Evaluation of Sample Preparation Procedures for Determination of Cr(VI) in Cr2O3 Pigments by Vis Spectrophotometry

Abstract Six sample preparation procedures were evaluated for selective extraction of Cr(VI) from commercial samples of chromium oxide green (Cr2O3) pigments prior to formation of its diphenylcarbazone complex [CrDPCO]- for determination by visible spectrophotometry: (I) water-soluble chromium; (II) EPA method 3060A without Mg2+; (III) EPA method 3060A with Mg2+; (IV) Na3PO4 based extraction; (V) method IRSA16 based on acidic extraction and; (VI) Na2CO3 based extraction. Evaluation of the influence of concomitant Cr(III) ions, time and stability of the [CrDPCO]- complex was investigated. Recoveries of soluble and insoluble Cr(VI) species were 86% and 80%, respectively, using procedure (VI). Direct calibration against aqueous standards prepared in the extraction medium was successful for Cr(VI) in the concentration range 0.05-1.50 μg L-1. Limits of detection and quantitation were 0.3 µg g-1 and 1.0 µg g-1, respectively, for 250 mg subsamples/25 mL. Procedure (VI) was applied to the analysis of four commercial samples of Cr2O3 pigments, three determined to have Cr(VI) within compliance limits below 1.0 µg g-1, but one at 16.6 ± 0.6 µg g-1, prohibiting use of this pigment in cosmetic formulations. This sample was conveniently employed to evaluate the accuracy of the method. The recommended procedure is simple and accurate and has been adopted by Tecpar's laboratory of Parana Institute of Technology (Curitiba, Brazil).

ICP OES Determination of Contaminant Elements Leached from Food Packaging Films

ABSTRACT Determination of potential contaminants elements in food packing films arising from contact with acidic aqueous foods was undertaken by inductively coupled plasma optical emission spectrometry (ICP OES) in accordance with DIN EN 1186-1. Test sections from plastic films were totally immersed in 3% w/v CH3COOH used as the food simulant. Testing was conducted under three conditions: (1) 10 days at 40 ºC; (2) 30 min at 70 ºC and 10 days at 40 ºC; and (3) 30 min at 100 ºC and 10 days at 40 ºC. These time and temperature conditions were considered to be the most severe situations likely to be encountered in practice. Several different containers were investigated, including a borosilicate glass beaker, a glass bottle used for food canning, as well as one of polystyrene. The glass bottle was selected for testing treatments according to procedure (3) and a polystyrene one was chosen for use with procedures (1) and (2). Limits of quantitation were adequate for the determination of Ag, B, Ba, Cd, Cr, Cu, Pb, Sb, Sn and Zn by solution nebulization ICP OES and As by chemical vapor generation (CVG-ICP OES). Results for the analysis of AccuStandard certified reference materials as well as spike recoveries show good agreement with expected concentrations, demonstrating the accuracy and precision of the determinations. Eleven samples of food packing material were analyzed. The lead was present in the range 4.8 - 85.3 µg L-1 in 10 of 11 evaluated packing material, showing the importance of quality control measures.

Chemical quality of bottled mineral waters from markets of Curitiba-PR-Brazil

ABSTRACT Twenty-seven bottled mineral waters from local markets in Curitiba, State of Paraná, Brazil were analyzed for a number of constituents, including: pH, conductivity, total dissolved solids, hardness, HCO3 - and CO 3 2-, as well as Ca2+, Mg2+, Na+, K+, NH4 + , F-, Cl-, NO3 -, NO2 - and SO4 2- by ion chromatography (IC); Al, Ba, Cd, Cr, Cu, Fe, Li, Mn, Ni, Sr, V and Zn by inductively coupled plasma optical emission spectrometry (ICP OES); Hg by cold vapor generation-ICP OES and As, Pb, Sb and Se by ICP-mass spectrometry (ICP-MS). The obtained limits of quantitation (LOQ) were adequate for the determination of all analytes using the various analytical techniques. Results for the analysis of AccuStandard certified reference materials QCS-01-5, QCS-02-R1-5 and TCLP-02-1 as well as spike recoveries to samples show acceptable values, within 90-111 % of expected concentrations with relative standard deviations below 10 %, demonstrating the accuracy of the determinations. Both NO2 - and NO 3 - were above the maximum limits set by Brazilian legislation in two samples, indicating a microbiological contamination. One imported sample presented As (6.1 ± 0.2 µg L-1) near the maximum limit (10 µg L-1) while all other elements of interest were below the values specified by Brazilian legislation. Principal component analysis revealed that four imported samples and one from the Minas Gerais State have the highest mineral concentrations.

Simultaneous determination of Pb and Cd in seafood by ICP OES with on-line pre-concentration by solid phase extraction with amberlite XAD-4 after complex formation with DDTP

An on-line method for Cd and Pb pre-concentration and simultaneous determination in acid digested seafood by inductively coupled plasma optical emission spectrometry (ICP OES) was developed. The on-line pre-concentration was based on the complex formation of the analytes with the ammonium salt of O,O-diethyldithiophosphate (DDTP) and using the Amberlite XAD-4 resin as a solid support in a homemade column. Different conditions of the flow injection system, such as solutions flow rates, nebulizer pressure and eluent concentration were optimized. Three certified reference materials of lobster hepatopancreas, dogfish liver and fish protein, three samples of fish muscle and three samples of shrimp were digested with HNO3, H2O2 and H2SO4 in a microwave system under reflux. DDTP was added in the solutions obtained, and the mixture was injected in the FI system. Calibration curves for Cd and Pb were obtained using the standard solutions in the concentration range 0.05-0.5 µg mL-1 in the digestion medium, submitted to the same pre-concentration procedure. The quantification limits (3.3 x LOD) for 5 min of pre-concentration time were 0.005 mg kg-1 Cd2+ and 0.1 mg kg-1 Pb2+ in the sample of fish or shrimp in natura, considering 1.0 g of the sample in a final volume of 50 mL. The agreement of the obtained concentrations with the certified ones (Student t-test, 95% confidence) and the recoveries of spiked real samples, from 90 to 120%, demonstrated good accuracy. Precision was also adequate, with relative standard deviations from 2 to 13%. The method was accurate, precise and certainly could be applied to the digested samples of different natures.

Fast assessment of mineral constituents in grass by inductively coupled plasma optical emission spectrometry

A method for evaluating inorganic constituents in the grass by ICP OES is proposed. The samples were digested with nitric acid plus hydrogen peroxide in a microwave system. Seventeen samples were collected in the metropolitan area of Curitiba and Castro in the Paraná State, Brazil. The following elements were studied: Al, As, Ba, Ca, Cd, Co, Cr, Cu, Fe, K, Mg, Mn, Mo, Na, Ni, P, Pb, Sb, Se and Zn. The linear coefficients of the curves were higher than 0.999 and the precision, expressed as the relative standard deviation, which was below 10%, being considered adequate. The accuracy was validated by using the recovery test (recoveries from 80 to 107%) and by the analysis of botanical certified materials. For one sample, two other digestion procedures, using two different mixtures of nitric and hydrochloric acids, produced results in agreement with the adopted procedure. Eleven out of the twenty studied elements could be quantified in real samples. High concentrations of Ca, K, Mg and P, the essential elements for bovines and other animals, were found. The results were evaluated using the principal component analysis that gathered the samples in three groups, according to the areas where the plants were grown.

Determination of trace metals in electrolytic copper by ICP OES and ICP-MS

O presente trabalho apresenta um estudo comparativo das técnicas ICP-MS e ICP OES com configuração axial e também de dois métodos diferentes de tratamento das amostras, ou seja, por dissolução total com e sem separação do cobre por eletrodeposição, para as determinações de As, Fe, Mn, Pb, Sb e Sn em amostras de cobre eletrolítico. Amostras comerciais e industriais foram dissolvidas com HNO3 5% v/v e o cobre foi eletrodepositado em meio de HNO3 (1,4% v/v) e H2SO4 (2,0% v/v). Verificou-se que a separação do cobre foi eficiente, contudo se constatou contaminação de Fe e Sn durante o processo de eletrodeposição. As determinações foram realizadas utilizando-se um ICP OES Axial Varian (Vista Pro) e um ICP-MS Perkin Elmer (Elan Sciex 6000). Foi aplicada a calibração externa, com soluções padrão contendo ou não cobre na concentração equivalente à da amostra. Os limites de detecção (3s, n=10) para a técnica de ICP OES foram bastante semelhantes na presença ou não do cobre). Já usando ICP-MS, os limites foram melhores na ausência do cobre. Com o objetivo de estabelecer o nível de significância entre as técnicas de quantificação, ou seja, entre ICP OES e ICP-MS,foi aplicado o teste t emparelhado, que demonstrou, para um nível de confiança de 95%, não haver diferença significativa, tanto para as soluções sem ou com cobre. Os resultados obtidos no presente trabalho demonstraram que as técnicas ICP-MS e ICP OES fornecem resultados similares em determinadas faixas de concentração dos analitos, podendo ambas serem utilizadas, no controle de qualidade do cobre eletrolítico. Contudo, a técnica ICP-MS foi superior em termos de limite de detecção.

Evaluation of arsenic and selenium in brazilian soluble coffee by inductively coupled plasma atomic emission spectromety with hydride generation / Evaluation of arsenic and selenium in brazilian soluble coffee by inductively coupled plasma atomic emission spectrometry with hydride generation

O presente trabalho descreve um método para determinaçäo de arsênio e selênio em café solúvel por espectrometria de emissäo atômica com plasma acoplado a geraçäo de hidretos, com o objetivo de atender aos limites estabelecidos pela legislaçäo brasileira de alimentos. Digestöes das amostras foram realizadas com ácido nítrico e peróxido de hidrogênio em sistema de microondas focalizadas. O excesso de ácido nítrico foi eliminado através de aquecimento lento e o selênio (VI) foi reduzido a selênio (IV) através de tratamento com ácido clorídrico 6 mol/L e aquecimento a 90§C em sistema de refluxo. A influência da acidez na sensibilidade foi investigada, sendo o meio mais estável a concentraçäo de ácido clorídrico de 6mol/L. Os limites de determinaçäo foram de 2.0ug/L para o As e 1.0ug/L para o Se. Os resultados das amostras enriquecidas demonstram a precisäo e exatidäo do método proposto

Avaliaçäo e definiçäo de procedimento de mineralizaçäo de amostras de café solúvel para determinaçäo de nutrientes e contaminantes inorgânicos por ICP-AES / Evaluation and establishment of the digestion procedure of soluble coffee for nutrient and inorganic contaminants determination by ICP-AES analysis

The objective of this report was the evaluation and establisment of an appropriate digestion procedure for soluble coffee, in order to determine, by ICP-AES(inductively coupled plasma atomic emission spectrometry), the following elements:Mg, Al, P, S, Ca, Mn, Fe, Na, K, Cr, Ni, Cu, Zn, As, Se, Cd, Sb, Pb and Hg. Six differents digestion procedures have been evaluated and classificated in three groups: (I) focused microwave system, (II) conventional wet digestion and (III) pressure digestion system by teflon bombs. Quick and safe digestion of the samples, with decreasing of the reactives, have been obtained by one of the procedures using focused microwaves system