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Separation and spectrophotometric determination of azide
Analytica Chimica Acta, 87 (1976) 243-246 0 Elsevier SciP>tific Publishing Company, Amsterdam -
Printed in The Netherlands
Short Communication
SEPARATION AZIDE
E. A. NEVES, Institute Sao Paul0
AND SPECTROPHOTOMETRIC
E. DE OLIVEIRA
de Quimica
DETERMINATION
OF
and L. SANT’AGOSTINO
da Universidade
de Srio Paula,
Cidade
Universitdria,
c. post.
20780.
(Brazil)
(Received 4th March 1976)
Azide ions form complexes with several metal cations and this has been used for the calorimetric determination of several cations in aqueous medium [l-7] _ Conversely, azide can be determined with iron(III) reagents [8-111. Azide can be determined calorimetrically with carbon disulphide [ 121, but this procedure is kinetic dependent, and this class of product is unstable [ 131. The present com?unication reports an azide determination with copper(I1) ions, in which CuN, is formed quantitatively. Although the sensitivity is not markedly better than that of the iron(II1) method, the proposed method is baaed on superiorspectral characteristics since at the X,, (375 nm) there is no reagent absorption; moreover, the pH conditions are less critical. A separation method is described for the recovery of azide as the volatile hydrazoic acid. This separation procedure should make it possible to determine azide by various electrometric methods. Experimental Apparatus and reagents. A Beckman DU spectrophotometer and 1O-mn-1 silica cells were used. A.R. or C.P. reagents were used. Sodium azide (Merck) was purified by dissolving in water, filtering and precipitating with ethanol. Standard solutions were prepared from the anhydrous salt; working solutions were prepared as needed by dilution. The distillation apparatus consisted of a large test tube (5-cm diam., 20-cm high) with a sidearm packed with glass wool to prevent carryover of spray. A rubber stopper carried the nitrogen inlet tube drawn out to a fine tip to provide regular bubbles, and a separating funnel for the introduction of hydrogen sulphate solution. From the sidearm, a right-angled tube with a medium pore filter at the tip led to the absorber, which was a lo-ml conical flask with a sidearm at the base fitted with two small bulbs angled upwards. Procedures. In the absence of interfering ions, pipette 1.0 ml of acetate buffer solution (1 M sodium acetate-O.1 M acetic acid) into a lo-ml volumetric flask, add an aliquot (up to 3 ml) of the aqueous test solution, mix, add 5 ml of 0.92 M copper nitrate solution (containing 10m3M HN03) and
244
dilute to the mark with water. Measure at 3’75 nm against a copperacetate buffer blank. Prepare a calibration graph similarly. In the presence of interfering ions, use the distillation apparatus. Mix a volume of the test solution with 2.0 ml of standard 1.00 M sodium hydroxide in the distillation tube, add 10 drops of the 30 % hydrogen peroxide, st$ wait for at least 3 min and then add 3 ml of freshly prepared alkaline tin(I1) solution. (1.6 % (w/v) SnCI, solution in 0.2 M HCI treated with 1 M NaOH until the tin(I1) hydroxide precipitate dissolves.) Place 5 ml of saturated potassium hydrogensulphate in the funnel and 5.00 ml of 0.300 M sodium hydroxide in the absorber, and connect up the apparatus. Transfer the contents of the funnel to the tube, and pass nitrogen for 20 min (about 2 bubbles/s). Add 5.00 ml of 0.330 M acetic acid to the absorption solution, mix and add 5.00 ml of 1.33 M copper nitrate containing low3 M HNO,. Measure the absorbance at 375 nm and calculate the azide content from a calibration plot established in the same way. Results and discussion Effect of reaction conditions. When a fixed azide concentration (2 lo4 M) was treated with increasing concentrations of copper(H), the absorbance at 375 nm became constant with copper(I1) concentrations above 0.1 M. A concentration of 0.46 M was used in the final method to ensure reproducibility. Under these conditions Beer’s law was followed; but the addition of sodium acetate (0.01 M) improved the sensitivity. Probably some azide remained as undissociated hydrazoic acid in the absence of sodium acetate; more than 0.1 M acetate decreased the absorbance, probably because of anion competition. After the separation of azide by distillation into an alkaline absorbent, acetic acid was used for neutralization; a high acetate ion concentration resulted from this procedure. In tests on 2 - 10e4 M azide in the presence of O-1 M sodium acetate, free acetic acid in the range 5 10-2-2.10-3 M did not affect the absorbance, and Beer’s law was still obeyed. Neither copper(I1) nor acetate buffer concentration were critical parameters for the direct determination of azide in absence of interfering agents but free acetic acid decreased the sensitivity somewhat at the lo-* M level. Under the recommended conditions, the molar absorptivity was about 1600 1 mol-’ cm-‘. Separation of azide. Azide was volatilized from acidic solution as hydrazoic acid, which was transferred with a flow of nitrogen and recovered in a sodium hydroxide solution. For displacement of azide, a saturated potassium hydrogensulphate solution gave the best results. The bubbling rate of nitrogen was not critical. To check the efficiency of the transference, two concentrations of sodium hydroxide absorption solution were tested with and without cooling; the results are shown in Table 1. Comparison with direct measurements showed that 99.4 % of azide was recovered in 0.300 M sodium hydroxide at room temperature, after a bubbling time of 20 min. The use of an ice bath was unnecessary. For the separation method, a Ringbom plot indicated an optimal range of l
l
245 TABLE
1
Effect of bubbling time on the recovery of 5.00 ml of sodium azide (5.0 = IO* M) in two different hydroxide concentrations, with and without cooling [NaOH] Time
= 0.10 Ma
= 0.30 Ma
[NaOH]
= 0.30 M
% Recovery
Time (mm)
% Recovery
Time (min)
% Recovery
79.0 86.0 97.5 99.2 98.0 75.4 46.0
5 1G 15 20 30 40 60
78.4 81.8 93.2 95.2 99.6 98.8 86.8
5 10 15 20 30 40 60
79.2
(mm) 5 10 15 20 30 40 60
[NaOH]
85.0 97.8 99.4 98.8 96.8 90.0
aAbsorption vessel immersed in an ice bath.
0.085-0.55 mM or 3.6-23 pg ml-’ for azide. At 90 % transmittance, the limiting azide concentration was 0.029 mM or 1.2 pg ml-‘. The precision of the method was tested by 20 measurements of two azide concentrations; for 4.00 pg ml-’ and 21 pg ml-‘, the absorbances were 0.151 and 0.795, respectively, with standard deviations of 0.0016 in both cases. Effect of diverse ions. Anions like CW, S03*-, Sz03*-, S406*-, S*-, I-, Cl-, Br-, SCN, interfere in the direct procedure by reacting with copper(I1) to form complexes or precipitates. Nitrite oxidizes azide to nitrogen in acidic medium, as do several other oxidants, e.g. Mn04-, Cr207*-, 10, or C103-. Some anions like chloride interfere only in concentrations higher than 0.1 M. The separation of azide, as described above, eliminates many potentially interfering ions, except for oxidants and those anions which are carried over, with hydrazoic acid, e.g. cyanide and some sulphur anions. Many cations interfere in the direct reaction of azide with copper(I1) by competition and formation of precipitates, or weak or strong complexes. In fact, azide must often be determined in strong inert complexes, e.g. of platinum(IV), or in sparingly soluble salts, e.g. Pb(N3)2. In such cases, HNs evolution may be retarded. The effects of interfering ions were examined at two azide concentrations (4 and 21 fig ml-‘); 500 times these concentrations of iirterfering agents was added in each experiment, and the azide was separated and determined as described. Oxidizing agents such as NO*-, MnO, and Cr04*- (Cr,O,*-) virtually destroyed the azide ions. The anions CN-, SOS*-, S203*-, S406*-, S*and I- caused negative errors of 0.5-2 %, when the azide concentration was 21 pg ml-‘, and negative errors up to 10 % for 4 pg ml-’ azide. The cations Ni”, CO’+, Cd**, Mn2+, Cu2+, Zn**, CI?, Fe3+, NH,+, Al* (added as nitrates) did not interfere in the azide separation and determination; mercury(I) and the chloro complexes of Pt(IV) and Pd(I1) caused 4 % low results for azide at 4 pg ml-’ but the error was negligible at 21 pg ml-‘.
246 All the above-mentioned interferences were eliminated by previous treatment of the test solution with alkaline hydrogen peroxide and subsequent
elimination of the excess with Sn(OH)3-. Azide ions show exceptionally high resistance to oxidizing agents in alkaline media; even permanganate has no effect. Under such conditions CN, SCN, NO1 and all the sulphur anions mentioned are oxidized. Platinum, gold, palladium and silver ions are reduced to the metals by alkaline hydrogen peroxide. When a strong acid is added to displace the hydrazoic acid, oxidants in the test solution and those formed by interaction with hydrogen peroxide in alkaline medium e.g. 103-, MnO(OH)*, Cr04*--, COG, can destroy hydrazoic acid. The addition of excess of tin(I1) to the alkaline solution eliminates the excess of hydrogen peroxide. When the solution is acidified, tin(I1) reacts preferentially with any remaining oxidants. The treatment with alkaline hydrogen peroxide did not affect the azide concentration Checks on the determination of 4 pg ml-’ azide in the presence of 500-fold amounts of strong interferences such as NO*-, Mn04- and Cr04*-, showed that recovery of azide was complete. This work was supported by the FAPESP and CNPq Foundations, to whom the authors are greatly indebted. REFERENCES 1
F. G. Sherif and A M. Awad,
2 3 4 5 6 7 8 9
24 B. P. P_ P. H G. C. Y.
Anal. Chim. Acta, 26 (1962) 235; J. Inorg. Nucl. Chem., (1962) 179. K. S. Nair, L. H. Prabhu and D. G. Vartak, J. Sci- Ind. Res., 203 (1961) 487. Senise and 0. E. S. Godinho, J. Inorg. Nucl. Chem., 23 (1970) 3641. Senise, J. Am_ Chem. Sot., 81 (1959) 4196. Senise and E. A Neves, J. Inorg. Nucl. Chem., 34 (1972) 1923; 33 (1971) 351. K. El-Shamy and M. F. Nassar, J. Inorg. Nuci. Chem., 16 (1960) 124. Saini and G. Ostacoli, J. Inorg. Nucl. Chem., 8 (1958) 346. E. Robertson and C. M. Austin, Anal. Chem., 29 (1957) 854. Mizushima and T. Sekine, Rep. Gov. Chem. Ind. Res. Inst Tokyo, 50 (1955) 255.
R M Wallace and E K. Dukes, J. Phys. Chem., 65 (1961) 2094; Anal. Chem_, 242. 11 A Anton, J. G. Dodd and A. E. Harvey Jr., Anal. Chem., 32 (1960) 1209. 12 G. S. Johar, Taianta, 19 (1972) 1461. 13 E. A. Neves and D. W. France, J. Inorg. Nucl. Chem., 36 (1974) 3851. 10
33 (1961)
Printed in The Netherlands
Short Communication
SEPARATION AZIDE
E. A. NEVES, Institute Sao Paul0
AND SPECTROPHOTOMETRIC
E. DE OLIVEIRA
de Quimica
DETERMINATION
OF
and L. SANT’AGOSTINO
da Universidade
de Srio Paula,
Cidade
Universitdria,
c. post.
20780.
(Brazil)
(Received 4th March 1976)
Azide ions form complexes with several metal cations and this has been used for the calorimetric determination of several cations in aqueous medium [l-7] _ Conversely, azide can be determined with iron(III) reagents [8-111. Azide can be determined calorimetrically with carbon disulphide [ 121, but this procedure is kinetic dependent, and this class of product is unstable [ 131. The present com?unication reports an azide determination with copper(I1) ions, in which CuN, is formed quantitatively. Although the sensitivity is not markedly better than that of the iron(II1) method, the proposed method is baaed on superiorspectral characteristics since at the X,, (375 nm) there is no reagent absorption; moreover, the pH conditions are less critical. A separation method is described for the recovery of azide as the volatile hydrazoic acid. This separation procedure should make it possible to determine azide by various electrometric methods. Experimental Apparatus and reagents. A Beckman DU spectrophotometer and 1O-mn-1 silica cells were used. A.R. or C.P. reagents were used. Sodium azide (Merck) was purified by dissolving in water, filtering and precipitating with ethanol. Standard solutions were prepared from the anhydrous salt; working solutions were prepared as needed by dilution. The distillation apparatus consisted of a large test tube (5-cm diam., 20-cm high) with a sidearm packed with glass wool to prevent carryover of spray. A rubber stopper carried the nitrogen inlet tube drawn out to a fine tip to provide regular bubbles, and a separating funnel for the introduction of hydrogen sulphate solution. From the sidearm, a right-angled tube with a medium pore filter at the tip led to the absorber, which was a lo-ml conical flask with a sidearm at the base fitted with two small bulbs angled upwards. Procedures. In the absence of interfering ions, pipette 1.0 ml of acetate buffer solution (1 M sodium acetate-O.1 M acetic acid) into a lo-ml volumetric flask, add an aliquot (up to 3 ml) of the aqueous test solution, mix, add 5 ml of 0.92 M copper nitrate solution (containing 10m3M HN03) and
244
dilute to the mark with water. Measure at 3’75 nm against a copperacetate buffer blank. Prepare a calibration graph similarly. In the presence of interfering ions, use the distillation apparatus. Mix a volume of the test solution with 2.0 ml of standard 1.00 M sodium hydroxide in the distillation tube, add 10 drops of the 30 % hydrogen peroxide, st$ wait for at least 3 min and then add 3 ml of freshly prepared alkaline tin(I1) solution. (1.6 % (w/v) SnCI, solution in 0.2 M HCI treated with 1 M NaOH until the tin(I1) hydroxide precipitate dissolves.) Place 5 ml of saturated potassium hydrogensulphate in the funnel and 5.00 ml of 0.300 M sodium hydroxide in the absorber, and connect up the apparatus. Transfer the contents of the funnel to the tube, and pass nitrogen for 20 min (about 2 bubbles/s). Add 5.00 ml of 0.330 M acetic acid to the absorption solution, mix and add 5.00 ml of 1.33 M copper nitrate containing low3 M HNO,. Measure the absorbance at 375 nm and calculate the azide content from a calibration plot established in the same way. Results and discussion Effect of reaction conditions. When a fixed azide concentration (2 lo4 M) was treated with increasing concentrations of copper(H), the absorbance at 375 nm became constant with copper(I1) concentrations above 0.1 M. A concentration of 0.46 M was used in the final method to ensure reproducibility. Under these conditions Beer’s law was followed; but the addition of sodium acetate (0.01 M) improved the sensitivity. Probably some azide remained as undissociated hydrazoic acid in the absence of sodium acetate; more than 0.1 M acetate decreased the absorbance, probably because of anion competition. After the separation of azide by distillation into an alkaline absorbent, acetic acid was used for neutralization; a high acetate ion concentration resulted from this procedure. In tests on 2 - 10e4 M azide in the presence of O-1 M sodium acetate, free acetic acid in the range 5 10-2-2.10-3 M did not affect the absorbance, and Beer’s law was still obeyed. Neither copper(I1) nor acetate buffer concentration were critical parameters for the direct determination of azide in absence of interfering agents but free acetic acid decreased the sensitivity somewhat at the lo-* M level. Under the recommended conditions, the molar absorptivity was about 1600 1 mol-’ cm-‘. Separation of azide. Azide was volatilized from acidic solution as hydrazoic acid, which was transferred with a flow of nitrogen and recovered in a sodium hydroxide solution. For displacement of azide, a saturated potassium hydrogensulphate solution gave the best results. The bubbling rate of nitrogen was not critical. To check the efficiency of the transference, two concentrations of sodium hydroxide absorption solution were tested with and without cooling; the results are shown in Table 1. Comparison with direct measurements showed that 99.4 % of azide was recovered in 0.300 M sodium hydroxide at room temperature, after a bubbling time of 20 min. The use of an ice bath was unnecessary. For the separation method, a Ringbom plot indicated an optimal range of l
l
245 TABLE
1
Effect of bubbling time on the recovery of 5.00 ml of sodium azide (5.0 = IO* M) in two different hydroxide concentrations, with and without cooling [NaOH] Time
= 0.10 Ma
= 0.30 Ma
[NaOH]
= 0.30 M
% Recovery
Time (mm)
% Recovery
Time (min)
% Recovery
79.0 86.0 97.5 99.2 98.0 75.4 46.0
5 1G 15 20 30 40 60
78.4 81.8 93.2 95.2 99.6 98.8 86.8
5 10 15 20 30 40 60
79.2
(mm) 5 10 15 20 30 40 60
[NaOH]
85.0 97.8 99.4 98.8 96.8 90.0
aAbsorption vessel immersed in an ice bath.
0.085-0.55 mM or 3.6-23 pg ml-’ for azide. At 90 % transmittance, the limiting azide concentration was 0.029 mM or 1.2 pg ml-‘. The precision of the method was tested by 20 measurements of two azide concentrations; for 4.00 pg ml-’ and 21 pg ml-‘, the absorbances were 0.151 and 0.795, respectively, with standard deviations of 0.0016 in both cases. Effect of diverse ions. Anions like CW, S03*-, Sz03*-, S406*-, S*-, I-, Cl-, Br-, SCN, interfere in the direct procedure by reacting with copper(I1) to form complexes or precipitates. Nitrite oxidizes azide to nitrogen in acidic medium, as do several other oxidants, e.g. Mn04-, Cr207*-, 10, or C103-. Some anions like chloride interfere only in concentrations higher than 0.1 M. The separation of azide, as described above, eliminates many potentially interfering ions, except for oxidants and those anions which are carried over, with hydrazoic acid, e.g. cyanide and some sulphur anions. Many cations interfere in the direct reaction of azide with copper(I1) by competition and formation of precipitates, or weak or strong complexes. In fact, azide must often be determined in strong inert complexes, e.g. of platinum(IV), or in sparingly soluble salts, e.g. Pb(N3)2. In such cases, HNs evolution may be retarded. The effects of interfering ions were examined at two azide concentrations (4 and 21 fig ml-‘); 500 times these concentrations of iirterfering agents was added in each experiment, and the azide was separated and determined as described. Oxidizing agents such as NO*-, MnO, and Cr04*- (Cr,O,*-) virtually destroyed the azide ions. The anions CN-, SOS*-, S203*-, S406*-, S*and I- caused negative errors of 0.5-2 %, when the azide concentration was 21 pg ml-‘, and negative errors up to 10 % for 4 pg ml-’ azide. The cations Ni”, CO’+, Cd**, Mn2+, Cu2+, Zn**, CI?, Fe3+, NH,+, Al* (added as nitrates) did not interfere in the azide separation and determination; mercury(I) and the chloro complexes of Pt(IV) and Pd(I1) caused 4 % low results for azide at 4 pg ml-’ but the error was negligible at 21 pg ml-‘.
246 All the above-mentioned interferences were eliminated by previous treatment of the test solution with alkaline hydrogen peroxide and subsequent
elimination of the excess with Sn(OH)3-. Azide ions show exceptionally high resistance to oxidizing agents in alkaline media; even permanganate has no effect. Under such conditions CN, SCN, NO1 and all the sulphur anions mentioned are oxidized. Platinum, gold, palladium and silver ions are reduced to the metals by alkaline hydrogen peroxide. When a strong acid is added to displace the hydrazoic acid, oxidants in the test solution and those formed by interaction with hydrogen peroxide in alkaline medium e.g. 103-, MnO(OH)*, Cr04*--, COG, can destroy hydrazoic acid. The addition of excess of tin(I1) to the alkaline solution eliminates the excess of hydrogen peroxide. When the solution is acidified, tin(I1) reacts preferentially with any remaining oxidants. The treatment with alkaline hydrogen peroxide did not affect the azide concentration Checks on the determination of 4 pg ml-’ azide in the presence of 500-fold amounts of strong interferences such as NO*-, Mn04- and Cr04*-, showed that recovery of azide was complete. This work was supported by the FAPESP and CNPq Foundations, to whom the authors are greatly indebted. REFERENCES 1
F. G. Sherif and A M. Awad,
2 3 4 5 6 7 8 9
24 B. P. P_ P. H G. C. Y.
Anal. Chim. Acta, 26 (1962) 235; J. Inorg. Nucl. Chem., (1962) 179. K. S. Nair, L. H. Prabhu and D. G. Vartak, J. Sci- Ind. Res., 203 (1961) 487. Senise and 0. E. S. Godinho, J. Inorg. Nucl. Chem., 23 (1970) 3641. Senise, J. Am_ Chem. Sot., 81 (1959) 4196. Senise and E. A Neves, J. Inorg. Nucl. Chem., 34 (1972) 1923; 33 (1971) 351. K. El-Shamy and M. F. Nassar, J. Inorg. Nuci. Chem., 16 (1960) 124. Saini and G. Ostacoli, J. Inorg. Nucl. Chem., 8 (1958) 346. E. Robertson and C. M. Austin, Anal. Chem., 29 (1957) 854. Mizushima and T. Sekine, Rep. Gov. Chem. Ind. Res. Inst Tokyo, 50 (1955) 255.
R M Wallace and E K. Dukes, J. Phys. Chem., 65 (1961) 2094; Anal. Chem_, 242. 11 A Anton, J. G. Dodd and A. E. Harvey Jr., Anal. Chem., 32 (1960) 1209. 12 G. S. Johar, Taianta, 19 (1972) 1461. 13 E. A. Neves and D. W. France, J. Inorg. Nucl. Chem., 36 (1974) 3851. 10
33 (1961)