Fast Sample Preparation Procedure Research Articles

Determination of cholesterol in food samples using dispersive liquid–liquid microextraction followed by HPLC–UV

A fast, simple, and sensitive sample preparation procedure based on dispersive liquid–liquid microextraction (DLLME) is proposed for the determination of cholesterol in food samples using isocratic reverse phase high performance liquid chromatography (RP-HPLC) and UV detection. The influence of several important parameters on extraction efficiency of cholesterol was evaluated. Under optimized conditions, a linear relationship was obtained between the peak area and the concentration of cholesterol in the range of 0.03–10 μg l −1. The detection and quantification limits were 0.01 and 0.03 μg l −1, respectively. Intra-day and inter-day precisions for the analysis of cholesterol were in the range of 1.0–3.1%. The applicability of the proposed method was demonstrated by analyzing cholesterol in milk, egg yolk and olive oil.

Dispersive liquid–liquid microextraction applied to the simultaneous derivatization and concentration of triclosan and methyltriclosan in water samples

A fast and novel sample preparation procedure for the determination of triclosan (TCS) and methyltriclosan (MTCS) in water samples is presented. Dispersive liquid–liquid microextraction, using a ternary mixture consisting of a disperser, an extractant and N-methyl- N-( tert-butyldimethylsilyl)trifluoroacetamide (MTBSTFA) as derivatization reagent, was used for the simultaneous derivatization, case of TCS, and concentration of both species in different water samples. Analytes were determined by gas chromatography with tandem mass spectrometry (GC–MS/MS). Influence of different factors on the performance of the sample preparation process is thoroughly discussed. Under final working conditions, a mixture of 1 mL of methanol, 40 μL of 1,1,1-trichloroethane and the same volume of MTBSTFA was added to 10 mL of water in a conical bottom glass tube. After centrifugation, the settled phase was injected directly in the chromatographic system. TCS was quantitatively extracted and converted into the corresponding tert-butyldimethylsilyl derivative, whereas for MTCS an extraction yield around 90% was attained. Limits of quantification between 2 and 5 ng L −1 and reproducibility values below 10% were achieved; moreover, the performance of the extraction process was scarcely affected by the type of water sample. Globally, these values are comparable, or even better, to those reported for other approaches applied to the determination of same compounds, with the advantage of a shorter sample preparation step. Analysis of surface and wastewater samples confirmed the ubiquitous presence of TCS in the aquatic environment at levels from 20 to 700 ng L −1.

Optimisation of a matrix solid-phase dispersion method for the determination of organophosphate compounds in dust samples

A fast and inexpensive sample preparation procedure based on the matrix solid-phase dispersion (MSPD) technique is proposed for the isolation of several organophosphate esters (mainly employed as flame retardants and plasticizers) from indoor dust samples. Extraction and clean-up were carried out in a single step and target compounds were determined by gas chromatography (GC) with nitrogen–phosphorus detection (NPD). The main parameters affecting extraction yield and selectivity, such as type and amount of dispersant material, clean-up co-sorbent and extraction solvent, were evaluated and optimised. Under final conditions, 0.5 g of dust were dispersed with equal amounts of anhydrous sodium sulphate and Florisil, and loaded on the top of a polypropylene cartridge containing 0.5 g of alumina. The dispersed sample was washed with 2 mL of n-hexane to remove the least polar interferences and analytes were eluted with 3 mL of acetone. Recoveries of the proposed method for spiked samples ranged from 80 to 116%, and the day-to-day variability remained between 5 and 10%. Data on levels of organophosphate species in dust from private houses and vehicle cabins are provided. In both cases, the lowest concentrations corresponded to the short chain, non-chlorinated, alkyl organophosphates, whereas mean values above 1 μg g −1 were measured for the rest of analytes.

Hepatic iron quantification by atomic absorption spectrophotometry: Full validation of an analytical method using a fast sample preparation

Atomic absorption spectrophotometry is considered the method of choice for hepatic iron quantification. The objective of the present study was to perform full validation assays of hepatic iron quantification by atomic absorption spectrophotometry, using a fast sample preparation procedure, following the guidelines from the International Conference on Harmonization. The following parameters were evaluated: specificity, linearity/range, precision, accuracy, limit of detection and limit of quantification. A good linear correlation was found (0.9948) in the concentration range evaluated (20‐ 120 ppb). The relative standard deviations were below 15% for accuracy, and below 10% for both day‐to‐day reproducibility and within‐days precision, and the repeatability of injections was 0.65%. Limit of detection was 2 ppb, and limit of quantification was 6 ppb. Fresh bovine liver tissue was used to evaluate the procedure of collecting samples by liver biopsies. These findings indicate that hepatic iron quantification by atomic absorption spectrophotometry can be reliably performed at the established conditions, and suggest the method is suitable for further use in clinical practice. Hepatic iron quantification by AAS is validated by the experiments performed in the present study.

Rapid Sample Preparation Method for LC−MS/MS or GC−MS Analysis of Acrylamide in Various Food Matrices

A fast and easy sample preparation procedure for analysis of acrylamide in various food matrices was developed and optimized. In its first step, deuterated acrylamide internal standard is added to 1 g of homogenized sample together with 5 mL of hexane, 10 mL of water, 10 mL of acetonitrile, 4 g of MgSO4, and 0.5 g of NaCl. Water facilitates the extraction of acrylamide; hexane serves for sample defatting; and the salt combination induces separation of water and acetonitrile layers and forces the majority of acrylamide into the acetonitrile layer. After vigorous shaking of the extraction mixture for 1 min and centrifugation, the upper hexane layer is discarded and a 1 mL aliquot of the acetonitrile extract is cleaned up by dispersive solid-phase extraction using 50 mg of primary secondary amine sorbent and 150 mg of anhydrous MgSO4. The final extract is analyzed either by liquid chromatography-tandem mass spectrometry or by gas chromatography-mass spectrometry (in positive chemical ionization mode) using the direct sample introduction technique for rugged large-volume injection.

Full validation of an electrothermal atomic absorption assay for zinc in hepatic tissue using a fast sample preparation procedure

The objective of this work was to develop and fully validate an analytical assay to quantify zinc in hepatic tissue. The procedure should be as simple and fast as possible in order to avoid sample contamination. The amount of sample used should also reflect the sample size usually obtained in clinical biopsies, which are about 3–4 mg at most. The validation protocol is in accordance to international guidelines, such as ICH and FDA. The parameters evaluated were precision, accuracy, range, limit of detection and limit of quantification. The method was evaluated in the 2.0–32.0 parts per billion (μg/l) range. Under the described conditions intra and inter day precision of the three levels of quality controls were lower than 9.06 and 5.27, respectively, expressed as relative standard deviation (RSD). The accuracy ranged from 86.35 to 114.71%. Limit of detection and limit of quantification were 0.60 and 2.0 μg/l, respectively. Fresh bovine liver samples were used in order to evaluate the clinical procedure used to collect biopsies. According to the results and experimental protocol, the method is fully validated and ready to use in clinical trials involving zinc quantitation using hepatic samples as small as 2.00 mg of dry tissue.

A multiresidue method for the simultaneous determination of ten macrolide antibiotics in human urine based on gradient elution liquid chromatography coupled to coulometric detection (HPLC–ECD)

A new generation of coulometric detector coupled to a high performance liquid chromatograph (HPLC) was used in this work with the aim of developing a multiresidue method allowing for the first time the separation, in a single run, of ten commercially available macrolide antibiotics, erythromycin (ERY), dirithromycin (DIR), tylosin (TYL), tilmicosin (TILM), spiramycin (SPI), josamycin (JOS), kitasamycin (KIT), rosamicin (ROS), roxithromycin (ROX) and oleandomycin (OLE). The procedure was therefore fully optimised for the separation of standard mixtures of the ten macrolides using a gradient elution on a C8 reversed phase HPLC column, and very reasonable resolution was achieved among the thirteen signals, arising from these ten. In the following step, the quantification of all the macrolides was achieved in standard mixtures, using ROX as an internal standard (I.S.), with detection limits, on column, below 2.5 ng for each. The method was then applied to the determination of macrolides in human urine, after a simple and fast sample preparation procedure involving liquid–liquid extraction. Calibration curves were carried out using the method of matrix-matching. The detection limits for each drug, in the human urine, were below 3 ng injected (equivalent to an initial concentration in the urine below 0.06 mg l −1). Overall recoveries of the entire method were estimated for each drug in human urine fortified at different levels of concentration within the linear range and averaged values were between 49.9 and 81.2% for low concentration levels and between 53.2 and 92.0% for high concentration levels for all macrolides.

In situ propylation using sodium tetrapropylborate as a fast and simplified sample preparation for the speciation analysis of organolead compounds using GC-MIP-AES

A fast and simple sample preparation procedure for the speciation of organolead compounds is described. Separation and detection of the different species was carried out using gas chromatography hyphenated to microwave-induced plasma atomic emission spectrometry. Derivatization was performed using in situ propylation with sodium tetrapropylborate in an acetic acid-sodium acetate buffer medium of pH 4.5 with simultaneous extraction of the propylated species into hexane. Detection limits (as Pb) ranging from 77 fg (0.15 ng kg –1 ) to 102 fg (0.21 ng kg –1 ) and relative standard deviations between 4 and 6% were achieved. Accuracy of the procedure was confirmed by analysis of a certified reference material (CRM 605, Road Dust), where the desorption of the different species from the matrix by acid leaching was also integrated in the derivatization and extraction step. The optimized sample preparation procedure was applied to the analysis of alpine snow sampled at the Mont-Blanc in France.

New sample preparation for quantitative laser desorption mass spectrometry and optical spectroscopy

Several analytical mass spectrometric and optical spectroscopic methods require a step during which a nonvolatile substance is desorbed by a laser pulse. It is, however, very difficult to use these methods for quantitative measurements because an accurate control over the amount desorbed by the laser pulse is generally not possible, especially when mixtures of several substances are used. We report a new fast and convenient sample preparation procedure that solves these problems. A solution of the analytes is mixed with a solution of poly(vinyl chloride) to obtain a homogeneous and vacuum-stable thin polymer membrane after the solvent has evaporated. Laser ablation is then performed directly from this membrane, allowing an accurate control of the amount of ablated analytes and excellent reproducibility. Quantitative laser desorption mass spectrometry over three orders of magnitude as well as optical spectroscopic measurements using this sample preparation method are demonstrated for polycyclic aromatic hydrocarbons.

Conditions for quantitation of dolichyl phosphate, dolichol, ubiquinone and cholesterol by HPLC.

Conditions for the isolation and quantitation of dolichyl phosphate, dolichol, cholesterol, and ubiquinone by reversed phase high performance liquid chromatography were investigated. A simple and fast sample preparation procedure using prepacked mini columns was employed. The UV spectra of the fractions obtained were examined and, in the case of dolichol compounds, the maximum absorbance around 205 nm was shown to be linearly dependent on the number of double bonds present in the isoprenolog. The analytical procedure described shows a very broad range of linearity (five orders of magnitude) and detects single dolichyl phosphate isoprenologs in amounts as small as 0.1 ng. The lowest overall recovery, that for dolichyl phosphate, is 77%. Use of isoprenolog 23 and ergosterol as internal standards reduced the variation in the method to 2.5, 4.0 and 5.5% for cholesterol, dolichyl phosphate and dolichol, respectively. The method described was employed to study the lipid composition of rat organs and biological variations in these compositions.