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Fluorimetric determination of trace quantities of mercury as an ion-association complex with rhodamine 6G in the presence of iodide
0039-9140/60/1101-0911$02.00/0
T&rP Vol. 27. pp. 9 I I to 913 0 palrunotl PressLtd 1980.Printed in Great Britain
FLUORIMETRIC DETERMINATION OF TRACE QUANTITIES OF MERCURY AS AN ION-ASSOCIATION COMPLEX WITH RHODAMINE 6G IN THE PRESENCE OF IODIDE M. VLIAYAKUIUR,T. V.
RAMAKRWINA
and G.
AI~AVAMIJDAN
Department of Chemistry, Indian Institute of Technology, Madras 600 036, India (Received 29 May 1979. Revised 31 March 1980. Accepted 20 May 1980) Summary-A procedure for the indirect fluorimetric determination of mercury(l1) is described, based on selective extraction of the ion-association complex formed between triiodomercurateJlI1)and Rhodamine 6G and subsequent release of the fluorescent Rhodamine 6G. The calibration curve is linear up to 1ppm of mercury(U). The few interferences are easily overcome. Three Ruorimetric procedures based on ion-association complexes have been reported for determination d trace quantities of mercury. Those based on extrac-
tion of the tetrachloromercurate(II)-Rhodamine B complex into benzene-ether mixture from acid medium’ and the extraction of the tetrabromomercurate(II~Butylrhodamine B complex into benzene’ are quite sensitive, but interference studies have not been reported. The procedure3 based on the reduction in fluorescence intensity of Rhodomine 6G by complexation with tetraiodomercurate(I1) is subject to interferences. During an investigation of this last complex4 we ‘found that addition of small amounts of oxygencontaining solvents such as acetone caused complete dissociation of the ion-association complex. This has &een made the basis of a sensitive and selective tiethod for indirect fluorimetric determination of : =cw(W.
with mixing, 2 ml each of acetate buffer, sodium chloride and potassium iodide solutions followed by 2.5 ml of Rhodamine 6G solution. Dilute to about 15 ml with water and shake gently for 2-3 min with 5 ml of the benzenecyclohexane solvent mixture. Discard the aqueous phase. Mix 2.5 ml of the organic extract with 5 ml of IBMK and measure its fluorescence intensity at 560 nm, using a 365~nm excitation filter. Subtract the blank reading and establish the concentration of mercury by reference to a calibration graph prepared by applying the procedure to O-7.5 ml of 2-ppm mercury(I1) solution in place of the sample solution.
EXPERIMENTAL
Apparatus A Carl Zeiss PMQ II spectrophotometer with a ZFM 4 fluorescence attachment provided with a 250-W mercury vapour lamp was used. Slit-widths of 1 mm for the excitation filter and 0.06mm for the emission monochromator were employed for the fluorescence measurements with 10 x 10 x 45 mm quartz cells with polished bottoms. Standard mercury(ll) solution (2 ppm). Prepare a lOOO-ppmsolution of mercury(I1) by dissolving 0.3385 g of mercury(I1) chloride in water and making UD to 250 ml. Dilute appropriately to obtain a 2-ppm s&&on.
The fluorescence intensity is unaffected by pH over the range l-7. The influence of the potassium iodide
Potassium iodide solution (100ppm).
and Rhodamine 6G concentrations is shown in Figs 3 and 4. On the basis of these studies, 2 ml of a IOO-ppm solution of potassium iodide and 2.5 ml of 0.005% Rhodamine 6G solution are chosen as optimal. The fluorescence intensity is unaffected by c@nges in the ionic strength of the aqueous phase. 4s the presence of an electrolyte assists in rapid phase separation, 2 ml of 3% solution of sodium chloride are added to the aqueous phase. Two minutes of
(pH 4.8). 0.5 M. Sodium chloride solution (3%).
Rhodamine 6G solution (0.005%). Solvent mixture. Thiopheae-free benzene and cyclohexane in 2: 1 ratio. lsoburyl methyl ketone (IBMK) procedure
Transfer a portion of sample solution containing up to I5 fig of mercury(U) into a 60.ml separating funnel Add, TAi. 21/l 1*--I
Preliminary studies indicated that at low .concentrations of iodide (OSmM), only extraction into benzene is selective. The precision of the results was found to improve when a 2: 1 mixture of thiophene free benzene and cyclohex’ane was used for the extraction. The complex extracted was readily broken up by the addition of acetone, methanol, IBMK or n-butanol; IBMK was chosen because of its low volatility. Figures 1 and2 present the excitation and emission spectra of the fluorescent species recorded with an Aminco-Bowman spectrofluorimeter with a 250-W xenon source. There are three excitation maxima at 388, 348 and 525 nm (in order of increasing prominence), and one emission maximum at 560 nm. As a mercury vapour lamp was to be used as the excitation source, a 36%nm filter was used. Effect of experimental variables
Acetate bu&r
Recommended
RESULTS AND DISCU!3SION
911
912
SHORT COMMUNlCATlONS
Enlorged y-scol
L
Wavelength
Fig. I.
Excitation
In nm
spectra (uncorrected):
Wavelength 9 pg of Hg(l1) treated
as in procedure.
Fig. 2. Emission spectra: (A) 0. (B) 3, (C) 6 and (D) 9 pg of shaking suffices for complete extraction and slight changes in the phase-volume ratio do not affect the fluorescence intensity. The fluorescence intensity of the liberated Rhodamine 6G is indefinitely stable, and varies linearly with mercury(H) concentration in the range 1-I 5 pg in 15 ml of aqueous phase. From 25 determinations at 15 pg of mc%cury(lI), the relative standard deviation is 3%. Effect of diverse ions The effect of 1 mg each of Li+, Ag+, Cu2+, Mgz+, Cal+ 3 Sr2+ Bazt Zn2+ Cd2+ BOi- Tl+ T13* AI3” Ce3’: LaJ+: Th4+: PbZ+,’ SnZ+, ‘~b*+: Bi3t:
pg of potosium
in nm
Hg(II).
H,AsO;, AsO:-, VO;, PO:-, NO;, NO;, Cr3+, so;-, s,o:-, SeO$-, TeO:-, CrzO:-, MoOi-, Mn2+, Cl-, Br-, ClO;, IO;, Fez+, Fe3+, wo:-, Co2+. Ni2*, Pd2+, Pt4+ and SCN- ions on the determination of 15 fig of mercury(H) ,was examined. Only Ag+, Bi3+, MOO:-. Sn*+, H,AsO; and S20:were found to interfere. BiJt and MOO:- were masked by the addition of 2 ml of 0.05M EDNA before addition of the other reagents. Interference of Sn2+, H,AsO; and S20$- was overcome by oxidation with bromine water and removal of excess of bromine by boiling. The only serious interference was from Ag’ and it was eliminated by centrifuging to
ml of 0005%
iodide in 15ml
Fig. 3. Effect of potassium iodide concentration: lipg
Rhodomine 6G
of Hg(II) treated as in procedure. with KI
concentration varied. Fig. 4. Effect of Rhodamine 6G concentration: 15 pg of H&II), 2OOpg of KI and O-5 ml of 0.005% Rhodamine 6G.
SHORT #ATIoNS
913
*
Table 1. Analysis of brine and chlor-alkali plant liquid wastes*
Total mercury found @25 ml Sample Weak’brine Cell wash water Hydrogen cooler water
Combined effluent water
Mercury added?, pg
Fraction taken for analysis ml
200 300 100 200 100 300 -
4.0 :::
z
Proposed method
Dithizone method 400 140
g 5:o
395 590 710 138 240 345 275 380 575 110
2.0 5.0
208 310
-
5.0 ::: 4.0
280 108
Recovery, % 98 102 100 101 100 99 101 100
* Collected at M/s Dhrangadhm Chemical Works, Arumuganeri, Tiiunelveli District, Tamil Nadu. t To 25 ml of sample before making up to 100 ml.
separate the silver iodide formed, before the addition
of Rhodamine 66 Analysis of brine and chlor-alkali plant liquid waste
Early results showed that when the procedure was applied to solutions containing l-10% sodium chloride and spiked with mercury(H), there was no loss of mercury. It was therefore decided to apply the method to the analysis of brine ‘and liquid wastes discharged by a chlor-alkali plant, for total inorganic mercury content. The liquid samples were pretreated, as described elsewhere,6 to convert all forms of mercury into mercury(II), and suitable fractions of the treated solution were analysed. Samples to which known amounts of mercury(H) were added were also analysed to establish the recovery. The results along with those obtained for the same samples by the dithizone procedure’ are presented in Table 1, and show that the method is reliable for thedetermination of mercury in these samples.
trofluorimetry. Even though it is less sensitive than the method based on the mercury-induced oxidation of thiamine to fluorescent thiochrome,’ it is rapid and hence may find useful applications when low concentrations of mercury are to be determined on a routine basis. It is suitable for analysis of trade effluents. Acknowledgements-One of us (MV) gratefully acknowledges the financial assistance provided by Council of Scientific and Industrial Research (New Delhi) and Department of Atomic Energy (Bombay). REFERENCES
1. A. I. Ivankova and D. P. Shcherbov, Tr. Kazakhsk.
2. 3. 4. 5.
CONCLUSIONS The
method reported offers a rapid and reliable means for the trace determination of mercury by spec-
6. 7.
Nauch. Issled. Inst. Mineral. Syr’ya. 1962, I, 227; Anal. Abstr., 1964, 11, 1643. I. A. Blyum, Zh. Analit. Khim., 1971, 26, 48; Anal. Abstr., 1972, 22, 2133. G. 1. Oshima and K. Nagaswa, Chem. Pharm. Bull. Tokyo, 1970, 18, 687; Anal. Abstr., 1971, 20, 3647. T. V. Ramakrishna, G. Aravamudan and M. Vijayakumar, Anal. Chim Acta. 1976, 84, 369. Mercury Analysis Working Party, BITC, ibid., 1974, 72, 37. E. B. Sandell. Calorimetric Determination of Traces oj Metals, 3rd Ed., Interscience. New York, 1954. J. Holzbecher and D. E. Ryan, Anal. Chim. Acta, 1973. 64.333.
T&rP Vol. 27. pp. 9 I I to 913 0 palrunotl PressLtd 1980.Printed in Great Britain
FLUORIMETRIC DETERMINATION OF TRACE QUANTITIES OF MERCURY AS AN ION-ASSOCIATION COMPLEX WITH RHODAMINE 6G IN THE PRESENCE OF IODIDE M. VLIAYAKUIUR,T. V.
RAMAKRWINA
and G.
AI~AVAMIJDAN
Department of Chemistry, Indian Institute of Technology, Madras 600 036, India (Received 29 May 1979. Revised 31 March 1980. Accepted 20 May 1980) Summary-A procedure for the indirect fluorimetric determination of mercury(l1) is described, based on selective extraction of the ion-association complex formed between triiodomercurateJlI1)and Rhodamine 6G and subsequent release of the fluorescent Rhodamine 6G. The calibration curve is linear up to 1ppm of mercury(U). The few interferences are easily overcome. Three Ruorimetric procedures based on ion-association complexes have been reported for determination d trace quantities of mercury. Those based on extrac-
tion of the tetrachloromercurate(II)-Rhodamine B complex into benzene-ether mixture from acid medium’ and the extraction of the tetrabromomercurate(II~Butylrhodamine B complex into benzene’ are quite sensitive, but interference studies have not been reported. The procedure3 based on the reduction in fluorescence intensity of Rhodomine 6G by complexation with tetraiodomercurate(I1) is subject to interferences. During an investigation of this last complex4 we ‘found that addition of small amounts of oxygencontaining solvents such as acetone caused complete dissociation of the ion-association complex. This has &een made the basis of a sensitive and selective tiethod for indirect fluorimetric determination of : =cw(W.
with mixing, 2 ml each of acetate buffer, sodium chloride and potassium iodide solutions followed by 2.5 ml of Rhodamine 6G solution. Dilute to about 15 ml with water and shake gently for 2-3 min with 5 ml of the benzenecyclohexane solvent mixture. Discard the aqueous phase. Mix 2.5 ml of the organic extract with 5 ml of IBMK and measure its fluorescence intensity at 560 nm, using a 365~nm excitation filter. Subtract the blank reading and establish the concentration of mercury by reference to a calibration graph prepared by applying the procedure to O-7.5 ml of 2-ppm mercury(I1) solution in place of the sample solution.
EXPERIMENTAL
Apparatus A Carl Zeiss PMQ II spectrophotometer with a ZFM 4 fluorescence attachment provided with a 250-W mercury vapour lamp was used. Slit-widths of 1 mm for the excitation filter and 0.06mm for the emission monochromator were employed for the fluorescence measurements with 10 x 10 x 45 mm quartz cells with polished bottoms. Standard mercury(ll) solution (2 ppm). Prepare a lOOO-ppmsolution of mercury(I1) by dissolving 0.3385 g of mercury(I1) chloride in water and making UD to 250 ml. Dilute appropriately to obtain a 2-ppm s&&on.
The fluorescence intensity is unaffected by pH over the range l-7. The influence of the potassium iodide
Potassium iodide solution (100ppm).
and Rhodamine 6G concentrations is shown in Figs 3 and 4. On the basis of these studies, 2 ml of a IOO-ppm solution of potassium iodide and 2.5 ml of 0.005% Rhodamine 6G solution are chosen as optimal. The fluorescence intensity is unaffected by c@nges in the ionic strength of the aqueous phase. 4s the presence of an electrolyte assists in rapid phase separation, 2 ml of 3% solution of sodium chloride are added to the aqueous phase. Two minutes of
(pH 4.8). 0.5 M. Sodium chloride solution (3%).
Rhodamine 6G solution (0.005%). Solvent mixture. Thiopheae-free benzene and cyclohexane in 2: 1 ratio. lsoburyl methyl ketone (IBMK) procedure
Transfer a portion of sample solution containing up to I5 fig of mercury(U) into a 60.ml separating funnel Add, TAi. 21/l 1*--I
Preliminary studies indicated that at low .concentrations of iodide (OSmM), only extraction into benzene is selective. The precision of the results was found to improve when a 2: 1 mixture of thiophene free benzene and cyclohex’ane was used for the extraction. The complex extracted was readily broken up by the addition of acetone, methanol, IBMK or n-butanol; IBMK was chosen because of its low volatility. Figures 1 and2 present the excitation and emission spectra of the fluorescent species recorded with an Aminco-Bowman spectrofluorimeter with a 250-W xenon source. There are three excitation maxima at 388, 348 and 525 nm (in order of increasing prominence), and one emission maximum at 560 nm. As a mercury vapour lamp was to be used as the excitation source, a 36%nm filter was used. Effect of experimental variables
Acetate bu&r
Recommended
RESULTS AND DISCU!3SION
911
912
SHORT COMMUNlCATlONS
Enlorged y-scol
L
Wavelength
Fig. I.
Excitation
In nm
spectra (uncorrected):
Wavelength 9 pg of Hg(l1) treated
as in procedure.
Fig. 2. Emission spectra: (A) 0. (B) 3, (C) 6 and (D) 9 pg of shaking suffices for complete extraction and slight changes in the phase-volume ratio do not affect the fluorescence intensity. The fluorescence intensity of the liberated Rhodamine 6G is indefinitely stable, and varies linearly with mercury(H) concentration in the range 1-I 5 pg in 15 ml of aqueous phase. From 25 determinations at 15 pg of mc%cury(lI), the relative standard deviation is 3%. Effect of diverse ions The effect of 1 mg each of Li+, Ag+, Cu2+, Mgz+, Cal+ 3 Sr2+ Bazt Zn2+ Cd2+ BOi- Tl+ T13* AI3” Ce3’: LaJ+: Th4+: PbZ+,’ SnZ+, ‘~b*+: Bi3t:
pg of potosium
in nm
Hg(II).
H,AsO;, AsO:-, VO;, PO:-, NO;, NO;, Cr3+, so;-, s,o:-, SeO$-, TeO:-, CrzO:-, MoOi-, Mn2+, Cl-, Br-, ClO;, IO;, Fez+, Fe3+, wo:-, Co2+. Ni2*, Pd2+, Pt4+ and SCN- ions on the determination of 15 fig of mercury(H) ,was examined. Only Ag+, Bi3+, MOO:-. Sn*+, H,AsO; and S20:were found to interfere. BiJt and MOO:- were masked by the addition of 2 ml of 0.05M EDNA before addition of the other reagents. Interference of Sn2+, H,AsO; and S20$- was overcome by oxidation with bromine water and removal of excess of bromine by boiling. The only serious interference was from Ag’ and it was eliminated by centrifuging to
ml of 0005%
iodide in 15ml
Fig. 3. Effect of potassium iodide concentration: lipg
Rhodomine 6G
of Hg(II) treated as in procedure. with KI
concentration varied. Fig. 4. Effect of Rhodamine 6G concentration: 15 pg of H&II), 2OOpg of KI and O-5 ml of 0.005% Rhodamine 6G.
SHORT #ATIoNS
913
*
Table 1. Analysis of brine and chlor-alkali plant liquid wastes*
Total mercury found @25 ml Sample Weak’brine Cell wash water Hydrogen cooler water
Combined effluent water
Mercury added?, pg
Fraction taken for analysis ml
200 300 100 200 100 300 -
4.0 :::
z
Proposed method
Dithizone method 400 140
g 5:o
395 590 710 138 240 345 275 380 575 110
2.0 5.0
208 310
-
5.0 ::: 4.0
280 108
Recovery, % 98 102 100 101 100 99 101 100
* Collected at M/s Dhrangadhm Chemical Works, Arumuganeri, Tiiunelveli District, Tamil Nadu. t To 25 ml of sample before making up to 100 ml.
separate the silver iodide formed, before the addition
of Rhodamine 66 Analysis of brine and chlor-alkali plant liquid waste
Early results showed that when the procedure was applied to solutions containing l-10% sodium chloride and spiked with mercury(H), there was no loss of mercury. It was therefore decided to apply the method to the analysis of brine ‘and liquid wastes discharged by a chlor-alkali plant, for total inorganic mercury content. The liquid samples were pretreated, as described elsewhere,6 to convert all forms of mercury into mercury(II), and suitable fractions of the treated solution were analysed. Samples to which known amounts of mercury(H) were added were also analysed to establish the recovery. The results along with those obtained for the same samples by the dithizone procedure’ are presented in Table 1, and show that the method is reliable for thedetermination of mercury in these samples.
trofluorimetry. Even though it is less sensitive than the method based on the mercury-induced oxidation of thiamine to fluorescent thiochrome,’ it is rapid and hence may find useful applications when low concentrations of mercury are to be determined on a routine basis. It is suitable for analysis of trade effluents. Acknowledgements-One of us (MV) gratefully acknowledges the financial assistance provided by Council of Scientific and Industrial Research (New Delhi) and Department of Atomic Energy (Bombay). REFERENCES
1. A. I. Ivankova and D. P. Shcherbov, Tr. Kazakhsk.
2. 3. 4. 5.
CONCLUSIONS The
method reported offers a rapid and reliable means for the trace determination of mercury by spec-
6. 7.
Nauch. Issled. Inst. Mineral. Syr’ya. 1962, I, 227; Anal. Abstr., 1964, 11, 1643. I. A. Blyum, Zh. Analit. Khim., 1971, 26, 48; Anal. Abstr., 1972, 22, 2133. G. 1. Oshima and K. Nagaswa, Chem. Pharm. Bull. Tokyo, 1970, 18, 687; Anal. Abstr., 1971, 20, 3647. T. V. Ramakrishna, G. Aravamudan and M. Vijayakumar, Anal. Chim Acta. 1976, 84, 369. Mercury Analysis Working Party, BITC, ibid., 1974, 72, 37. E. B. Sandell. Calorimetric Determination of Traces oj Metals, 3rd Ed., Interscience. New York, 1954. J. Holzbecher and D. E. Ryan, Anal. Chim. Acta, 1973. 64.333.