Determination of selenium in dietary supplements by optical emission spectrometry after alkaline dissolution and subsequent headspace solid phase microextraction.

Headspace solid phase microextraction (HSSPME) of chemically generated selenium hydride from alkaline solution followed by thermal desorption (TD) coupled directly to a microwave plasma (MWP) source has been examined for the optical emission spectrometric (OES) determination of Se. Various chemical and operating parameters including the NaBH(4) and HCl concentrations as well as the fiber exposure time and desorption temperature have been optimized. Alternatively, continuous hydride generation (HG) from alkaline medium and inductively coupled plasma (ICP) may be used for Se determination by OES. With the procedure developed, the determination of Se in dietary supplements at the tens of µgg(-1) level and an accuracy of 3-6% could be performed even in the presence of the 1000-fold excess of Fe and Cu. Additionally, Se was determined in the NIST 8418 material (Wheat gluten) with a certified concentration of Se of 2.58 ± 0.19 µgg(-1), and a value of 2.45 ± 0.25 µgg(-1) was found using HG-HSSPME-MWP-OES. The detection limit for Se (3.2 ng ml(-1)) with the proposed procedure was comparable to those obtained with HG-ICP-OES and the calibration curve was linear of about 2 orders of magnitude.

Preconcentration of by living bacteria immobilized on for microwave induced plasma optical emission spectrometry with continuous powder introduction.

The analytical potential of living bacteria Lactobacillus plantarum for the preconcentration of selenium from mineral water and beer samples followed by the selenium determination by continuous powder introduction microwave induced plasma-optical emission spectrometry (CPI-MIP-OES) has been investigated. The use of the bacteria immobilized on silica permits on-column preconcentration of selenium with minimum sample pretreatment by the pH adjustment. Experimental conditions for the preconcentration were optimized and the mechanism of the biosorption was investigated. Results showed that the use of the preconcentration stage leads to the substantial lowering of the detection limit of selenium by OES. The detection limit of 52 ng g-1 by the CPI-MIP-OES was achieved which corresponds to 0.06 ng mL-1 in the sample solution regarding the preconcentration factor of 1000. Precision of 5 replicate measurements expressed as relative standard deviation was about 3%. The utility of the method was demonstrated in the determination of selenium in hard drinking water ERM-CA011a as well as in mineral water and beer samples.

Selective determination of Fe(III) in Fe(II) samples by UV-spectrophotometry with the aid of quercetin and morin.

Selective UV-spectrophotometric methods for determination of iron(III) in iron(II) samples have been developed. The methods are based on the interaction of Fe(III) with quercetin and morin, compounds of the flavonoid group. Redox reactions occurring between Fe(III) ions and the reagents used make the basis for the detection. Iron(II) does not react with quercetin and morin under the conditions applied [aqueous-methanolic (3:2) soluions, 0.3 mol L(-1) HCl, 1.2 x 10(-4) mol L(-1) quercetin (morin)] and does not interfere with the determination of Fe(III). Iron(III) can be determined up to 15 microg mL(-1) using both the examined systems. The detection limits are 0.06 and 0.38 microg mL(-1) when using quercetin or morin, respectively. The method with quercetin was applied to the determination of Fe(III) (ca. 0.2%) in a Fe(II) pharmaceutical product.