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Indirect spectrophotometric determination of sulphide with the ternary complex system Ag(I)—phen—BPR
Talunro. Vol. 28. pp. 853 10 854. 1981
0039.9140/S I j I 10853.02SO2.00/0 CopyrIght 0 1981 Pergamon Press Ltd
Prmted m Great Elntam. All rights reserved
SHORT
COMMUNICATIONS
INDIRECT SPECTROPHOTOMETRIC DETERMINATION OF SULPHIDE WITH THE TERNARY COMPLEX SYSTEM Ag(I)-phen-BPR WEI Fu-SHENG, Department
(Receiced Summary-Trace
ZHU
of Chemistry,
YIJ-REI, YIN FANG and SHEN NAI-KUI China University of Science and Technology, Hefei, Anhui. China
1 December
1980. Accepted
22 April
1981)
amounts
of sulphide can be determined from its effect on the ternary complex system Red (BPR), and l,lO-phenanthroline (phen). Sulphide in the range 5-120 ng/ml causes a decrease in absorption, that is a linear function of the concentration. Common metal ions such as Na+. K+, Cal’, Mg’+, Al’+, Mn2+ and anions such as F-, Cl-, NO;, SO:-, CO:-, and PO:- at the 4 pg/ml level or more do not interfere, but I- or CN- must be absent.
of Ag’, Bromopyrogallol
ternary complex system Ag(I)-phen-BPR and its application to the spectrophotometric determination of silver, and to indirect determination of cyanide were first reported by Dagnall and West.le3 This colour system is very sensitive, but must be applied rapidly because it is easy for a blue precipitate to appear. We have tried using gelatine (0.5% water aqueous solution) as protective agent and found that it stabilizes the coloured complex for over 10 hr. We have also found that traces of sulphide can suppress the colour reaction. On the basis of this effect, we have worked out an indirect method for spectrophotometric determination of sulphide. This paper reports the optimal conditions for this determination. It is more sensitive than the Methylene Blue method4 and the mercury chloranilate,5 copper diethyldithiocarbamate’ and copper thiothenoyltrifluoroacetane indirect methods. The general procedure is simple and the reproducibility good. It is satisfactory for determination of soluble sulphide in domestic sewage.
General
The
procedure
To a 25-ml standard
flask, add 1 ml of 20% ammonium acetate solution, 1 ml of O.lM EDTA, 0.5 ml of gelatine solution, 0.5 ml of l,lO-phenanthroline solution, test solution containing up to 3.0 pg of sulphide and 25 pg of silver(I), mix and add 1.0 ml of BPR solution and make up to volume with water. Mix well. After 10 min measure the absorbance in a l-cm cell at 640 nm against a reference blank containing all the reactants except silver(I) and sulphide. Determination
of soluble sulphide
Reagents
Prepare a 2.5-mg/ml stock solution and standardize it with sodium chloride. Protect it from sunlight and dilute to 25 pg/ml as working standard. Standard sulphide solurion 1.0 mg/ml. Use Na,S.9H,O of general-reagent grade, and standardize.’ Protect it from air and just before use dilute to 5.0 pg/ml as working standard. Bromopyrogullol Red (BPR) solution, O.OZS”;. Dissolve 25.0 mg of BPR in 100 ml of 12, ammonium acetate. Use a freshly prepared solution. I,l0-Phenanthroline Gelarine solution.
AND DISCUSSION
The mechanism ofthe indirect determination ofsulphide
EXPERIMENTAL
silver
sewuge
To 100 ml of sample add 1 ml of 0.333M potassium alum and 1 ml of IN sodium hydroxide to remove sus-, pended organic material and heavy metals. Mix well. Let stand awhile to settle. Pipette l-15 ml of the supernatant liquid into a 25-ml standard flask, and then apply the general procedure. Recovery of a spike of sulphide added to the supernatant liquid is 93- 1039,. and the coefficient of variation for the determination is 4.59; (0.68 ppm of sulphide. 11 variates).
RESULTS
Standard
in domestic
solurion.
solution. 0._74:, in alcohol. O.SP; in water.
853
The composition of the blue ternary complex was found to be [Ag(phen),], BPR by Dagnall and West.’ If a soluble sulphide is added to the system insoluble silver sulphide is formed; the concentration of free silver decreases and so does the colour of the solution. Figure 1 shows that the absorption spectrum of the Ag+-phen-BPR-S2mixture is similar to that of Ag+-phen-BPR, and i.,,,,, of both spectra is at the same wavelength. A mole-ratio plot shows that the reacting ratio of silver(I) to sulphide in this system is 2:l.
854
SHORT COMMUNICATIONS
plete within 5 min and the absorbance remains constant for 12 hr. The order of addition of reagents should be that given in the general procedure, especially the addition of sulphide. If the sulphide is added last, the system takes longer to reach equilibrium. Calibration and interferences
20
19
16
17
16
15
14
wave No. , 1000 cm-’
Fig. 1. Absorption spectra: (a) 0.001% BPR vs. water; (b) BPR as (a), plus 25 pg or Ag+ ; (c) BPR and Ag+ as (b), plus 1.30 pg of s -.
The calibration graph shows a linear decrease in the absorbance of a fixed amount of ternary complex as the sulphide concentration is increased up to 3.0 pg/25 ml. There was no interference from ammonium acetate (600 mg); EDTA (50 mg); Li+, Na’, K+, Zn”, Cl-. F-, NO;, SOi- (each 1.0 mg); Be’+, Mg’+, Ca2+. Sr2+, Ba’+, A13+, As3+, Cr3+, Mn2+. Co:-. SO:-. PO:(each 100 pg); Fe3+. Pb2+, Cd*+. SCN-, S#(each 10 l.(g) in determination of 2.5 kg of sulphide. Cyanide and iodide cannot be tolerated at all. REFERENCES
The molar absorptivity of the ternary complex is 5.1 x lo4 I.mole-‘.cm-’ at 635 nm,’ so the effective molar “desorptivity” of sulphide in this reaction is - 1.02 x lo5 I.mole-‘.cm-‘. Selection ofprotective colloid and the order of addition Since the blue colour formed by silver(I) with phen-BPR is unstable, Triton X-100, starch and gelatine were tried as protective colloids, and gelatine proved the best. With Triton X-100 a precipitate appears within 30 min, and a 1% starch solution stabilizes the colour for only about 2 hr, whereas with 0.5% gelatine solution the colour development is com-
1. R. M. Dagnall and T. S. West, Taluntu, 1964. It, 1533. 2. Idem. ibid., 1964, 11, 1627. 3. R. M. Dagnall, M. T. El-Ghamry and T. S. West. ibid..
1968, 15, 107. 4. 2. Marczenko,
Spectrophotometric Drrermination of Chichester, 1976. and W. Hinze, Anal. Chem., 1971, 43,
&ments. p. 506. Horwood, R. E. Humphrey
1100.
_
1973. 33, 691. T. Nakamura, Bunseki Kagaku, D. M. Degudii and K. A. Kitamura. ibid., 1978, 27, 527. Standard Methods for the Examination Waste Water, 14th Ed.. American
of
Water
and
Public Health Association, American Water Works Association and Water Pollution Control Federation, 1976.
0039.9140/S I j I 10853.02SO2.00/0 CopyrIght 0 1981 Pergamon Press Ltd
Prmted m Great Elntam. All rights reserved
SHORT
COMMUNICATIONS
INDIRECT SPECTROPHOTOMETRIC DETERMINATION OF SULPHIDE WITH THE TERNARY COMPLEX SYSTEM Ag(I)-phen-BPR WEI Fu-SHENG, Department
(Receiced Summary-Trace
ZHU
of Chemistry,
YIJ-REI, YIN FANG and SHEN NAI-KUI China University of Science and Technology, Hefei, Anhui. China
1 December
1980. Accepted
22 April
1981)
amounts
of sulphide can be determined from its effect on the ternary complex system Red (BPR), and l,lO-phenanthroline (phen). Sulphide in the range 5-120 ng/ml causes a decrease in absorption, that is a linear function of the concentration. Common metal ions such as Na+. K+, Cal’, Mg’+, Al’+, Mn2+ and anions such as F-, Cl-, NO;, SO:-, CO:-, and PO:- at the 4 pg/ml level or more do not interfere, but I- or CN- must be absent.
of Ag’, Bromopyrogallol
ternary complex system Ag(I)-phen-BPR and its application to the spectrophotometric determination of silver, and to indirect determination of cyanide were first reported by Dagnall and West.le3 This colour system is very sensitive, but must be applied rapidly because it is easy for a blue precipitate to appear. We have tried using gelatine (0.5% water aqueous solution) as protective agent and found that it stabilizes the coloured complex for over 10 hr. We have also found that traces of sulphide can suppress the colour reaction. On the basis of this effect, we have worked out an indirect method for spectrophotometric determination of sulphide. This paper reports the optimal conditions for this determination. It is more sensitive than the Methylene Blue method4 and the mercury chloranilate,5 copper diethyldithiocarbamate’ and copper thiothenoyltrifluoroacetane indirect methods. The general procedure is simple and the reproducibility good. It is satisfactory for determination of soluble sulphide in domestic sewage.
General
The
procedure
To a 25-ml standard
flask, add 1 ml of 20% ammonium acetate solution, 1 ml of O.lM EDTA, 0.5 ml of gelatine solution, 0.5 ml of l,lO-phenanthroline solution, test solution containing up to 3.0 pg of sulphide and 25 pg of silver(I), mix and add 1.0 ml of BPR solution and make up to volume with water. Mix well. After 10 min measure the absorbance in a l-cm cell at 640 nm against a reference blank containing all the reactants except silver(I) and sulphide. Determination
of soluble sulphide
Reagents
Prepare a 2.5-mg/ml stock solution and standardize it with sodium chloride. Protect it from sunlight and dilute to 25 pg/ml as working standard. Standard sulphide solurion 1.0 mg/ml. Use Na,S.9H,O of general-reagent grade, and standardize.’ Protect it from air and just before use dilute to 5.0 pg/ml as working standard. Bromopyrogullol Red (BPR) solution, O.OZS”;. Dissolve 25.0 mg of BPR in 100 ml of 12, ammonium acetate. Use a freshly prepared solution. I,l0-Phenanthroline Gelarine solution.
AND DISCUSSION
The mechanism ofthe indirect determination ofsulphide
EXPERIMENTAL
silver
sewuge
To 100 ml of sample add 1 ml of 0.333M potassium alum and 1 ml of IN sodium hydroxide to remove sus-, pended organic material and heavy metals. Mix well. Let stand awhile to settle. Pipette l-15 ml of the supernatant liquid into a 25-ml standard flask, and then apply the general procedure. Recovery of a spike of sulphide added to the supernatant liquid is 93- 1039,. and the coefficient of variation for the determination is 4.59; (0.68 ppm of sulphide. 11 variates).
RESULTS
Standard
in domestic
solurion.
solution. 0._74:, in alcohol. O.SP; in water.
853
The composition of the blue ternary complex was found to be [Ag(phen),], BPR by Dagnall and West.’ If a soluble sulphide is added to the system insoluble silver sulphide is formed; the concentration of free silver decreases and so does the colour of the solution. Figure 1 shows that the absorption spectrum of the Ag+-phen-BPR-S2mixture is similar to that of Ag+-phen-BPR, and i.,,,,, of both spectra is at the same wavelength. A mole-ratio plot shows that the reacting ratio of silver(I) to sulphide in this system is 2:l.
854
SHORT COMMUNICATIONS
plete within 5 min and the absorbance remains constant for 12 hr. The order of addition of reagents should be that given in the general procedure, especially the addition of sulphide. If the sulphide is added last, the system takes longer to reach equilibrium. Calibration and interferences
20
19
16
17
16
15
14
wave No. , 1000 cm-’
Fig. 1. Absorption spectra: (a) 0.001% BPR vs. water; (b) BPR as (a), plus 25 pg or Ag+ ; (c) BPR and Ag+ as (b), plus 1.30 pg of s -.
The calibration graph shows a linear decrease in the absorbance of a fixed amount of ternary complex as the sulphide concentration is increased up to 3.0 pg/25 ml. There was no interference from ammonium acetate (600 mg); EDTA (50 mg); Li+, Na’, K+, Zn”, Cl-. F-, NO;, SOi- (each 1.0 mg); Be’+, Mg’+, Ca2+. Sr2+, Ba’+, A13+, As3+, Cr3+, Mn2+. Co:-. SO:-. PO:(each 100 pg); Fe3+. Pb2+, Cd*+. SCN-, S#(each 10 l.(g) in determination of 2.5 kg of sulphide. Cyanide and iodide cannot be tolerated at all. REFERENCES
The molar absorptivity of the ternary complex is 5.1 x lo4 I.mole-‘.cm-’ at 635 nm,’ so the effective molar “desorptivity” of sulphide in this reaction is - 1.02 x lo5 I.mole-‘.cm-‘. Selection ofprotective colloid and the order of addition Since the blue colour formed by silver(I) with phen-BPR is unstable, Triton X-100, starch and gelatine were tried as protective colloids, and gelatine proved the best. With Triton X-100 a precipitate appears within 30 min, and a 1% starch solution stabilizes the colour for only about 2 hr, whereas with 0.5% gelatine solution the colour development is com-
1. R. M. Dagnall and T. S. West, Taluntu, 1964. It, 1533. 2. Idem. ibid., 1964, 11, 1627. 3. R. M. Dagnall, M. T. El-Ghamry and T. S. West. ibid..
1968, 15, 107. 4. 2. Marczenko,
Spectrophotometric Drrermination of Chichester, 1976. and W. Hinze, Anal. Chem., 1971, 43,
&ments. p. 506. Horwood, R. E. Humphrey
1100.
_
1973. 33, 691. T. Nakamura, Bunseki Kagaku, D. M. Degudii and K. A. Kitamura. ibid., 1978, 27, 527. Standard Methods for the Examination Waste Water, 14th Ed.. American
of
Water
and
Public Health Association, American Water Works Association and Water Pollution Control Federation, 1976.