect of the concentration of luminol and K3Fe(CN)6 on the increased CL intensity is examined as shown in Fig. 7. It could be found from Fig. 7A that the CL intensity increases with the increase of luminol concentration in the range of 1.0 10 8 to 1.0 10 3 mol L 1. However, the CL intensity of the blank becomes very strong when the concentration of luminol was higher than 1.0 10 4 mol L 1. Considering the CL intensity and the consumption of the reagents, the concentration of luminol solution was adjusted to 1.0 10 4 mol L 1 for the following research work. The effect of K3Fe(CN)6 concentration in the range of 1.0 10 6 to 1.0 10 4 mol L 1 on the CL intensity is also examined and shown in Fig. 7B. It was found that the relative CL intensity increased with the increase of K3Fe(CN)6 concentration and reached a plateau at 1.0 10 3 mol L 1. Therefore, 1.0 10 3 mol L 1 was selected as the optimal concentration in the following study. 3.5. CL mechanism In order to investigate CL mechanism of luminol–K3Fe(CN)6– gold nanoparticles system, UV–vis absorption spectra are recorded and shown in Fig. 8. It could be found that the maximum surface plasma resonance (SPR) absorption band of 38 nm gold nanoparticles is located at 520 nm, with two absorption peaks of luminol located at 295 nm and 355 nm, and two absorption peaks of K3Fe(CN)6 located at 300 nm and 420 nm, respectively. When gold nanoparticles were mixed with K3Fe(CN)6, all absorption peaks still could be obtained, suggesting that gold nanoparticles did not react with K3Fe(CN)6. When luminol was added in the above mixing solution, the absorption peak of K3Fe(CN)6 located at 300 nm decreased apparently, while the SPR of gold nanoparticles changes a little, suggesting that luminol could react with K3Fe(CN)6 and could not react with gold nanoparticles. Moreover, the maximum SPR absorption band of gold nanoparticles did not change during mixing with luminol and K3Fe(CN)6 revealed that gold nanoparticles did not
30000 20000
CL intensity/a.u.
10000 0 0.0000
0.0002
0.0004
0.0006
0.0008
0.0010
0.000
0.001
0.002
0.003
0.004
0.005
8000 4000 0
C/mol L-1 Fig. 7. Effects of luminol concentration (A) and K3Fe(CN)6 concentration (B) on luminol–K3Fe(CN)6–GNP CL signals. pH, 9.6; CBS, 0.1 mol L 1; ascorbic acid, 1.0 10 6 mol L 1.
38nm GNP K3Fe(CN)6 K3Fe(CN)6-38nm GNP K3Fe(CN)6-38nm GNP-luminol luminol
Absorption
3.4. Effect of concentration of luminol and K3Fe(CN)6
2
1
0 300
400
500
600
700
Wavelength/nm Fig. 8. UV–vis absorption of 38 nm gold nanoparticles, luminol, K3Fe(CN)6, and their mixing solutions.
200 160 CL intensity/a.u.
Therefore, carbonate buffer solution (CBS) was selected as the working medium. The pH of CL system was investigated over the range of 8.6– 10.5. The CL intensity increased gradually from 8.6 to 9.6 and the maximum CL intensity was obtained at pH 9.6. Thus, a pH of 9.6 (0.1 mol L 1 CBS) was chosen as optimum for further experiments.
353
luminol-K3Fe(CN)6 luminol-K3Fe(CN)6-38nm GNP
120 80 40 0 350
400
450
500
550
Wavelength/nm
Fig. 9. CL spectra of luminol–K3Fe(CN)6 CL system in the absence and presence of 38 nm gold nanoparticles. luminol, 1.0 10 4 mol L 1; K3Fe(CN)6, 1.0 10 3 mol L 1; pH, 9.6; CBS, 0.1 mol L 1; ascorbic acid, 1.0 10 6 mol L 1.
participate CL reactions and the enhancing effect of gold nanoparticles should result from its catalytic effect. The CL spectra of luminol–K3Fe(CN)6 system and luminol–K3Fe (CN)6–gold nanoparticles system are obtained and shown in Fig. 9. It was found that the maximum emission for all cases was 425 nm, revealing that the luminophor for the CL system was still the excited state of 3-aminophthalate anion (AP2 ). That is to say, the presence of gold nanoparticles did not generate a new lumnophor for this CL system. According to Shevlin's result [23], the mechanism for the luminol–K3Fe(CN)6 CL system should be as follows: luminol was firstly oxidized by ferricyanide to generate luminol radical. Then, in the presence of oxygen and ferrocyanide, luminol radical was oxidized to hydroxyl hydroperoxide (LOO ) which could be decomposed to form the excited state AP2 and emit light. Gold nanoparticles could catalyze the oxidation reaction between the luminol radical and oxygen, resulting in an enhancement of the CL signal [17]. Kubo et al. reported that luminol could react with ascorbic acid to generate chemiluminescence in the presence of hexacyanoferrate. They proposed that ascorbic acid could reduce oxygen to superoxide radical in alkaline solution [22]. The produced superoxide radical reacted with luminol to generate light emission. Chen et al. reported the ascorbate radical will be formed by the oxidation of ascorbic acid which could enhance electrochemiluminescence of lucigenin [24]. It has already been proven that gold
354
Y.P. Dong et al. / Journal of Luminescence 154 (2014) 350–355
9000
Table 2 Determination of ascorbic acid in tap water and some real samples.
8000 Sample
Initially present (mol L 1)
Added amount (mol L 1)
Found amounta (mol L 1)
Recovery (%)
Tap water Vc tablet Orange juice
0 5.06 10 7 2.12 10 7
1.0 10 7 1.0 10 7 1.0 10 7
0.98 10 7 6.09 10 7 3.09 10 7
98 103 97
3.5
6000
log(I-I )
CL intensity/a.u.
7000
1µM
5000
3.0
2.5
4000
0
2.0
3000
-10
-9
-8
-7
-6
a
logC
Mean of three determinations.
2000 1000 0 0
5
10
15
20
25
Time/s Fig. 10. Relationship between the CL intensity and 0, 0.0001, 0.0005, 0.001, 0.01, 0.3, 0.5, 0.8, 1.0 μM ascorbic acid from bottom to top. The inset is the linear calibration plot for ascorbic acid. luminol, 1.0 10 4 mol L 1; K3Fe(CN)6, 1.0 10 3 mol L 1; pH, 9.6; CBS, 0.1 mol L 1.
Table 1 Comparison of the analytical data obtained by some CL method for the determination of ascorbic acid. CL Systems
Lucigenin Luminol–Fe3 þ –H2O2 H2O2–HCO3 –CdSe/CdS QDs Peroxynitrous acid Ce(IV)–Rhodamine B Luminol–K3Fe(CN)6–GNPs
Linear range (mol L 1)
9
4
1.0 10 –3.0 10 1.0 10 11–1.0 10 7 1.0 10 7–1.0 10 4 5.0 10 9–5.0 10 5 3.8 10 13–1.0 10 10 1.0 10 10–1.0 10 6
acceptable reproducibility. Therefore, gold nanoparticles involved luminol CL system could be successfully applied in ascorbic acid detection. Although the detection sensitivity of this CL system might be lower than some reported CL systems, this work still reveal the fact that nanoparticles might find its more application in CL detection, which is very important to the application research of various nanoparticles. The proposed method was applied to the determination of ascorbic acid in some real samples, such as fruit juice and vitamin C tablets, to which known amount of ascorbic acid standards were added. The results shown in Table 2 revealed that the determination of ascorbic acid in the real sample is satisfied.
Detection limit (mol L 1)
References
4. Conclusions
– 1.0 10 12 6.7 10 9 5.0 10 10 1.0 10 13 2.0 10 11
[28] [11] [10] [29] [9] this work
Gold nanoparticles could catalyze the chemiluminescence of luminol–K3Fe(CN)6 system and 38 nm gold nanoparticle exhibited the best catalyzing effect. The CL of luminol–K3Fe(CN)6–gold nanoparticles system could be strongly enhanced by the presence of ascorbic acid. Based on its enhancing effect, a novel CL method with a lower detection limit and wider linear range was developed for the determination of ascorbic acid and good recovery was obtained in the detection of ascorbic acid in some real samples.
nanoparticles exhibit excellent electrocatalytic activity towards the electro-oxidation of ascorbic acid [25,26]. From the results of spectral experiments, we could find that gold nanoparticles could not react with luminol or K3Fe(CN)6. Therefore, it is reasonable to deduce that gold nanoparticles could catalyze the oxidation of ascorbic acid to generate ascorbate radicals. The ascorbate radicals could then react with dissolved oxygen to generate superoxide radical which could react with luminol to generate strong CL emission.
Acknowledgments This work is financially supported by National Natural Science Foundation of China (Nos. 61271156, and 21207001), Natural Science Foundation of Anhui Province (1408085MF114), China Postdoctoral Science Foundation (2013M541637) and Innovation Team Project of AHUT (No. TD201204). References
3.6. Analytical application Generally, chemiluminescence signal can be described as a function of the analyte concentration. However, a linear representation could also be described as a plot of the logarithm of the relative chemiluminescence signal as a function of the logarithm of the analyte concentration [27]. Under the optimized experimental conditions, the calibration curve was found to be linear from 1.0 10 10 1.0 10 6 mol L 1 and a regression equation was log (I I0)¼ 6.1639 þ 0.4046 logC (R ¼0.998), where I I0 is the relative CL intensity and C is the concentration of ascorbic acid (Fig. 10). The detection limit (S/N ¼3) was 2.0 10 11 mol L 1. The relative standard deviation (RSD) of 10 parallel measurements at 1.0 10 6 mol L 1 ascorbic acid was 0.71%. The RSD of six parallel measurements in one week was 5.4%. The linear range and the detection limit of the proposed method are compared with the earlier reports in Table 1. The results indicate that the proposed CL system has good linearity, relatively high sensitivity and
[1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11] [12] [13] [14] [15] [16] [17] [18]
A. Aoki, T. Matsue, I. Uchida, Anal. Chem. 64 (1992) 44. A.M. Farrington, N. Jagota, J.M. Slater, Analyst 119 (1994) 233. M.A. Koupparis, P. Anagnostopoulou, H.V. Malmstadt, Talanta 32 (1985) 411. Q.L. Wang, Z.H. Liu, L.Y. Mao, R.X. Cai, Chin. J. Anal. Chem 28 (2000) 1229. J.K. Kwakye, Talanta 51 (2000) 197. R. Shakya, D.A. Navarre, J. Agric. Food. Chem. 54 (2006) 5253. S. Ashok Kumar, P.H. Lo, S.M. Chen, Biosens. Bioelectron. 24 (2008) 518. X.M. Cao, L.Q. Luo, Y.P. Ding, X.L. Zou, R.X. Bian, Sensor. Actuators B 129 (2008) 941. Y.J. Ma, M. Zhou, X.Y. Jin, B.Z. Zhang, H. Chen, N.Y. Guo, Anal. Chim. Acta 464 (2002) 289. H. Chen, R.B. Li, L. Lin, G.S. Guo, J.M. Lin, Talanta 81 (2010) 1688. A.A. Alwarthan, Analyst 118 (1993) 639. L. Wang, P. Yang, Y.X. Li, C.Q. Zhu, Talanta 70 (2006) 219. X. Wang, N. Na, S.C. Zhang, Y.Y. Wu, X.R. Zhang, J. Am. Chem. Soc. 129 (2007) 6062. N. Na, S.C. Zhang, X. Wang, X.R. Zhang, Anal. Chem. 81 (2009) 2092. Z.F. Zhang, H. Cui, C.Z. Lai, L.J. Liu, Anal. Chem. 77 (2005) 3324. H. Cui, Z.F. Zhang, M.J. Shi, Y. Xu, L. Wu, Anal. Chem. 77 (2005) 6402. H. Cui, Z.F. Zhang, M.J. Shi, J. Phys. Chem. B 109 (2005) 3099. C.F. Duan, H. Cui, Z.F. Zhang, B. Liu, J.Z. Guo, W. Wang, J. Phys. Chem. C 111 (2007) 4561.
Y.P. Dong et al. / Journal of Luminescence 154 (2014) 350–355
[19] [20] [21] [22] [23] [24]
S.F. Li, X.Z. Li, J. Xu, X.W. Wei, Talanta 75 (2008) 32. H.R. Schroeder, F.M. Yeager, Anal. Chem. 50 (1978) 1114. S. Link, M.A. El-sayed, Int. Rev. Phys. Chem. 19 (2002) 409. H. Kubo, A. Toriba, Anal. Chim. Acta 353 (1997) 345. P.B. Shevlin, H.A. Neufeld, J. Org. Chem. 35 (1970) 2178. J.H. Chen, Z.Y. Lin, G.N. Chen, Electrochim. Acta 52 (2007) 4457.
355
[25] P. Kannan, S. Abraham John, Anal. Biochem. 386 (2009) 65. [26] A. Sivanesan, P. Kannan, S.A. John, Electrochim. Acta 52 (2007) 8118. [27] S. Meseguer-Lloret, S. Torres-Cartas, M.C. Gomez-Benito, Anal. Bioanal. Chem. 398 (2010) 3175. [28] T. Perez-Ruiz, C. Martinez-Lozano, A. Sanz, Anal. Chim. Acta 308 (1995) 299. [29] Z.H. Wang, X. Teng, C. Lu, Analyst 137 (2012) 1876.
Contents lists available at ScienceDirect
Journal of Luminescence journal homepage: www.elsevier.com/locate/jlumin
Flow injection-chemiluminescence determination of ascorbic acid based on luminol–ferricyanide–gold nanoparticles system Yong Ping Dong a,n, Ting Ting Gao a, Xiang Feng Chu a, Jun Chen a, Cheng Ming Wang b,n a b
School of chemistry and chemical engineering, Anhui University of Technology, Maanshan, China, 243002 Hefei National Laboratory for Physical Science at the Microscale, University of Science and Technology of China, Hefei, China, 230026
art ic l e i nf o
a b s t r a c t
Article history: Received 29 September 2013 Received in revised form 9 May 2014 Accepted 11 May 2014 Available online 20 May 2014
A novel flow-injection chemiluminescence (CL) method for the determination of ascorbic acid (AA) is proposed, based upon its enhancing effect on the CL reaction of luminol with ferricyanide catalyzed by gold nanoparticles in alkaline solution. Different sizes gold nanoparticles exhibited different catalyzing effect towards luminol CL and 38 nm gold nanoparticles exhibited the best enhancing effect. Under the optimal experimental conditions, a linear relationship was obtained between the CL intensity and the concentration of ascorbic acid in the range of 1.0 10 10–1.0 10 6 mol L 1. The detection limit was 2.0 10–11 mol 1 and the relative standard deviation for 1.0 10 6 mol L 1 ascorbic acid was 0.71% (n ¼10). This method has been successfully applied in the determination of ascorbic acid in several real samples. & 2014 Elsevier B.V. All rights reserved.
Keywords: Chemiluminescence Ascorbic acid Gold nanoparticles Luminol Ferricyanide
1. Introduction Ascorbic acid, also known as vitamin C, plays an essential role in biological metabolism and its determination has attracted great attention in bioanalysis [1]. Meanwhile, recent advancement in food and pharmaceutical industries also requires a simple and sensitive method for ascorbic acid evaluation [2]. Numerous methods, such as titrimetry [3], fluorimetry [4], spectrometry [5], chromatography [6], electrochemistry [7,8], and chemiluminescence (CL) [9–11], have been employed in the detection of ascorbic acid. Among these techniques, the CL method has the advantage of simple equipment and produces low back ground signals for the emission of CL coming from the chemical reaction. Coupling with flow injection analysis (FIA), the classical CL systems, such as luminol, lucigenin, peroxalate, potassium permanganate and Ce (IV) have been widely developed and employed to applications. For example, ascorbic acid has been detected with cerium (IV)–rhodamine B CL system [9], hydrogen peroxide–sodium hydrogen carbonate–CdSe/CdS quantum dot CL system [10], and luminol–Fe3 þ –hydrogen peroxide CL system [11]. However, the CL intensity of traditional system is weak, as a result, the detection sensitivity is limited. Therefore, it is necessary to find some new substances to enhance the CL intensity.
n
Corresponding authors. Tel.: þ 86 555 2311807, 86 551 63606447. E-mail addresses: [email protected] (Y.P. Dong), [email protected] (C.M. Wang). http://dx.doi.org/10.1016/j.jlumin.2014.05.011 0022-2313/& 2014 Elsevier B.V. All rights reserved.
Recently, metal nanoparticles which can participate in CL reactions as catalyst, reductant, luminophore or energy accepter have been under intense investigation [12–14]. Among these metal nanoparticles, gold nanoparticles (GNPs) are the most famous and have been explored in various CL systems. For example, Cui et al. reported that GNPs could catalyze CL reactions of luminol–H2O2 system, bis (2, 4, 6-trichlorophenyl) oxalate–H2O2 system, KIO4– NaOH–Na2CO3, and luminol–K3Fe(CN)6 system [15–18]. Li et al. found gold nanoparticles could enhance CL signal of luminol–KIO4 system in alkaline solution and polyphenols could be detected sensitively based on their inhibiting effect [19]. It was reported in the above result that small size gold nanoparticles could inhibit CL of luminol–ferricyanide system, whereas large scale gold nanoparticles could enhance this CL. The enhancement of large size gold nanoparticles was ascribed to the catalysis of gold nanoparticles in the electron-transfer process during the luminol CL reaction and the relatively low quenching efficiency of the luminolphor by gold nanoparticles [18]. Although the enhancing effect of gold nanoparticles on luminol–ferricyanide CL system has already been found, however, the analytical application of luminol–ferricyanide CL system catalyzed by gold nanoparticles in the detection of ascorbic acid has not been reported. In this paper, it was found that ascorbic acid could enhance CL signal of the luminol–ferricyanide–gold nanoparticles and the CL intensity is dependent on ascorbic acid concentration. Based on this phenomenon, a new, simple, and sensitive method is proposed for the determination of ascorbic acid, which has been successfully used to detect ascorbic acid in real samples with satisfactory results.
Y.P. Dong et al. / Journal of Luminescence 154 (2014) 350–355
351
used for determining the ascorbic acid content by the proposed FIA–CL method.
2. Experimental section 2.1. Chemicals and solutions A 1.0 10 2 mol L 1 stock solution of luminol was prepared by dissolving luminol (Sigma) in 0.1 mol L 1 sodium hydroxide solution without further purification. Working solutions of luminol were prepared by diluting the stock solution in 0.1 mol L 1 Na2CO3– NaHCO3 buffer solution (CBS). A 1.0 g L 1 HAuCl4 stock solution was prepared by dissolving 1 g of HAuCl4 in 1 L of redistilled water and stored at 4 1C. All of other reagents were of analytical grade, and redistilled water was used throughout. 2.2. Synthesis of gold nanoparticles Colloidal solutions of 16-, 25-, 38-, 68-, 99-diameter gold nanoparticles were synthesized by the citrate reduction method according to the Ref. 17 A typical synthesis procedure is as follows: A 50 mL portion of HAuCl4 (10 2%, w/w) solution was heated to boil. While stirring vigorously, different amount of 1% trisodium citrate was added rapidly. The solution was maintained at the boiling point for 15 min, during which time a color change from gray to blue to purple was observed. The heating source was removed and the colloid was kept at room temperature for 15 min and stored at 4 1C. 2.3. CL measurements
3.1. CL between luminol and gold nanoparticles It has been already proven that gold nanoparticles could catalyze different CL systems. For example, gold nanoparticles of different sizes could enhance the CL of luminol–H2O2 system, and the most intensive CL signals were obtained with 38-nm-diameter gold nanoparticles [16]. Gold nanoparticles could react with a potassium periodate–sodium hydroxide–carbonate system to generate chemiluminescence and the light intensity increased linearly with the concentration of the gold nanoparticles [17]. However, the application of gold nanoparticles catalyzed CL system is seldom reported. In the present work, different sizes gold nanoparticles are synthesized and characterized by UV–vis absorption spectra as shown in Fig. 2. The results revealed that the maximum surface plasma resonance (SPR) absorption band was evidently red-shifted with the increase of diameter of gold nanoparticles. The SPR absorption intensity of the gold nanoparticles increased with increasing gold nanoparticles size, reached the maximum at 38 nm gold colloids, and then decreased with further increase of the particle size. In order to investigate the influence of gold nanoparticles on luminol CL, gold nanoparticles were mixed with luminol in pH 9.6 CBS. As shown in Fig. 3 that extremely weak CL emission could be found in alkaline solution, suggesting that OH could react with luminol to generate light emission in the presence of dissolved oxygen, which was also reported by other work [20]. When different sizes of gold nanoparticles were added in alkaline luminol solution, CL signal was apparently enhanced. With the increase of gold nanoparticles size, the CL intensity increased and reached the maximum at 38 nm. With further increase gold nanoparticles size, the CL intensity began to decrease. It was suggested that when gold nanoparticles get larger than 38 nm, the active surface areas of gold nanoparticles decrease with increasing particle size, and the catalytic efficiency of the gold nanoparticles decreased accordingly. When the size of gold nanoparticles is smaller than 38 nm, its active surface area will increase and its catalytic efficiency will also increase. However, it could be found from the UV–vis spectra that SPR absorption intensity of the gold nanopartilces decrease with the decreasing size below 38 nm in diameter, reached the maximum with 38 nm gold nanoparticles, and then decreased once again with further increase of the particle size. SPR absorption intensity is considered to be an indicator of
0.10
Absorption
The CL measurements were conducted on a model MPI-F flowinjection CL analysis system. The diagram of CL measurement is shown in Fig. 1. PTFE tubing (0.8 mm i.d.) was used to connect all components in the flow system. Two peristaltic pumps were used to deliver all solution. In flow injection analysis system, the flow rates of luminol, K3Fe(CN)6, GNPs, and CBS were 3.0 mL min 1. Ascorbic acid standard solution or sample solution was injected into the CBS stream by a loop valve injector, which mixed with GNPs solution through a three-way piece. Luminol is mixed with K3Fe (CN)6 by another three-way piece. The solutions from two threeway piece were mixed in a spiral flow CL cell, which was placed in front of the photomultiplier tube. The CL intensity was recorded as the peak height. The net CL intensity ΔI¼ Is I0 was used for the quantitative determination, where Is and I0 were the CL intensity of sample and blank solutions, respectively. The high voltage applied to the photomultiplier tube was maintained at 600 V throughout. A known amount of the powders of vitamin C tablets was weighted and dissolved to the required volume with 0.1 mol L 1 carbonate buffer solution. Fruit juice was extracted and centrifuged until a clear liquid was obtained. Weighed amounts of these liquids were diluted to a known volume with 0.1 mol L 1 carbonate buffer solution. The known amount of ascorbic acid standard solution was added in the samples and the final solutions were
3. Results and discussion
luminol K3Fe(CN)6
0.05
GNPs MPI-F
CBS/AA
Peristaltic pump
waste
Fig. 1. Schematic diagram of flow-injection chemiluminescence detection system.
0.00 300
16nm 25nm 38nm 68nm 99nm
400
500
600
700
800
Wavelength/nm Fig. 2. UV–vis absorption spectra of different size gold nanoparticles.
352
Y.P. Dong et al. / Journal of Luminescence 154 (2014) 350–355
180
3000
160
luminol luminol-99nm GNP luminol-25nm GNP luminol-16nm GNP luminol-68nm GNP luminol-38nm GNP
CL intensity/a.u.
120 100 80 60
luminol luminol-k3Fe(CN)6
2500
luminol-K3Fe(CN)6-16nmGNP CL intensity/a.u.
140
luminol-K3Fe(CN)6-25nmGNP
2000
luminol-K3Fe(CN)6-38nmGNP luminol-K3Fe(CN)6-68nmGNP
1500
luminol-K3Fe(CN)6-99nmGNP 1000
40
500
20 0
0
-20 0
5
10
15
20
25
0
30
5
10
Time/s
3.2. Gold nanoparticles catalyzed luminol and K3Fe(CN)6 CL system Despite gold nanoparticles could enhance CL with luminol, the CL intensity is too weak to be applied. Therefore, different CL systems, such as luminol–H2O2, luminol–KMnO4, luminol–KIO3, luminol–K3Fe(CN)6, were selected to investigate the influence of gold nanoparticles on traditional CL systems. It was found that gold nanoparticles could significantly enhance CL signals of these systems. However, the obtained CL emission of luminol–K3Fe(CN)6 system is most stable and the enhancing effect of gold nanoparticles on luminol–K3Fe(CN)6 CL system was most significantly. Therefore, luminol–K3Fe(CN)6 system was used as a model to investigate the effect of gold nanoparticles on traditional CL emission. The effect of different size gold nanoparticles on luminol–K3Fe (CN)6 CL is investigated and shown in Fig. 4. It could be found that 38 nm gold nanoparticles exhibited the best enhancing effect, which is also in accordance with the results of Ref. [17]. It was reported that some reducing agents could decrease or increase luminol CL in alkaline solution [22]. Therefore, in the present study, some reducing reagents, such as citric acid, ascorbic acid, and cysteine, were added into luminol–K3Fe(CN)6–gold nanoparticles CL system to investigate their effects on CL signal. Fig. 5shows that cysteine can decrease CL signal while ascorbic acid and citric acid can enhance CL signal. Though citric acid could also enhance luminol CL, the enhancing effect of ascorbic acid is more significantly than that of citric acid, suggesting that citric acid might not influence the detection of ascorbic acid with the present luminol CL system. In order to support this assumption, the CL intensity was recorded by adding citric acid into ascorbic acid solution. The results revealed that only 3.4% increase in CL intensity was obtained after citric acid was added. Therefore, the interference from citric acid in the detection of ascorbic acid is not very serious. The possibility of using luminol–K3Fe(CN)6–gold nanoparticles CL system to detect ascorbic acid was investigated in the following text. Fig. 6 shows that ascorbic acid can enhance luminol–K3Fe(CN)6 CL signal. However, the enhancing effect of ascorbic acid to luminol–K3Fe (CN)6 CL was more significant in the presence of 38 nm gold nanoparticles, which suggested that the detection of ascorbic acid using luminol–K3Fe(CN)6–gold nanoparticles CL system will be more sensitive.
25
9000 8000
CL intensity/a.u.
the electron density in the conduction bands of nanoparticles, which is very important for the catalytic effect of gold nanoparticles [21]. Therefore, the catalytic effects also decreased with decreasing size below 38 nm in diameter due to the decrease in electron density with the decreasing particle size. These results reveal that gold nanoparticles could catalyze luminol CL.
20
Fig. 4. Enhancing effect of different sizes of gold nanoparticles on luminol–K3Fe (CN)6 CL system. luminol, 1.0 10 4 mol L 1; K3Fe(CN)6, 1.0 10 3 mol L 1; pH, 9.6; CBS, 0.1 mol L 1.
7000
luminol-K3Fe(CN)6-GNP-ascorbic acid
6000
luminol-K3Fe(CN)6-GNP-citric acid
5000
luminol-K3Fe(CN)6-GNP-cysteine
4000
luminol-K3Fe(CN)6-GNP
3000 2000 1000 0 -1000 -2
0
2
4
6
8
10
12
14
16
18
20
22
24
Time/s
Fig. 5. Effects of different reducing reagents on luminol–K3Fe(CN)6 CL catalyzed by 38 nm gold nanoparticles. luminol, 1.0 10 4 mol L 1; K3Fe(CN)6, 1.0 10 3 mol L 1; pH, 9.6; CBS, 0.1 mol L 1; ascorbic acid, 1.0 10 6 mol L 1; citric acid, 1.0 10 6 mol L 1; cysteine, 1.0 10 6 mol L 1.
9000
luminol-K3Fe(CN)6
8000
luminol-K3Fe(CN)6−AA
7000 CL intensity/a.u.
Fig. 3. Chemiluminescence of luminol catalyzed by different sizes of gold nanoparticles in alkaline aqueous solution. luminol, 1.0 10 4 mol L 1; pH, 9.6; CBS, 0.1 mol L 1.
15 Time/s
luminol-K3Fe(CN)6-38nmGNP
6000
luminol-K3Fe(CN)6-38nmGNP−AA
5000 4000 3000 2000 1000 0 0
5
10
15
20
25
30
Time/s Fig. 6. Enhancing effect of ascorbic acid on luminol–K3Fe(CN)6 CL system in the absence and presence of 38 nm gold nanoparticles. luminol, 1.0 10 4 mol L 1; K3Fe(CN)6, 1.0 10 3 mol L 1; pH, 9.6; CBS, 0.1 mol L 1; ascorbic acid, 1.0 10 6 mol L 1.
3.3. Effect of media and pH It is well known that luminol CL occurs in alkaline mediums. Various buffer solutions, such as NaH2PO4–Na2HPO4, Na2CO3– NaHCO3, NaOH–Na2B4O7 at 0.1 mol L 1 were examined and the strongest CL signal was obtained in Na2CO3–NaHCO3 medium.
Y.P. Dong et al. / Journal of Luminescence 154 (2014) 350–355
The effect of the concentration of luminol and K3Fe(CN)6 on the increased CL intensity is examined as shown in Fig. 7. It could be found from Fig. 7A that the CL intensity increases with the increase of luminol concentration in the range of 1.0 10 8 to 1.0 10 3 mol L 1. However, the CL intensity of the blank becomes very strong when the concentration of luminol was higher than 1.0 10 4 mol L 1. Considering the CL intensity and the consumption of the reagents, the concentration of luminol solution was adjusted to 1.0 10 4 mol L 1 for the following research work. The effect of K3Fe(CN)6 concentration in the range of 1.0 10 6 to 1.0 10 4 mol L 1 on the CL intensity is also examined and shown in Fig. 7B. It was found that the relative CL intensity increased with the increase of K3Fe(CN)6 concentration and reached a plateau at 1.0 10 3 mol L 1. Therefore, 1.0 10 3 mol L 1 was selected as the optimal concentration in the following study. 3.5. CL mechanism In order to investigate CL mechanism of luminol–K3Fe(CN)6– gold nanoparticles system, UV–vis absorption spectra are recorded and shown in Fig. 8. It could be found that the maximum surface plasma resonance (SPR) absorption band of 38 nm gold nanoparticles is located at 520 nm, with two absorption peaks of luminol located at 295 nm and 355 nm, and two absorption peaks of K3Fe(CN)6 located at 300 nm and 420 nm, respectively. When gold nanoparticles were mixed with K3Fe(CN)6, all absorption peaks still could be obtained, suggesting that gold nanoparticles did not react with K3Fe(CN)6. When luminol was added in the above mixing solution, the absorption peak of K3Fe(CN)6 located at 300 nm decreased apparently, while the SPR of gold nanoparticles changes a little, suggesting that luminol could react with K3Fe(CN)6 and could not react with gold nanoparticles. Moreover, the maximum SPR absorption band of gold nanoparticles did not change during mixing with luminol and K3Fe(CN)6 revealed that gold nanoparticles did not
30000 20000
CL intensity/a.u.
10000 0 0.0000
0.0002
0.0004
0.0006
0.0008
0.0010
0.000
0.001
0.002
0.003
0.004
0.005
8000 4000 0
C/mol L-1 Fig. 7. Effects of luminol concentration (A) and K3Fe(CN)6 concentration (B) on luminol–K3Fe(CN)6–GNP CL signals. pH, 9.6; CBS, 0.1 mol L 1; ascorbic acid, 1.0 10 6 mol L 1.
38nm GNP K3Fe(CN)6 K3Fe(CN)6-38nm GNP K3Fe(CN)6-38nm GNP-luminol luminol
Absorption
3.4. Effect of concentration of luminol and K3Fe(CN)6
2
1
0 300
400
500
600
700
Wavelength/nm Fig. 8. UV–vis absorption of 38 nm gold nanoparticles, luminol, K3Fe(CN)6, and their mixing solutions.
200 160 CL intensity/a.u.
Therefore, carbonate buffer solution (CBS) was selected as the working medium. The pH of CL system was investigated over the range of 8.6– 10.5. The CL intensity increased gradually from 8.6 to 9.6 and the maximum CL intensity was obtained at pH 9.6. Thus, a pH of 9.6 (0.1 mol L 1 CBS) was chosen as optimum for further experiments.
353
luminol-K3Fe(CN)6 luminol-K3Fe(CN)6-38nm GNP
120 80 40 0 350
400
450
500
550
Wavelength/nm
Fig. 9. CL spectra of luminol–K3Fe(CN)6 CL system in the absence and presence of 38 nm gold nanoparticles. luminol, 1.0 10 4 mol L 1; K3Fe(CN)6, 1.0 10 3 mol L 1; pH, 9.6; CBS, 0.1 mol L 1; ascorbic acid, 1.0 10 6 mol L 1.
participate CL reactions and the enhancing effect of gold nanoparticles should result from its catalytic effect. The CL spectra of luminol–K3Fe(CN)6 system and luminol–K3Fe (CN)6–gold nanoparticles system are obtained and shown in Fig. 9. It was found that the maximum emission for all cases was 425 nm, revealing that the luminophor for the CL system was still the excited state of 3-aminophthalate anion (AP2 ). That is to say, the presence of gold nanoparticles did not generate a new lumnophor for this CL system. According to Shevlin's result [23], the mechanism for the luminol–K3Fe(CN)6 CL system should be as follows: luminol was firstly oxidized by ferricyanide to generate luminol radical. Then, in the presence of oxygen and ferrocyanide, luminol radical was oxidized to hydroxyl hydroperoxide (LOO ) which could be decomposed to form the excited state AP2 and emit light. Gold nanoparticles could catalyze the oxidation reaction between the luminol radical and oxygen, resulting in an enhancement of the CL signal [17]. Kubo et al. reported that luminol could react with ascorbic acid to generate chemiluminescence in the presence of hexacyanoferrate. They proposed that ascorbic acid could reduce oxygen to superoxide radical in alkaline solution [22]. The produced superoxide radical reacted with luminol to generate light emission. Chen et al. reported the ascorbate radical will be formed by the oxidation of ascorbic acid which could enhance electrochemiluminescence of lucigenin [24]. It has already been proven that gold
354
Y.P. Dong et al. / Journal of Luminescence 154 (2014) 350–355
9000
Table 2 Determination of ascorbic acid in tap water and some real samples.
8000 Sample
Initially present (mol L 1)
Added amount (mol L 1)
Found amounta (mol L 1)
Recovery (%)
Tap water Vc tablet Orange juice
0 5.06 10 7 2.12 10 7
1.0 10 7 1.0 10 7 1.0 10 7
0.98 10 7 6.09 10 7 3.09 10 7
98 103 97
3.5
6000
log(I-I )
CL intensity/a.u.
7000
1µM
5000
3.0
2.5
4000
0
2.0
3000
-10
-9
-8
-7
-6
a
logC
Mean of three determinations.
2000 1000 0 0
5
10
15
20
25
Time/s Fig. 10. Relationship between the CL intensity and 0, 0.0001, 0.0005, 0.001, 0.01, 0.3, 0.5, 0.8, 1.0 μM ascorbic acid from bottom to top. The inset is the linear calibration plot for ascorbic acid. luminol, 1.0 10 4 mol L 1; K3Fe(CN)6, 1.0 10 3 mol L 1; pH, 9.6; CBS, 0.1 mol L 1.
Table 1 Comparison of the analytical data obtained by some CL method for the determination of ascorbic acid. CL Systems
Lucigenin Luminol–Fe3 þ –H2O2 H2O2–HCO3 –CdSe/CdS QDs Peroxynitrous acid Ce(IV)–Rhodamine B Luminol–K3Fe(CN)6–GNPs
Linear range (mol L 1)
9
4
1.0 10 –3.0 10 1.0 10 11–1.0 10 7 1.0 10 7–1.0 10 4 5.0 10 9–5.0 10 5 3.8 10 13–1.0 10 10 1.0 10 10–1.0 10 6
acceptable reproducibility. Therefore, gold nanoparticles involved luminol CL system could be successfully applied in ascorbic acid detection. Although the detection sensitivity of this CL system might be lower than some reported CL systems, this work still reveal the fact that nanoparticles might find its more application in CL detection, which is very important to the application research of various nanoparticles. The proposed method was applied to the determination of ascorbic acid in some real samples, such as fruit juice and vitamin C tablets, to which known amount of ascorbic acid standards were added. The results shown in Table 2 revealed that the determination of ascorbic acid in the real sample is satisfied.
Detection limit (mol L 1)
References
4. Conclusions
– 1.0 10 12 6.7 10 9 5.0 10 10 1.0 10 13 2.0 10 11
[28] [11] [10] [29] [9] this work
Gold nanoparticles could catalyze the chemiluminescence of luminol–K3Fe(CN)6 system and 38 nm gold nanoparticle exhibited the best catalyzing effect. The CL of luminol–K3Fe(CN)6–gold nanoparticles system could be strongly enhanced by the presence of ascorbic acid. Based on its enhancing effect, a novel CL method with a lower detection limit and wider linear range was developed for the determination of ascorbic acid and good recovery was obtained in the detection of ascorbic acid in some real samples.
nanoparticles exhibit excellent electrocatalytic activity towards the electro-oxidation of ascorbic acid [25,26]. From the results of spectral experiments, we could find that gold nanoparticles could not react with luminol or K3Fe(CN)6. Therefore, it is reasonable to deduce that gold nanoparticles could catalyze the oxidation of ascorbic acid to generate ascorbate radicals. The ascorbate radicals could then react with dissolved oxygen to generate superoxide radical which could react with luminol to generate strong CL emission.
Acknowledgments This work is financially supported by National Natural Science Foundation of China (Nos. 61271156, and 21207001), Natural Science Foundation of Anhui Province (1408085MF114), China Postdoctoral Science Foundation (2013M541637) and Innovation Team Project of AHUT (No. TD201204). References
3.6. Analytical application Generally, chemiluminescence signal can be described as a function of the analyte concentration. However, a linear representation could also be described as a plot of the logarithm of the relative chemiluminescence signal as a function of the logarithm of the analyte concentration [27]. Under the optimized experimental conditions, the calibration curve was found to be linear from 1.0 10 10 1.0 10 6 mol L 1 and a regression equation was log (I I0)¼ 6.1639 þ 0.4046 logC (R ¼0.998), where I I0 is the relative CL intensity and C is the concentration of ascorbic acid (Fig. 10). The detection limit (S/N ¼3) was 2.0 10 11 mol L 1. The relative standard deviation (RSD) of 10 parallel measurements at 1.0 10 6 mol L 1 ascorbic acid was 0.71%. The RSD of six parallel measurements in one week was 5.4%. The linear range and the detection limit of the proposed method are compared with the earlier reports in Table 1. The results indicate that the proposed CL system has good linearity, relatively high sensitivity and
[1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11] [12] [13] [14] [15] [16] [17] [18]
A. Aoki, T. Matsue, I. Uchida, Anal. Chem. 64 (1992) 44. A.M. Farrington, N. Jagota, J.M. Slater, Analyst 119 (1994) 233. M.A. Koupparis, P. Anagnostopoulou, H.V. Malmstadt, Talanta 32 (1985) 411. Q.L. Wang, Z.H. Liu, L.Y. Mao, R.X. Cai, Chin. J. Anal. Chem 28 (2000) 1229. J.K. Kwakye, Talanta 51 (2000) 197. R. Shakya, D.A. Navarre, J. Agric. Food. Chem. 54 (2006) 5253. S. Ashok Kumar, P.H. Lo, S.M. Chen, Biosens. Bioelectron. 24 (2008) 518. X.M. Cao, L.Q. Luo, Y.P. Ding, X.L. Zou, R.X. Bian, Sensor. Actuators B 129 (2008) 941. Y.J. Ma, M. Zhou, X.Y. Jin, B.Z. Zhang, H. Chen, N.Y. Guo, Anal. Chim. Acta 464 (2002) 289. H. Chen, R.B. Li, L. Lin, G.S. Guo, J.M. Lin, Talanta 81 (2010) 1688. A.A. Alwarthan, Analyst 118 (1993) 639. L. Wang, P. Yang, Y.X. Li, C.Q. Zhu, Talanta 70 (2006) 219. X. Wang, N. Na, S.C. Zhang, Y.Y. Wu, X.R. Zhang, J. Am. Chem. Soc. 129 (2007) 6062. N. Na, S.C. Zhang, X. Wang, X.R. Zhang, Anal. Chem. 81 (2009) 2092. Z.F. Zhang, H. Cui, C.Z. Lai, L.J. Liu, Anal. Chem. 77 (2005) 3324. H. Cui, Z.F. Zhang, M.J. Shi, Y. Xu, L. Wu, Anal. Chem. 77 (2005) 6402. H. Cui, Z.F. Zhang, M.J. Shi, J. Phys. Chem. B 109 (2005) 3099. C.F. Duan, H. Cui, Z.F. Zhang, B. Liu, J.Z. Guo, W. Wang, J. Phys. Chem. C 111 (2007) 4561.
Y.P. Dong et al. / Journal of Luminescence 154 (2014) 350–355
[19] [20] [21] [22] [23] [24]
S.F. Li, X.Z. Li, J. Xu, X.W. Wei, Talanta 75 (2008) 32. H.R. Schroeder, F.M. Yeager, Anal. Chem. 50 (1978) 1114. S. Link, M.A. El-sayed, Int. Rev. Phys. Chem. 19 (2002) 409. H. Kubo, A. Toriba, Anal. Chim. Acta 353 (1997) 345. P.B. Shevlin, H.A. Neufeld, J. Org. Chem. 35 (1970) 2178. J.H. Chen, Z.Y. Lin, G.N. Chen, Electrochim. Acta 52 (2007) 4457.
355
[25] P. Kannan, S. Abraham John, Anal. Biochem. 386 (2009) 65. [26] A. Sivanesan, P. Kannan, S.A. John, Electrochim. Acta 52 (2007) 8118. [27] S. Meseguer-Lloret, S. Torres-Cartas, M.C. Gomez-Benito, Anal. Bioanal. Chem. 398 (2010) 3175. [28] T. Perez-Ruiz, C. Martinez-Lozano, A. Sanz, Anal. Chim. Acta 308 (1995) 299. [29] Z.H. Wang, X. Teng, C. Lu, Analyst 137 (2012) 1876.