Analytical Performance of Hollow Anode-Solution Cathode Glow Discharge-Atomic Emission Spectrometry

Fast and simple analysis of the content of Zn, Mg, Ca, Na, and K in selected beverages widely consumed by athletes by flowing liquid cathode atmospheric pressure glow discharge optical emission spectrometry

An atmospheric pressure glow discharge (APGD) system, generated between a flowing liquid cathode (FLC) and a gas (He) jet anode, was applied for the determination of Zn, Mg, Ca, Na, and K in selected beverages commonly chosen by athletes (namely Coca-Cola Zero, energy and vitamin drinks, pre-workout, branched-chain amino acids, almond drink, and whey protein) by optical emission spectrometry (OES). In some cases (i.e., Coca-Cola, energy drink, and almond drink), sugared and sugar-free versions of the beverages were analyzed with the purpose of establishing the impact of added sugar on the analyte signal intensities. The analysis was performed after a simplified sample preparation procedure, which involved only their dilution and acidification with HNO₃ to a concentration of 0.2 mol L^-1. To determine the most suitable conditions for performing the analysis, optimization of the crucial operating parameters and sample dilution was carried out. Under the compromise conditions, the instrumental detection limits (DLs) were established and found to be 21, 0.91, 20, 0.062, and 0.14 μg L^-1 for Zn, Mg, Ca, Na, and K, respectively. Due to the relatively low detection limits, the analyte content could be determined for a fairly high dilution, being concurrently the same for all analytes, which further simplified the whole procedure. It was found that the vast majority of samples could be determined using external calibration with simple standard solutions. The standard addition technique used for calibration was only required for the determination of Mg in three samples. The analysis results were consistent (in the majority of cases the recovery values were in the range of 88-111%) with the values obtained for the reference method (inductively coupled plasma optical emission spectrometry, ICP-OES), which proved the reliability of the results obtained from the developed FLC-APGD-OES system.

Development of a Portable Method for Serum Lithium Measurement Based on Low-Cost Miniaturized Ultrasonic Nebulization Coupled with Atmospheric-Pressure Air-Sustained Discharge

An accurate, rapid but cheap, and portable method for monitoring of serum lithium (Li) is highly desirable for mental patients who take Li medicine for treatment. Conventional techniques are usually bulky, costly, and cannot provide on-site real-time measurements. Herein, a miniaturized, reliable, cost-effective, and portable optical emission method for rapid and sensitive determination of serum Li was developed based on a combination of miniaturized ultrasonic nebulization (MUN) and a low-power (≈22 W) atmospheric-pressure air-sustained discharge (APAD) excitation source. The proposed method eliminates the use of any compressed gas or pump and can achieve serum Li detection within 40 s with low sample consumption (less than 20 μL serum). Except for dilution with water, no extra treatment is needed for serum Li analysis by MUN-APAD-OES. In addition, it offers a significant advantage of good tolerance to the coexisting high concentration of Na, K, Ca, and Mg, which is in contrast with the obvious matrix effect encountered in conventional inductively coupled plasma optical emission spectrometry (ICP-OES). Different operating parameters affecting the performance of MUN-APAD-OES were evaluated. Under optimized conditions, the detection limit of Li (670.8 nm) was calculated to be 0.6 μg L^-1 (6 μg L^-1 in serum). Finally, the accuracy of the proposed method was validated by the analysis of two certified reference materials (Seronorm serum L-1 and L-2 RUO), six real human serum samples, and eight real animal serum samples. All of the results indicate that the low-cost and low-power MUN-APAD-OES provides a promising reliable method for on-site serum Li measurement and may also be extended to other elements.

Five years of innovations in development of glow discharges generated in contact with liquids for spectrochemical elemental analysis by optical emission spectrometry

The newest achievements in the field of glow microdischarges generated in contact with a flowing liquid cathode (FLC) and a flowing liquid anode (FLA), used as the excitation sources for optical emission spectrometry (OES), were summarized herein. The design of recently reported discharge systems was compared and comprehensively discussed. A lot of effort was devoted to evaluate the effect of selected operating parameters, i.e., discharge voltage and current, sample flow rate, sample pH, jet-supporting gas flow rate, and discharge gap, on the microplasma stability and the intensity of measurable analytical signals. Furthermore, the influence of chemical modifiers, i.e., organic acids, alcohols, and surfactants, aimed at improving the sensitivity and reducing matrix effects, was referred to as well. Finally, the analytical performance and the application of these promising excitation sources for the elemental analysis of different-matrix samples were presented.