Microwave plasma-atomic emission spectrometric (MP-AES) determination of magnesium in flakes
Iga Rybicka, Bartosz Tołkacz and Anna Gliszczyńska-Świgło
Department of Technology and Instrumental Analysis, Poznań University of Economics and Business, al. Niepodległości 10, 61-875, Poznań, POL
Microwave plasma-atomic emission spectrometery (MP-AES) is an alternative to popular atomic spectroscopy in a flame (F-AAS). This method costs less, is safer and offers the same (or better) detection limits and linearity range compared to methods requiring flammable gases. Despite the fact that more laboratories decide to be equipped with MP-AES, the literature on the methods for determination of minerals in food samples is still limited. Therefore, the aim the study was to develop the method for magnesium (Mg) determination in food matrix (spelled and millet flakes) using MP-AES.
An Agilent 4210 Microwave Plasma Atomic Emission Spectrometer (Agilent Technologies, Melbourne, Australia) equipped with SPS4 Autosampler was used in the study. Easy-fit torch, OneNeb nebulizer and inert double-pass spray chamber were applied. Nitrogen was delivered by nitrogen generator Zefiro MP (Cinel Strumenti Scientifici, Vigonza, Italy).
The analytical wavelength was 383.829 nm, viewing position: 0, nebulizer gas flow 0.9 mL/min, background correction: auto, number of replicates: 3, read time: 3 s, sample uptake time: 45 s (fast pump), stabilization time: 10 s, rinse time: 20 s (fast pump). The linearity was verified for Mg standards of 0-25 µg/mL and R2 was over 0.999. The accuracy of the method was verified using Certified Reference Material BCR-191 Brown Bread. The found value was 0.53 ± 0.02 g/kg, the indicate value was 0.5 g/kg. The LOD was calculated from blank samples and was 0.07 µg/mL, whereas LOQ was 0.21 µg/mL.
In the study, 14 flakes (7 spelled and 7 millet) were analyzed. The flakes were 100% from each grain with no addition of fruits or other grains. Samples, in triplicate, were mineralized with nitric acid in microwave digestion system (MARS 6, CEM, Matthews, USA) and diluted to 50 mL with demineralized water. Quantitative analyses were performed using 2 calibration curves.
Mg is an important macroelement in human diet. Recommended Daily Allowance (RDA) for Mg for middle-aged woman is 320 mg per day and for middle-aged man – 420 mg per day. Grain products, also flakes, can be an important source of Mg. The content of Mg in spelled flakes was comparable between products analyzed and ranged from 113 to 139 mg in 100 g (in average 122 mg/100 g). The portion of 40 g spelled flakes would cover about 14-17% and 11-13% of Mg RDA for woman and man, respectively. The content of Mg in millet flakes was more diverse. These flakes contained from 44 to 115 mg in 100 g (in average 73 mg/100 g). The portion of 40 g millet flakes would cover 6-14% of RDA for Mg for woman and 4-11% for man, but for 5 out of 7 samples would not exceed 9% (woman) or 7% (man). In general, spelled flakes are better source of Mg than millet flakes and MP-AES is suitable method for Mg determinations in different flakes.