High Performance Liquid Chromatography Clean-up Research Articles

Improving the Determination of Carbon Isotope Ratios of Endogenous Steroids Found in Human Serum.

The determination of serum concentrations of testosterone (T) and 4-androstenedione (A4) was implemented into the steroidal module of the Athlete Biological Passport in 2023. Monitoring T, A4, and the ratio of T/A4 in a longitudinal manner enables the detection of the misuse of low-dose T administrations especially in female athletes, whereas urinary markers of the steroid profile may not be influenced significantly. In contrast to the urinary steroid profile, knowledge on confounding factors regarding serum concentrations of T and A4 is yet comparably scarce, and corroborating exogenous sources of the target analytes by isotope ratio mass spectrometry (IRMS) is desirable. In a recent study, it was demonstrated that carbon isotope ratios (CIRs) of serum steroids can be determined if analyte concentrations permit. The therein-employed method utilized 2D-GC/IRMS, and only a limited number of potential endogenous reference compounds were available. The here-presented approach uses complementary analyte purification strategies, addressing previous limitations. A high-performance liquid chromatography cleanup was developed and fully validated for serum steroids in order to enable all doping control laboratories to potentially implement this method alongside existing protocols for urinary steroids. Besides the already-investigated endogenous steroids cholesterol, dehydroepiandrosterone sulfate, androsterone sulfate, and epiandrosterone sulfate, two additional steroids were included in the test menu, namely, pregnenolone sulfate and 5-androstene-3β,17β-diol sulfate. Serum steroid concentrations down to 25 ng/mL were found to allow robust CIR determinations, and a reference population encompassing 124 male and female athlete samples was investigated to enable the calculation of population-based thresholds for all relevant steroid combinations.

Quartz Crystal Microbalance as a Holistic Detector for Quantifying Complex Organic Matrices during Liquid Chromatography: 1. Coupling, Characterization, and Validation.

A matrix in highly complex samples can cause adverse effects on the trace analysis of targeted organic compounds. A suitable separation of the target analyte(s) and matrix before the instrumental analysis is often a vital step for which chromatographic cleanup methods remain one of the most frequently used strategies, particularly high-performance liquid chromatography (HPLC). The lack of a simple real-time detection technique that can quantify the entirety of the matrix during this step, especially with gradient solvents, renders optimization of the cleanup challenging. This paper, along with a companion one, explores the possibilities and limitations of quartz crystal microbalance (QCM) dry-mass sensing for quantifying complex organic matrices during gradient HPLC. To this end, this work coupled a QCM and a microfluidic spray dryer with a commercial HPLC system using a flow splitter and developed a calibration and data processing strategy. The system was characterized in terms of detection and quantification limits, with LOD = 4.3-15 mg/L and LOQ = 16-52 mg/L, respectively, for different eluent compositions. Validation of natural organic matter in an environmental sample against offline total organic carbon analysis confirmed the approach's feasibility, with an absolute recovery of 103 ± 10%. Our findings suggest that QCM dry-mass sensing could serve as a valuable tool for analysts routinely employing HPLC cleanup methods, offering potential benefits across various analytical fields.

Improved Method for Differentiation of Synthetic and Natural Endogenous Anabolic Steroids using Gas Chromatography Isotope Ratio Mass Spectrometry (GC/C/IRMS) followed by Two-Fold High Performance Liquid Chromatography (HPLC) Cleanup Method: A Perspective

Abstract: Background: Androgenic Anabolic Steroids (AAS) are also synthetic derivatives of testosterone, modified to improve its anabolic actions. The misuse of AAS is of particular concern in sports and society. Gas chromatography-mass spectrometry had some limitations and allows identification and characterization of steroids and their metabolites in the urine but may not be able to distinguish between pharmaceutical (Exogenous) and endogenous origin. Thus, it is of great importance to discriminate endogenous steroids such as testosterone or testosterone prohormones from their chemically identical synthetic copies. The abuse of Androgenic Anabolic Steroids (AAS) by sports person is banned by World Anti-doping Agency (WADA) as per the WADA Prohibited list 2019. Methodology: The gas chromatography-combustion/isotope ratio mass spectrometry (GC/C/IRMS) technique differentiates between natural and synthetic endogenous steroids by comparing compounds specific 13C/12C ratio. However, the analytes have to be efficiently isolated and purified prior to GC/C/IRMS analysis. Results and Discussion: HPLC Cleanup method prior to analysis by GC−C/IRMS needs to be developed and validated for discriminating the origin of anabolic androgenic steroids. These methods involves the solid-phase extraction, enzymatic hydrolysis with β-glucuronidase, HPLC-fractionation for the cleanup and analysis by GC−C/IRMS. The difference (Δ13C) of urinary δ13C values between synthetic analogues and Endogenous Reference Compounds (ERC) by GC-C/IRMS would be used to elucidate the origin of steroids. The present perspective gives an overview of the use of anabolic-androgenic steroids in sport and methods used in anti-doping laboratories for their detection in urine, with special emphasis on GC−C/ IRMS technique after two-fold HPLC cleanup. Key words: Endogenous Steroids, Exogenous Steroids, HPLC Cleanup, Doping, GC/C/ IRMS.

The Development of an Automated Clean-up for Fat Extracts in the Routine Analysis of Organochlorine Compounds in Fish Meat

The present work describes the development of a new, automatic High Performance Liquid Chromatography (HPLC) Clean-up step, in the methodology of sample preparation and multi-residue determination of organochlorine compounds (OCs) in fish meat. 24 OCs were taken into study. In addition 7 Polychlorinated Biphenyls (PCBs), 7 chlorobenzene compounds and one 2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD) were investigated. The HPLC conditions were established in accordance with the validated traditional Clean-up step of the laboratory. The technique was applied on a dilution of analytes of interest in order to establish the period of time in which the compounds are eluted. Another set of experiments involved fish oil, in order to identify and separate the fat fraction from the analytes. To confirm the findings of the experiments mentioned above, extracts of fish samples obtained after Accelerated Solvent Extraction (ASE) were examined. The samples were spiked with the analytes of interest before HPLC clean-up step and quantified through Gas Chromatography coupled with tandem Mass Spectrometry (GC-MS/MS). A HPLC clean-up technique lasting 38 minutes/sample was developed. The method is not suitable for OCs such as Endosulfansulfat and Endrine Ketone due to the very low recovery results.Â

Method for the determination of concentration and stable carbon isotope ratios of atmospheric phenols

Abstract. A method for the determination of the stable carbon isotopic composition of atmospheric nitrophenols in the gas and particulate phases is presented. It has been proposed to use the combination of concentration and isotope ratio measurements of precursor and product to test the applicability of results of laboratory studies to the atmosphere. Nitrophenols are suspected to be secondary products formed specifically from the photooxidation of volatile organic compounds. XAD-4TM resin was used as an adsorbent on quartz filters to sample ambient phenols using conventional high volume air samplers at York University in Toronto, Canada. Filters were extracted in acetonitrile, with a HPLC (high-performance liquid chromatography) clean-up step and a solid phase extraction step prior to derivatization with BSTFA (bis(trimethylsilyl) trifluoroacetamide). Concentration measurements were done with gas chromatography–mass spectrometry and gas chromatography–isotope ratio mass spectrometry was used for isotope ratio analysis. The technique presented allows for atmospheric compound-specific isotopic composition measurements for five semi-volatile phenols with an estimated accuracy of 0.3–0.5‰ at atmospheric concentrations exceeding 0.1 ng m−3 while the detection limits for concentration measurements are in the pg m−3 range. Isotopic fractionation throughout the entire extraction procedure and analysis was proven to be below the precision of the isotope ratio measurements. The method was tested by conducting ambient measurements from September to December 2011.

Novel evidence for natural formation of dioxins in ball clay

Elevated concentrations of dioxins in ancient ball clay from the Mississippi Embayment suggest natural formation of dioxins in the environment. Evidence for such natural formation in ball clay derives from unique congener profiles in undisturbed ancient clay deposits and from the lack of other anthropogenic contaminants. Here we present novel evidence of natural formation of dioxins based on congener-specific carbon isotopic analysis of octachlorodibenzo- p-dioxin (OCDD) in ball clays from the USA and Japan. The analyses were performed using a combination of double-column high performance liquid chromatography clean-up and two-dimensional gas chromatography–isotope ratio mass spectrometry. Elevated concentrations of OCDD found in ball clays from the USA and Japan were isotopically distinguished from the anthropogenic source materials (fly ash and pentachlorophenol) and environmental samples (sediment and soil). The isotopic signatures and the occurrence of OCDD in ancient ball clays deposited in the Tertiary Era provide evidence for the in situ formation of dioxins.

Determination of the origin of urinary norandrosterone traces by gas chromatography combustion isotope ratio mass spectrometry

On the one hand, 19-norandrosterone (NA) is the most abundant metabolite of the synthetic anabolic steroid 19-nortestosterone and related prohormones. On the other hand, small amounts are biosynthesized by pregnant women and further evidence exists for physiological origin of this compound. The World Anti-Doping Agency (WADA) formerly introduced threshold concentrations of 2 or 5 ng of NA per ml of urine to discriminate 19-nortestosterone abuse from biosynthetic origin. Recent findings showed however, that formation of NA resulting in concentrations in the range of the threshold levels might be due to demethylation of androsterone in urine, and the WADA 2006 Prohibited List has defined NA as endogenous steroid. To elucidate the endogenous or exogenous origin of NA, (13)C/(12)C-analysis is the method of choice since synthetic 19-nortestosterone is derived from C(3)-plants by partial synthesis and shows delta(13)C(VPDB)-values of around -28 per thousand. Endogenous steroids are less depleted in (13)C due to a dietary mixture of C(3)- and C(4)-plants. An extensive cleanup based on two high performance liquid chromatography cleanup steps was applied to quality control and doping control samples, which contained NA in concentrations down to 2 ng per ml of urine. (13)C/(12)C-ratios of NA, androsterone and etiocholanolone were measured by gas chromatography/combustion/isotope ratio mass spectrometry. By comparing delta(13)C(VPDB)-values of androsterone as endogenous reference compound with NA, the origin of NA in doping control samples was determined as either endogenous or exogenous.

Automated determination of amisulpride by liquid chromatography with column switching and spectrophotometric detection

A fully automated chromatographic method including on-line blood serum or plasma clean-up, isocratic high-performance liquid chromatography (HPLC) and spectrophotometric detection was developed for quantitative analysis of the new antipsychotic drug amisulpride. After injection of serum or plasma onto the HPLC system and clean-up on a pre-column (10×4.0 mm I.D.) filled with Silica CN 20 μm (pore size 10 nm) by an eluent consisting of 8% acetonitrile in deionized water, the chromatographic separation was performed on Lichrospher CN (5 μm; 250×4.6 mm I.D.) by an eluent consisting of 50% acetonitrile and 50% aqueous potassium phosphate buffer (0.008 M, pH 6.4). The UV detector was set at 254 nm. The limit of quantification was about 10 μg/l. The method revealed linearity between 10 and 600 μg/l (correlation coefficients R 2>0.9996). The inter-assay reproducibility (coefficient of variation) of quality control samples was between 2.8 and 11.3%. Inaccuracy was between −0.6 and +9.1%. The performance of daily calibration standards revealed an imprecision always below 15% and maximum inaccuracy of 7.7%. The method can be applied to therapeutic drug monitoring as well as pharmacokinetic studies of amisulpride.

High-performance liquid chromatography versus solid-phase extraction for post-derivatization cleanup prior to gas chromatography-electron-capture negative-ion mass spectrometry of N1,N3-bis-(pentafluorobenzyl)-N7-(2-[pentafluorobenzyloxy]ethyl)xanthine, a product derived from an ethylene oxide DNA adduct

N7-(2-Hydroxyethyl)xanthine (N7-HEX), as a standard, has been measured at the low picomole level by the following sequence of steps: (1) derivatization with pentafluorobenzyl bromide: (2) post-derivatization sample cleanup by reversed-phase high-performance liquid chromatography (HPLC) or silica solid-phase extraction; and (3) separation/detection by gas chromatography electron-capture negative-ion mass spectrometry (GC-ECNI-MS). The average yield of product from the two sample cleanup procedures applied to 95 pg (0.48 pmol) of N7-HEX was comparable: 60% for HPLC; 56% for solid-phase extraction. The reaction blanks (0 pg N7-HEX) showed an interfering GC-ECNI-MS peak after HPLC cleanup. This problem was not encountered with solid-phase extraction, which, along with its greater convenience, made it the preferred technique for post-derivatization sample cleanup.

Comparison of HPLC and solid phase clean-up methods for identification of PCBs in cod-liver oil by HRGC/MS-SIM technique

A group of non-planar PCBs (IUPAC nos. 28, 52, 101, 118, 138, 153, and 180) was identified in a cod-liver oil product by using high resolution gas chromatography-mass spectrometry (HRGC/MS) in electron impact (EI) and negative chemical ionization (NCI) modes. The cod-liver oil samples were prepared either in a cyano column by high performance liquid chromatography (HPLC) or by a solid phase extraction (SPE) clean-up procedure that included e.g. purified charcoal treatment. The two methods of sample preparation were evaluated on the basis of the detectabilities of the congeners. The GC/MS-SIM method allowed quantitative monitoring of congeners nos. 52, 101, 118, 138, 153, and 180 at low concentration levels. Detection limits were 1.2 pg and 130 fg (m/z 292.00) in EI and NCI modes, respectively. The determination levels in EI and NCI were 1.8 pg and 290 fg in HPLC followed by HRGC/MS and 170 pg and 27 pg in SPE followed by HRGC/MS. The linear range was from 5.0 pg/μl to 1.0 ng/μl and from 1.0 pg/μl to 1.0 ng/μl in EI and NCI modes, respectively. In addition, the co-planar PCBs, PCDDs, and PCDFs were also screened and two of the chlorinated furanes were identified by HRGC/MS-NCI after separation from non-planar PCBs by SPE. In this case the only congeners that could be quantified were 2,3,4,7,8-PCDF and 1,2,3,4,6,7,8-HCDF, the detection limit for them being 740 fg (m/z 351.90) with NCI. SPE allows the separation of the planar and non-planar compounds, but LC separation is more effective for separation of the compounds of interest from the matrix. LC clean-up is easier and faster to perform than SPE clean-up.

Analytical methodology of the Dow Chemical Company for the determination of selected chlorinated dibenzo-p-dioxins and dibenzofurans in stack gas effluent matrices: Part II: Isomer method for determination of tetra- through octa-chlorinated congener group “2378”-substituted isomer concentrations

This procedure is a modification of the analytical method presented in Part I. It permits the determination of “2378”-substituted CDD and CDF isomers (chlorinated dibenzo-p-dioxins and dibenzofurans), over the range of congener groups having from four to eight chlorine substituents, in stack gas effluent samples containing both gaseous and particulate emissions. Stack gas samples are collected isokinetically from an operating process vent to the atmosphere using a United States Environmental Protection Agency (US EPA) modified Method 5 sample collection train. Analytes are recovered by subjecting the entire contents of a sampling train to extraction with benzene so as to produce a total-sample-crude-extract. An aliquot of the crude extract is fortified with [ 13C 12]-labeled CDD/CDF isomer internal standards and subjected to a 2-dimensional HPLC (high performance liquid chromatography) cleanup procedure that is designed to isolate the seven “2378”-CDD and ten “2378”-CDF isomers into separate fractions from a single analysis aliquot. Final HRGC-LRMS (high resolution gas chromatography - low resolution mass spectrometry) examination of these fractions provides the necessary qualitative and quantitative data for each analyte.