Assessing the internal standardization of the direct multi-element determination in beer samples through microwave-induced plasma optical emission spectrometry.

An evaluation of different elements (Be, Ga, In, Sc, and Y) as internal standards was performed to determine the content of Al, Ba, Co, Cr, Cu, Fe, Mn, Ni, Sr, Zn, Ca, Mg, Na, K in beer samples through microwave induced plasma optical emission spectrometry. The analytes were determined after simple dilutions of the samples with a 1.0 M nitric acid solution at a 1:4 ratio (sample: acid solution) with the addition of the IS. The analytical performance for each potential IS was established based on the limit of detection, limit of quantification, addition and recovery tests and accuracy obtained in the determination of each analyte. Each analyte responded differently when internal standardization was applied, and as such, the evaluation of each IS is important in the development of the method. In the presence of the recommended internal standard, the limit of detection varied, in µg L-1, from 0.23 to 4.6 for the microelements and between 10 and 620 for the macroelements. The limit of quantification, in µg L-1, was between 0.78 and 15.4 and between 30 and 970 for the microelements and macroelements, respectively. The precisions of the measurements, expressed as the relative standard deviation (n = 10; 0.50 and 3.0 mg L-1 of each analyte), were lower than 1.0% for all analytes. The proposed method was applied for the multi-element determination in commercial beer samples and the results were compared with those obtained by inductively coupled plasma optical emission spectrometry after sample digestion.

Determination of phospholipids in soybean lecithin samples via the phosphorus monoxide molecule by high-resolution continuum source graphite furnace molecular absorption spectrometry.

This paper presents a method for determining phospholipids in soybean lecithin samples by phosphorus determination using high-resolution continuum source graphite furnace molecular absorption spectrometry (HR-CS GF MAS) via molecular absorption of phosphorus monoxide. Samples were diluted in methyl isobutyl ketone. The best conditions were found to be 213.561nm with a pyrolysis temperature of 1300°C, a volatilization temperature of 2300°C and Mg as a chemical modifier. To increase the analytical sensitivity, measurement of the absorbance signal was obtained by summing molecular transition lines for PO surrounding 213nm: 213.561, 213.526, 213.617 and 213.637nm. The limit of detection was 2.35mgg-1 and the precision, evaluated as relative standard deviation (RSD), was 2.47% (n=10) for a sample containing 2.2% (w/v) phosphorus. The developed method was applied for the analysis of commercial samples of soybean lecithin. The determined concentrations of phospholipids in the samples varied between 38.1 and 45% (w/v).