Karve & Gholave: Journal of aoaC InternatIonal vol. 94, no. 2, 2011 627 Solid-Phase Extraction and Atomic Absorption Spectrometric Determination of Cobalt Using an Octadecyl Bonded Silica Membrane Disk Modifed with Cyanex 272 Manjusha Karve and Jayram V. Gholave University of Mumbai, Department of Chemistry, Vidyanagari, Mumbai - 400 098, India Received April 16, 2010. Accepted by AK June 28, 2010. Corresponding author’s e-mail: mkarve@yahoo.com, manjusha@chem.mu.ac.in RESIDUES AND TRACE ELEMENTS A simple SPE method for determination of cobalt(II) using a C18 bonded silica membrane disk impregnated with Cyanex 272 has been developed. Cobalt(II) was quantitatively sorbed at pH 6.0 from a sample solution and eluted using 10.0 mL 1.0 M HNO 3 prior to its fame atomic absorption spectrometric determination. The infuence of eluting agents, the minimum volume and maximum fow rate of the eluent, and interfering ions on cobalt(II) was studied. The method developed for cobalt(II) had an LOD of 1.4 µg/L, and a preconcentration factor >200 with an RSD of 0.6%. The reusability of the modifed disk was for 40 cycles. The method was applied for the determination of cobalt in certifed samples, urine, and industrial sludge samples. C obalt is an essential trace element but is toxic at high levels. It is also an industrially important element. Cobalt alloys are used for manufacturing aircraft engines, cutting tools, knee joints, etc. Colored glasses, ceramics, and paints also contain cobalt compounds (1). Its entry into the environment is largely due to the indiscriminant discharge and its wide use in these industries. The role of cobalt in vitamin B12 is well known, and high doses of cobalt supplement may result in its deposition in the body. A noninvasive method to check the cobalt level in a body is normally carried out by analysis of urine for cobalt. A fame atomic absorption spectrophotometer is a relatively inexpensive instrument available in many laboratories for elemental analysis. However, for accurate and sensitive detection at trace levels, a separation and preconcentration step is required. In recent years, SPE has come to the forefront as an enrichment method (2). Methods have been extensively reported for SPE of cobalt(II) using silica (3), cellulose (4), polyurethane foam (5), multiwalled carbon nano tube (6), alumina (7), polymeric materials (8–13), and zeolite (14) as solid supports. Some of these methods were based on a synthetic route for the preparation of the solid phase, and none gave very good reusability. Some procedures were also reported using impregnation of a solid support (15–18) for detection of cobalt(II) in a variety of samples. The use of C18 silica gel membrane disks as a solid support has been reported (19–21) for the preconcentration of cobalt(II). Although impregnation involves physical interaction with the solid support, the use of a C18 disk as a solid support resulted in not only a faster fow rate but also good reusability (22, 23). Lower fow rates often limit the use of large volume of samples, hence restricting the LOD of cobalt(II). Cyanex 272 [bis(2,4,4-trimetylpentyl)phosphinic acid] is a liquid exchanger that extracts cobalt(II) by a cation exchange mechanism (24). The structure of a major component of Cyanex 272 is depicted in Figure 1. A C18 disk impregnated with Cyanex 272 combines the advantages of the high effciency of chromatography and high distribution coeffcient of liquid exchangers. The high surface area of the modifed disk permits use of high fow rates resulting in faster separation on account of better kinetics. The present work aimed at developing a simple, sensitive, and economical method for fame atomic absorption spectroscopy (FAAS) determination of trace amounts of cobalt(II) using C18 disks impregnated with Cyanex 272. Various parameters like the amount of Cyanex 272, pH and volume of the sample solution, different types and volumes of eluents, amount of sample, and eluent fow rates were studied to optimize quantitative sorption-desorption of cobalt(II). The method was successfully applied for determination of cobalt from urine and industrial sludge samples. The method developed was validated by analysis of QC Standard 21 (Product No. QC 21–xxx, Lot No. 904-0363) and Water Pollution Standard (Product No. WPS1–xxx, Lot No. 810-1012R; UHG Labs, Manchester, NH) and cobalt(II) by FAAS. Experimental Apparatus An AAnalyst200 atomic absorption spectrophotometer equipped with a multielement hollow-cathode lamp was Downloaded from https://academic.oup.com/jaoac/article/94/2/627/5655501 by guest on 20 October 2020