Lucija Zupančič-Kralj

Solid-phase microextraction

Abstract In recent years, much attention in analytical chemistry has been paid to sample preparation techniques, especially those which minimise the consumption of organic solvents. One of the most promising of these, solid-phase microextraction (SPME), is presented in both its theoretical and practical aspects. Conditions which affect its performance are assessed, as are the problems which may arise from its use. Finally, some typical applications are listed, highlighting the methods sensitivity and precision, and the range of samples where SPME can be used successfully.

Multiresidue method for determination of 90 pesticides in fresh fruits and vegetables using solid-phase extraction and gas chromatography-mass spectrometry

A multiresidue method for analysis of 90 pesticides with different physico-chemical properties in fruits and vegetables was developed. The method involves a rapid and small-scale extraction procedure with acetone using vortex mixing. Solid-phase extraction (SPE) on a highly cross-linked polystyrene divinylbenzene column (LiChrolut EN) was used for clean-up and pre-concentration of the pesticides from the water-diluted acetone extracts. For most fruit and vegetable samples this partial clean-up was sufficient, but some of them with more co-extracting substances need further clean-up (cereals, spinach, carrots, etc.). Diethylaminopropyl (DEA) modified silica was used for efficient removal of interferences caused by various organic acids, sugars, etc. The pesticide residues were determined by gas chromatography with a mass selective detector (GC-MS). The majority of pesticide recoveries for various fruits and vegetables were >80% in the concentration range from 0.01 to 0.50 mg/kg, except for the most polar pesticides (methamidophos, acephate, omethoate) which cannot be determined by this method. The limit of quantitation for most of the pesticides was 0.01 mg/kg with majority of relative standard deviations (R.S.D.s) below 10%.

Investigations of the determination and transformations of diazinon and malathion under environmental conditions using gas chromatography coupled with a flame ionisation detector.

Degradation of two model insecticides, diazinon and malathion, and their degradation products 2-isopropyl-6-methyl-4-pyrimidinol--IMP (diazinon hydrolysis product) and malaoxon (malathion oxidation product) was compared and studied in the environment. The pesticides and their metabolites were extracted from samples (water, soil, chicory) with ethyl acetate and subsequently the extracts were analyzed by GC/FID. It was shown that hydrolysis is the major process in the degradation of these pesticides in water. In fact, 95% of diazinon was degraded, and only 10% of malathion was oxidised. In soil 30% of diazinon exposed to the sunlight was decomposed by photolysis, whereas in soil left in the darkness no degradation products were observed. In soil left under environmental conditions, 90% of diazinon was degraded and 40% from its initial concentration was transformed into IMP. The concentrations of the pesticides after 21 days on chicory were under maximal allowable concentration, which is 0.5 ppm for malathion and for diazinon. The concentration of malaoxon was more than twice as high as the allowable value, which is for the sum of malathion and malaoxon 3 ppm.

Optimisation of programmable temperature vaporizer-based large volume injection for determination of pesticide residues in fruits and vegetables using gas chromatography-mass spectrometry.

The applicability of programmable temperature vaporizer (PTV) solvent vent injection to the gas chromatographic (GC) determination of pesticide residues in fruits and vegetables was evaluated with the aim of miniaturizing the current multiresidue method. For that purpose 24 pesticides representing different chemical classes were initially chosen for optimisation of the large volume injection (LVI) parameters. Various parameters related to the optimum injector performance were tested for several types of packed and empty liners using both fast (at-once) and speed-controlled PTV solvent vent injection of standard solutions in ethyl acetate. In the next step, several packed and empty liners were evaluated for their suitability for pesticide multiresidue analysis. Parameters identified as optimal were then applied for PTV solvent vent injection of sample extracts prepared using the miniaturized multiresidue method to assess the long-term stability of the system. The combined use of large volume injection of 10 microl ethyl acetate extract into an empty multi-baffled or a CarboFrit packed liner using PTV injectors and GC-MS analysis enabled the detection and quantification of 124 pesticides in fruit and vegetable samples at the 0.01 mg/kg level using miniaturized reversed-phase solid-phase extraction (RP-SPE) of diluted acetone extract and clean-up on a small anion-exchange SPE column.

Identification of gentamicin impurities by liquid chromatography tandem mass spectrometry.

An HPLC/MS/MS method was developed for identification of impurities in gentamicin. The HPLC was performed on a Synergy Hydro-RP column using 50 mM trifluoroacetic acid (TFA), pH 2 adjusted with ammonium solution and methanol as mobile phase. All impurities in gentamicin were separated from main gentamicin components. Atmospheric pressure chemical ionization (APCI) was used and product mass spectra of protonated molecules were acquired. Seventeen impurities were detected in gentamicin. Reference compounds: gentamicins: C2b, B, B1, G-418, sisomicin, garamine and gentamines: C1, C1a, C2, C2a were used for spectra interpretation and impurities identification. All MS/MS spectra were interpreted and fragmentation transitions for gentamicins and in general for aminoglycoside antibiotics (AG) were proposed. All impurities were identified. More than one isomere were proposed for three impurities.

Determination of tramadol in human plasma by capillary gas chromatography-mass spectrometry using solid-phase extraction

An analytical method using solid-phase extraction, capillary gas chromatography and mass selective detection in the electron-impact ionization (EI) mode was developed for the determination of tramadol (2-[(dimethylamino)methyl]-1-(3-methoxyphenyl)cyclohexanol) in human plasma. The advantages of this method are the high sensitivity and selectivity and the linearity over the concentration range 2-500 ng/ml. Quantification was made using nefopam as an internal standard, and the detection limit was found to be 1 ng/ml. The standard deviations of the intra-day precision test ranged from 4.5 to 6.0% with respect to the concentration. Accuracy ranged from 1.0 to 4.0% (inter-day). The method was used for the determination of tramadol in a bioequivalence study.

Effect of column temperature on the behaviour of some angiotensin converting enzyme inhibitors during high-performance liquid chromatographic analysis

The chromatographic behaviour of the ACE inhibitors lisinopril, enalapril and its two degradation products, enalaprilat (hydrolytic degradation product) and diketopiperazine (DKP) (cyclization degradation product) was studied as a function of column temperature and pH of the mobile phase. The rate of isomerization (which influences the peak shape or even peak splitting during chromatographic analysis) increases with temperature. The shape of the chromatographic peak for enalapril, enalaprilat and lisinopril is also pH dependent. At high temperature (80 degrees C) and low pH (pH=2) all studied compounds appear on the chromatogram as a narrow chromatographic peak. Chromatographic peaks become broader or they split by lowering the column temperature. Enalapril appears at 6 degrees C on the chromatogram in two peaks which belong to its cis- and trans-rotation isomers. Separation of the rotamers was confirmed by NMR spectroscopy.

Changes in odour of bartlett pear brandy influenced by sunlight irradiation

Sensory evaluation of Bartlett pear brandy revealed differences in taste and smell between the brandy in colourless and green bottles. To determine the differences in chemical composition, headspace sampling with solid-phase microextraction combined with gas chromatography-mass spectrometry was applied. The major aroma components in pear brandy stored in green bottles were ethyl trans-2-cis-4-decadienoate (68 ppm), ethyl trans-2-trans-4-decadienoate (21 ppm) and methyl trans-2-cis-4-decadienoate (27 ppm). In pear brandy kept in colourless bottles, the concentration of trans-2-cis-4-isomeres was lower and the concentrations of other possible isomeres were higher. Results show a pronounced difference in the concentration ratios among isomeres of ethyl 2,4-decadienoate and methyl 2,4-decadienoate in both samples. Sunlight irradiation was found to be the reason for these changes. It was confirmed that trans-2-cis-4-isomere partly converts to the other three isomeres during UV irradiation.

Comparison of gas chromatographic and spectrophotometric techniques for the determination of formaldehyde in water

Abstract Formaldehyde was determined in aqueous samples by four different analytical procedures (two spectrphotometric and two gas chromatographic). In the spectrophotometric procedures chromatogropic acid and 3-methyl-2-benzothiazolone hydrazone were used. For gas chromatography either an electron-captive or a flame ionization detector were used, and for sample preparation liquid-liquid extraction in the former and solid-phase extraction in the latter case were used. The concentration range covered was between 0.06 and 20 mg/l. Calibration plots and detection limits were optimized for all four procedures.

Assessment of polychlorobiphenyls in human/poultry fat and in hair/plumage from a contaminated area

Abstract HR gas chromatographic PCB patterns in human/poultry fat tissue and hair/plumage in samples from a polluted region of Bela Krajina /Slovenia/ were investigated. The concentration of PCBs in human adipose tissue was found to be 9.62 μg/g in comparison to 0.67 μg/g in the adipose tissue of the non-exposed population, and in poultry fat 12.80 μg/g on a fat basis. The corresponding values in human hair and poultry plumage were 0.90 μg/g and 0.20 μg/g of original weight. The difference in PCB patterns between fat and hair can be attributed to the different routes of contamination (ingestion, air transport), to the time of exposure and physicochemical properties (octanol- water partition coefficients, Henrys law constants and the metabolism) of some individual congeners. Hair could be used for the assessment of ingestion of contaminated food and of the PCB levels in the air. In fat tissue PCB congeners with higher metabolic stability are enriched, whereas in hair PCB congeners with higher concentrations in air and with high octanol- water partition coefficients predominate.