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Simplified and rapid determination of Ca, K, Mg, and Na in fruit juices by flowing liquid cathode atmospheric glow discharge optical emission spectrometry

Novel atmospheric pressure glow discharge (APGD) plasma sustained between a miniaturized flowing liquid cathode (FLC) and a pin-type anode was applied as an excitation source for the determination of Ca, K, Mg, and Na in fruit (apple, banana, blackcurrant, lemon, lime, pomegranate, quince, and tomato) juices by optical emission spectrometry. A simplified sample preparation procedure of juices, involving only their 1000-fold dilution and acidification with HNO3 to a concentration of 0.1 mol L−1, was proposed. The content of K and Na was determined using simple standard solutions for calibration, while the determination of Ca and Mg required the use of the standard addition method, due to matrix effects. Under the optimal conditions, the developed method assured instrumental detection limits of 5.69 (Ca), 0.14 (K), 0.63 (Mg), and 0.02 (Na) μg L−1. Owing to such low detection limits, the content of all studied metals could be determined using only one sample dilution. The proposed FLC APGD OES method was established to provide reliable results with high accuracy and very good precision.