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Extraction and atomic-absorption spectrometric determination of trace copper with zinc dibenzyldithiocarbamate
222 (’ Elscvicr
SHORT
Scientific
Publishing
Company.
Arltrl~~rictr Cliifnircc Acfu, 70 ( 1974) 222-226 Amstcrdum -. Printed in The Netherlands
COMMUNICATION
Extraction and atomic-absorption zinc dibenzyldithiocarbamate*
spectrometric
determination
of trace
coprder with
In order to increase the sensitivity of analysis, the atomic absorption spectrometric determination of copper has been made by extracting copper as a pyrollidinedithiocarbamate (APDC) complex l4 or diethyldithiocarbamate (DDC) complex’ from an aqueous solution into methyl isobutyl ketone (MIBK) and by spraying the MIBK extract into the flame. However, these analytical procedures are complicated and their application to practical samples is restricted, because the reagents (APDC and NaDDC) are too unstable to be used with acid solutions so that the pH before extraction must be controlled in a suitable range. In the present work, micro amounts of copper were determined by extraction as a copper dibenzyldithiocarbamate (CUDBC) chelate”-” from various acidic media into MIBK. followed by introduction of the extract into an air-acetylene flame, The method established is relatively simple and has the advantage of using a fairly wide range of acidities compared to the_APDC or DDC method. Apparatus. The atomic absorption measurements were made with a Hitachi Model 207 atomic absorption spectrophotometer equipped with a copper hollowcathode lamp (324.8 nm). An air-acetylene flame was used with a water-cooled lo-cm slot burner. Reagents. A stock copper solution was prepared by dissolving 1.000 g of electrolytic copper in 50 ml of 6 M nitric acid, and diluting the resulting solution with water to 1 1 in a volumetric flask. Working standards ( 20.1 p.p.m.) were prepared by suitably diluting an aliquot of the stock solution with dilute nitric acid. For standard solutions in other acids, an aliquot of the stock solution was evaporated to dryness, the residue was dissolved in the desired acid, and the solution was again evaporated to dryness. This treatment was repeated until the residue was free of nitrate. The final residue was dissolved in the desired acid and diluted to a known volume. ZnDBC-MIBK solution ( < 0.07%) was prepared by dissolving ZnDBC (laboratory reagent; B.D.H.) in MIBK by shaking for about 20 min. The solution was stored in an amber glass-stoppered bottle in a refrigerator. * Paper read at the Meeting
of the Chemical
Society
of Japan,
Hiroshima.
October,
1970.
SHORT
223
COMMUNICATION
Other reagents were of analytical-reagent grade. General procedure. Shake 25 ml of an acidic solution containing less than 5 pg of copper(I1) for a certain time (240 shakes/min) with 5 ml of ZnDBC-MIBK solution in a 50-ml separatory funnel. Separate the phases and centrifuge the extract for 2 min at 3000 rev min- ‘. Measure the absorbance of copper in the extract against a reagent blank. The ambient temperature was fairly constant at 20+ 2°C. Results
cmtl discussion Atomic absorption of copper. Initially, the effects of variation in the airacetylene flow ratio and the hollow-cathode lamp current on the absorbance of copper were examined at the burner height adjusted for maximal absorption. On the basis of these tests, the optimal air flow rate was 11 1 min-’ and the acetylene flow rate 1.75 1 min- ’ ; the dependence of the absorbance on the air-fuel ratio was smallest under these conditions, changes in the acetylene flow from 1.5 to 2.25 1 min-1 being without effect. When the lamp current was increased in the range 3-8 mA, the absorbance decreased gradually, but remained essentially constant in the range lo-15 mA. All subsequent measurements were made at 11 mA. ESftcr of’ shaking time on the extraction. The effect of the shaking time on the extractions of the CuDBC complex from various acidic solutions into MIBK was studied. No perceptible change in the absorbance of copper occurred at shaking times from 1 to 7 min in extractions from 0.2 A4 perchloric acid solution. In contrast, the absorbance for extraction from 0.2 M hydrochloric or nitric acid solution increased up to shaking times of 4 min; extraction from 0.75 M sulfuric acid increased steeply with shaking time up to 3 min. Therefore, a shaking time of 5 min was used in all further extractions. Ejyect of acidity anti reagent concentration 011 the extraction of copper. Tests were made to determine the conditions that would allow quantitative extraction of copper into MIBK. Figure 1 shows plots of absorbance us. acidity for copper extractions from nitric, hydrochloric, sulfuric or perchloric acid with 0.05% ZnDBC-MIBK solution. In further tests, the initial acidity of the aqueous phase was adjusted to be about 0.2 M in nitric, hydrochloric or perchloric acid or about 0.75 M in sulfuric acid; constant absorbance with excellent sensitivity was obtained in the ranges 0.1-0.3 M for nitric and perchloric acids, 0.1-0.9 M for hydrochloric acid; and 0.6
-
01 0
I
1
Initial
acidity,
N
3
2
Fig. 1. ENcct of acid concentration on absorbnncc 1. HCIO.,; II. HNOJ; III. HCI; IV, HISOd.
of copper.
Cu ‘+. 0.12
p.p.m.: ZnDBC-MIBK,
O.OS”/,.
224
SHORT
COMMUNICATION
0.05-0.25 M or 0.4-l h4 for sulfuric acid. Deviations in the absorbance were large in the range above 1 M for sulfuric acid. The reason why the absorbance of copper decreased drastically in the acidity region above 0.4 M of nitric or perchloric acid may be that the CuDBC complex produced was decomposed by the oxidizing action of the acid. Tests of the variation of copper absorbance with increasing concentrations of,ZnDBC in MIBK in the different acid solutions showed that the optimal concentration of ihe reagent was in the range 0.04’~,-0.07’9& within which range the copper absorbance remained constant for a particular acid. In all further work, 5 ml of a O.OSOA,ZnDBC-MIBK solution was chosen as the optimum for all the acids used. Stahiliry of’ r/w CuDBC cor~plex. To check the stability. several solutions were extracted as described under the recommended procedure, and the separatory funnels were stood under diffuse daylight. The absorbances of the organic phase were measured by atomic-absorption spectrometry at different times after extraction. The absorbance of copper in extractions from hydrochloric or sulfuric acid solution was constant for at least 1 h. The absorbance increased slightly for standing times above 45 min in the case of nitric acid. and above 35 min in the case of perchloric acid. The ZnDBC-MIBK solution, which was kept in a dark refrigerator, was stable for at least 3 months.
0
0.04
t 0 p.p.nl*
0.12
0.06
I
1
1
2
cu2+
in initial
0.16
0.20
t
8
3
aqueous
(I-EC,
4
(P)
phase
Fig. 2. Calibration curves. I-IV: ZnDBC-MIBK cxtruction (1. 0.2 M HCIO,; II, 0.2 M 0.2 M HCI; IV. 0.75 M H2S04). V: Without extraction (0.75 M HaSO aqueous solution).
HNO,:
111.
SHORT
225
COMMUNICATION
Preparutiort of. calihratiort curves. Calibration curves were prepared by extracting varying amounts of copper from nitric, hydrochloric, sulfuric or perchloric acid solutions by the recommended procedure. As Fig. 2 shows, each calibration curve(I-IV) obtained was linear for the concentration range O-O.2 p.p.m. of copper in the initial aqueous solution. The ratio of the sensitivity for copper between the extraction method (IV) and the aqueous method (V) was about 27.6. The precision of the measurements was tested by repeatedly measuring the absorbance of 10 identical sample solutions. The results (Table I) show that the extraction method provides greater precision than the aqueous method. EI ISION
DATA
xr of dctcrminutions .____ .--
in each set: _.--.-Estrctcriotr
10) -.--.- ~-~ tm~tlrod
HC104(0.2 .___-.[p.p.m.
in initial
absorbance :icnt of vuriation
TABLE EFFECT Ior
aq.
M) -
0.12
(‘x,)
---
0.12
0.12
0.406
0.385
I.:!
I.1
0.375 0.8
0.370 1.4
M)
OF DIVE.RSE -. --_ A~rroro~r (1~1)
IONS
ON
THE
DETERMINATION --
Rccovcrg HCIO,
Bi3 +
ci12+ C02+ Fe= * Hg” + MO”+ Ni2+ We+
HCl(0.2
M)
H,SO,
(0.75
M)
II
100 200 10 25 50 100 IO0 1000 100 1000 100 1000 100 200 IO0 1000 100
1000 100 IO00 __~
” Each aquccws
solution
(0.2
M)
99.6 100 100 101 102 102 100 100 102 100 98.9 99.0 98.4 9&O 98.4 IO1 100 99.6
HNO,
(0.2 M)
100 100 100 100 102 101 100 102 100 101 98.0 101 98.4 98.4 100 101 100 101 99.6 99.6
100 100 contnincd
OF COPPER -
(7,)
-4T+
.--
Aq1reous m!rlrot/ HzSOJ(0.75 M) --3.00
HNO,(O.2 0.12
0.409 1.0
--.---
0.12 p.p.m.
or copper(
NC-1 (0.2 M) -101 102 101 102 102 101 too 100 100 101 99.9 99.9 98.7 100 101 101 100 99.8 98.9 99.6
HzSO., (0.75 100 101 101 93.6 92.1 90.0 99.0 98.7 100 100 101 100 100 96 100 97.3 99.7 99.0 101 101
M)
226
SHORT
COMMUNICATION
Itrterferences. The effects of the main interfering elements, listed by Martens on the extraction method were tested for different acid et al.= and Wilson”, media. The results are summarized in Table II. Bismuth(II1) in sulfuric acid medium interfered seriously with the determination of copper. but there were no other significant interferences. Recommeded procedure Shake 25 ml of an acidic solution (0.2 M in the case of nitric, hydrochloric or perchloric acid, or 0.75 M in the case of sulfuric acid) containing not less than 5 /cg of copper for about 5 min (240 shakes/min) with 5 ml of 0.050/, ZnDBC-MIBK solution in a 50-ml separatory funnel. Separate the phases and of copper centrifuge the extract for 2 min at 3000 rev min - ‘. Measure the absorbance in the supernatant extract against a reagent blank. The operating conditions of the instrument are as hollows: wavelength, 324.8 nm; lamp current, 11 mA; slit width, 0.18 nm; burner height adjusted for maximal absorption; pressure and flow rate of air, 1.8 kg cms2, 1 I 1 min-‘; pressure and flow rate of acetylene, 0.5 kg cmw2, 1.75 1 min- ‘. The author expresses his deep gratitude to Dr. Hidehiro GotB of the President of Toyama University, Prof. Dr. Taitiro Fujinaga of Kyoto University, Prof. Dr. ShigerG Ikeda of Osaka University and Prof. Dr. Kenjiro Hayashi of Yamaguchi University, for their kind guidance. REFERENCES I 2 3 4 5 6 7 8 9
J. E. Allan, Specrrochim. Acrcc. 17 (1961) 459. D. J. Trent and W. Slavin. At. Absorprim News/err.. 3 (1964) 118. M. Nagura and lida, Btoweki Kogak~c. 17 (1968) 1513. Y. Ynmamoto, T. Kumamuru. Y. Hayashi and M. Kankc. B:trjsrki Kugulw, I. Atsuya, Bwwki Kagak~c, 15 (1966) 247. R. I. Martens and R. E. Githcns. Sr.. Armf. Chetn., 24 (1952) 991. D. C. Abbott and J. R. Harris. Awl_w (Lomb). 87 (1962) 487. A. L. Wilson. Ardysr (Lcmh~. 87 (1962) 8W. 0. P. Bharguva. Tohru. 16 (1969) 743.
20 (1971)
347.
SHORT
Scientific
Publishing
Company.
Arltrl~~rictr Cliifnircc Acfu, 70 ( 1974) 222-226 Amstcrdum -. Printed in The Netherlands
COMMUNICATION
Extraction and atomic-absorption zinc dibenzyldithiocarbamate*
spectrometric
determination
of trace
coprder with
In order to increase the sensitivity of analysis, the atomic absorption spectrometric determination of copper has been made by extracting copper as a pyrollidinedithiocarbamate (APDC) complex l4 or diethyldithiocarbamate (DDC) complex’ from an aqueous solution into methyl isobutyl ketone (MIBK) and by spraying the MIBK extract into the flame. However, these analytical procedures are complicated and their application to practical samples is restricted, because the reagents (APDC and NaDDC) are too unstable to be used with acid solutions so that the pH before extraction must be controlled in a suitable range. In the present work, micro amounts of copper were determined by extraction as a copper dibenzyldithiocarbamate (CUDBC) chelate”-” from various acidic media into MIBK. followed by introduction of the extract into an air-acetylene flame, The method established is relatively simple and has the advantage of using a fairly wide range of acidities compared to the_APDC or DDC method. Apparatus. The atomic absorption measurements were made with a Hitachi Model 207 atomic absorption spectrophotometer equipped with a copper hollowcathode lamp (324.8 nm). An air-acetylene flame was used with a water-cooled lo-cm slot burner. Reagents. A stock copper solution was prepared by dissolving 1.000 g of electrolytic copper in 50 ml of 6 M nitric acid, and diluting the resulting solution with water to 1 1 in a volumetric flask. Working standards ( 20.1 p.p.m.) were prepared by suitably diluting an aliquot of the stock solution with dilute nitric acid. For standard solutions in other acids, an aliquot of the stock solution was evaporated to dryness, the residue was dissolved in the desired acid, and the solution was again evaporated to dryness. This treatment was repeated until the residue was free of nitrate. The final residue was dissolved in the desired acid and diluted to a known volume. ZnDBC-MIBK solution ( < 0.07%) was prepared by dissolving ZnDBC (laboratory reagent; B.D.H.) in MIBK by shaking for about 20 min. The solution was stored in an amber glass-stoppered bottle in a refrigerator. * Paper read at the Meeting
of the Chemical
Society
of Japan,
Hiroshima.
October,
1970.
SHORT
223
COMMUNICATION
Other reagents were of analytical-reagent grade. General procedure. Shake 25 ml of an acidic solution containing less than 5 pg of copper(I1) for a certain time (240 shakes/min) with 5 ml of ZnDBC-MIBK solution in a 50-ml separatory funnel. Separate the phases and centrifuge the extract for 2 min at 3000 rev min- ‘. Measure the absorbance of copper in the extract against a reagent blank. The ambient temperature was fairly constant at 20+ 2°C. Results
cmtl discussion Atomic absorption of copper. Initially, the effects of variation in the airacetylene flow ratio and the hollow-cathode lamp current on the absorbance of copper were examined at the burner height adjusted for maximal absorption. On the basis of these tests, the optimal air flow rate was 11 1 min-’ and the acetylene flow rate 1.75 1 min- ’ ; the dependence of the absorbance on the air-fuel ratio was smallest under these conditions, changes in the acetylene flow from 1.5 to 2.25 1 min-1 being without effect. When the lamp current was increased in the range 3-8 mA, the absorbance decreased gradually, but remained essentially constant in the range lo-15 mA. All subsequent measurements were made at 11 mA. ESftcr of’ shaking time on the extraction. The effect of the shaking time on the extractions of the CuDBC complex from various acidic solutions into MIBK was studied. No perceptible change in the absorbance of copper occurred at shaking times from 1 to 7 min in extractions from 0.2 A4 perchloric acid solution. In contrast, the absorbance for extraction from 0.2 M hydrochloric or nitric acid solution increased up to shaking times of 4 min; extraction from 0.75 M sulfuric acid increased steeply with shaking time up to 3 min. Therefore, a shaking time of 5 min was used in all further extractions. Ejyect of acidity anti reagent concentration 011 the extraction of copper. Tests were made to determine the conditions that would allow quantitative extraction of copper into MIBK. Figure 1 shows plots of absorbance us. acidity for copper extractions from nitric, hydrochloric, sulfuric or perchloric acid with 0.05% ZnDBC-MIBK solution. In further tests, the initial acidity of the aqueous phase was adjusted to be about 0.2 M in nitric, hydrochloric or perchloric acid or about 0.75 M in sulfuric acid; constant absorbance with excellent sensitivity was obtained in the ranges 0.1-0.3 M for nitric and perchloric acids, 0.1-0.9 M for hydrochloric acid; and 0.6
-
01 0
I
1
Initial
acidity,
N
3
2
Fig. 1. ENcct of acid concentration on absorbnncc 1. HCIO.,; II. HNOJ; III. HCI; IV, HISOd.
of copper.
Cu ‘+. 0.12
p.p.m.: ZnDBC-MIBK,
O.OS”/,.
224
SHORT
COMMUNICATION
0.05-0.25 M or 0.4-l h4 for sulfuric acid. Deviations in the absorbance were large in the range above 1 M for sulfuric acid. The reason why the absorbance of copper decreased drastically in the acidity region above 0.4 M of nitric or perchloric acid may be that the CuDBC complex produced was decomposed by the oxidizing action of the acid. Tests of the variation of copper absorbance with increasing concentrations of,ZnDBC in MIBK in the different acid solutions showed that the optimal concentration of ihe reagent was in the range 0.04’~,-0.07’9& within which range the copper absorbance remained constant for a particular acid. In all further work, 5 ml of a O.OSOA,ZnDBC-MIBK solution was chosen as the optimum for all the acids used. Stahiliry of’ r/w CuDBC cor~plex. To check the stability. several solutions were extracted as described under the recommended procedure, and the separatory funnels were stood under diffuse daylight. The absorbances of the organic phase were measured by atomic-absorption spectrometry at different times after extraction. The absorbance of copper in extractions from hydrochloric or sulfuric acid solution was constant for at least 1 h. The absorbance increased slightly for standing times above 45 min in the case of nitric acid. and above 35 min in the case of perchloric acid. The ZnDBC-MIBK solution, which was kept in a dark refrigerator, was stable for at least 3 months.
0
0.04
t 0 p.p.nl*
0.12
0.06
I
1
1
2
cu2+
in initial
0.16
0.20
t
8
3
aqueous
(I-EC,
4
(P)
phase
Fig. 2. Calibration curves. I-IV: ZnDBC-MIBK cxtruction (1. 0.2 M HCIO,; II, 0.2 M 0.2 M HCI; IV. 0.75 M H2S04). V: Without extraction (0.75 M HaSO aqueous solution).
HNO,:
111.
SHORT
225
COMMUNICATION
Preparutiort of. calihratiort curves. Calibration curves were prepared by extracting varying amounts of copper from nitric, hydrochloric, sulfuric or perchloric acid solutions by the recommended procedure. As Fig. 2 shows, each calibration curve(I-IV) obtained was linear for the concentration range O-O.2 p.p.m. of copper in the initial aqueous solution. The ratio of the sensitivity for copper between the extraction method (IV) and the aqueous method (V) was about 27.6. The precision of the measurements was tested by repeatedly measuring the absorbance of 10 identical sample solutions. The results (Table I) show that the extraction method provides greater precision than the aqueous method. EI ISION
DATA
xr of dctcrminutions .____ .--
in each set: _.--.-Estrctcriotr
10) -.--.- ~-~ tm~tlrod
HC104(0.2 .___-.[p.p.m.
in initial
absorbance :icnt of vuriation
TABLE EFFECT Ior
aq.
M) -
0.12
(‘x,)
---
0.12
0.12
0.406
0.385
I.:!
I.1
0.375 0.8
0.370 1.4
M)
OF DIVE.RSE -. --_ A~rroro~r (1~1)
IONS
ON
THE
DETERMINATION --
Rccovcrg HCIO,
Bi3 +
ci12+ C02+ Fe= * Hg” + MO”+ Ni2+ We+
HCl(0.2
M)
H,SO,
(0.75
M)
II
100 200 10 25 50 100 IO0 1000 100 1000 100 1000 100 200 IO0 1000 100
1000 100 IO00 __~
” Each aquccws
solution
(0.2
M)
99.6 100 100 101 102 102 100 100 102 100 98.9 99.0 98.4 9&O 98.4 IO1 100 99.6
HNO,
(0.2 M)
100 100 100 100 102 101 100 102 100 101 98.0 101 98.4 98.4 100 101 100 101 99.6 99.6
100 100 contnincd
OF COPPER -
(7,)
-4T+
.--
Aq1reous m!rlrot/ HzSOJ(0.75 M) --3.00
HNO,(O.2 0.12
0.409 1.0
--.---
0.12 p.p.m.
or copper(
NC-1 (0.2 M) -101 102 101 102 102 101 too 100 100 101 99.9 99.9 98.7 100 101 101 100 99.8 98.9 99.6
HzSO., (0.75 100 101 101 93.6 92.1 90.0 99.0 98.7 100 100 101 100 100 96 100 97.3 99.7 99.0 101 101
M)
226
SHORT
COMMUNICATION
Itrterferences. The effects of the main interfering elements, listed by Martens on the extraction method were tested for different acid et al.= and Wilson”, media. The results are summarized in Table II. Bismuth(II1) in sulfuric acid medium interfered seriously with the determination of copper. but there were no other significant interferences. Recommeded procedure Shake 25 ml of an acidic solution (0.2 M in the case of nitric, hydrochloric or perchloric acid, or 0.75 M in the case of sulfuric acid) containing not less than 5 /cg of copper for about 5 min (240 shakes/min) with 5 ml of 0.050/, ZnDBC-MIBK solution in a 50-ml separatory funnel. Separate the phases and of copper centrifuge the extract for 2 min at 3000 rev min - ‘. Measure the absorbance in the supernatant extract against a reagent blank. The operating conditions of the instrument are as hollows: wavelength, 324.8 nm; lamp current, 11 mA; slit width, 0.18 nm; burner height adjusted for maximal absorption; pressure and flow rate of air, 1.8 kg cms2, 1 I 1 min-‘; pressure and flow rate of acetylene, 0.5 kg cmw2, 1.75 1 min- ‘. The author expresses his deep gratitude to Dr. Hidehiro GotB of the President of Toyama University, Prof. Dr. Taitiro Fujinaga of Kyoto University, Prof. Dr. ShigerG Ikeda of Osaka University and Prof. Dr. Kenjiro Hayashi of Yamaguchi University, for their kind guidance. REFERENCES I 2 3 4 5 6 7 8 9
J. E. Allan, Specrrochim. Acrcc. 17 (1961) 459. D. J. Trent and W. Slavin. At. Absorprim News/err.. 3 (1964) 118. M. Nagura and lida, Btoweki Kogak~c. 17 (1968) 1513. Y. Ynmamoto, T. Kumamuru. Y. Hayashi and M. Kankc. B:trjsrki Kugulw, I. Atsuya, Bwwki Kagak~c, 15 (1966) 247. R. I. Martens and R. E. Githcns. Sr.. Armf. Chetn., 24 (1952) 991. D. C. Abbott and J. R. Harris. Awl_w (Lomb). 87 (1962) 487. A. L. Wilson. Ardysr (Lcmh~. 87 (1962) 8W. 0. P. Bharguva. Tohru. 16 (1969) 743.
20 (1971)
347.