M.J. Santos-Delgado

Determination of PAH in food samples by HPLC with fluorimetric detection following sonication extraction without sample clean-up

A rapid method is proposed for the determination of 16 polycyclic aromatic hydrocarbons (PAH) in non-fatty food (mashed potato, potato and toasted bread samples) based on their extraction with ethyl ether-methylene chloride (1:1) by sonication, and subsequent separation by high-performance liquid chromatography (HPLC) with fluorimetric detection. A Hypersil Green PAH column was used with a gradient of acetonitrile-water as the mobile phase, together with a programme of ten excitation and emission wavelength pairs. At levels 1.60-2320 microg kg(-1), mean recoveries of PAH were in the range 70-86% for mashed potato, potato and toasted bread samples. The relative standard deviations were in the range 4.2-11% (n = 6). Total PAH found in mashed potato were in the range 9.35-17.1 microg kg(-1), in potato samples 8.47-17.2 microg kg(-1) and in toasted bread samples 7.38-18.0 microg kg(-1), with relative standard deviations in the range 0.8-12%. Only chrysene, determined in Ortiz toasted bread (7.38 microg kg(-1)), has carcinogenic properties.

Direct determination of monolinuron, linuron and chlorbromuron residues in potato samples by gas chromatography with nitrogen–phosphorus detection ☆

A gas chromatography with nitrogen-phosphorus detection direct method for methoxyurea herbicide determination in powdered potato and fresh potato samples has been developed. A previous study of the thermal stability of the phenylurea herbicides seems to confirm that the ones containing the methoxy radical, i.e. monolinuron, linuron and chlorbromuron, were stable. The herbicides were extracted from the sample through liquid-liquid extraction with dichloromethane-light petroleum (1:1), followed by solid-phase extraction in a C8 cartridge. The recoveries were in the range 84-95% for powdered potato and 86-101% for fresh potato. The RSD values were less than 10%, at 0.1 microg g(-1) concentration level (n = 4) for both types of samples. Detection limits of the method were 7.0-30 ng g(-1) for powdered potato and 6.0-50 ng g(-1) for fresh potato.

Determination of carbamate, phenylurea and phenoxy acid herbicide residues by gas chromatography after potassium tert-butoxide/dimethyl sulphoxide/ethyl iodide derivatization reaction.

The usefulness of the potassium tert-butoxide/dimethyl sulphoxide/ethyl iodide reaction with carbamate and phenylurea herbicides, and its application to phenoxy acids as a way to prevent hazards and toxicity of the sodium hydride/dimethyl sulphoxide/methyl iodide reaction was studied. Using factorial design optimization of this reaction was carried out. A solid-phase extraction method using dimethyl sulphoxide as eluent on-line with this reaction was developed to determine these herbicides in water samples by gas chromatography-mass spectrometry. Relative standard deviation values were lower than 10% for most of the herbicides in multicomponent trace determinations. Detection limits were in the 0.110-0.652 ng L(-1) concentration range. The validity of the method was confirmed by recovery studies from natural water samples.

An improved method for the spectrophotometric determination of fluoride by addition of sodium dodecyl sulphate to the fluoride/lanthanum (III)/Alizarin fluorine blue system

Abstract The conventional spectrophotometric method for the determination of fluoride, based on the fluoride/lanthanum(III)/alizarin fluorine blue ternary complex, is improved by addition of sodium dodecyl sulphate. In 15% (v/v) acetone medium, the absorbance of the binary reagent complex is decreased and the reaction time is only 3 min under sonication. Beers Law is obeyed at 574 nm for fluoride concentrations in the ranges 0.075–0.30 and 0.20–1.2 mg 1−1; the apparent molar absorptivities are (1.6 ± 0.1) × 104 and (1.5 ± 0.1) × 104 mol−1 cm−1 fluoride levels, respectively. This method is applied to the determination of fluoride in bottled mineral waters.

Flow-injection spectrophotometric determination of fluoride based on alizarin fluorine blue in the presence of sodium dodecyl sulphate

Abstract The stopped-flow reagent-injection method proposed for the spectrophotometric determination of fluoride with lanthanum (III)/alizarin fluorine blue in the presence of sodium dodecyl sulphate at pH 4.6 (λ max =574 nm) provides a linear calibration graph for 0.08–1.2 mg l −1 fluoride. The relative standard deviation ( n =10) was 0.2% at 0.60 mg l −1 fluoride. The sampling rate was 60 h −1 . The method is applied to sea and bottled mineral waters with satisfactory results.

Simultaneous flow-injection determination of o- and p-nitrophenol using a photodiode-array detector

Abstract A flow-injection method is proposed for the simultaneous determination of o - and p -nitrophenol. It is based on formation and extraction of ion pairs using tetrabutylammonium as counter ion at pH 7.4 and diode-array spectrophotometric detection at 260 and 410 nm for o - and p -nitrophenol, respectively. The calibration graphs were linear from 0.1 to 12 mg 1 −1 , the relative standard deviation ( n = 8) at 6 mg 1 −1 was 0.15% for both o - and p -nitrophenol and the detection limits were 0.03 mg 1 −1 .

Simultaneous enantiomeric determinations of acid and ester imidazolinone herbicides in a soil sample by two-dimensional direct chiral liquid chromatography

A two-dimensional HPLC method for the simultaneous direct chiral enantiomeric determination of acid and ester IMI herbicides has been described. Difficulties arising from differences in polarity were overcome. Firstly, the imazaphyr, imazethapyr and imazamethabenz methyl herbicides were separated in a C18 achiral column. Then, their respective enantiomers were separated using a protein chiral AGP(TM) column; a heart-cut mode was used. Mobile phases of the two systems were compatibilized, after optimizing by factorial design using multiple response analysis. The proposed method has been validated by recovery studies from an enriched soil sample. Important enantiomer parameters such as enantioresolution higher than 1.12, enantiomeric ratio (ER) close to 1 and enantiomeric fraction (EF) around 0.5 were obtained for standards, confirming that herbicides are present as racemates.

Free D-amino acids determination in ready-to-eat cooked ham irradiated with electron-beam by indirect chiral HPLC

Potential racemization of L-amino acids (AA) in ready-to-eat (RTE) cooked ham after hygienization by electron-beam irradiation between 1 and 8kGy was studied. An indirect chiral method based on the derivatization reaction of AA with o-phthaldialdehyde and N-acetyl-L-cysteine followed by reversed-phase HPLC and fluorimetric detection was applied to detect ten enantiomeric pairs of free AA (Asp, Ser, Thr, Ala, Tyr, Val, Trp, Phe and Leu). Five of the D-AA were not found in any of the samples analyzed; the other five remaining D-AA (D-Asp, D-Ser, D-Ala, D-Val and D-Leu) were detected both in irradiated and non-irradiated cooked ham samples, their content being in the range 1.25-13.79μg/g. Although significant differences appeared for a few of the samples and doses, no positive correlation between the D-AA content and the irradiation doses was observed. Therefore, the electron-beam irradiation technique could be useful for sanitation of packed RTE cooked ham at doses allowed by WHO and EU, since it remains chemically safe to eat.

Selective determination of Triton-type non-ionic surfactants in different samples by on-line clean-up and FIA

SummaryA FIA method is proposed for the determination of non-ionic surfactants, applying spectrophotometric detection. The method is based on the formation of a “surfactant-K+-picrate” adduct and subsequent extraction into 1,2-dichloroethane. The method can handle samples containing large excesses of ionic and amphoteric surfactants, which are retained on ion-exchange columns inserted in the flow system. Beers law is obeyed at 380 nm in the 0.02–1.2 mg·l−1 range for Triton-type non-ionic surfactants (X-100, X-405 and WR-1339). Relative standard deviation (n=10) is 0.3% at the 0.5 mg·l−1 level. The method has been applied to several samples and its applicability evaluated by ANOVA statistical comparison with two other methods.

Multivariate analysis of chlorophenols by diode array spectrophotometry

Abstract A multivariate-multicomponent analysis method for the determination of chlorophenols by diode array derivative spectrophotometry is proposed. The method is based on extraction of chlorophenols directly or as ion pairs with tetrabutylammonium as the counterion in chloroform at pH 9.1. Prediction and quantitative determinations (within the concentration range 3.0–15.0 mg liter−1) of two-, three-, and four component mixtures were possible using multivariate calibration of first-derivative spectra and a multicomponent analysis computer program based on least-squares regression.