An introductory review on the application of principal component analysis in the data exploration of the chemical analysis of food samples.

Principal component analysis (PCA) is currently one of the most used multivariate data analysis techniques for evaluating information from food analysis. In this review, a brief introduction to the theoretical principles that underlie PCA will be given, in addition to presenting the most commonly used computer programs. An example from the literature was discussed to illustrate the use of this chemometric tool and interpretation of graphs and parameters obtained. A list of recently published articles will also be presented, in order to show the applicability and potential of the technique in the food analysis field.

Multivariate optimization of a dispersive liquid-liquid microextraction method for determination of copper and manganese in coconut water by FAAS.

In this study, multivariate methodologies were applied in the optimization of a dispersive liquid-liquid microextraction (DLLME) method, aiming at the determination of Cu and Mn in coconut water samples by flame atomic absorption spectrometry. Some extractors (chloroform and CCl4), dispersants (ethanol, methanol and acetonitrile) and complexing agents (5-Br-PADAP and Dithzone) were previously tested in the extraction. A mixture design was used to optimize the component proportions formed by chloroform (10%), acetonitrile (76%), and 0.020% 5-Br-PADAP solution (14%). Doehlert design optimized the variables pH, NaCl, and buffer amounts for the extraction of both metals. The following analytical characteristics, respectively for Cu and Mn, were accessed: limit of quantification (4.83 and 3.32 µg L-1), enrichment factors (11 and 8 fold), and precision (6.6 and 6.0% RSD, n = 10). Addition/recovery tests of the analytes allowed to find values in the range of 96.5-120% for Cu and 99-107% for Mn.

Doehlert design in the optimization of procedures aiming food analysis - A review.

In the present paper is presented a review on the application of Doehlert design in the optimization of some of the steps of analytical procedures aimed the analysis of food samples. The theoretical principles and the main characteristics of this type of design are described. In addition, the main advantages and limitations of Doehlert design over other designs (Central Composite Design and Box-Behnken) and its application in the area of food analysis are discussed. Finally, to illustrate its potential, some examples of Doehlert design application in other areas of food chemistry without the purpose of analytical determination will be briefly presented.

Multivariate optimization of a goat meat alkaline solubilization procedure using tetramethylammonium hydroxide for metals determination using FAAS.

In the present work, multivariate designs were used to optimize an alkaline dissolution, assisted by ultrasound energy, procedure of goat meat using tetramethylammonium hydroxide (TMAH) aiming to determine Ca, Cu, Fe, K, Mg, Na and Zn by flame atomic absorption (FAAS) and emission (FAES) spectrometry. The optimal conditions found for the dissolution were in the following ranges: 0.4-0.5 g for the sample mass, 12-15 min of sonication and using 700-1000 µL of 25% TMAH at a temperature of 50 °C. The obtained limits of quantification varied between 0.221 (Mg) and 7.60 (Ca) µg g-1. Accuracy was assessed by comparing the results obtained by applying the proposed method with the digestion in an acid medium using a digesting block and by analyzing bovine liver certified reference material. The application of a t-test revealed that, at a 95% confidence level, there were no significant differences between the values obtained.

An alkaline dissolution-based method using tetramethylammonium hydroxide for metals determination in cow milk samples.

This study approaches the development of a method for the determination of Ca, Mg, Zn, and Fe in liquid and powdered cow milk. The method is based on sample dissolution assisted by ultrasound energy in tetramethylammonium hydroxide (TMAH) media and determination by flame atomic absorption spectrometry (FAAS). Central composite design (CCD) associated with response surface methodology and desirability function allowed the fast and efficient optimization of the variables involved in the performance of the dissolution. The developed dissolution method allowed Ca, Fe, Zn, and Mg determination in milk samples with adequate analytical characteristics for these determinations. Addition/recovery tests and analysis of a certified reference material of skimmed powdered milk (ERM-BD150) have shown that this method presents enough accuracy to carry out these analyses.

Simultaneous optimization of multiple responses and its application in Analytical Chemistry - A review.

This manuscript covers the application of the main techniques for simultaneous optimization of multiple responses generated by the application of multivariate designs (two-factor factorial, Central Composite, Doehlert, etc.) or by chromatographic runs in the development of analytical methods. Special attention will be given to the graphical method, desirability function, multiple response function and chromatographic response functions, since they are more frequently used in the analytical area. The advantages, disadvantages, limitations, and potentialities of these methods will also be addressed, as well as some of their applications, commenting on real examples from the literature. Some less usual methods in multiple response optimization in Analytical Chemistry will also be commented.

Doehlert design in the optimization of ultrasound assisted dissolution of fish fillet samples with tetramethyl ammonium hydroxide for metals determination using FAAS.

Doehlert design and desirability function were used in the optimization of an ultrasound assisted dissolution method of fish fillet samples with tetramethyl ammonium hydroxide (TMAH) for the determination of Ca, Fe, Zn and Mg by flame atomic absorption spectrometry. The variables values after optimization were 620 µL (volume of TMAH), 25 min (sonication time) and 46 °C (bath temperature). The quantification limits for Ca, Mg, Fe and Zn were 56, 107, 23 and 2.9 µg g-1, respectively. Accuracy was evaluated by comparing the results generated from the analysis of the samples treated by the proposed method and by wet digestion. Additionally, accuracy for Fe and Zn was assessed by the analysis of certified reference materials Tort-3 (Lobster hepatopancreas), ERM-CE 278 (mussel tissue) and Dolt-4 (Fish liver). There were no significant differences between the results obtained at a 95% confidence level when results were evaluated by t-test application.

Evaluation of macro and micronutrient elements content from soft drinks using principal component analysis and Kohonen self-organizing maps.

This study approaches the determination of nine elements from Brazilian carbonated soft drinks of several flavors and manufactures using inductively coupled plasma optical emission spectrometry (ICP OES). The concentrations of the elements varied as follows: (in µg L-1: Cu: 4.00-78.0; Fe: 74.0-506; Mn: 20.0-66.0; Zn: 104-584) and (in mg L-1: Ca: 4.81-16.2; K: 6.73-260; Na: 26.0-175; S: 1.43-5.41; P: 0.186-219). Principal component analysis has shown some tendencies to form two groups according to the drink flavor (orange and cola), but only cola presented a clear and complete separation. Using Kohonen maps, it was observed a tendency to form three flavor groups: (i) cola, (ii) orange and lemon, and (iii) guarana. However, this last tool proved to be more accurate in the groups' formation.

Screening of Passiflora L. mineral content using principal component analysis and Kohonen self-organizing maps.

A method using digestion with diluted nitric acid and inductively coupled plasma optical emission spectrometry was applied to determine metal ions in the peel, pulp, and seed of Passiflora edulis f. flavicarpa and Passiflora cincinnata cultivated in the Bahia state, Brazil. Plasma parameters (radio frequency power and argon flow rates) were optimized. The quantification limits (µg g-1) were: Ca (43.0); Co (1.3); Cu (10.0); Fe (10.0); K (20.0); Mg (26.6); Mn (0.33); Na (56.6) and Zn (10.0). The accuracy of the method was evaluated by the analysis of certified reference materials (NIST 1567a Wheat Flour and NIST 1577b Bovine Liver). Recovery studies were carried out and values found were between 89 and 120%. PCA and Kohonen self-organizing maps showed the formation of groups, corresponding to the fruit parts. Thus, passion fruit has great importance and biological potential, due to its high content of K and low Na.

Multivariate Exploratory Analysis of Metals and Phosphorus Concentrations of Leachates Collected Monthly from a Municipal Sanitary Landfill.

Concentrations of 11 elements (P, Cu, Ni, Co, Pb, Ca, Mn, Fe, Zn, Cr and Al) were measured in leachate samples collected monthly from the municipal landfill in Jequié, Bahia, Brazil. P (0.943-23.8 mg L(-1)), Ca (19.90-129 mg L(-1)) and Fe (0.115-2.87 mg L(-1)) were found in the highest levels, while Cu (

Synthesis and application of a new thiazolylazo reagent for cloud point extraction and determination of cobalt in pharmaceutical preparations.

The synthesis and characterization of the reagent 2-(5-bromothiazolylazo)-4-chlorophenol and its application in the development of a preconcentration procedure for cobalt determination using flame atomic absorption spectrometry after cloud point extraction is presented. This procedure is based on cobalt complexing and entrapment of the metal chelates into micelles of a surfactant-rich phase of Triton X-114. The preconcentration procedure was optimized by using a response surface methodology through the application of the Box-Behnken matrix. Under optimum conditions, the procedure determined the presence of cobalt with an LOD of 2.8 microg/L and LOQ of 9.3 microg/L. The enrichment factor obtained was 25. The precision was evaluated as the RSD, which was 5.5% for 10 microg/L cobalt and 6.9% for 30 microg/L. The accuracy of the procedure was assessed by comparing the results with those found using inductively coupled plasma-optical emission spectrometry. After validation, the procedure was applied to the determination of cobalt in pharmaceutical preparation samples containing cobalamin (vitamin B12).

Use of constrained mixture design for optimization of method for determination of zinc and manganese in tea leaves employing slurry sampling.

A slurry suspension sampling technique has been developed for manganese and zinc determination in tea leaves by using flame atomic absorption spectrometry. The proportions of liquid-phase of the slurries composed by HCl, HNO(3) and Triton X-100 solutions have been optimized applying a constrained mixture design. The optimized conditions were 200mg of sample ground in a tungsten carbide balls mill (particle size<100 microm), dilution in a liquid-phase composed by 2.0 mol L(-1) nitric, 2.0 mol L(-1) hydrochloric acid and 2.5% Triton X-100 solutions (in the proportions of 50%, 12% and 38% respectively), sonication time of 10 min and final slurry volume of 50.0 mL. This method allowed the determination of manganese and zinc by FAAS, with detection limits of 0.46 and 0.66 microg g(-1), respectively. The precisions, expressed as relative standard deviation (RSD), are 6.9 and 5.5% (n=10), for concentrations of manganese and zinc of 20 and 40 microg g(-1), respectively. The accuracy of the method was confirmed by analysis of the certified apple leaves (NIST 1515) and spinach leaves (NIST 1570a). The proposed method was applied for the determination of manganese and zinc in tea leaves used for the preparation of infusions. The obtained concentrations varied between 42 and 118 microg g(-1) and 18.6 and 90 microg g(-1), respectively, for manganese and zinc. The results were compared with those obtained by an acid digestion procedure and determination of the elements by FAAS. There was no significant difference between the results obtained by the two methods based on a paired t-test (at 95% confidence level).

Thermospray generation directly into a flame furnace--an alternative to improve the detection power in atomic absorption spectrometry.

Recent developments and applications in the production of thermosprays directly into flame furnaces to improve the analytical sensitivity in atomic absorption spectrometry are reviewed in this manuscript. Principles, characteristics, instrumentation, and applications of this analytical technique for trace elements determination in several matrices are discussed. The use of preconcentration procedures to allow low detection limits for ultra-trace levels using TS-FF-AAS is presented and current perspectives and future trends of this technique are also discussed.

Application of multivariate techniques in the optimization of a procedure for the determination of bioavailable concentrations of Se and As in estuarine sediments by ICP OES using a concomitant metals analyzer as a hydride generator.

A procedure has been developed for the determination of bioavailable concentrations of selenium and arsenic in estuarine sediments employing inductively coupled plasma optical emission spectrometry (ICP OES) using a concomitant metals analyzer device to perform hydride generation. The optimization of hydride generation was done in two steps: using a two-level factorial design for preliminary evaluation of studied factors and a Doehlert design to assess the optimal experimental conditions for analysis. Interferences of transition metallic ions (Cd(2+), Co(2+), Cu(2+), Fe(3+) and Ni(2+)) to selenium and arsenic signals were minimized by using higher hydrochloric acid concentrations. In this way, the procedure allowed the determination of selenium and arsenic in sediments with a detection limit of 25 and 30 microg kg(-1), respectively, assuming a 50-fold sample dilution (0.5 g sample extraction to 25 mL sample final volume). The precision, expressed as a relative standard deviation (% RSD, n=10), was 0.2% for both selenium and arsenic in 200 microg L(-1) solutions, which corresponds to 10 microg g(-1) in sediment samples after acid extraction. Applying the proposed procedure, a linear range of 0.08-10 and 0.10-10 microg g(-1) was obtained for selenium and arsenic, respectively. The developed procedure was validated by the analysis of two certified reference materials: industrial sludge (NIST 2782) and river sediment (NIST 8704). The results were in agreement with the certified values. The developed procedure was applied to evaluate the bioavailability of both elements in four sediment certified reference materials, in which there are not certified values for bioavailable fractions, and also in estuarine sediment samples collected in several sites of Guanabara Bay, an impacted environment in Rio de Janeiro, Brazil.

Development of a new sequential injection in-line cloud point extraction system for flame atomic absorption spectrometric determination of manganese in food samples.

A preconcentration method for manganese determination by sequential injection cloud point extraction with subsequent detection by flame atomic absorption spectrometry (FAAS) has been developed. The enrichment of Mn was performed after a preliminary on-line cloud point extraction and entrapment of manganese-containing surfactant aggregated within a minicolumn packed with cotton. The laboratory-made reagent 4-(5'-bromo-2'-thiazolylazo)orcinol (Br-TAO) and the surfactant Triton X-114 were used for cloud point extraction. The manganese ions were eluted with sulphuric acid solution and directly introduced into the FAAS. Chemical and flow variables affecting the preconcentration were studied. Using a sample volume of 2.80 mL the limit of detection and enrichment factor were calculated to be 0.5 microg L(-1) and 14, respectively. The sample frequency is 48 h(-1), considering a total run cycle of 75 s. The accuracy of the proposed method has been demonstrated by the analysis of the certified reference biological materials rice flour and tomato leaves. The method has been applied to determination of manganese in food samples.

Response surface methodology (RSM) as a tool for optimization in analytical chemistry.

A review about the application of response surface methodology (RSM) in the optimization of analytical methods is presented. The theoretical principles of RSM and steps for its application are described to introduce readers to this multivariate statistical technique. Symmetrical experimental designs (three-level factorial, Box-Behnken, central composite, and Doehlert designs) are compared in terms of characteristics and efficiency. Furthermore, recent references of their uses in analytical chemistry are presented. Multiple response optimization applying desirability functions in RSM and the use of artificial neural networks for modeling are also discussed.