Solid-phase spectrophotometry (SPS) has been applied to analysis trace amounts of selenium in several real matrixes such as water, soil, plant materials, human hair, and to synthetic samples of cosmetic preparations. Selenium (IV) was sorbed in a dextran type lipophilic gel as a complex with 2,3-dichloro-6-(2,7-dihydroxy-naphthylazo)quinoxaline (DCDHNAQ), whereas Se(VI) was determind after boiling in HCl for 10 min to convert Se(VI) to Se(IV). Resin phase absorbances at 588 and 800 nm were measured directly which allowed the determination of selenium in the range 0.2– 3.3 μg L−1 with a relative standard deviation of 1.22 %. The influences of the analytical parameters including pH of the aqueous solution, amounts of DCDHNAQ, sample volume were investigated. The molar absorptivities were found to be 1.09× 106 , 4.60 × 106 and 1.23 × 107 L mol−1 cm−1 for 100, 500 and 1000 mL, respectively. The detection and quantification limits of the 500 mL sample method are 110 ng L−1 and 360 ng L−1 when using 50 mg of dextran type lipophilic gel. For a 1000 mL sample, the detection and quantification limits are 60 ng L−1 and 200 ng L−1 using 50 mg of the exchanger. Increasing the sample volume can enhance the sensitivity. No considerable interferences have been observed from other investigated anions and cations on the selenium determination.
J. AOAC Inter, 45 (2012) 246-255.