Coupled high-performance liquid chromatography-gas chromatography for the determination of pesticide residues in biological matrices

A fully automated high-performance liquid chromatography-gas chromatography (HPLC-GC) network is described. A ten-port valve set up as a loop type LC-GC interface allowed the transfer of large LC effluent fractions into the gas chromatograph by concurrent solvent evaporation. The system performed highly efficient sample enrichment and clean up by LC and on-line GC separation with sensitive electron-capture detection. The efficiency of the system was demonstrated by application to the trace analysis of N-(3-chloro-2,6-dimethylphenyl)-N-(2-oxotetrahydrofuranyl)-2-me thoxyacetamide (CGA 80000) in various crops and soil samples. The residue level determined was 0.02 mg/kg for crop samples and 0.01 mg/kg for soil samples. The relative standard deviations of the calibration graphs were in the range 2-5%; the mean recovery was greater than 85%.     

On-line coupled liquid chromatography-gas chromatography

On-line coupled liquid chromatography–gas chromatography (LC–GC) is a powerful technique that combines the best features of LC and GC and is ideal for the analysis of complex samples. This review describes the unique features of on-line coupled LC–GC. The different interfaces and evaporation techniques are presented, along with their advantages and disadvantages. Guidelines are given for selecting a suitable LC–GC technique and representative applications are noted.     

On-line reversed-phase liquid chromatography-gas chromatography coupled to mass spectrometry for enantiomeric analysis of chiral compounds in fruit beverages

A method based on the on-line coupling of reversed phase liquid chromatography with gas chromatography/mass spectrometry (RPLC-GC-MS) for the chiral evaluation of characteristic constituents of fruit beverage aroma was investigated. The consideration of a variety of parameters involved in the transfer step allowed to achieve relative standard deviations ranging from 0.4 to 10% in most cases and detection limits from 0.2 to 2.5 mg/l. By applying the developed method to fruit beverages, racemic mixtures of ethyl 2-methylbutanoate and gamma-nonalactone were found. This fact suggests the eventual addition of artificial aromas. The method proposed in the present work can be useful to assess reliably the authenticity of aqueous samples, such as fruit beverages.     

Implementation of Hadamard encoding for rapid multisample analysis in liquid chromatography

Multiplexing based on pseudo‐binary modulation sequences is known to increase the signal‐to‐noise ratio. In this work, Hadamard transform multiplexing is used in high‐performance liquid chromatography to increase the sample throughput. Using structured modulation sequences to encode and control sample injections in combination with a fitting algorithm to deconvolute the complex data allowed us to evaluate convoluted chromatograms of up to 128 samples containing three and five analytes, respectively, with good accuracy (<2% deviation). In comparison to conventional high‐performance liquid chromatography the analysis time could be reduced by 30 and 55%, respectively.     

Coupled column liquid chromatography for the rapid determination of N-methylcarbamates and some of their main metabolites in water

Summary A sensitive and selective coupled-column liquid chromatography (LC-LC) method was developed for the trace level determination of some N-methylcarbamates and some of their main metabolites as aldicarb, aldicarb-sulphoxide, aldicarb-sulphone, carbofuran and 3-hydroxicarbofuran in drinking and ground waters. The limit of determination can be reduced to 0.1 μg.L⁻¹ by solid phase extraction with a subsequent evaporation step. Environmental samples spiked at 0.1 μg.L⁻¹ were preconcentrated off-line with graphite carbon and then analyzed by LC-LC with UV detection yielding average recoveries between 81–109% (n=5) with RSD between 5–9%. The overall procedure allowed a sample throughput of up to 30 samples per day.     

Analysis of steryl esters in cocoa butter by on-line liquid chromatography-gas chromatography.

On-line liquid chromatography-gas chromatography (LC-GC) has been applied to the analysis of steryl esters in cocoa butter. Separation of the steryl esters was achieved after on-line transfer to capillary GC. HPLC removes the large amount of triglycerides and pre-separates the components of interest, thus avoiding time-consuming sample preparation prior to GC analysis. The identities of the compounds were confirmed by GC-MS investigation of the collected HPLC fraction and by comparison of the mass spectra (chemical ionization using ammonia as ionization gas) to those of synthesized reference compounds. Using cholesteryl laurate as internal standard, steryl esters were quantified in commercial cocoa butter samples, the detection limit being 3 mg/kg and the quantification limit 10 mg/kg, respectively. Only slight differences in percentage distributions of steryl esters depending on the geographical origin of the material were observed. The patterns were shown to remain unchanged after deodorization. The method described might be a valuable tool for authenticity assessment of cocoa butter.     

Determination by coupled high-performance liquid chromatography-gas chromatography of the beta-blocker levomoprolol in plasma following ophthalmic administration

Levomoprolol is a beta-blocking agent used in the topical treatment of glaucoma. The necessity for comparing the plasma levels of a drug administered by the ophthalmic route with those obtained following systemic treatment requires increasingly sensitive methods in order to determine the low plasma concentrations produced by the administration of eye drops. On-line high-performance liquid chromatography-gas chromatography and concurrent solvent evaporation proved to be advantageous in the determination of levomoprolol in human plasma. Levomoprolol was determined by capillary gas chromatography (GC) with electron-capture detection (ECD) after solid-phase extraction from plasma and derivatization. Quantitation was based on the internal standard method. The detection limit of 0.2 ng/ml is 50 times lower than that obtained with previous GC methods involving on-column injection and ECD.     

Comparison of three spectrophotometric methods for the determination of gamma-oryzanol in rice bran oil

A comparison of the results obtained by applying three spectrophotometric methods (at fixed wavelength, second-derivative and multicomponent analysis) to the determination of gamma-oryzanol in rice bran oil is reported.At fixed wavelength the results are more accurate when using isopropyl alcohol, rather than n-heptane, to dilute the oil samples, because the absorption bands of gamma-oryzanol are red-shifted and the absorbance, measured at lambda(max)=327 nm, is less affected by the interference of the oil "matrix" (lambda(max)=314 nm in n-heptane).However, to obtain accurate results also in oils with a low content of gamma-oryzanol, it is necessary to perform the analysis using second-derivative ((2)D330.365) or multicomponent (lambda=310-360 nm) methods. The first one fully removes the interference of oil matrix whilst the second, which needs a specific computational program to process the spectrophotometric data, furnishes evidence the presence of some unexpected interference in the analysis and/or standards which are not representative of the analysed samples, from the square root of the sum of the squared differences at each point between the linear combination of the standards and the unknown spectra (RMS error).Finally, some aspects of the chemical, spectroscopic (UV, IR) and thermoanalytical (TG, DSC) behaviour of gamma-oryzanol and the values of the parameters which enable "computation" of its UV spectra are reported.     

Memory effects with the on-column interface for on-line coupled high performance liquid chromatography-gas chromatography: The Y-interface

When using the on-column interface for on-line high performance liquid chromatography (HPLC)-gas chromatography (GC), there is a memory effect typically equivalent to 0.5–3% of the previous transfer. The shape of peaks distorted as a result of incomplete reconcentration of the initial bands enabled mapping of the distribution of the solute material in the uncoated precolumn and deriving the mechanism which causes the memory effect. The relatively slow transfer of HPLC eluent causes liquid being sucked backwards into the narrow interspace between the transfer line and the precolumn wall. Solvent is evaporated into the passing carrier gas and is replaced by more eluent pulled into this zone, resulting in enrichment of solute material. At the end of the transfer, some of this solute material enters the transfer line and remains there up to the subsequent transfer of an HPLC fraction. This problem is avoided by replacing the on-column injector used as interface by a Y-piece in which the eluent flow from HPLC and the carrier gas are joined. The memory effect was reduced to below 0.02%.     

Automated multiresidue analysis of pesticides in olive oil by on-line reversed-phase liquid chromatography-gas chromatography using the through oven transfer adsorption-desorption interface

A multiresidue, automated and rapid method for the determination of pesticide residues in olive oil is presented. The method employs the through oven transfer adsorption-desorption interface for the on-line coupling of reversed-phase liquid chromatography and gas chromatography. In this fully automated system, olive oil is directly injected with no sample pre-treatment step other than filtration. Methanol-water is used as eluent in the liquid chromatography pre-separation step. The selected liquid chromatography fraction containing the pesticides is automatically transferred to the gas chromatography. The liquid chromatography column flow during elution is different from the flow during the transfer. Using a flame ionisation detector, pesticide detection limits varied from 0.1 to 0.3 mg/l.     

Pressurised hot water extraction coupled on-line with liquid chromatography-gas chromatography for the determination of brominated flame retardants in sediment samples

Pressurised hot water extraction (PHWE) was coupled on-line with liquid chromatography-gas chromatography (LC-GC) to determine brominated flame retardants in sediment samples. After extraction with pressurised hot water the analytes were adsorbed in a solid-phase trap. The trap was dried with nitrogen and the analytes were eluted to the LC column, where the extract was cleaned, concentrated and fractionated before transfer to the GC system. The fraction containing the brominated flame retardants was transferred to the GC system via an on-column interface. The PHWE-LC-GC method was linear from 0.0125 to 2.5 microg with limits of detection in the range 0.70-1.41 ng/g and limits of quantification 6.16-12.33 ng/g.     

高效液相色谱-气相色谱在线联用同时测定土壤中饱和烃和芳香烃

为加强对土壤中石油烃类污染物的风险管控,生态环境部已将石油烃类列为土壤中的重点监测项目.石油烃源于石油与合成油,是涵盖一定碳数范围的碳氢化合物,主要分为饱和烃和芳香烃两大类.芳香烃通常是高度烷基化的单环、双环与多环芳烃,其对人和动物的毒性较饱和烃大很多,因此,仅仅测定土壤中总石油烃含量难以准确评估其环境毒性.目前环境领...     

Determination of trans octadecenoic acids by silver-ion chromatography-gas liquid chromatography: an intercomparison of methods

Several silver-ion chromatography-gas liquid chromatography (GLC) techniques for the determination of trans octadecenoic acids in partially hydrogenated vegetable fats were collaboratively evaluated. Twelve laboratories participated in the study. All collaborators used high polarity fused silica capillary columns for the separation of fatty acid methyl esters by GLC; 7 collaborators isolated trans monoenes by silver-ion liquid chromatography (Ag-LC) and the remainder used silver-ion thin-layer chromatography (Ag-TLC). Eight artificially prepared materials [soybean oil spiked with either methyl elaidate, trielaidin, or trans octadecenoates isolated from partially hydrogenated sunflower oil (PHSO)] and 2 matrix materials (PHSO and a blend of PHSO and palm oil) served as test samples. Ag-TLC and Ag-LC proved to be equivalent techniques for the prefractionation of trans monoenes. Recovery of methyl elaidate, trielaidin, or trans octadecenoates isolated from PHSO varied between 97.9-103.7% over a concentration range of 1 to 30 g trans fatty acids/100 g. Reproducibility relative standard deviation (RSDR) for the spiked samples were in the range of 3.1-8.6% for 30-1% trans monoene content. For the 2 matrix samples (mean 3.75 and 19.08% trans monoene content) RSDR was 13.2 and 3.6%. The hyphenated techniques tested proved to be highly accurate and sufficiently precise methods for the determination of trans monoenes in partially hydrogenated vegetable fats. Procedural variations of the silver-ion chromatography prefractionation step (separation mode, mobile phase, and detection systems) did not significantly influence the results of the test. Therefore, silver-ion chromatography is a robust method, which does not need rigorous standardization to achieve high precision of test results. A further benefit of the hyphenated technique is that any type of efficient polar capillary column can be used.     

Use of absorbent materials in on-line coupled reversed-phase liquid chromatography-gas chromatography via the through oven transfer adsorption desorption interface

The use of absorbents as retaining materials in the through oven transfer adsorption desorption interface (TOTAD) of an on-line coupled reversed-phase liquid chromatography-gas chromatography system (RPLC-GC) is proposed for the first time. A comparative study of an adsorbent (Tenax TA) and two absorbents, namely polydimethylsiloxane and poly(50% phenyl/50% methylsiloxane) is performed to establish the best experimental conditions for the automated and simultaneous determination of 15 organophosphorus and organochlorine pesticide residues in olive oil. The proposed method provides satisfactory repeatability (RSDs lower, in general, than 8.5%) and sensitivity (limits of detection ranging from 0.6 to 81.9 microg/L) for the investigated compounds.     

Validation of a robust and rapid liquid chromatography tandem mass spectrometric method for the quantitative analysis of navitoclax

The Bcl-2 family small molecule inhibitor navitoclax is being clinically evaluated to treat multiple cancers including lymphoid malignancies and small cell lung cancer. A sensitive and reliable method was developed to quantitate navitoclax in human plasma using liquid chromatography with tandem mass spectrometry with which to perform detailed pharmacokinetic studies. Sample preparation involved protein precipitation using acetonitrile. Separation of navitoclax and the internal standard, navitoclax-d8, was achieved with a Waters Acquity UPLC BEH C₁₈ column using isocratic flow over a 3 min total analytical run time. A SCIEX 4500 triple quadrupole mass spectrometer operated in positive electrospray ionization mode was used for the detection of navitoclax. The assay range was 5–5,000 ng/ml and proved to be accurate (89.5–104.9%) and precise (CV ≤ 11%). Long-term frozen plasma stability for navitoclax at −70°C was at least 43 months. The method was applied for the measurement of total plasma concentration of navitoclax in a patient receiving a 250 mg daily oral dose.     

Automated on-line gel permeation chromatography-gas chromatography for the determination of organophosphorus pesticides in olive oil

An on-line combination of gel permeation chromatography and gas chromatography has been designed using either a laboratory-built or a commercially available LC-GC apparatus to determine organophosphorus pesticides in olive oil. Gel permeation chromatography was used for sample pretreatment, viz. to separate the low-molecular-mass pesticides from the higher-molecular-mass fat constituents of the oil. A mixture of n-decane and the azeotropic mixture of ethyl acetate and cyclohexane was found to give an adequate separation between the fat and the organophosphorus pesticides. The pesticide-containing fraction, monitored by a UV detector, was transferred on-line to the gas chromatograph using a loop-type interface. n-Decane (6%, v/v) was added to the eluent in order to widen the application range of the transfer technique towards more volatile pesticides. After solvent evaporation through the solvent vapour exit and subsequent GC separation, the compounds were selectively detected with a thermionic or a flame photometric detector. The set-up allowed the direct analysis of oil samples after dilution in the gel permeation chromatography eluent without further sample clean-up. Detection limits were about 5 and 10 μg/kg with the thermionic and the flame photometric detector, respectively, when using an injection volume of only 30 μl of the 20-fold diluted oil. The total procedure was linear in the 0.01–10 mg/kg range for both detectors. For twenty organophosphorus pesticides, the relative standard deviations were 3–13% at the 20–60 μg/kg level.     

Appropriate column configurations for the rapid analysis and semipreparative purification of the radiolabeled drug flutamide by high-performance liquid chromatography

Flutamide, marketed as Eulexin, is used for treatment of metastic prostatic carcinoma. Purity of a radiolabeled batch for metabolism studies was first determined by reversed-phase HPLC on a 5 microm, 150x4.6 mm analytical column. The separation was then scaled up to give a semipreparative column (5 microm, 250x10 mm) purification procedure. Fraction analysis was done on a short rapid analysis (5 microm, 50x3.0 mm) column. Analysis of the final product was performed on the analytical column. All columns were YMC-Pack ODS-AQ. The analytical work involved large mass injections in order to have the required amounts of radioactivity needed for accurate impurity profile determinations, and the preparative work involved masses much larger than the calculated scale-up values. Ultraviolet and radiochromatograms of the drug on the various column configurations are compared. A 95.7% recovery of product was obtained, with radiochemical purity increased from 95.0 to 99.8%.