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Flow-Injection Spectrophotometric Determination of Hydrazine
MICROCHEMICAL JOURNAL ARTICLE NO.
56, 269–275 (1997)
MJ961403
Flow-Injection Spectrophotometric Determination of Hydrazine Ali A. Ensafi1 and B. Naderi College of Chemistry, Isfahan University of Technology, Isfahan, Iran Received January 19, 1996; accepted July 19, 1996
A flow-injection spectrophotometric method for the determination of hydrazine is described. The method is based on the inhibitory effect of hydrazine on the reaction of thionine with nitrite in acidic media. The decolorization of thionine by the reaction with nitrite was used to monitor the reaction spectrophotometrically at 602 nm. The variables that affected the reaction rate were fully investigated and the optimum conditions were established. Hydrazine can be determined in the range 2.0–40.0 mg/ml with a limit of detection of 1.0 mg/ml. The relative standard deviation for 10 replicate determinations of 7.0 mg/ml hydrazine is 3.3%. The method is simple, rapid, and widely applicable. q 1997 Academic Press
INTRODUCTION
Hydrazine and its derivatives have been used in industry and agriculture. Hydrazine is a toxic substance. Thus, there has been an increasing demand for a highly sensitive, rapid, automated, and selective method for determination of hydrazine in various samples. Various methods such as spectrophotometry (1), potentiometry (2, 3), coulometry (4, 5), amperometry (6–8), titrimetry (9), and ion selective electrode (10, 11) have been used for the determination of hydrazine. Recently, a range of sophisticated commercial detectors for hydrazine have been described and their relative merits compared (12). Many automatic flow-injection techniques have been used for the determination of hydrazine (13–20). Some of the sensitive methods are based on construction of chemically modified electrodes (13–16) and thus require special equipment and carefully controlled conditions or, in some, a complete report on selectivity. A Flow-injection spectrophotometric methods (17–20) are used for determination of low levels of hydrazine based on its reaction with dimethyl benzaldehyde (18) and 4-dimethyl-aminobenzaldehyde (19). But these methods require special equipment (expensive diode-array detection system) (17, 20) or have a high limit of detection with low precision (18, 19). This paper describes the development of a new flow-injection method for the determination of hydrazine based on its inhibitory effect on the oxidation of thionine by nitrite in sulfuric acid media. This method is new, rapid, simple, and relatively selective and sensitive and requires only a simple photometer with a flow cell for analysis. 1
To whom correspondence should be addressed. 269 0026-265X/97 $25.00 Copyright q 1997 by Academic Press All rights of reproduction in any form reserved.
ah08$$1403
06-12-97 20:55:50
micas
AP: MCH
270
ENSAFI AND NADERI
EXPERIMENTAL
Reagents Doubly distilled water and analytical reagent-grade chemicals were used throughout. Thionine solution (1.05 1 1003 M) was prepared by dissolving 0.0600 g of thionine (Aldrich) in water and diluting to 250 ml in a 250-ml standard flask. Nitrite solution (1000 mg/ml) was prepared by dissolving 0.1500 g of sodium nitrite (Merck) in water in a 100-ml standard flask. A stock solution of hydrazine (1000 mg/ml) was prepared by dissolving hydrazinium sulfate (Merck) in water. Apparatus A Shimadzu Model SPD-6AV spectrophotometer with a 20-ml flow cell, a 12channel Desaga peristaltic pump, a Rheodyne injector, a mixing chamber, and a Varian recorder Model 9167 were used. All the solutions were previously heated to a working temperature, 30 { 0.17C, in a thermostated bath. Manifold and Procedure A three-line flow-injection manifold was employed. Water, thionine solution, and a mixture of sulfuric acid and nitrite were pumped at a constant flow rate of 0.5 ml/ min for each solution through silicon tubing of 1.0-mm i.d. via a Teflon mixing chamber. Solution entered the flow-through cell of the spectrophotometer via 170-cm Teflon tubing of reaction coil of 1.0-mm i.d., and the absorbance was monitored at 602 nm. A 170-ml hydrazine sample was then injected by the sample injector system into the H2O stream. During each injection, the increase in absorbance was recorded. The reaction coil is submerged in a water bath. A mixture of 1.0 N sulfuric acid and 1.6 1 1004 M thionine solution, 4.00 mg/ml nitrite solution, and water are each pumped at a flow rate of 0.5 ml/min. An 170-ml sample volume containing between 2.0 and 40.0 mg/ml hydrazine is injected into the carrier (water). The absorbance of thionine (at 602 nm) is measured and recorded. RESULTS AND DISCUSSION
Thionine is a dye and has been used as an indicating reagent for the determination of strong oxidation agents (21) and nitrite (22) by catalytic effects on the oxidation of dye by bromate. This dye can be oxidized rapidly in the presence of trace amounts of nitrite in acidic media, and a colorless product is produced. On the other hand, when trace amounts of hydrazine are added to the mixture of the reaction, the reaction rate strongly decreases. This is due to the reaction of hydrazine and nitrite, which inhibits the reaction of thionine with nitrite. Thus, the decrease in the reaction rate of thionine and nitrite causes an increase in the absorbance. The absorbance change was measured against hydrazine concentration. Effect of Variables The influence of sulfuric acid, nitrite, thionine, and temperature was investigated with 170 ml of 5.0 mg/ml hydrazine solution at 307C, pump flow rate of 0.5 ml/min, and reaction coil length of 170 cm.
ah08$$1403
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micas
AP: MCH
FLOW-INJECTION SPECTROPHOTOMETRY OF HYDRAZINE
271
FIG. 1. Effect of (a) sulfuric acid concentration and (b) nitrite concentration on peak height.
The influence of sulfuric acid and nitrite concentration was studied in the range 0.20–3.0 N and 0.20–4.00 mg/ml, respectively (Fig. 1). The results show that 1.0 N sulfuric acid and 4.00 mg/ml nitrite solution are the best. Thus, 1.0 N sulfuric acid and 4.00 mg/ml nitrite solution were selected. The influence of thionine concentration in the range 2.1–16.8 1 1005 M on sensitivity was studied. Figure 2 shows that by increasing the concentration of thionine, the
ah08$$1403
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AP: MCH
272
ENSAFI AND NADERI
FIG. 2. Effect of thionine concentration on sensitivity.
sensitivity was increased. Thus, 1.68 1 1004 M thionine solution was selected for routine work. Higher concentrations of the dye cannot be used due to absorptivity. The influence of temperature on sensitivity was studied in the range 5–607C. Increasing the temperature from 5 to 307C increased peak height, but at the higher
FIG. 3. Effect of (a) reagent flow rate, (b) reaction coil length, and (c) sample injection volume on peak height.
ah08$$1403
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AP: MCH
273
FLOW-INJECTION SPECTROPHOTOMETRY OF HYDRAZINE TABLE 1 Effect of Foreign Species on the Determination of 2.0 mg/ml Hydrazine
Tolerance limit (mg/ml)
Species Ag (I), Mn (II), Zn (II), Cd (II), U (VI), Ni (II), La (III), Ca (II), Co (II), Fe (III), Pb (II), Cu (II), Hg (II), Al (III), Sr (II), Na/, K/, NH4/, Bi (III), 0 20 20 30 0 0 0 20 20 20 C2O20 4 , ClO4 , SO4 , CO3 , PO4 , NO2 , IO3 , F , Cr2O7 , BO3 , P2O7 , (CH3)2CO, HCHO, NH2CONH2 , CH3CHO, thiourea, acetone, methyl ethyl ketone, ethanol Ba (II), Br0, SCN0, NH4OCl, NH2OH, V (III), ascorbic acid, HONH3Cl, formaldehyde S2O20 3 , phenyl hydrazine a
500a 100 10
Maximum species concentration tested.
temperature, peak height decreased. This effect is due to the fact that at high temperature (ú307C), the blank reaction rate was increased. Influence of Manifold Variables The influence of pump flow rate, sample injection volume, and length of reaction coil was studied in the presence of optimum reagent concentration and temperature with the 10.0 mg/ml hydrazine solution. In the application of any kinetic reaction, the change in reaction rate (in the absorbance) depends on the residence time of the sample zone in the system, i.e., on the flow rate and length of reaction coil. The effect of pump flow rate on peak height was studied over the range 0.25–0.75 ml/min in each stream. The lower flow rates gave higher peaks, but at 0.60 ml/min and greater values, peak height reproducibility was poor and the peak broadened, leading to lower sample throughput (Fig. 3a).
TABLE 2 Determination of Hydrazine Added to Water Sample Hydrazine concentration (mg/ml) Sample River water
Drinking water
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Added
Found
Recovery (%)
10.0 15.0 20.0 25.0 10.0 15.0 20.0 25.0
10.1 14.9 19.7 25.3 10.2 15.3 19.7 25.2
101 99 98 101 102 102 98 101
micas
AP: MCH
274
ENSAFI AND NADERI
Therefore, 0.50 ml/min was selected as the best compromise between the conflicting demands of reproducibility, sensitivity, and sample throughput. Reaction coils of 170–300 cm in length were tested. The peaks became higher as the length of coil increased (Fig. 3b). Thus, 300 cm of reaction coil was selected. The effect of sample injection volume was also studied in the range 110–450 ml (Fig. 3c). The magnitude of the signal increased by increasing the injected sample volume up to 170 ml. Above a sample volume of 170 ml, there was only a slight increase in peak height. Therefore, this sample volume can be considered optimum. Determination of Hydrazine Hydrazine can be determined in the range 2–40 mg/ml under the optimized conditions. The linear plot of peak height versus concentration had a correlation coefficient of 0.9999. The repeatability of the method is good. The relative standard deviations for 10 replicate determinations of 7.0, 15.0, and 20.0 mg/ml hydrazine were 3.30, 1.10, and 0.94%, respectively. The experimental limit of detection was 1.0 mg/ml hydrazine. The sampling rate was about 35–40 samples per hour. Interference The effect of various compounds, cations, and anions on the determination of 10.0 mg/ml hydrazine was studied with the optimum reagents and manifold variables at 307C. The results are summarized in Table 1. The tolerance limit was defined as the concentration of added species causing less than 3% relative error. Most anions, cations, and other compounds did not interfere with the determination. Application to Real Samples Hydrazine can be determined in water samples by the proposed method after addition to drinking water and river water. The results are shown in Table 2. CONCLUSION
This method can be used to determine hydrazine at levels as low as 1.0 mg/ml without the need for any preconcentration step and in the presence of large amounts of ammonia. This method is very rapid, simple, and more selective than other kinetic and FIA methods reported. REFERENCES 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12.
Dias, F.; Olojola, A. S.; Juselskis, B. Talanta 1979, 26, 47. Mcbride, W. R.; Heny, R. A.; Skolnic, S. Anal. Chem. 1951, 23, 890. Chunxu, Z.; Jinsheng, C.; Yaping, Z. Fenxi Haqxue 1992, 20, 294 (Chem. Abstr. 1992, 116, 2681386e). Athanasio-Malaki, E.; Koupparis, M. K. Talanta 1989, 36, 431. Szebelledy, L.; Somogyi, Z. Z. Anal. Chem. 1983, 112, 391. Jeffrey, W.; Rehrsson, R.; Susan, L.; Todd, L. Am. Ind. Hyg. Assoc. J. 1993, 54, 285. Mallelo, S. P.; Khandelwal, B. L. Mikrochim. Acta 1977, II(3/4), 245. Ikeda, S.; Sutake, H.; Kohri, Y. Chem. Lett. 1984, 6, 873. Huamin, J.; Weiying, H.; Erkany, W. Talanta 1992, 39, 45. Gawargious, Y. A.; Beseda, A. Talanta 1975, 22, 757. Ratcliffe, N. M. Anal. Chim. Acta 1990, 239, 257. Safavi, A.; Ensafi, A. A. Anal. Chim. Acta 1995, 300, 307.
ah08$$1403
06-12-97 20:55:50
micas
AP: MCH
FLOW-INJECTION SPECTROPHOTOMETRY OF HYDRAZINE 13. 14. 15. 16. 17. 18. 19. 20. 21. 22.
275
Hou, W.; Wang, E. Anal. Chim. Acta 1992, 257, 275. Korfhage, K. M.; Ravichandran, K.; Baldwine, R. P. Anal. Chem. 1984, 56, 1514. Wang, J.; Golden, T.; Li, R. Anal. Chem. 1988, 60, 1642. Wang, J.; Naser, N.; Angnes, L. Anal. Chem. 1992, 64, 1285. Gutierrez, M. C.; Gomez-Hens, A.; Perez-Bendito, D. Anal. Chim. Acta 1989, 225, 115. Novak, M.; Hlatky, J. Chem. Listy 1988, 82, 1307 (Chem. Abstr. 1989, 110, 185033u). Balconi, M. L.; Sigon, F.; Borgarello, M.; Ferraroli, R.; Realini, F. Anal. Chim. Acta 1990, 234, 167. Basson, W. D.; Staden, J. F. Analyst 1978, 103, 998. Pedreno, C. S.; Sierra, M. T.; Sierra, M. I.; Sanz, A. Analyst 1987, 112, 837. Lozana, C. M.; Ruiz, T. P.; Tomas, V.; Yague, E. Analyst 1988, 113, 1057.
ah08$$1403
06-12-97 20:55:50
micas
AP: MCH
56, 269–275 (1997)
MJ961403
Flow-Injection Spectrophotometric Determination of Hydrazine Ali A. Ensafi1 and B. Naderi College of Chemistry, Isfahan University of Technology, Isfahan, Iran Received January 19, 1996; accepted July 19, 1996
A flow-injection spectrophotometric method for the determination of hydrazine is described. The method is based on the inhibitory effect of hydrazine on the reaction of thionine with nitrite in acidic media. The decolorization of thionine by the reaction with nitrite was used to monitor the reaction spectrophotometrically at 602 nm. The variables that affected the reaction rate were fully investigated and the optimum conditions were established. Hydrazine can be determined in the range 2.0–40.0 mg/ml with a limit of detection of 1.0 mg/ml. The relative standard deviation for 10 replicate determinations of 7.0 mg/ml hydrazine is 3.3%. The method is simple, rapid, and widely applicable. q 1997 Academic Press
INTRODUCTION
Hydrazine and its derivatives have been used in industry and agriculture. Hydrazine is a toxic substance. Thus, there has been an increasing demand for a highly sensitive, rapid, automated, and selective method for determination of hydrazine in various samples. Various methods such as spectrophotometry (1), potentiometry (2, 3), coulometry (4, 5), amperometry (6–8), titrimetry (9), and ion selective electrode (10, 11) have been used for the determination of hydrazine. Recently, a range of sophisticated commercial detectors for hydrazine have been described and their relative merits compared (12). Many automatic flow-injection techniques have been used for the determination of hydrazine (13–20). Some of the sensitive methods are based on construction of chemically modified electrodes (13–16) and thus require special equipment and carefully controlled conditions or, in some, a complete report on selectivity. A Flow-injection spectrophotometric methods (17–20) are used for determination of low levels of hydrazine based on its reaction with dimethyl benzaldehyde (18) and 4-dimethyl-aminobenzaldehyde (19). But these methods require special equipment (expensive diode-array detection system) (17, 20) or have a high limit of detection with low precision (18, 19). This paper describes the development of a new flow-injection method for the determination of hydrazine based on its inhibitory effect on the oxidation of thionine by nitrite in sulfuric acid media. This method is new, rapid, simple, and relatively selective and sensitive and requires only a simple photometer with a flow cell for analysis. 1
To whom correspondence should be addressed. 269 0026-265X/97 $25.00 Copyright q 1997 by Academic Press All rights of reproduction in any form reserved.
ah08$$1403
06-12-97 20:55:50
micas
AP: MCH
270
ENSAFI AND NADERI
EXPERIMENTAL
Reagents Doubly distilled water and analytical reagent-grade chemicals were used throughout. Thionine solution (1.05 1 1003 M) was prepared by dissolving 0.0600 g of thionine (Aldrich) in water and diluting to 250 ml in a 250-ml standard flask. Nitrite solution (1000 mg/ml) was prepared by dissolving 0.1500 g of sodium nitrite (Merck) in water in a 100-ml standard flask. A stock solution of hydrazine (1000 mg/ml) was prepared by dissolving hydrazinium sulfate (Merck) in water. Apparatus A Shimadzu Model SPD-6AV spectrophotometer with a 20-ml flow cell, a 12channel Desaga peristaltic pump, a Rheodyne injector, a mixing chamber, and a Varian recorder Model 9167 were used. All the solutions were previously heated to a working temperature, 30 { 0.17C, in a thermostated bath. Manifold and Procedure A three-line flow-injection manifold was employed. Water, thionine solution, and a mixture of sulfuric acid and nitrite were pumped at a constant flow rate of 0.5 ml/ min for each solution through silicon tubing of 1.0-mm i.d. via a Teflon mixing chamber. Solution entered the flow-through cell of the spectrophotometer via 170-cm Teflon tubing of reaction coil of 1.0-mm i.d., and the absorbance was monitored at 602 nm. A 170-ml hydrazine sample was then injected by the sample injector system into the H2O stream. During each injection, the increase in absorbance was recorded. The reaction coil is submerged in a water bath. A mixture of 1.0 N sulfuric acid and 1.6 1 1004 M thionine solution, 4.00 mg/ml nitrite solution, and water are each pumped at a flow rate of 0.5 ml/min. An 170-ml sample volume containing between 2.0 and 40.0 mg/ml hydrazine is injected into the carrier (water). The absorbance of thionine (at 602 nm) is measured and recorded. RESULTS AND DISCUSSION
Thionine is a dye and has been used as an indicating reagent for the determination of strong oxidation agents (21) and nitrite (22) by catalytic effects on the oxidation of dye by bromate. This dye can be oxidized rapidly in the presence of trace amounts of nitrite in acidic media, and a colorless product is produced. On the other hand, when trace amounts of hydrazine are added to the mixture of the reaction, the reaction rate strongly decreases. This is due to the reaction of hydrazine and nitrite, which inhibits the reaction of thionine with nitrite. Thus, the decrease in the reaction rate of thionine and nitrite causes an increase in the absorbance. The absorbance change was measured against hydrazine concentration. Effect of Variables The influence of sulfuric acid, nitrite, thionine, and temperature was investigated with 170 ml of 5.0 mg/ml hydrazine solution at 307C, pump flow rate of 0.5 ml/min, and reaction coil length of 170 cm.
ah08$$1403
06-12-97 20:55:50
micas
AP: MCH
FLOW-INJECTION SPECTROPHOTOMETRY OF HYDRAZINE
271
FIG. 1. Effect of (a) sulfuric acid concentration and (b) nitrite concentration on peak height.
The influence of sulfuric acid and nitrite concentration was studied in the range 0.20–3.0 N and 0.20–4.00 mg/ml, respectively (Fig. 1). The results show that 1.0 N sulfuric acid and 4.00 mg/ml nitrite solution are the best. Thus, 1.0 N sulfuric acid and 4.00 mg/ml nitrite solution were selected. The influence of thionine concentration in the range 2.1–16.8 1 1005 M on sensitivity was studied. Figure 2 shows that by increasing the concentration of thionine, the
ah08$$1403
06-12-97 20:55:50
micas
AP: MCH
272
ENSAFI AND NADERI
FIG. 2. Effect of thionine concentration on sensitivity.
sensitivity was increased. Thus, 1.68 1 1004 M thionine solution was selected for routine work. Higher concentrations of the dye cannot be used due to absorptivity. The influence of temperature on sensitivity was studied in the range 5–607C. Increasing the temperature from 5 to 307C increased peak height, but at the higher
FIG. 3. Effect of (a) reagent flow rate, (b) reaction coil length, and (c) sample injection volume on peak height.
ah08$$1403
06-12-97 20:55:50
micas
AP: MCH
273
FLOW-INJECTION SPECTROPHOTOMETRY OF HYDRAZINE TABLE 1 Effect of Foreign Species on the Determination of 2.0 mg/ml Hydrazine
Tolerance limit (mg/ml)
Species Ag (I), Mn (II), Zn (II), Cd (II), U (VI), Ni (II), La (III), Ca (II), Co (II), Fe (III), Pb (II), Cu (II), Hg (II), Al (III), Sr (II), Na/, K/, NH4/, Bi (III), 0 20 20 30 0 0 0 20 20 20 C2O20 4 , ClO4 , SO4 , CO3 , PO4 , NO2 , IO3 , F , Cr2O7 , BO3 , P2O7 , (CH3)2CO, HCHO, NH2CONH2 , CH3CHO, thiourea, acetone, methyl ethyl ketone, ethanol Ba (II), Br0, SCN0, NH4OCl, NH2OH, V (III), ascorbic acid, HONH3Cl, formaldehyde S2O20 3 , phenyl hydrazine a
500a 100 10
Maximum species concentration tested.
temperature, peak height decreased. This effect is due to the fact that at high temperature (ú307C), the blank reaction rate was increased. Influence of Manifold Variables The influence of pump flow rate, sample injection volume, and length of reaction coil was studied in the presence of optimum reagent concentration and temperature with the 10.0 mg/ml hydrazine solution. In the application of any kinetic reaction, the change in reaction rate (in the absorbance) depends on the residence time of the sample zone in the system, i.e., on the flow rate and length of reaction coil. The effect of pump flow rate on peak height was studied over the range 0.25–0.75 ml/min in each stream. The lower flow rates gave higher peaks, but at 0.60 ml/min and greater values, peak height reproducibility was poor and the peak broadened, leading to lower sample throughput (Fig. 3a).
TABLE 2 Determination of Hydrazine Added to Water Sample Hydrazine concentration (mg/ml) Sample River water
Drinking water
ah08$$1403
06-12-97 20:55:50
Added
Found
Recovery (%)
10.0 15.0 20.0 25.0 10.0 15.0 20.0 25.0
10.1 14.9 19.7 25.3 10.2 15.3 19.7 25.2
101 99 98 101 102 102 98 101
micas
AP: MCH
274
ENSAFI AND NADERI
Therefore, 0.50 ml/min was selected as the best compromise between the conflicting demands of reproducibility, sensitivity, and sample throughput. Reaction coils of 170–300 cm in length were tested. The peaks became higher as the length of coil increased (Fig. 3b). Thus, 300 cm of reaction coil was selected. The effect of sample injection volume was also studied in the range 110–450 ml (Fig. 3c). The magnitude of the signal increased by increasing the injected sample volume up to 170 ml. Above a sample volume of 170 ml, there was only a slight increase in peak height. Therefore, this sample volume can be considered optimum. Determination of Hydrazine Hydrazine can be determined in the range 2–40 mg/ml under the optimized conditions. The linear plot of peak height versus concentration had a correlation coefficient of 0.9999. The repeatability of the method is good. The relative standard deviations for 10 replicate determinations of 7.0, 15.0, and 20.0 mg/ml hydrazine were 3.30, 1.10, and 0.94%, respectively. The experimental limit of detection was 1.0 mg/ml hydrazine. The sampling rate was about 35–40 samples per hour. Interference The effect of various compounds, cations, and anions on the determination of 10.0 mg/ml hydrazine was studied with the optimum reagents and manifold variables at 307C. The results are summarized in Table 1. The tolerance limit was defined as the concentration of added species causing less than 3% relative error. Most anions, cations, and other compounds did not interfere with the determination. Application to Real Samples Hydrazine can be determined in water samples by the proposed method after addition to drinking water and river water. The results are shown in Table 2. CONCLUSION
This method can be used to determine hydrazine at levels as low as 1.0 mg/ml without the need for any preconcentration step and in the presence of large amounts of ammonia. This method is very rapid, simple, and more selective than other kinetic and FIA methods reported. REFERENCES 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12.
Dias, F.; Olojola, A. S.; Juselskis, B. Talanta 1979, 26, 47. Mcbride, W. R.; Heny, R. A.; Skolnic, S. Anal. Chem. 1951, 23, 890. Chunxu, Z.; Jinsheng, C.; Yaping, Z. Fenxi Haqxue 1992, 20, 294 (Chem. Abstr. 1992, 116, 2681386e). Athanasio-Malaki, E.; Koupparis, M. K. Talanta 1989, 36, 431. Szebelledy, L.; Somogyi, Z. Z. Anal. Chem. 1983, 112, 391. Jeffrey, W.; Rehrsson, R.; Susan, L.; Todd, L. Am. Ind. Hyg. Assoc. J. 1993, 54, 285. Mallelo, S. P.; Khandelwal, B. L. Mikrochim. Acta 1977, II(3/4), 245. Ikeda, S.; Sutake, H.; Kohri, Y. Chem. Lett. 1984, 6, 873. Huamin, J.; Weiying, H.; Erkany, W. Talanta 1992, 39, 45. Gawargious, Y. A.; Beseda, A. Talanta 1975, 22, 757. Ratcliffe, N. M. Anal. Chim. Acta 1990, 239, 257. Safavi, A.; Ensafi, A. A. Anal. Chim. Acta 1995, 300, 307.
ah08$$1403
06-12-97 20:55:50
micas
AP: MCH
FLOW-INJECTION SPECTROPHOTOMETRY OF HYDRAZINE 13. 14. 15. 16. 17. 18. 19. 20. 21. 22.
275
Hou, W.; Wang, E. Anal. Chim. Acta 1992, 257, 275. Korfhage, K. M.; Ravichandran, K.; Baldwine, R. P. Anal. Chem. 1984, 56, 1514. Wang, J.; Golden, T.; Li, R. Anal. Chem. 1988, 60, 1642. Wang, J.; Naser, N.; Angnes, L. Anal. Chem. 1992, 64, 1285. Gutierrez, M. C.; Gomez-Hens, A.; Perez-Bendito, D. Anal. Chim. Acta 1989, 225, 115. Novak, M.; Hlatky, J. Chem. Listy 1988, 82, 1307 (Chem. Abstr. 1989, 110, 185033u). Balconi, M. L.; Sigon, F.; Borgarello, M.; Ferraroli, R.; Realini, F. Anal. Chim. Acta 1990, 234, 167. Basson, W. D.; Staden, J. F. Analyst 1978, 103, 998. Pedreno, C. S.; Sierra, M. T.; Sierra, M. I.; Sanz, A. Analyst 1987, 112, 837. Lozana, C. M.; Ruiz, T. P.; Tomas, V.; Yague, E. Analyst 1988, 113, 1057.
ah08$$1403
06-12-97 20:55:50
micas
AP: MCH