Wagna Piler Carvalho dos Santos

Sample Preparation for the Determination of Metals in Food Samples Using Spectroanalytical Methods—A Review

Abstract The present article gives an overview of recent publications and modern techniques of sample preparation for food analysis employing atomic and inorganic mass spectrometric techniques, such as flame atomic absorption spectrometry, chemical vapor generation atomic absorption and atomic fluorescence spectrometry, graphite furnace atomic absorption spectrometry, inductively coupled plasma optical emission spectrometry, and inductively coupled plasma mass spectrometry. Among the most frequently applied sample preparation techniques for food analysis are dry ashing, usually with the addition of an ashing aid, and acid digestion, preferably with the assistance of microwave energy. Slurry preparation, particularly with the assistance of ultrasound, is increasingly used to reduce acid consumption and sample preparation time. Direct analysis of solid samples is gaining importance in the field of food analysis as it offers the highest sensitivity, avoids the use of acids and other aggressive reagents, makes possible the analysis of micro‐samples, and can be applied for fast screening analysis, e.g., of fresh meat.

A critical evaluation of digestion procedures for coffee samples using diluted nitric acid in closed vessels for inductively coupled plasma optical emission spectrometry

The efficiency of diluted nitric acid solutions for digesting regular coffee samples was evaluated employing two closed vessel procedures: one was based on microwave-assisted heating and the other was based on conductive heating using pressurized Parr bomb. The efficiency of digestion was evaluated by determining residual carbon content (RCC) and residual acidity. The digestion was effective using both procedures, i.e. there were no solid residues after the decomposition reactions when using up to 3.5 mol L(-1) nitric acid solutions. It was demonstrated that the digestion procedures are critically dependent on reactions occurring in liquid and gas phase and that the formation of NO and its conversion to NO2 by O2 exerts a major effect in the oxidation of organic matter. These processes are more effective in closed vessels heated by microwave radiation due to the greater volume of these flasks and the temperature gradient that exists during the first step of the digestion process. The proposed model for the digestion processes in diluted nitric acid solution is corroborated by data about consumption of acid during the digestion and by measuring the pressure during the whole process.

Optimisation of focused-microwave assisted digestion procedure for Kjeldahl nitrogen determination in bean samples by factorial design and Doehlert design

In the present paper a focused-microwave Kjeldahl digestion procedure without metal catalyst for nitrogen determination in bean samples was developed. Temperature at which the decomposition plateau occurs, mass of potassium sulphate and either volume of sulphuric acid or hydrogen peroxide were optimised. Results of the two-level full factorial design (2(4)) based on an analysis of variance demonstrated that only the decomposition plateau temperature and the sulphuric acid volume were statistically significant. Optimal conditions for the digestion of bean samples were obtained by using Doehlert design. The modified digestion procedure of 0.25g of bean samples has been performed in 27min at optimised conditions. The accuracy of the developed procedure by the analysis of the two certified reference materials, peach leaves (NIST 1547) and apple leaves (NIST 1515). The t-test applied to the results revealed that they are in agreement (p > 0.05) with the certified values. The precision, expressed as relative standard deviation (R.S.D.) was of 0.96% for four successive Kjeldahl nitrogen determinations. In addition, interlaboratory exercises were performed with several bean samples in reference Brazilian food control laboratory.

Planejamento fatorial aplicado à digestão de amostras de feijão assistida por radiação microondas

The use of factorial design was evaluated for optimization of focused-microwave-assisted digestion of bean samples. Calcium, Fe, Mg, Mn and Zn percentual recoveries were determined in digestates after focused-microwave-assisted digestion according to factorial design procedures. A cavity microwave digestion was carried out to certify the elemental compositions obtained. The accuracy was checked using a standard reference material, the NIST SRM 8433 - Corn Bran. Results are in agreement with certified values at the 95% confidence limit when the Student t-test was used. Volumes of nitric and sulfuric acid, temperature, and the interplay between HNO3 and H2SO4 initial volumes were significant variables according to P-values in the analysis of variance (ANOVA).

Mineral composition of Lippia alba (Mill.) N.E. Brown leaves

Leaves of Lippia alba (Mill.) N.E. Brown are used for the preparation of tea infusions that are employed in folk medicine. In this paper, the mineral composition of Lippia alba (Mill.) leaves, collected from different Brazilian cities, was evaluated. The samples were digested using nitric acid and hydrogen peroxide on a hot plate and were analyzed using inductively coupled plasma optical emission spectrometry (ICP OES). SRM 1515 apple leaves from NIST were used for checking accuracy. The results demonstrated that calcium, magnesium and phosphorus have average contents of 1,950, 2,856 and 2,335 mg 100 g -1 , respectively, and concentration ranges of 767-3,887, 314-8,591 and 247-9,214 mg 100 g -1 , respectively. The microelements barium, zinc, copper, iron, manganese and nickel have average contents of 2.16, 2.95, 0.94, 11.2, 4.25 and 0.09 mg 100 g -1 , respectively, and concentration ranges of 0.66-7.1, 1.35-6.3, 0.33-1.7, 0.98-34, 0.82-7.4 and 0.03-0.15 mg 100 g −1 , respectively. The data were also evaluated using principal component analysis (PCA).

Bioaccessibility assessment of toxic and essential elements in produced pulses, Bahia, Brazil

The objective of this study was to analyze the effect of heat treatment on the bioaccessibility of major (K, Ca, Mg, P) and trace elements (As, Ba, Cu, Fe, Mn, Cd, Cr, Hg, Mo, Ni, Pb, Se, Sb, Sn, and Zn) in three different pulse species: Vigna unguiculata L. Walp (cowpea beans), Cajanus cajan L. (pigeon pea) and Lablab purpureus L. Sweet (mangalo). Analyte concentrations were determined in the samples by inductively coupled plasma mass spectrometry and inductively coupled plasma optical emission spectrometry. The results showed that thermal processing can affect the concentrations of the elements investigated in pulse samples. The influence of the heat treatment can range between legume species and chemical elements, as well as with the type of heat treatment, dry, wet, conductive heating and using microwaves.