Feasibility of a simple laser-induced breakdown spectroscopy (LIBS) device has been investigated for the analysis of Mg and Ca in edible salts. The LIBS spectrometer was assembled with a compact low-power diode-pumped solid-state laser (DPSSL) and a non-gated low-resolution handheld spectrometer. A simple sampling process was employed for on-site application. A piece of filter paper was dipped in the aqueous solution of a sample salt and dried for analysis using LIBS. Maintaining the sample surface height at the optimum position was critical to generate plasmas persistently due to the low pulse energy of the DPSSL. The varying height of the filter paper surface was monitored and compensated, while the sample stage was translated to collect spectra from different positions. The variation of line intensities of Mg and Ca could be attributed to the inhomogeneous distribution of dry residues. To correct this, the peak that consists of the Na(I) and C(II) lines at 568 nm was employed as a reference signal for intensity normalization of the analyte Mg(II) and Ca(II) lines. For edible salt products, the normalized Mg(II) and Ca(II) line intensities could be well correlated with the concentrations of Mg and Ca determined using inductively coupled plasma optical emission spectroscopy. Our results indicate that a simple LIBS device in combination with the simple sampling method is promising as an on-site salt quality assessment methodology.
Toxicity due to arsenic (As) in food has been mostly assessed by the determination of total As amount. Although the toxicity depends on the chemical forms, the sample can be determined to be safe if the total As concentration is less than the maximum allowable amounts of the toxic arsenic compounds. In this work, the accuracy of total As analysis for rice and oyster samples was significantly influenced by the matrix effect and the chemical forms. The matrix effect could be effectively corrected by employing the appropriate internal standard, tellurium. The As species such as As(V), As(III), monomethylarsonic acid, dimethylarsinic acid, and arsenobetaine showed significantly different sensitivities in the inductively coupled plasma mass spectrometry analysis for rice and oyster samples. This indicates that the total As determined without any information of the chemical species and matching sensitivities of samples and standards may be inaccurate.
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