QuEChERS: a new sample preparation approach for the determination of ibuprofen and its metabolites in soils

Ibuprofen is one of the most used active pharmaceutical ingredients worldwide. A new method for the analysis of ibuprofen and its metabolites, hydroxyibuprofen and carboxyibuprofen, in soils is presented. The extraction of these compounds from the soil matrices was performed by using a modified quick, easy, cheap, effective, rugged, and safe (QuEChERS) method. The method involves a single extraction of the investigated compounds with purified water (acidified at pH 2.5 with hydrochloric acid), and a slow and continuous addition of the QuEChERS content, followed by the addition of acidified acetonitrile (1% acetic acid), prior to the determination by liquid chromatography coupled with fluorescence detection (LC–FLD). Validation studies were carried out using soil samples with a range of organic carbon contents. Recoveries of the fortified samples ranged from 79.5% to 101%. Relative standard deviations for all matrix–compound combinations did not exceed 3%. The method quantification limits were ≤22.4 μg kg−1 in all cases. The developed method was applied to the analysis of sixteen real samples.

Optimization and validation of organochlorine compounds in adipose tissue by SPE-gas chromatography

Scientific evidence has shown an association between organochlorine compounds (OCC) exposure and human health hazards. Concerning this, OCC detection in human adipose samples has to be considered a public health priority. This study evaluated the efficacy of various solid-phase extraction (SPE) and cleanup methods for OCC determination in human adipose tissue. Octadecylsilyl endcapped (C18-E), benzenesulfonic acid modified silica cation exchanger (SA), poly (styrene-divinylbenzene (EN) and EN/RP18 SPE sorbents were evaluated. The relative sample cleanup provided by these SPE columns was evaluated using gas chromatography with electron capture detection (GC–ECD). The C18-E columns with strong homogenization were found to provide the most effective cleanup, removing the greatest amount of interfering substance, and simultaneously ensuring good analyte recoveries higher than 70%. Recoveries>70% with standard deviations (SD)<15% were obtained for all compounds under the selected conditions. Method detection limits were in the 0.003–0.009 mg/kg range. The positive samples were confirmed by gas chromatography coupled with tandem mass spectrometry (GC-MS/MS). The highest percentage found of the OCC in real samples corresponded to HCB, o,p′-DDT and methoxychlor, which were detected in 80 and 95% of samples analyzed respectively. Copyright © 2012 John Wiley & Sons, Ltd.

Determination of tartaric acid in wines by FIA with tubular tartrate-selective electrodes

A flow injection analysis (FIA) system comprising a tartrate- (TAT) selective electrode has been developed for determination of tartaric acid in wines. Several electrodes constructed for this purpose had a PVC membrane with a complex of quaternary ammonium and TAT as anion exchanger, a phenol derivative as additive, and a more or less polar mediator solvent. Characterization of the electrodes showed behavior was best for membranes with o-nitrophenyl octyl ether as solvent. On injection of 500 μL into a phosphate buffer carrier (pH = 3.1; ionic strength 10–2 mol/L) flowing at 3 mL/min, the slope was 58.06 ± 0.6 with a lower limit of linear range of 5.0 × 10–4 mol/L TAT and R2 = 0.9989. The interference of several species, e.g. chloride, bromide, iodide, nitrate, gallic acid, tannin, sucrose, glucose, fructose, acetate, and citrate, was evaluated in terms of potentiometric selectivity coefficients. The Hofmeister series was followed for inorganic species and the most interfering organic ion was citrate. When red and white wines were analyzed and the results compared with those from an independent method they were found to be accurate, with relative standard deviations below 5.0%.

A multiresidue method for the analysis of carbamate and urea pesticides from soils by microwave-assisted extraction and liquid chromatography with photodiode array detection

A multiresidue approach using microwave-assisted extraction and liquid chromatography with photodiode array detection was investigated for the determination of butylate, carbaryl, carbofuran, chlorpropham, ethiofencarb, linuron,metobromuron, and monolinuron in soils. The critical parameters of the developed methodology were studied. Method validation was performed by analyzing freshly and aged spiked soil samples. The recoveries and relative standard deviations reached using the optimized conditions were between 77.0 ± 0.46% and 120 ± 2.9% except for ethiofencarb (46.4 ± 4.4% to 105 ± 1.6%) and butylate (22.1 ± 7.6% to 49.2 ± 11%). Soil samples from five locations of Portugal were analysed.

Determination of free furfuryl alcohol in foundry resins by chromatographic techniques

Two chromatographic methods, gas chromatography with flow ionization detection (GC–FID) and liquid chromatography with ultraviolet detection (LC–UV), were used to determine furfuryl alcohol in several kinds of foundry resins, after application of an optimised extraction procedure. The GC method developed gave feasibility that did not depend on resin kind. Analysis by LC was suitable just for furanic resins. The presence of interference in the phenolic resins did not allow an appropriate quantification by LC. Both methods gave accurate and precise results. Recoveries were >94%; relative standard deviations were ≤7 and ≤0.3%, respectively for GC and LC methods. Good relative deviations between the two methods were found (≤3%).

Determination of chlorfenvinphos in soils by microwave-assisted extraction and stripping voltammetry with an ultramicroelectrode

A methodology for the determination of the pesticide chlorfenvinphos by microwave-assisted solvent extraction and square-wave cathodic stripping voltammetry at a mercury film ultramicroelectrode in soil samples is proposed. Optimization of microwave solvent extraction performed with two soils, selected for having significantly different properties, indicated that the optimum solvent for extracting chlorfenvinphos is hexane-acetone (1:1, v/v). The voltammetric procedure is based on controlled adsorptive accumulation of the insecticide at the potential of -0.60 V (vs. Ag/AgCl) in the presence of Britton-Robinson buffer (pH 6.2). The detection limit obtained for a 10 s collection time was 3.0 x 10-8 mol l-1. The validity of the developed methodology was assessed by recovery experiments at the 0.100 µg g-1 level. The average recoveries and standard deviations for the global procedure reached byMASE-square-wave voltammetry were 90.2±2.8% and 92.1±3.4% for type I (soil rich in organic matter) and type II (sandy soil) samples, respectively. These results are in accordance to the expected values which show that the method has a good accuracy.

Electrochemical determination of citalopram by adsorptive stripping voltammetry–determination in pharmaceutical products

The electrochemical behavior of citalopram was studied by square-wave and square-wave adsorptive-stripping voltammetry (SWAdSV). Citalopram can be reduced and accumulated at a mercury drop electrode, with a maximum peak current intensity being obtained at a potential of approximately -1.25V vs. AgCl/Ag, in an aqueous electrolyte solution of pH 12. A SWAdSV method has been developed for the determination of citalopram in pharmaceutical preparations. The method shows a linear range between 1.0x10-7 and 2.0x10-6 mol L-1 with a limit of detection of 5x10-8 mol L-1 for an accumulation time of 30 s. The precision of the method was evaluated by assessing the repeatability and intermediate precision, achieving good relative standard deviations in all cases (≤2.3%). The proposed method was applied to the determination of citalopram in five pharmaceutical products and the results obtained are in good agreement with the labeled values.

Determination of polyphenols in wines by reaction with 4-aminoantipyrine and photometric flow-injection analysis

A new flow-injection analytical procedure is proposed for the determination of the total amount of polyphenols in wines; the method is based on the formation of a colored complex between 4-aminoantipyrine and phenols, in the presence of an oxidizing reagent. The oxidizing agents hexacyanoferrate(III), peroxodisulfate, and tetroxoiodate(VII) were tested. Batch trials were first performed to select appropriate oxidizing agents, pH, and concentration ratios of reagents, on the basis of their effect on the stability of the colored complex. Conditions selected as a result of these trials were implemented in a flow-injection analytical system in which the influence of injection volume, flow rate, and reaction- coil length, was evaluated. Under the optimum conditions the total amount of polyphenols, expressed as gallic acid, could be determined within a concentration range of 36 to 544 mg L–1, and with a sensitivity of 344 L mol–1 cm–1 and an RSD <1.1%. The reproducibility of analytical readings was indicative of standard deviations <2%. Interference from sugars, tartaric acid, ascorbic acid, methanol, ammonium sulfate, and potassium chloride was negligible. The proposed system was applied to the determination of total polyphenols in red wines, and enabled analysis of approximately 55 samples h–1. Results were usually precise and accurate; the RSD was <3.9% and relative errors, by the Folin–Ciocalteu method, <5.1%.

Biosensor based on multi-walled carbon nanotubes paste electrode modified with laccase for pirimicarb pesticide quantification

This study focused on the development of a sensitive enzymatic biosensor for the determination of pirimicarb pesticide based on the immobilization of laccase on composite carbon paste electrodes. Multi- walled carbon nanotubes(MWCNTs)paste electrode modified by dispersion of laccase(3%,w/w) within the optimum composite matrix(60:40%,w/w,MWCNTs and paraffin binder)showed the best performance, with excellent electron transfer kinetic and catalytic effects related to the redox process of the substrate4- aminophenol. No metal or anti-interference membrane was added. Based on the inhibition of laccase activity, pirimicarb can be determined in the range 9.90 ×10- 7 to 1.15 ×10- 5 molL 1 using 4- aminophenol as substrate at the optimum pH of 5.0, with acceptable repeatability and reproducibility (relative standard deviations lower than 5%).The limit of detection obtained was 1.8 × 10-7 molL 1 (0.04 mgkg 1 on a fresh weight vegetable basis).The high activity and catalytic properties of the laccase- based biosensor are retained during ca. one month. The optimized electroanalytical protocol coupled to the QuEChERS methodology were applied to tomato and lettuce samples spiked at three levels; recoveries ranging from 91.0±0.1% to 101.0 ± 0.3% were attained. No significant effects in the pirimicarb electro- analysis were observed by the presence of pro-vitamin A, vitamins B1 and C,and glucose in the vegetable extracts. The proposed biosensor- based pesticide residue methodology fulfills all requisites to be used in implementation of food safety programs.

Development of a simple analytical method for the simultaneousdetermination of paracetamol, paracetamol-glucuronide andp-aminophenol in river water

Paracetamol is among the most worldwide consumed pharmaceuticals. Although its occurrence in the environment is well documented, data about the presence of its metabolites and transformation products is very scarce. The present work describes the development of an analytical method for the simultaneous determination of paracetamol, its principal metabolite (paracetamol-glucuronide) and its main transformation product (p-aminophenol) based on solid phase extraction (SPE) and high performance liquid chromatography coupled to diode array detection (HPLC-DAD). The method was applied to analysis of river waters, showing to be suitable to be used in routine analysis. Different SPE sorbents were compared and the use of two Oasis WAX cartridges in tandem proved to be the most adequate approach for sample clean up and pre-concentration. Under optimized conditions, limits of detection in the range 40–67 ng/L were obtained, as well as mean recoveries between 60 and 110% with relative standard deviations (RSD) below 6%. Finally, the developed SPE-HPLC/DAD method was successfully applied to the analysis of the selected compounds in samples from seven rivers located in the north of Portugal. Nevertheless all the compounds were detected, it was the first time that paracetamol-glucuronide was found in river water at concentrations up to 3.57 μg/L.

Optimization of QuEChERS procedure coupled to GC-ECD for organochlorine pesticide determination in carrot samples

An optimised version of the Quick, Easy, Cheap, Effective, Rugged and Safe (QuEChERS) method for simultaneous determination of 14 organochlorine pesticides in carrots was developed using gas chromatography coupled with electron-capture detector (GC-ECD) and confirmation by gas chromatography tandem mass spectrometry (GC-MS/MS). A citrate-buffered version of QuEChERS was applied for the extraction of the organochlorine pesticides, and for the extract clean-up, primary secondary amine, octadecyl-bonded silica (C18), magnesium sulphate (MgSO4) and graphitized carbon black were used as sorbents. The GC-ECD determination of the target compounds was achieved in less than 20 min. The limits of detection were below the EUmaximum residue limits (MRLs) for carrots, 10–50 μg kg−1, while the limit of quantification did exceed 10 μg kg−1 for hexachlorobenzene (HCB). The introduction of a sonication step was shown to improve the recoveries. The overall average recoveries in carrots, at the four tested levels (60, 80, 100 and 140 μg kg−1), ranged from 66 to 111% with relative standard deviations in the range of 2– 15 % (n03) for all analytes, with the exception of HCB. The method has been applied to the analysis of 21 carrot samples from different Portuguese regions, and β-HCH was the pesticide most frequently found, with concentrations oscillating between less than the limit of quantification to 14.6 μg kg−1. Only one sample had a pesticide residue (β-HCH) above the MRL, 14.6 μg kg−1. This methodology combines the advantages of both QuEChERS and GC-ECD, producing a very rapid, sensitive and reliable procedure which can be applied in routine analytical laboratories.

MIP-graphene-modified glassy carbon electrode for the determination of trimethoprim

A novel sensitive electrochemical sensor was developed by electropolymerization of pyrrole(PY)and molecularly imprinted polymer (MIP)which was synthesized onto a glassy carbon electrode (GCE) in aqueous solution using cyclic voltammetry in the presence of Trimethoprim (TMP) as template molecules. Furthermore,a previous electrode modification was performed by deposition of a suspension of graphene on the electrode's surface. The performance of the imprinted and non-imprinted (NIP) films was evaluated by impedance spectroscopy (EIS) and cyclic voltammetry (CV) of a ferric solution. The molecularly imprinted film exhibited a high selectivity and sensitivity toward TMP. The sensor presented a linear range, between peak current intensity and logarithm of TMP concentration between 1.0x10-6 and 1.0x10-4 M. The results were accurate (with recoveries higher than 94%), precise (with standard deviations less than 5%) and the detection limit was 1.3x10-7 M. The new sensor is selective, simple to construct and easy to operate. The MIP sensor was successfully applied to quantify TMP in urinesamples.

Elétrodo de pasta de carbono molecularmente impresso para deteção voltamétrica de Furazolidona

A furazolidona é uma substância ativa do medicamento Giarlam que contém um espetro anti-bacteriano relativamente amplo e que é frequentemente usado para tratar certas doenças bacterianas e protozoárias no homem. A maioria dos fármacos exige uma dosagem que garanta os níveis de segurança e eficácia de atuação. A necessidade de dosear os medicamentos e os seus metabólitos exige o desenvolvimento constante de métodos analíticos eficientes. Neste trabalho desenvolveu-se um novo sensor eletroquímico para a deteção da furazolidona, baseado num elétrodo de pasta de carbono modificado com um polímero molecularmente impresso. A procura de novos materiais que permitam uma melhor seletividade e sensibilidade aos sistemas de deteção é especialmente importante no desenvolvimento de métodos analíticos. Os polímeros molecularmente impressos enquadram-se nesse perfil e o seu uso tem vindo a ser cada vez mais frequente como ferramenta importante em química analítica. Assim, sintetizou-se um polímero com cavidades seletivas para a Furazolidona. Este polímero foi, misturado com grafite e perafina de modo a produzir uma pasta de carbono. Uma seringa de plástico foi usada como suporte da pasta de carbono. O comportamento eletroquímico do sensor foi avaliado e diversas condições de utilização foram estudadas e otimizadas. O sensor apresenta um comportamento linear entre a intensidade do pico e a concentração numa gama de concentrações entre 1 e 100 μM, um limite de deteção de 1 μM e uma precisão (repetibilidade) inferior a 7%. A aplicabilidade do sensor fabricado em amostras complexas foi avaliada pela deteção do fármaco em amostras de urina.

Molecularly imprinted electrochemical sensor for ochratoxin A detection in food samples

A novel electrochemical sensor for ochratoxin A (OTA) detection was fabricated through the modification of a glassy carbon electrode (GCE) with multiwalled carbon nanotubes (MWCNTs) and a molecularly imprinted polymer (MIP). The MWCNTs dramatically promoted the sensitivity of the developed sensor, while polypyrrole (PPy) imprinted with OTA served as the selective recognition element. The imprinted PPy film was prepared by electropolymerization of pyrrole in the presence of OTA as a template molecule via cyclic voltammetry (CV). The electrochemical oxidation of OTA at the developed sensor was investigated by CV and differential pulse voltammetry (DPV). The developed MIP/MWCNT/GCE sensor showed a linear relationship, when using DPV, between peak current intensity and OTA concentration in the range between 0.050 and 1.0 μM, with limits of detection (LOD) and quantification of 0.0041 μM (1.7 μg/L) and 0.014 μM (5.7 μg/L) respectively. With the developed sensor precise results were obtained; relative standard deviations of 4.2% and 7.5% in the evaluation of the repeatability and reproducibility, respectively. The MIP/MWCNT/GCE sensor is simple to fabricate and easy to use and was successfully applied to the determination of OTA in spiked beer and wine samples, with recoveries between 84 and 104%, without the need of a sample pre-treatment step.

Prevalência de Osteoporose numa amostra de mulheres Portuguesas

A osteoporose é uma doença crónica e progressiva. O diagnóstico baseia-se na avaliação de densidade mineral óssea (DMO), por absorciometria bifotónica por RX (DXA) e no conceito operacional da Organização Mundial de Saúde (OMS) indicando que a doença acontece para valores de DMO inferiores a 2,5 desvios-padrão do valor médio máximo para mulheres jovens, saudáveis de etnia caucasóide. Existe variabilidade nos valores de pico de massa óssea entre diferentes populações. Este estudo pretende avaliar a prevalência de osteoporose quando utilizada a base de referência do equipamento e quando utilizada a base de dados para score-T construída a partir da amostra.