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Chemiluminescence determination of nitrate with photochemical activation in a flow injection system
Talanta, Vol. 42, No. 3, pp. 437-440, 1995
Pergamon
0039-9140(95)01431-4
CHEMILUMINESCENCE WITH
DETERMINATION
PHOTOCHEMICAL
ACTIVATION
INJECTION
Copyright ~) 1995 Elsevier Science Ltd Printed in Great Britain. All rights reserved 0039-9140/95 $9.50 + 0.00
OF
NITRATE
IN A FLOW
SYSTEM
L t u RENMIN, LIU DAOJIE, SUN AILING a n d LIU GUIHUA Department of Chemistry, Liaocheng Teachers College, Shandong, P.R. China
(Received 17 May 1994. Reeised 19 September 1994. Accepted 23 September 1994)
Summary--A chemiluminescence
flow injection system is described for the determination of nitrate, involving use of a laboratory-built flow-through photochemical reactor. O p t i m u m analytical conditions were established. The linear range for nitrate is 7 × 10 -~ 1 × 10-4M. The sampling frequency is 60 samples per hour. The relative standard deviation for 1 × 10 7 1 x 10 6 and I × 10 5M nitrate is 0.97, 0.84 and 0.76%, respectively. The method has been applied to the determination of nitrate in natural water samples, and recoveries of 96 103% have been attained.
INTRODUCTION
Photochemical analysis is based on the utilization of photochemical reaction in the process of analysis. It has been increasingly used in various fields, owing to its high sensitivity and selectivity. Flow injection analysis (FIA) offers high throughput, cost-effective performance and versatility. The combination of FIA technique with photochemical analysis provides a novel means for studies of photochemical analysisJ 7 The amperometric determination of oxalate based on the photochemical reaction taking place in the reaction coil of a FIA system that was irradiated with visible light has been reportedJ A second approach to the photochemical determination of this analyte was based on the use of an amperometric flow cell with several optical fiber, which irradiated the sample only in the flow c e l l / A similar use of a photochemical reaction in FIA, with unstable compounds such as phenothiazines under ultraviolet radiation was reported? The simultaneous determination of chlorprolazine and promethazine using different configurations for implementation of the photochemical reactions was also reported. 4 Another FIA system involving photochemical reaction is on-line photochemical oxidation of organoarsenicals to inorganic arsenic. 5 In our previous work, a flow-through photochemical reactor was constructed and used in a FIA system for the determination of nitrite based on its inhibitory effect on the photochemical reaction between iodine and ethylenediaminete437
traacetic acid. 6 A second approach of our work to photochemical determination in a FIA system was simultaneous determination of iron(II) and iron(III) based on the photochemical reduction of iron(lII)-l,10-phenanthroline complex to iron(II)-I,10-phenanthroline complex/ When an acidified nitrate solution is irradiated with ultraviolet light, species like peroxonitrite are formed in the solution, which are the oxidants of iuminol. Chemiluminescence was found to appear after mixing an alkaline luminol solution and an acidified nitrate solution initially irradiated with a mercury lamp. A conventional chemiluminescence method was established by Kalinichenko et al. s In the present work, a flow-through photochemical reactor was constructed and used for the study of determination of nitrate in a FIA system, based on the photochemical activation and chemiluminescence reactions. The proposed method shows high sensitivity, selectivity and speed.
EXPERIMENTAL
Reagents
A standard stock solution of nitrate was prepared at 0.1M with analytical pure sodium nitrate. The working solution was prepared by diluting the stock solution with a sulfuric acid solution at pH 5.0. The carrier solution was sulfuric acid solution, pH 5.0.
438
LiE RENMINet al. s
40
cD
Luminoi
W
ml/min W Fig. 1. Schematic diagram of the FIA system. P, Peristaltic pump; S, sample; V, injection valve; PR, photochemical reactor; LI, L2, connection tube; D, detector; R, recorder; C, carrier; W, waste. The luminol reagent solution was 5 × 10-SM with 0.1M potassium hydroxide. Apparatus
The flow injection manifold used is shown in Fig. 1. The peristaltic pump, injection valve and chemiluminescence detector are a FICT-8604 chemiluminescence analyzer (Jiangsu Electroanalytical Instrument Plant). The chemiluminescence signal was recorded with an XWT-S platform recorder (The Third Automatic Instrument Plant of Shanghai). A photochemical reactor (made in this laboratory, Fig. 2) was used in the FIA system. A iminodiacetyl ligand exchange resin column was used in the FIA system to remove the interference of Fe 3+, Cu ~+, Co 2+ and Ni 2+. Procedure
The FIA system was connected up with P T F E tubing (0.8 m m i.d.) according to the arrangement shown in Fig. 1. The flow-rates of carrier and luminol reagent were adjusted according to the parameters given in Fig. 1. The sampling time was 20 sec and the injection time 40 sec. So the sampling frequency was 60 samples/hr. The chemiluminescence signal was recorded with the recorder. Nitrate was determined according to the peak height.
.~30 ~Q
/
/
20
10
! I
I 50
I
100
I
I
150 200 250 cm Fig. 3. Influence of the length of reaction tube of the photochemical reactor. 0
A series of nitrate standard solution was prepared and injected into the carrier before and after the sample runs.
RESULTS AND DISCUSSION Photochemical reactor
The main parts of the photochemical reactor are the light source and reaction tube. Nitrate has an absorption peak at 202 nm (e = 9500) and an absorption peak at 304 nm (~ = 9 ) . When the acidified nitrate solution is irradiated with ultraviolet light, species like peroxonitrite are formed, which are oxidants of luminol. A G G Z - 1 2 5 W high-pressure mercury lamp was used as the light source for the photochemical reactor. An auger-type quartz tube was used as the reaction tube of the photochemical reactor. Its length was found to have a significant effect on the photochemical activation. Higher sensitivity can be obtained when a longer reaction tube is used. Figure 3 shows the influence of the length of reaction tube on the determination of 1.0 × 10-6M nitrate. It can be seen from Fig. 3 that the chemiluminescence intensity basically reached the maximum when a 200 cm long
Air
50F
III
40 7°'~
220
1
/o.o'°'oo
"7:,
V
T
2
°~o--o--o~o,~o~
!
!
8.0cm I I I Cool air Fig. 2. Schematic diagram of the flow-through photochemical reactor.
10 0
2
I
4
I
6
I
8
I
10
I
12
I
14
pH
Fig. 4. Influence of pH. (I) Carrier: (2) luminal reagent.
Chemiluminescence determination of nitrate
"°I
Table 1. Effect of foreign ions on the determination of 1.0 x 10-6M nitrate
/" " e~e
311
~'O
I 7
I 6
Tolerated molar ratio (ion:nitrate)
Foreign ion
,.
1 8
439
I 5
-lg C Fig. 5. Influence of the concentration of luminol.
reaction tube was used. In the following experiments, a 200 cm long reaction tube was used.
Connection tube L~ and L2 The lifetime of the photochemical product, like peroxonitrite, and the chemiluminescence between the product and luminol is relatively short. Hence, the length of the connection tubes L~ and L 2 must be short. In the following experiments, the length of L~ is 15 cm, and L2 is 5 cm.
Effect of pH Keeping the pH of the mixture of carrier and luminol reagent solution constant, the influence of the pH of the carrier on the determination of 1 × 10 6 M nitrate was studied. Keeping the pH of the carrier constant, the influence of luminol reagent solution on the determination was studied. All the results are shown in Fig. 4. In the following experiments, the pH of the carrier was controlled at 5.0, and that of luminol reagent solution at 13.0.
Concentration of luminol The influence of the concentration of luminol on the determination of i.0 x 10 6 M nitrate (Fig. 5). Figure 5 shows that high chemiluminescence intensity can be attained when a luminol of high concentration is used. However, a spill-
CI-, F - , SO~-, C l O g , PO] Ap +, Zn -'+, Cd 2+, Fe-'~ Br-, VOw, WO 4 , NH + Mn 2+ Fe 3~ 1-, C1Oj , CrO~ , NO., Cu 2+, Co -'+, Ni 2+ BrO 3 , lO 3 , MoO~ Fe 3+ Cu:+, Co'-+, Ni 2+
10,000 1000 30 15 10 2 1 0.5 0.1" 0.01"
*No iminodiacetyl ligand exchange resin column in FIA system.
over signal is given out by the chemiluminescence analyzer when the concentration of luminol is higher than l x 10 a M , and this made the determination impossible. In the following experiments, a 5 x 1 0 5 M luminol solution was used.
Calibration According to the proposed procedure, the calibration graph was established with standard solutions of nitrate. The linear range for nitrate is from 7.0 × 10 8 to 1.0 × 104M. The precision for the determination of nitrate was measured by analysing 1.0 x 10 -7, 1.0 × 10 6 and 1.0 x 10 5M nitrate standard solution 11 times. The relative standard deviations were 0.97, 0.84 and 0.76, respectively.
Interference of foreign ions The interference of a number of foreign ions was studied by addition of such ions to 1.0 × l0 6 M nitrate. The results listed in Table 1 show the high selectivity of the method (with a relative error of less than 5%),
Applications Natural water samples were determined by the proposed method and the cadmium column
Table 2. Determination of nitrate in natural water samples
Sample Tap water River water Lake water Well water Deep well water
Data obtained by the proposed method (rng /I.)
Data obtained by cadmium reduction method (mg /l.)
Relative
0.64 1.14 2.06 0.88 1.26
0.67 1.12 2.10 0.90 1.23
-4.5 1.8 1.9 - 2.2 2.4
(%)
LIu RENMIN et al.
440
Table 3. Recovery of nitrate from natural water samples
Sample Tap water River water Lake water Well water Deep well water
Nitrate found
Total nitrate present after addition
Recovery
(mg/I.)
(mg/I.)
( %)
0.64 I. 14 2.06 0.88 1.26
1.66 2.10 3.09 1.86 2.26
102 96 103 98 100
REFERENCES 1. L. E. Leon, A. Rios, M. D. Luque de Castro and
reduction method. 9 The results are listed in Table 2. Table 3 shows the results obtained with the proposed method for natural water samples to which 1.0 mg/1. nitrate was added. It can be seen from Table 3 that recoveries o f 94-103% can be attained.
M. Valcarcel, Analyst, 1990, 115, 1549. 2. L. E. Leon, A. Rios, M. D. Luque de Castro and M. Valcarcel, Anal. Chim. Acta, 1990, 234, 227. 3, D. Chen, A. Rios, M. D. Luque de Castro and M. Valcarcel, Analyst, 1991, 116, 171. 4, D. Chen, A. Rios, M. D. Luque de Castro and M. Valcarcel, Talanta, 1991, 38, 1227. 5. R. H. Atallah and D. A. Kalman, Talanta, 1991, 38, 167. 6. R. Liu and D. Liu, Analyst, 1991, 116, 497. 7. R. Liu, D. Liu and A. Sun, Analyst, 1992, 117, 1767. 8. I. E. Kalinichenko, N. F. Kushchevskaya and A. T. Pilipenko, Zh. Anal. Khim., 1988, 43, I051. 9. The Compiling Group of Analytical Methods of Water and Waste Water of Bureau of Environmental Protection, Analytical Method for Water and Waste Water, Third Ed. p. 269. Chinese Environmental Science Press, Beijing, 1989.
Pergamon
0039-9140(95)01431-4
CHEMILUMINESCENCE WITH
DETERMINATION
PHOTOCHEMICAL
ACTIVATION
INJECTION
Copyright ~) 1995 Elsevier Science Ltd Printed in Great Britain. All rights reserved 0039-9140/95 $9.50 + 0.00
OF
NITRATE
IN A FLOW
SYSTEM
L t u RENMIN, LIU DAOJIE, SUN AILING a n d LIU GUIHUA Department of Chemistry, Liaocheng Teachers College, Shandong, P.R. China
(Received 17 May 1994. Reeised 19 September 1994. Accepted 23 September 1994)
Summary--A chemiluminescence
flow injection system is described for the determination of nitrate, involving use of a laboratory-built flow-through photochemical reactor. O p t i m u m analytical conditions were established. The linear range for nitrate is 7 × 10 -~ 1 × 10-4M. The sampling frequency is 60 samples per hour. The relative standard deviation for 1 × 10 7 1 x 10 6 and I × 10 5M nitrate is 0.97, 0.84 and 0.76%, respectively. The method has been applied to the determination of nitrate in natural water samples, and recoveries of 96 103% have been attained.
INTRODUCTION
Photochemical analysis is based on the utilization of photochemical reaction in the process of analysis. It has been increasingly used in various fields, owing to its high sensitivity and selectivity. Flow injection analysis (FIA) offers high throughput, cost-effective performance and versatility. The combination of FIA technique with photochemical analysis provides a novel means for studies of photochemical analysisJ 7 The amperometric determination of oxalate based on the photochemical reaction taking place in the reaction coil of a FIA system that was irradiated with visible light has been reportedJ A second approach to the photochemical determination of this analyte was based on the use of an amperometric flow cell with several optical fiber, which irradiated the sample only in the flow c e l l / A similar use of a photochemical reaction in FIA, with unstable compounds such as phenothiazines under ultraviolet radiation was reported? The simultaneous determination of chlorprolazine and promethazine using different configurations for implementation of the photochemical reactions was also reported. 4 Another FIA system involving photochemical reaction is on-line photochemical oxidation of organoarsenicals to inorganic arsenic. 5 In our previous work, a flow-through photochemical reactor was constructed and used in a FIA system for the determination of nitrite based on its inhibitory effect on the photochemical reaction between iodine and ethylenediaminete437
traacetic acid. 6 A second approach of our work to photochemical determination in a FIA system was simultaneous determination of iron(II) and iron(III) based on the photochemical reduction of iron(lII)-l,10-phenanthroline complex to iron(II)-I,10-phenanthroline complex/ When an acidified nitrate solution is irradiated with ultraviolet light, species like peroxonitrite are formed in the solution, which are the oxidants of iuminol. Chemiluminescence was found to appear after mixing an alkaline luminol solution and an acidified nitrate solution initially irradiated with a mercury lamp. A conventional chemiluminescence method was established by Kalinichenko et al. s In the present work, a flow-through photochemical reactor was constructed and used for the study of determination of nitrate in a FIA system, based on the photochemical activation and chemiluminescence reactions. The proposed method shows high sensitivity, selectivity and speed.
EXPERIMENTAL
Reagents
A standard stock solution of nitrate was prepared at 0.1M with analytical pure sodium nitrate. The working solution was prepared by diluting the stock solution with a sulfuric acid solution at pH 5.0. The carrier solution was sulfuric acid solution, pH 5.0.
438
LiE RENMINet al. s
40
cD
Luminoi
W
ml/min W Fig. 1. Schematic diagram of the FIA system. P, Peristaltic pump; S, sample; V, injection valve; PR, photochemical reactor; LI, L2, connection tube; D, detector; R, recorder; C, carrier; W, waste. The luminol reagent solution was 5 × 10-SM with 0.1M potassium hydroxide. Apparatus
The flow injection manifold used is shown in Fig. 1. The peristaltic pump, injection valve and chemiluminescence detector are a FICT-8604 chemiluminescence analyzer (Jiangsu Electroanalytical Instrument Plant). The chemiluminescence signal was recorded with an XWT-S platform recorder (The Third Automatic Instrument Plant of Shanghai). A photochemical reactor (made in this laboratory, Fig. 2) was used in the FIA system. A iminodiacetyl ligand exchange resin column was used in the FIA system to remove the interference of Fe 3+, Cu ~+, Co 2+ and Ni 2+. Procedure
The FIA system was connected up with P T F E tubing (0.8 m m i.d.) according to the arrangement shown in Fig. 1. The flow-rates of carrier and luminol reagent were adjusted according to the parameters given in Fig. 1. The sampling time was 20 sec and the injection time 40 sec. So the sampling frequency was 60 samples/hr. The chemiluminescence signal was recorded with the recorder. Nitrate was determined according to the peak height.
.~30 ~Q
/
/
20
10
! I
I 50
I
100
I
I
150 200 250 cm Fig. 3. Influence of the length of reaction tube of the photochemical reactor. 0
A series of nitrate standard solution was prepared and injected into the carrier before and after the sample runs.
RESULTS AND DISCUSSION Photochemical reactor
The main parts of the photochemical reactor are the light source and reaction tube. Nitrate has an absorption peak at 202 nm (e = 9500) and an absorption peak at 304 nm (~ = 9 ) . When the acidified nitrate solution is irradiated with ultraviolet light, species like peroxonitrite are formed, which are oxidants of luminol. A G G Z - 1 2 5 W high-pressure mercury lamp was used as the light source for the photochemical reactor. An auger-type quartz tube was used as the reaction tube of the photochemical reactor. Its length was found to have a significant effect on the photochemical activation. Higher sensitivity can be obtained when a longer reaction tube is used. Figure 3 shows the influence of the length of reaction tube on the determination of 1.0 × 10-6M nitrate. It can be seen from Fig. 3 that the chemiluminescence intensity basically reached the maximum when a 200 cm long
Air
50F
III
40 7°'~
220
1
/o.o'°'oo
"7:,
V
T
2
°~o--o--o~o,~o~
!
!
8.0cm I I I Cool air Fig. 2. Schematic diagram of the flow-through photochemical reactor.
10 0
2
I
4
I
6
I
8
I
10
I
12
I
14
pH
Fig. 4. Influence of pH. (I) Carrier: (2) luminal reagent.
Chemiluminescence determination of nitrate
"°I
Table 1. Effect of foreign ions on the determination of 1.0 x 10-6M nitrate
/" " e~e
311
~'O
I 7
I 6
Tolerated molar ratio (ion:nitrate)
Foreign ion
,.
1 8
439
I 5
-lg C Fig. 5. Influence of the concentration of luminol.
reaction tube was used. In the following experiments, a 200 cm long reaction tube was used.
Connection tube L~ and L2 The lifetime of the photochemical product, like peroxonitrite, and the chemiluminescence between the product and luminol is relatively short. Hence, the length of the connection tubes L~ and L 2 must be short. In the following experiments, the length of L~ is 15 cm, and L2 is 5 cm.
Effect of pH Keeping the pH of the mixture of carrier and luminol reagent solution constant, the influence of the pH of the carrier on the determination of 1 × 10 6 M nitrate was studied. Keeping the pH of the carrier constant, the influence of luminol reagent solution on the determination was studied. All the results are shown in Fig. 4. In the following experiments, the pH of the carrier was controlled at 5.0, and that of luminol reagent solution at 13.0.
Concentration of luminol The influence of the concentration of luminol on the determination of i.0 x 10 6 M nitrate (Fig. 5). Figure 5 shows that high chemiluminescence intensity can be attained when a luminol of high concentration is used. However, a spill-
CI-, F - , SO~-, C l O g , PO] Ap +, Zn -'+, Cd 2+, Fe-'~ Br-, VOw, WO 4 , NH + Mn 2+ Fe 3~ 1-, C1Oj , CrO~ , NO., Cu 2+, Co -'+, Ni 2+ BrO 3 , lO 3 , MoO~ Fe 3+ Cu:+, Co'-+, Ni 2+
10,000 1000 30 15 10 2 1 0.5 0.1" 0.01"
*No iminodiacetyl ligand exchange resin column in FIA system.
over signal is given out by the chemiluminescence analyzer when the concentration of luminol is higher than l x 10 a M , and this made the determination impossible. In the following experiments, a 5 x 1 0 5 M luminol solution was used.
Calibration According to the proposed procedure, the calibration graph was established with standard solutions of nitrate. The linear range for nitrate is from 7.0 × 10 8 to 1.0 × 104M. The precision for the determination of nitrate was measured by analysing 1.0 x 10 -7, 1.0 × 10 6 and 1.0 x 10 5M nitrate standard solution 11 times. The relative standard deviations were 0.97, 0.84 and 0.76, respectively.
Interference of foreign ions The interference of a number of foreign ions was studied by addition of such ions to 1.0 × l0 6 M nitrate. The results listed in Table 1 show the high selectivity of the method (with a relative error of less than 5%),
Applications Natural water samples were determined by the proposed method and the cadmium column
Table 2. Determination of nitrate in natural water samples
Sample Tap water River water Lake water Well water Deep well water
Data obtained by the proposed method (rng /I.)
Data obtained by cadmium reduction method (mg /l.)
Relative
0.64 1.14 2.06 0.88 1.26
0.67 1.12 2.10 0.90 1.23
-4.5 1.8 1.9 - 2.2 2.4
(%)
LIu RENMIN et al.
440
Table 3. Recovery of nitrate from natural water samples
Sample Tap water River water Lake water Well water Deep well water
Nitrate found
Total nitrate present after addition
Recovery
(mg/I.)
(mg/I.)
( %)
0.64 I. 14 2.06 0.88 1.26
1.66 2.10 3.09 1.86 2.26
102 96 103 98 100
REFERENCES 1. L. E. Leon, A. Rios, M. D. Luque de Castro and
reduction method. 9 The results are listed in Table 2. Table 3 shows the results obtained with the proposed method for natural water samples to which 1.0 mg/1. nitrate was added. It can be seen from Table 3 that recoveries o f 94-103% can be attained.
M. Valcarcel, Analyst, 1990, 115, 1549. 2. L. E. Leon, A. Rios, M. D. Luque de Castro and M. Valcarcel, Anal. Chim. Acta, 1990, 234, 227. 3, D. Chen, A. Rios, M. D. Luque de Castro and M. Valcarcel, Analyst, 1991, 116, 171. 4, D. Chen, A. Rios, M. D. Luque de Castro and M. Valcarcel, Talanta, 1991, 38, 1227. 5. R. H. Atallah and D. A. Kalman, Talanta, 1991, 38, 167. 6. R. Liu and D. Liu, Analyst, 1991, 116, 497. 7. R. Liu, D. Liu and A. Sun, Analyst, 1992, 117, 1767. 8. I. E. Kalinichenko, N. F. Kushchevskaya and A. T. Pilipenko, Zh. Anal. Khim., 1988, 43, I051. 9. The Compiling Group of Analytical Methods of Water and Waste Water of Bureau of Environmental Protection, Analytical Method for Water and Waste Water, Third Ed. p. 269. Chinese Environmental Science Press, Beijing, 1989.