Maria Lurdes Felsner

Direct determination of Pb in raw milk by graphite furnace atomic absorption spectrometry (GF AAS) with electrothermal atomization sampling from slurries

Milk is an important food in the human diet due to its physico-chemical composition; therefore, it is necessary to monitor contamination by toxic metals such as Pb. Milk sample slurries were prepared using Triton X-100 and nitric acid for direct analysis of Pb using graphite furnace atomic absorption spectrometry - GF AAS. After dilution of the slurries, 10.00µl were directly introduced into the pyrolytic graphite tube without use of a chemical modifier, which acts as an advantage considering this type of matrix. The limits of detection and quantification were 0.64 and 2.14µgl-1, respectively. The figures of merit studied showed that the proposed methodology without pretreatment of the raw milk sample and using external standard calibration is suitable. The methodology was applied in milk samples from the Guarapuava region, in Paraná State (Brazil) and Pb concentrations ranged from 2.12 to 37.36µgl-1.

Optimization of mobile phase for separation of carbohydrates in honey by high performance liquid chromatography using a mixture design

Um planejamento de misturas foi usado para otimizar a composicao da fase movel para a separacao dos carboidratos em mel por Cromatografia Liquida de Alta Eficiencia. Nove fases moveis ternarias de acetonitrila, agua e acetato de etila, correspondendo a um planejamento centroide simplex com pontos axiais foram testadas para separar os carboidratos mais frequentemente encontrados em amostras de mel. Os resultados sugerem que um modelo cubico especial descreve precisamente as mudancas nas proporcoes destes solventes na fase movel proxima a regiao otima da separacao dos picos. A adicao de um terceiro solvente, acetato de etila, a fase movel binaria de agua e acetonitrila permitiu uma melhora significativa na separacao dos carboidratos que pode ser aplicada a analise quantitativa destes compostos em mel.

Analytical MethodsDirect determination of Pb in raw milk by graphite furnace atomic absorption spectrometry (GF AAS) with electrothermal atomization sampling from slurries

Milk is an important food in the human diet due to its physico-chemical composition; therefore, it is necessary to monitor contamination by toxic metals such as Pb. Milk sample slurries were prepared using Triton X-100 and nitric acid for direct analysis of Pb using graphite furnace atomic absorption spectrometry - GF AAS. After dilution of the slurries, 10.00µl were directly introduced into the pyrolytic graphite tube without use of a chemical modifier, which acts as an advantage considering this type of matrix. The limits of detection and quantification were 0.64 and 2.14µgl-1, respectively. The figures of merit studied showed that the proposed methodology without pretreatment of the raw milk sample and using external standard calibration is suitable. The methodology was applied in milk samples from the Guarapuava region, in Paraná State (Brazil) and Pb concentrations ranged from 2.12 to 37.36µgl-1.

Development and in house validation of a new thermogravimetric method for water content analysis in soft brown sugar.

Recently the use of brown sugar has increased due to its nutritional characteristics, thus requiring a more rigid quality control. The development of a method for water content analysis in soft brown sugar is carried out for the first time by TG/DTA with application of different statistical tests. The results of the optimization study suggest that heating rates of 5°C min(-1) and an alumina sample holder improve the efficiency of the drying process. The validation study showed that thermo gravimetry presents good accuracy and precision for water content analysis in soft brown sugar samples. This technique offers advantages over other analytical methods as it does not use toxic and costly reagents or solvents, it does not need any sample preparation, and it allows the identification of the temperature at which water is completely eliminated in relation to other volatile degradation products. This is an important advantage over the official method (loss on drying).

Clay and charcoal composites: characterisation and application of factorial design analysis for dye adsorption

The characterisation of smectite clay, charcoal and prepared clay-charcoal composites was carried out through the X-ray diffractometry, energy dispersive X-ray spectroscopy (EDS), simultaneous thermal analysis (TGA/DTA), infrared spectroscopy (FTIR) and scanning electron microscopy (SEM). The analysis revealed the composites to have different characteristics from the precursor clay and charcoal, and a peak displacement (d001) was observed through the X-ray diffraction; this suggests the incorporation of charcoal into the clay lamellas and the formation of a new phase. Tests of adsorption with methylene blue dye were also carried out to evaluate the percentage of dye removal by the adsorbent, in which the composites presented better results than charcoal, indicating great potential for industrial use. A 23 factorial design was employed to evaluate the influence of temperature, ionic strength and pH on the adsorption of methylene blue using the AV50 composite that presented the best adsorption efficiency.

A validated fast difference spectrophotometric method for 5-hydroxymethyl-2-furfural (HMF) determination in corn syrups

Corn syrups, important ingredients used in food and beverage industries, often contain high levels of 5-hydroxymethyl-2-furfural (HMF), a toxic contaminant. In this work, an in house validation of a difference spectrophotometric method for HMF analysis in corn syrups was developed using sophisticated statistical tools by the first time. The methodology showed excellent analytical performance with good selectivity, linearity (R2=99.9%, r>0.99), accuracy and low limits (LOD=0.10mgL-1 and LOQ=0.34mgL-1). An excellent precision was confirmed by repeatability (RSD (%)=0.30) and intermediate precision (RSD (%)=0.36) estimates and by Horrat value (0.07). A detailed study of method precision using a nested design demonstrated that variation sources such as instruments, operators and time did not interfere in the variability of results within laboratory and consequently in its intermediate precision. The developed method is environmentally friendly, fast, cheap and easy to implement resulting in an attractive alternative for corn syrups quality control in industries and official laboratories.

Rapid Screening Method for Detecting Ethinyl Estradiol in Natural Water Employing Voltammetry

17α-Ethinyl estradiol (EE2), which is used worldwide in the treatment of some cancers and as a contraceptive, is often found in aquatic systems and is considered a pharmaceutically active compound (PhACs) in the environment. Current methods for the determination of this compound, such as chromatography, are expensive and lengthy and require large amounts of toxic organic solvents. In this work, a voltammetric procedure is developed and validated as a screening tool for detecting EE2 in water samples without prior extraction, clean-up, or derivatization steps. Application of the method we elaborate here to EE2 analysis is unprecedented. EE2 detection was carried out using differential pulse adsorptive cathodic stripping voltammetry (DP AdCSV) with a hanging mercury drop electrode (HMDE) in pH 7.0 Britton-Robinson buffer. The electrochemical process of EE2 reduction was investigated by cyclic voltammetry at different scan rates. Electroreduction of the hormone on a mercury electrode exhibited a peak at −1.16 ± 0.02 V versus Ag/AgCl. The experimental parameters were as follows: −0.7 V accumulation potential, 150 s accumulation time, and 60 mV s−1 scan rate. The limit of detection was 0.49 μg L−1 for a preconcentration time of 150 s. Relative standard deviations were less than 13%. The method was applied to the detection of EE2 in water samples with recoveries ranging from 93.7 to 102.5%.

VALIDAÇÃO INTRALABORATORIAL DA DETERMINAÇÃO DE METILTESTOSTERONA EM ÁGUAS NATURAIS POR VOLTAMETRIA USANDO ELETRODO DE GOTA PENDENTE DE MERCÚRIO

17α-methyltestosterone (17α-MT) is a hormone used in medicine and aquaculture which can be found in natural waters. It is considered an emerging organic pollutant and its accurate and precise analysis is required. Therefore, this study presents the in-house validation of a new voltammetric methodology for 17α-MT analysis in natural waters. A hanging mercury drop electrode and NaOH 5.0×10-3 mol L-1 solution as the electrolyte were employed in the voltammetric determinations. To confirm the presence of 17α-MT in water samples quantitative analysis was performed by ESI-MS/MS. The methodology exhibited good selectivity, linearity, accuracy (recovery of between 100.4 and 108.8%) and precision (RSDs for repeatability of 2.85% and for intermediate precision of 14.10%, with n = 5, respectively). LOD and LOQ were 3.07 µg L-1 and 10.78 µg L-1, respectively. The methodology was suitable for determination of 17α-MT in natural waters due to low-cost, good performance and no sample pre-treatment required.

Development of an Electroanalytical Methodology for Determination of Pesticide Glyphosate in Environmental Samples

This paper describes the development of an electroanalytical methodology using square wave voltametry (SWV) and hanging mercury drop electrode (HMDE) for determining the pesticide glyphosate in samples of natural waters. The electroactivity of glyphosate on the mercury electrode was obtained by complexation with Cu(II) were evaluated in the study the voltammetric parameters and experimental involved in the electrochemical reduction, such as: concentration of Cu(II), an effect of supporting electrolytes at different pH values and parameters of SWV. The best results were obtained in solution of NaNO2 the 0,10 mol L , pH 6,5, concentration of Cu(II) of 2,61 x 10 mol L, pre-concentration time of 120 sec, using the frequency of application of pulses of potential of 100 sec, amplitude of pulses of potential of 50 mV and increase of sweep of 6 mV. The complex Cu(II)-glyphosate showed only a reduction peak at 0,1 V with quasi reversible process controlled by diffusion of the species on the electrode surface. Calibration curves were constructed and the detection limits (LD) and of quantification (LQ) obtained were (22,04 ± 0,42) μg L and (73,46 ± 1,41) μg L, respectively. The recovery tests showed values of (100,27 ± 1,96) % in pure water laboratory and (99,12 ± 2,14) % in real sample. Additionally, the methodology was applied for determination of glyfhosate in water sample collected in the creek from the Santa Clara, in the municipality of Candói/PR, with a value of (311,02 ± 23,72) μg L glyphosate present in the sample. The percentage recovery in the investigated samples were above 99%, thus the gliphosate can be quantified in water samples by the proposed method.

Precisão dos métodos refratométricos para análise de umidade em mel

For the determination of the moisture contents of honey, the Brazilian legislation adopts the refractometric method proposed by AOAC. However, in other work, the authors observed that the crystallization interferes in the refractive index measurement when the honey sample if encountered crystallized and, therefore, moisture contents overestimated were obtained. The European Honey Commission (EHC), adopt other refractometric method that use a pre-treatment of sample when this one was crystallized. So, the objective of this work was to compare the precision of these refractometric methods by different statistical techniques and it establish thus the more adequate procedure for moisture analysis in honey. The results of t-tests analysis in the 95% confidence level for the average moisture contents of the honey samples suggested that there were significant differences between the two-refractometric methods (AOAC e EHC) only for the crystallized samples. The analysis of standard deviations by application of F-test and building of confidence intervals shown that the EHC method was more precise than the AOAC methodology for the crystallized honey samples. In this way, it may be suggested the adoption by Brazilian legislation of refractometric method of EHC, as official method, by this one not present systematic errors.