Liquid-phase microextraction and fibre-optics-based cuvetteless CCD-array micro-spectrophotometry for trace analysis

• Published in: Analytica chimica acta Vol. 648; no. 2; pp. 183 - 193
• Main Authors: Sharma, Nisha, Pillai, Aradhana K.K.V., Pathak, Neeraj, Jain, Archana, Verma, Krishna K.
• Format: Journal Article
• Language: English
• Published: Amsterdam Elsevier B.V 26.08.2009; Elsevier
• Subjects: Ammonia; Analytical chemistry; Charged couple device-array; Chemistry; Chlorine; Exact sciences and technology; Fibre optics; Iodine; Liquid-phase microextraction; Micro-spectrophotometry; Spectrometric and optical methods; Thiols; Ammonia; Liquid-phase microextraction; Thiols; Charged couple device-array; Chlorine; Micro-spectrophotometry; Fibre optics; Iodine; Solid phase extraction; Dyes; Microanalysis; Liquid phase; Solvent extraction; Chemical enrichment; Detection limit; Oxidation; Optical fiber; Trace analysis; Thiol; Iodides; Starch; Ion pair; Sample handling; Chlorine dioxide; Organic solvent; Microextraction; Headspace; Spectrophotometry
• ISSN: 0003-2670; 1873-4324
• DOI: 10.1016/j.aca.2009.07.006

Liquid-phase microextraction (LPME) has been investigated for trace analysis in the present work in conjunction with fibre-optic-based micro-spectrophotometry which accommodates sample volume of 1 μL placed between the two ends of optical fibres. Methods have been evolved for the determination of (i) 1–100 μM and 0.5–20 μM of thiols by single drop microextraction (SDME) and LPME in 25 μL of the organic solvent, respectively, involving their reaction with the Ellman reagent and ion pair microextraction of thiolate ion formed; (ii) 70 μg to 7 mg L −1 of chlorine/chlorine dioxide by headspace in-drop reaction with alternative reagents, viz., mixed phenylhydrazine-4-sulphonic acid and N-(1-naphthyl)ethylenediamine dihydrochloride, o-dianisidine, o-tolidine, and N, N-diethyl- p-phenylenediamine; (iii) 0.2–4 mg L −1 of ammonia by reaction with 2,4-dinitro-1-fluorobenzene to give 2,4-dinitroaniline which was diazotized and coupled with 1-naphthylamine, the resulting dye was subjected to preconcentration by solid-phase extraction and LPME; and (iv) 25–750 μg L −1 of iodide/total iodine by oxidation of iodide by 2-iodosobenzoate, microextraction of iodine in organic solvent, and re-extraction into aqueous starch-iodide reagent drop held in the organic phase. LPME using 25–30 μL of organic solvent was found to produce more sensitive results than SDME. The cuvetteless spectrophotometry as used in combination with sample handling techniques produced limits of detection of analytes which were better than obtained by previously reported spectrophotometry.