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This work presents a critical review of multivariate techniques employed for optimization of methods developed in food analysis. A comparison between the response surface methodologies has been performed, it evidencing advantages and drawbacks of these. Applications of the main chemometric tools (central composite and Box Behnken designs and Doehlert matrix) often utilized for optimization of sample preparation procedures and also instrumental conditions of analytical techniques for determination of organic and inorganic species in food samples are shown. Also, a brief discussion on the use of multiple responses and robustness test in food analysis has been presented.

A new procedure developed based on a preconcentration system using a dispersive liquid-liquid microextraction technique based on solidification of floating organic drop (DLLME-SFO) was combined with the molecular absorption spectrometry to determine uranium using 2-(5-bromo-2-pyridylazo)-5-(diethylamino)-phenol (Br-PADAP) as the complexing reagent. The optimization step was performed using two-level factorial design and the Box-Behnken design. The parameters analyzed were pH, Br-PADAP volume, extractant solvent volume and disperser solvent volume. The method allowed determining uranium with a limit of detection of 0.46 μg L− 1, limit of quantification 1.53 μg L− 1. The enrichment factor was estimated to be 76-fold. The precision expressed as relative standard deviation (RSD) for uranium concentrations of 2 and 10 μg L− 1 was 4.91% and 1.85% (n = 15), respectively. Accuracy was assessed using recovery values ranging from 95.28% to 103.86%, which proves that this method does not suffer from a matrix effect and can be satisfactorily applied. The proposed method was applied to determine uranium in human milk samples. Fifteen samples were analyzed, and the uranium concentration ranged from 45.87 ± 3.62 μg L− 1 to 160.97 ± 7.00 μg L− 1.

This study proposes a methodology of determination of cadmium and manganese in food samples using an aqueous two-phase system without extracting agent with F AAS detection. In order to choose the best system for preconcentration, an experimental design with Doehlert matrix was employed, allowing the determination of the system composed by PEO400 + K2HPO4 + H2O with the best extraction efficiency. This same study verified that pH does not influence the extraction percentage. Still in the optimization stage, the best conditions were tie-line length = 53.3%w; mass ratio between bottom and top phases = 0.029; and extraction time = 18hs. The method reached values of LOD (0.45 µg.Kg−1 for Cd(II) and 6.4 µg.Kg−1 for Mn(II)), LOQ (1.5 µg.Kg−1 for Cd(II) and 21 µg.Kg−1 for Mn(II)) and enrichment factor (16 for Cd(II) and 45 for Mn(II)) suitable to determine both analytes in food samples. The intra and inter-day relative standard deviation ranged from 3.28 to 4.37%, and from 5.05 to 6.60% for Cd(II) and Mn(II), respectively. The analysis of the NIST 1575a certified sample had a recovery of 98.2% for cadmium, and NIST 1515 presented recovery of 99.2% for manganese, showing high accuracy. The method was applied to samples of green tea and soluble coffee, and the recovery tests obtained results ranging from 94.0 to 110%. Therefore, the proposed methodology is efficient and without using an extractor, being a highly accurate and environmentally safe alternative for the determination of trace levels of metal in food samples.

The present paper reports the advantages, drawbacks and applications of the main techniques of sample preparation employed during the determinations of total mercury and methylmercury in food matrices employing analytical methods such as: cold vapor atomic absorption spectrometry (CV AAS), cold vapor atomic fluorescence spectrometry (CV AFS), inductively coupled plasma mass spectrometry (ICP-MS), voltammetry, and neutron activation analysis. The use of slurry sampling, solid sampling, microwave assisted extraction, reflux system by cold finger and Vigreux column was discussed. Also a brief text on the use of chromatographic techniques for the speciation analysis of mercury is presented. A list of 134 references is cited and the analytical characteristics of some these procedures proposed are shown as tables.

Caigua (in Brazil “maxixe do reino”) is a fruit that is generally consumed either cooked or even raw as salad. This fruit has been used as a food and also in folk medicine. In this work, the mineral composition of Caigua was determined for the first time. Twenty-nine samples from five farms located in the southwestern region of Bahia, Brazil were acquired and analyzed using inductively coupled plasma optical emission spectrometry. The elements determined in this fruit included calcium, magnesium, sodium, potassium, phosphorus, manganese, iron, zinc, copper and vanadium. Principal component analysis (PCA) and hierarchical cluster analysis (HCA) were applied to evaluate the obtained results. The average concentrations of the determined elements (expressed as mg 100g−1) were as follows: 0.91 for sodium, 152 for potassium, 19.4 for phosphorus, 11.9 for calcium, 8.4 for magnesium, 0.074 for manganese, 0.21 for iron, 0.013 for copper, 0.13 for zinc and 0.015 for vanadium.

In this work, the mineral composition of fresh bovine milk obtained from the milk-producing areas of the Brazilian State of Sergipe was examined. A dry-ashed digestion method and the ICP OES technique were used for the quantification of mineral elements ( e.g. , Ca, Mg, K, Na, P, Sr and Zn) in 27 samples of milk collected from properties located in milk-producing areas around Nossa Senhora da Gloria. The following ranges of values (% m/v) were obtained: 0.063 to 0.117 for Ca; 0.060 to 0.114 for P; 0.024 to 0.064 for Na; and 0.087 to 0.164 for K. The ranges of values (mg L − 1 ) for the other mineral elements were also found: 0.68 to 1.89 for Sr; 2.46 to 5.73 for Zn; and 54.2 to 109.9 for Mg. Additionally, the exploratory evaluation of the 27 milk samples was performed using principal component analysis (PCA) involving seven variables dealing with the effect of different management systems (conventional and organic) on milk composition. The results show that there are indeed differences between the mineral composition of milk from properties that use organic practices and those that use conventional management practices.

A procedure is proposed for the direct determination of manganese and iron in wine employing fast sequential flame atomic absorption spectrometry and the reference element technique to correct for matrix effects. Cobalt, silver, nickel and indium have been tested as reference elements. The results demonstrated that cobalt and indium at a concentration of 2 and 10 mg L−1 were efficient for quantification of manganese and iron, respectively. Under these conditions, manganese and iron could be determined with quantification limits of 27 and 40 μg L−1, respectively. The proposed method was applied to the determination of manganese and iron in 16 wine samples. The content of manganese varied from 0.78 to 2.89 mg L−1 and that of iron from 0.88 to 9.22 mg L−1. The analytical results were compared with those obtained by inductively coupled plasma optical emission spectrometry after complete mineralization using acid digestion. The statistical comparison by a t-test (95% confidence level) showed no significant difference between the results.

Spectrometric techniques for the analysis of trace cadmium have developed rapidly due to the increasing need for accurate measurements at extremely low levels of this element in diverse matrices. This review covers separation and preconcentration procedures, such as electrochemical deposition, precipitation, coprecipitation, solid phase extraction, liquid-liquid extraction (LLE) and cloud point extraction (CPE), and consider the features of the their application with several spectrometric techniques.

The first publication on the use of polyurethane foam (PUF) for sorption processes dates back to 1970, and soon after the material was applied for separation processes. The application of PUF as a sorbent for solid phase extraction of inorganic analytes for separation and pre-concentration purposes is reviewed. The physical and chemical characteristics of PUF (polyether and polyester type) are discussed and an introduction to the characterization of these sorption processes using different types of isotherms is given. Separation and pre-concentration methods using unloaded and loaded PUF in batch and on-line procedures with continuous flow and flow injection systems are presented. Methods for the direct solid sampling analysis of the PUF after pre-concentration are discussed as well as approaches for speciation analysis. Thermodynamic proprieties of some extraction processes are evaluated and the interpretation of determined parameters, such as enthalpy, entropy and Gibbs free energy in light of the physico-chemical processes is explained.

The present paper proposes an on-line pre-concentration system for cadmium determination in drinking water using flame atomic absorption spectrometry (FAAS). Cadmium(II) ions are retained as 1-(2-pyridylazo)-2-naphthol (PAN) complex at the walls of a knotted reactor, followed of elution using hydrochloric acid solution. The optimization was performed in two steps using factorial design for preliminary evaluation and a Box–Behnken design for determination of the critical experimental conditions. The variables involved were: sampling flow-rate, reagent concentration, pH and buffer concentration, and as response the analytical signal (absorbance). The validation process was performed considering the parameters: linearity and other characteristics of the calibration curve, analytical features of on-line pre-concentration system, precision, effect of other ions in the pre-concentration system and accuracy. Using the optimized experimental conditions, the procedure allows cadmium determination with a detection limit (3 σ / S) of 0.10 μg L− 1, a quantification limit (10 σ / S) of 0.33 μg L−1, and a precision, calculated as relative standard deviation (RSD) of 2.7% (n = 7) and 2.4% (n = 7) for cadmium concentrations of 5 and 25 μg L− 1, respectively. A pre-concentration factor of 18 and a sampling frequency of 48 h−1 were obtained. The recovery for cadmium in the presence of several ions demonstrated that this procedure could be applied for the analysis of water samples. The method was applied for cadmium determination in drinking water samples collected in Salvador City, Brazil. The cadmium concentrations found in five samples were lower than the maximum permissible levels established by the World Health Organization.