(14) B. T. CrOll and G. M.
Simkins, Analvst(London),97 (1 153h 281 (1972) (Gas Chromatographic Determination), (15) B. T. Croll, Analyst(London), 96 (1138),67 (1971) (Gas Chromatographic Determination). (16) M. Richards, J. Chromatogr., 115,259-261 (1975) (Ion Exclusion Determination). (17) D. J. Patel. R. A. Bhatt, and S.L. Bafna, Chem. hd. (London),21 10, (1967) (ion Exclusion Determination).
(18) H. A. Laitinen, "Chemical Analysis", McGraw-Hill, New York, 1960,Chap. 26. (19) "Guide for Measures of Precision and Accuracy", Anal. Chem., 47,2527 ( 1975).
RECEIVED for review July 9, 1976. Accepted September 23,
1976.
Liquid-Li quid Extraction of Cadmiurn with DiethyIdithiocarbamic Acid Sixto Bajo and Armin Wyttenbach' Swiss Federal Institute for Reactor Research, 5303 Wiirenlingen, Switzerland
The extractlonof Cd2+ with zinc bis(diethyldlthiocarbamate), Zn[(C2H5)2NCS2]2, from acid solutlons and wlth HDDC from alkaline solutions Is investigated. It Is shown that extractlon with HDDC from 5 N NaOH and back-extraction with 2 N HCI offers a fast and selective isolation of Cd2+ from a variety of matrices; the only Interference found was TI1+. Applicatlons of thls separation scheme to the isolation of Cd from flssion products and to the determination of Cd by neutron activation analysis in metallic zinc and in geological and blologlcal materlals are glven. The recovery of Cd is quantitative and there is therefore no need to determine the chemical yield of the separation. The recovefed Cd is of high radiochemical purlty.
In recent years there is growing concern about the role of Cd as a poison in food, water, and air. In fact, Cd can be found consistently in human tissues, although it is not considered to be an essential element. This situation calls for ever more sensitive determinations of Cd. Most methods which have the necessary sensitivity require an isolation of Cd from the matrix prior to its determination; hence, it is of great importance to have methods which can isolate Cd quantitatively, simply, and reasonably fast from a variety of matrices. This is especially true for the determination of Cd by neutron activation, where it is hardly ever possible to measure Cd without chemical separations. Customary separation schemes make use of separations with an anion exchanger in HC1 or HBr, or of liquid-liquid extractions with a variety of complexants; for a review of separation methods, see (1-3). Most of these methods are lengthy and do not work quantitatively. This is one of the reasons why activation analysis is seldom used for Cd (4).The situation is perhaps best characterized by the work of some authors who developed a separation scheme for Cd, only to find that it was not specific enough to be applied (5).The most promising approach seems to be extraction of Cd from alkaline solutions by dithizone, but there is conflicting evidence as to the completeness of extraction as well as to the purity of the extracted Cd (6-8). The present work deals with the extraction by diethyldithiocarbamate, (CzH&NCSZ-, (in the following denoted as DDC), which proved t o be fast, quantitative, and specific. Although applications only to fission product solutions and to neutron activation samples are given, application to nonradioactive samples seems feasible. EXPERIMENTAL Reagents. Zn(DDC)Z was prepared and analyzed as described previously (9). The solid product was dissolved in CHC13 to give a 5 158
ANALYTICAL CHEMISTRY, VOL. 49, NO. 1, JANUARY 1977
X 10-3 M solution, the titer of which was stable for at least 5 months if kept in a dark bottle. HDDC was prepared for every analysis by shaking equal volumes of Zn(DDC)Z/CHC13and HCl1 N. Because of the fast decomposition of HDDC in aqueous acid solutions (IO),shaking times must not be longer than 20 s. The resulting organic phase contains HDDC and is free from Zn. Extractions. Unless otherwise noted, the aqueous phase had a volume of 100 ml and contained 100 pg Cd2+. The organic phase (CHCI,J had a volume of 30 ml and was 1.7 X M in Zn(DDC)2or 3.4 X IO+j M in HDDC; this quantity of reagent is roughly 60 times the amount theoretically necessary to complex 100 pg of Cd. Extractions were done on a shaking machine with a frequency of 6 s-l and an amplitude of 6 cm. Counting. Counting in experiments with only one tracer was done in a NaI well-type crystal; in all other cases, a well-type Ge(Li) de' tector was used.
RESULTS A N D DISCUSSION Extraction of Cd2+from Acid Solutions by Zn(DDC)2. The extraction of Cd2+ by Zn(DDC)2 from various acids is given in Figure 1. Extraction time was 2 min, which is long enough to reach equilibrium. For (H) 2 0.2 the reagent Zn(DDC)Z is for practical purposes completely protonated; it can then be shown that the experimentally found extraction of Cd2+ from HC104 and "03 corresponds to an extraction constant K e x , C d of 105.6. The solid line I in Figure 1was calculated using this value. It is seen that there is reasonable agreement between the calculated and the experimentally found extraction. Extraction from HC1 is obviously repressed in comparison to extraction from HC104 or " 0 3 . This is due to the formation of chloro complexes of cadmium with a corresponding decrease in the conditional extraction constant. Taking into account the appropriate a values for the chloro complexes and using again a K e x , C d of 105.6results in the solid line 11in Figure 1,which is seen to be in excellent agreement with the experimental values. The a values used in this calculation were calculated from data in reference (11)for an ionic strength of 0.1. The apparent enhancement of extraction from H3POd is due to the incomplete dissociation of this acid. Extraction from HzSO4 (not shown in Figure 1) is slightly higher than from HC104. The value of 105.6for the extraction constant K e x , C d which fits our results is roughly the same as the value of lo5.*found for CC14 (12),but is a t variance with the value of 104.4given for CHC13 (13). Extraction of Cd2+ by HDDC. The extraction of Cd2+ by HDDC, from aqueous solutions of pH ranging from 2 to 11, was evaluated. The aqueous solutions contained a NaOH/ citrate or a NaOH/NaHzP04 buffer. Extractions lasted for 2
Table I. Ions that Do Not Interfere with the Complete Extraction of Cd2+from 5 N NaOH by HDDC Weight of the ion, g
Ion Acetate
Remarks
10
~13+
1 1 1
As3+ As5+ Au3+ Bi3+ Borate BrCa2+ Citrate c104co2+ C032Cr6+ Fe3+ Ga3+ Ge4+ Glycerine HzOz IIns+ Mg2+ Mo fi+ NH4+ Ni2+ NOzNosP043Sb3+ Se4+ SiOaZSnz+ Sn4+
0.1 1
5 2 0.2 20 10 0.1 5
a
b
Table 11. Conditions Leading to Incomplete Extraction of Cd from 5 N NaOH by HDDC Cd recovered,
Ion
Compound used
Weight of the ion, g
CNCNc10Cr3+ Cr3+ Cu2+ S2Tl+
KCN KCN NaClO CrC13-6HzO CrC13.6HzO CuS04.5HzO NazS TlzS04
0.1 1.0 2 ml s o h , 13-14% 0.1 1.0 1.0 0.1 1.0
a
YO
100 45 0 100 25 0.8a
0.2 0
Aqueous phase contained 25 ml of glycerine.
C
1
i
b
1 1
25 ml 10 ml30% 1 1
0.2
I
o /
I
d b
1
10 ml13 M 1
b
10 10
Na3PO4.12H20 SbClq H2Se03 NazSiOs SnC12.2Hz0 SnC14.4HzO SORZNazS03 Tartrate C4Hfi06 Te4+ TeOz Trichloroace- HCClsC00 tate V5+
vzo5
WC+ Zn2+
WOs ZnO
1 1 1
5 1 1
5 20 1
I
IO
I
I
0. I
normality of acid
Figure 1. Extraction of Cd2+ from acid solutions by Zn(DDC), Aqueous phase: 100 ml, either H2P04 ( A ) , HClO4 (O), " 0 3 (X) or HCI (0). Organic phase: 30 ml, 1.7 X M Zn(DDQ2 in CHC13. The two solid lines are calculated extraction curves for Kex = IO5 (see text);the dashed line is drawn through the experimental points for H3P04
5 1 1
5
Aqueous phase contained 25 ml of glycerine and shaking time was 2 min. Aqueous phase contained 10 g of tartaric acid. Aqueous phase contained 2 g of tartaric acid. d Aqueous phase contained 10 ml of glycerine.
min and were followed by a washing with 10 ml CHC13 for 30 s. The combined organic phases were found to contain 299.8% of the Cd in all cases. Extraction from NaOH between 0.1 and 10 N was also evaluated; in this case shaking times were varied from 1to 8 min, and Cd contents from 1 kg to 2 mg. Extraction was quantitative in all cases. Thus HDDC compares favorably with the reagent dithizone, which does not extract Cd quantitatively from alkaline solutions by one single extraction step ( I , 6). I n t e r f e r e n c e by O t h e r Elements in the E x t r a c t i o n of Cd2+ from 5 N N a O H by HDDC. Table I gives the ions that were shown not to interfere with the complete extraction of 100 Fg Cd2+from 5 N NaOH by HDDC for 1min. It is evident that the extraction is quantitative from a variety of matrices.
Table I1 gives the conditions where extraction of Cdz+is not complete. Cu2+ and Tll+ obviously have larger conditional extraction constants than Cd2+ and therefore use up the reagent preferentially; if only a few 100 Fg of these elements are present however, they will not impede complete extraction of Cd2+,provided enough reagent is used. KCN (in quantities larger than 0.1 g) and S2- mask Cd and impede its extraction. CIO1- destroys the reagent by oxidation. Selectivity of the E x t r a c t i o n f r o m 5 N NaOH by HDDC. Coextraction of other elements together with Cd2+ was evaluated by extracting 5 N NaOH containing suitably marked ions in the 100-1000 Mg range with HDDC for 1 min. The following ions showed extractions smaller than 0.3%: A$+, Cr", Crfi+,Fe3+, In3+, Mn2+, Mo6+, Se4+, Sb3+, and Zn2+. Alkalies, earth alkalies and rare earth elements are known not to extract with DDC and were not tested. Substantial extraction (the percentage given in brackets) was found for: Agl+ (80%), Bi3+ (65%), Co2+ (33%), Cu2+ (loo%),Hg2+ (86%),Tll+ (100%). Back-extraction of Cd2+with HC12 N leaves most of these ions in the organic phase; only the following ions were found to accompany Cd2+ through the extraction-back-extraction cycle (percentages refer to the amount originally present in the starting solution): Agl+ (60%),Tll+ (100%). Extraction of Ag+ can be completely suppressed by adding 100 mg KCN to the aqueous phase, which was shown not to interfere with the extraction of Cd2+ (Table 11). ANALYTICAL CHEMISTRY, VOL. 49, NO. 1, JANUARY 1977
159
Table 111. Results of Neutron Activation Analysis for Cd Sample
No. of replicates
Bovine liver SRM-1577 Bowen's kale Oyster MA-M-1 (IAEA) Peridotite PCC-1 (USGS) Zinc granulate pA Merck
6
Mean value, PPm 0.29
9 6
1.03 2.45
0.10 0.13
0.80 best mean value, range 0.38-1.06 ( 1 5 ) 2.3 f 0.2 average (16)
3
0.016
0.001
0.1 order of magnitude ( 1 7 ) ,0.015 (18)
3
1.12
0.01
specified lo4 for 64Cu and >lo6 for 69mZn.The quantitative results are given in Table 111. LITERATURE C I T E D L. C. Thomas and G. J. Chamberlain, "Colorimetric Chemical Analytical Methods", 8th ed., The Tintometer Ltd., Salisbury, England, 1974. D. P. Scherbov and M. A. Matveets, "Analytical Chemistry of Cadmium", Nauka, Moscow, 1973 (through J. I. Dinnin. Anal. Chem., 47, 97R (1975)). 0.G. Koch and G. A. Koch-Dedic, "Handbuch der Spurenanalyse", Part 1, Springer Verlag, Berlin-Heidelberg-New York, 1974. P. Dulski and P. Moller, "Neutronenaktivierungsspektrometrie und Neutronenaktivierungsanalyse in der geochemischen Analytik", Hahn-Meitner-lnstitut fur KernforschungBerlin GmbH, Report-177, 1975. K. Ljunggren, B. Sjostrand, A. G. Johnels, M. Olsson, G. Otterlind, and T. Westermark, in "Nuclear Techniques in Environmental Pollution", IAEA, Vienna, 1971, p 373. J. R. DeVoe and W. Meinke, Anal. Chem., 31, 1428 (1959). H.K. J. Hahn, J. L. Sullivan, A. J. Blotcky, L. J. Arsenault, and A. D. May, Radiochim. Acta, 13, 55 (1969). K. W. Liebermann and H. H. Kramer, Anal. Chem., 42, 266 (1970). A . Wyttenbach and S. Bajo, Anal. Chern., 47, 1813 (1975). S. J. Joris, K. I. Aspila, and C. L. Chakrabarti, Anal. Chem., 41, 1441 (1969).
(1 1) A. Ringbom, "Complexation in Analytical Chemistry", Interscience, New York, 1963,p 315. (12)J. Stary in "MTP International Review of Science, Physical Chemistry, Series One", Vol. 12,Butterworths,London, 1973,p 279. (13)A. Wyttenbach and S. Bajo. Anal. Chem., 47, 2 (1975). (14) P. D. LaFleur, J. Radioanal. Chem., 19, 227 (1974). (15)H. J. M. Bowen. J. Radioanal. Chem., 19, 215 (1974).
(16) International Laboratory of
Marine Radioactivity, Principality of Monaco, Progress Report No. 13,June 1976. (17)F. J. Flanagan, Geochim. Cosmochim. Acta, 37, 1169 (1973). (18) K. J. R. Rosman and J. R. De Laeter, Chem. Geol., 13,69 (1974). RECEIVEDfor review May 3,1976. Accepted September 30, 1976.
Thin-Layer Chromatographic Determination of Hydrazine in Aqueous and Alcoholic Media Maria Bordun,* Joseph M. O'Connor, Gandharva R. Padmanabhan, and Joseph A. Mollica Ciba-Geigy Corporation, Pharmaceuticals Division, Analytical Research and Development, Suffern, N. Y. 1090 1
A rapid and efficient procedure for the determination of hydrazine as an azlne derivative has been developed. Hydrazine may be readily detected down to 0.002% in aqueous and aicoholic media.
Recent studies on evaluation of recovered solvents in our laboratory required the development of a rapid and efficient method of analysis for hydrazine a t low levels. A thin-layer chromatographic method of analysis which consists of reacting hydrazine and p -dimethylaminobenzaldehyde for a specified time and chromatographing the resulting derivative satisfied this need. The method is fast, simple, sensitive, and relatively free from intaferences. A survey of the literature showed that hydrazine has been analyzed extensively by a variety of methods including spot tests (1-7), colorimetry (8-15), titrimetry (16-18), and chromatography (19-21). The existing methodology was not applicable to our needs, being either too time consuming, complicated, or lacking the required sensitivity. The p -dimethylaminobenzaldehyde reacts preferentially with hydrazine and hydrazine compounds substituted in only one amino group to form the corresponding derivative as described by F. Feigl (21). The thin-layer chromatographic method described herein is based on this reaction and is specific for the detection of hydrazine and may be used for the determination of hydrazine or related compounds in water or other solvents. The lower limit of detection of hydrazine by this method was found t o be 0.2 bg. The solubility of hydrazine and its salts and the rate of formation of the azine derivatives were studied in the solvents of interest. The compounds under investigation were dissolved in water, 95%ethanol, and methanol. These solvents were of immediate interest and do not react with p-dimethylarninobenzaldehyde. Hydrazine and its salts react in the same manner towards the derivatizing reagent. Because of its insolubility in alcohols, the sulfate salt was analyzed only in water (Table I).
EXPERIMENTAL Equipment. Analtech precoated Silica Gel GF plates with a 250-p layer thickness were used for the investigation. Reagents and Solutions. p-Dimethylaminobenzaldehyde was obtained from K & K Laboratories. Hydrazine and hydrazine acetate were obtained from Eastman Organic Chemicals. Hydrazine sulfate and dihydrochloride salts were obtained from Fisher Scientific. The chemicals were used without further purification. Preparation of p-Dimethylaminobenzaldehyde Derivatization Solution. p-Dimethylaminobenzaldehyde, 1.0 g, is dissolved in 100 ml of 6 N hydrochloric acid.
Procedure. Add 3.0 ml of the 1%p-dimethylaminobenzaldehyde solution to a 10-ml volumetric flask containing 10 mg of hydrazine and make up to volume with the appropriate solvent (95% ethanol, methanol, or water). The standard solution is then shaken thoroughly and allowed to stand for 20 min. Concomitantly, add 3.0 ml of the 1%p-dimethylaminobenzaldehyde solution to a 10-ml volumetric flask containing 7.0 ml of sample, shake thoroughly, and allow to stand for 20 min. Ten p1 of the standard and sample solutions are spotted 2 cm from the bottom of the plate, dried under a stream of nitrogen, and developed in a chloroform-methanol-ammonium hydroxide (85:15:1) solvent system. The chamber is saturated for 1h prior to use. After developing the solvent front to 15 cm, the plate is removed and air dried for 15 to 30 min. Detection. The hydrazine derivative, p-dimethylaminobenzalazine, is detected in visible light and appears as a yellow spot against the white background; after the plate is sprayed with the Dragendorff's reagent, the color changes to an intense orange, which facilitates detection of the derivative at low levels. The derivative may also be detected by long and short UV light.
RESULTS AND DISCUSSION The procedure described above is specific for hydrazine. I t is based on the reaction of hydrazine with p-dimethylaminobenzaldehyde to form an intensely orange to orange-yellow colored azine solution. Akio Tsuji reported a spot-test procedure for hydrazine using a modification of this reaction (4). In the system developed herein, the azine travels as a yellow spot and is easily detectable. The following materials were screened by us for interference and found t o be unreactive with p-dimethylaminobenzaldehyde: alcohols, water, methyl isobutyl ketone, and primary, secondary, and tertiary aliphatic amines (Table I). Some aromatic amines, urea, and adrenaline were reported to react but the distinctive orange colored solution to some extent (6); is produced only with hydrazine (4,6). The screening results are shown in Table I. The lower limit of detection and the optimum reaction time were determined experimentally. In these experiments, the volume of derivatizing reagent-1% p-dimethylaminobenzaldehyde solution-was kept constant while varying the quantity of hydrazine in the system. Solutions of the derivatizing reagent and hydrazine (0.02,0.2,1.0, and 10 mg) were prepared in 95% ethanol, thoroughly mixed and allowed to stand for 15,20,30, and 60min. The resulting solutions were spotted and developed as described in the Experimental section. The rate study showed that formation of the azine derivative a t these concentrations was optimized a t a reaction time of 20 min; similar reaction times have been reported by Akio Tsuji (4)and by M. Pesez and A. Petit (6). In the above experiments the azine derivative was detected ANALYTICAL'CHEMISTRY, VOL. 49, NO. 1, JANUARY 1977
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