Experimental design in the optimization of a microwave acid digestion procedure for the determination of metals in biomorphic ceramic samples by inductively coupled plasma mass spectrometry and atomic absorption spectrometry

Method optimization for heavy metal determination in milk powder: application to milk samples from Greece

The scope of this study was the development, optimization and validation of an analytical method for the determination of selected heavy metals and trace elements (As, Hg, Se, Cd, Cu, Pb, Mn, Fe, Ni, Zn, Cr) in milk powder, using microwave-assisted digestion. A statistical experimental design approach using central composite design (CCD) was carried out, to investigate the effects of three independent pretreatment variables (final digestion temperature (°C), HNO₃ concentration (in % w/v), microwave hold time) on the heavy metal recovery of spiked undigested milk powder sample and to calculate the variable factor values which produce the optimum recovery. CCD results revealed that the optimum digestion conditions, with respect to maximum recovery were as follows: temperature 190 °C, HNO₃ 56.8% w/v, and digestion time of 8.47 min. The method was fully validated. Recoveries for all metals ranged between 92 and 108% while intra-day repeatability was below 6.59% (rsd). A certified reference material (ERM BD 150) that included 8 out of the total 11 heavy metals of the present study (Hg, Se, Cd, Cu, Pb, Mn, Ni, and Zn) was used to test the accuracy of the method where acceptable recovery values ranging between 96 and 107% were obtained. High heavy metal recoveries, short digestion time, and low acid consumption were the advantages of the pretreatment method. The analytical process was successfully applied for the determination of heavy metals in different milk samples from the Greek market. Heavy metal concentrations for Ni, Cr, Pb, Cd, Se, Mn, and Cu measured in this study reached 307, 102, 8.01, 5.96, 60.2, 519, and 438 μg/kg wet weight (ww), respectively. Zn and Fe were found at concentrations ranging 3.21-8.39 and 0.170-10.1 mg/kg ww, respectively. Risk assessment based on the WHO tolerable daily intake levels and the calculated target hazard quotients revealed that the consumption of the selected milk samples is considered safe.

Optimizing Mass Spectrometry Analyses: A Tailored Review on the Utility of Design of Experiments

Mass spectrometry (MS) has emerged as a tool that can analyze nearly all classes of molecules, with its scope rapidly expanding in the areas of post-translational modifications, MS instrumentation, and many others. Yet integration of novel analyte preparatory and purification methods with existing or novel mass spectrometers can introduce new challenges for MS sensitivity. The mechanisms that govern detection by MS are particularly complex and interdependent, including ionization efficiency, ion suppression, and transmission. Performance of both off-line and MS methods can be optimized separately or, when appropriate, simultaneously through statistical designs, broadly referred to as "design of experiments" (DOE). The following review provides a tutorial-like guide into the selection of DOE for MS experiments, the practices for modeling and optimization of response variables, and the available software tools that support DOE implementation in any laboratory. This review comes 3 years after the latest DOE review (Hibbert DB, 2012), which provided a comprehensive overview on the types of designs available and their statistical construction. Since that time, new classes of DOE, such as the definitive screening design, have emerged and new calls have been made for mass spectrometrists to adopt the practice. Rather than exhaustively cover all possible designs, we have highlighted the three most practical DOE classes available to mass spectrometrists. This review further differentiates itself by providing expert recommendations for experimental setup and defining DOE entirely in the context of three case-studies that highlight the utility of different designs to achieve different goals. A step-by-step tutorial is also provided.

Old and New Flavors of Flame (Furnace) Atomic Absorption Spectrometry

This paper presents some recent applications of Flame Atomic Absorption Spectrometry (FAAS) to different matrices and samples. The time window selected was from 2006 up to March, 2011, and several aspects related to food, biological fluids, environmental, and technological samples analyses were reported and discussed. In addition, the chemometrics application for FAAS methods development was also taken into account, as well as the use of metal tube atomizers in air/acetylene flame. Preconcentration methods coupled to FAAS were discussed, and several approaches related to speciation, flotation, ionic liquids, among others were discussed. This paper can be interesting for researchers and FAAS users in order to see the state of the art of this technique.