Atomic absorption method for the determination of trace amount of chromium (VI) with ionpair extraction of dimercaptomaleonitrile-chromium (III) complex

• Published in: BUNSEKI KAGAKU Vol. 27; no. 3; pp. 142 - 147
• Main Authors: INOUE, Sadanobu, YOTSUYANAGI, Takao, SASAKI, Mitsuo, AOMURA, Kazuo
• Format: Journal Article
• Language: Japanese
• Published: The Japan Society for Analytical Chemistry 05.03.1978
• Subjects: Atomic absorption spectrophotometry; Chromium(VI); Dimercaptomaleonitrile; Extraction; Ion-pair
• ISSN: 0525-1931
• DOI: 10.2116/bunsekikagaku.27.3_142

Dimercaptomaleonitrile (maleonitriledithiol, MNT or H2L) reacts rapidly with chromium(VI) to form water soluble complex, CrL33-, which can be quantitatively extracted into methyl isobutyl ketone (MIBK) and chloroform, respectively, as an ion-pair with tetrabutylammonium cation (TBA+ or Bu4N+), [(Bu4N)3CrL33-]0. The ion-pair extraction constant (Kex) of CrL33- ion with TBA+ in chloroform was estimated to be Kex= [(Bu4N)3CrL3]0 [CrL33-]-1 [Bu4N+]-3 =1017.76±0.09(I=0.3, Na2SO4). Based on this extraction reaction, a new sensitive method for the determination of chromium(VI) by atomic absorption spectrophotometry was proposed: In a separatory funnel, take an aliquot of sample solution containing less than 75 μg of chromium, and add 10 mg of Na2L, 1 cm3 of 2 mol dm-3 acetate buffer solution (pH 5.2) and 2 cm3 of 3.75 × 10-2 mol dm-3 TBABr solution. Dilute the mixture to 100 cm3 with distilled water. Extract the ion-pair with 10 cm3 of MIBK by shaking for 2 minutes and allow to stand for 30 minutes. Separate the organic phase and measure the absorbance at 3579 Å with an atomic absorption spectrophotometer. The sensitivity of this method was 0.096 μg Cr(VI) cm-3/1%A. For the determination of 50μg chromium(VI), 100μg of chromium(III) did not interfere, furthermore, 5 mg of Cr(III) was tolerated when Cr(III) was extracted at pH 2.5 (sensitivity: 0.156 μg Cr(VI) cm-3/%). The tolerance limits for various foreign ions were also determined.