Mercury(II) determination in commercial cosmetics and local Thai traditional medicines by flow injection spectrophotometry

OBJECTIVE

The proposed method was developed for the enhancement of sensitivity for Hg(II) determination using dithizone by adding SDS in the presence of ascorbic acid in sulphuric acid medium.

METHOD

The method was based on the reaction between Hg(II) and 1,5-diphenylthiocarbazone (dithizone), in the presence of sodium dodecyl sulphate (SDS) as an anionic surfactant (to avoid solvent extraction) and ascorbic acid in a slightly acidic medium resulting in a soluble orange coloured Hg(II)-dithizone complex which gave the maximum absorption at 490 nm. No extraction system was required in this method.

RESULT

Under the optimum conditions, a linear calibration graph was obtained over the concentration range of 0.05-1.50 μg mL(-1). The method was characterized by a limit of detection (LOD, defined as 3σ) and limit of quantification (LOQ, defined as 10σ) of 0.03 and 0.14 μg mL(-1), respectively. The relative standard deviations for replicate injection were 1.32 and 0.78% (n = 11) for 0.05 and 0.20 μg mL(-1) of Hg(II) standard solutions, respectively. The developed method has been satisfactorily applied for Hg(II) determination in commercial cosmetics and local Thai traditional medicines. Results obtained by the proposed method are compared favourably with those analysed by ICP-MS.

CONCLUSION

Enhancement of sensitivity and rapidity for Hg(II) assay by FIA could be achieved by adding SDS in ascorbic acid. The method would be useful for routine analysis of Hg(II) in real samples.

Miniaturization of spectrophotometry based on micro flow analysis using norfloxacin as less-toxic reagent for iron determination

A micro flow analysis (μFA) system has been designed and fabricated for determination of total iron. The system consists of a microchannels fabricated by etching the polymethyl methacrylate (PMMA) by using laser ablation techniques and a sealed polydimethylsiloxane (PDMS) as top plate. The PMMA micro-flow was topped with a home-made polydimethylsiloxane (PDMS) micro-flow through cell, which was integrated with light emitting diode (LED) as light source and a USB 2000 spectrometer as detector. The proposed μFA system was applied to determination of Fe(III) using norfloxacin as a less-toxic complexing agent in an acetate buffer solution pH 4.0, resulting in a yellow colored complex which gave the maximum absorption at 430nm. Under the optimum conditions, a linear calibration graph was obtained in the concentration range of 0.20-5.00mgL(-1). The limit of detection (LOD, defined as 3σ) and limit of quantification (LOQ, defined as 10σ) were 0.12 and 0.45mgL(-1), respectively. The relative standard deviation (R.S.D.) for repeatability and reproducibility were less than 1.50% and 1.24% (n=11) for 0.2mgL(-1) and 1.0mgL(-1) Fe(III), respectively. The proposed method was successfully applied to the determination of total iron in water samples, validated by the FAAS standard method after digestion by HNO3 and H2O2.