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Gradient Performance Problems — A Case StudyThe gradient linearity and step tests are two of the most useful performance tests that can be made for a liquid chromatography (LC) system. These check the linearity of gradient generation and the accuracy of mobile phase proportioning. These tests, and examples of problems detected as a result of these tests, have been the subject of at least seven "LC Troubleshooting" columns over the last 18 years.1–7 We strongly recommend that every LC system undergo these tests at least on an annual basis, and preferably semiannually. When a new and different example of a problem detected by these tests is discovered, it is hard to bypass the opportunity to share it with our readers. So this month, you get yet another example of how an LC system can fail.
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The Use of Thin-Layer Chromatography with Direct Bioautography for Antimicrobial AnalysisThis article gives an overview of screening methods for the detection of antimicrobials, including dilution and diffusion methods and bioautography, mainly direct bioautography. The thin-layer chromatography method with direct bioautography was worked out to analyse enrofloxacin and ciprofloxacin residues in milk.
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Experimental Proofs of a Correlation Between the Coefficients for the Slope of the Response Line and the Response Factor of an ELSDThe authors describe a study that was conducted to evaluate the correlation between the slope of the response line and the response factor of an ELSD that are ordinarily regarded as independent numerical coefficients.
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Water Injections in GC — How Wet Can You Get?The author reports results from a systematic study of the effect of water injections on column performance with a number of common GC stationary phases.
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Analysis of Combinatorial Natural Products by HPLC and CEIn this article the authors report on a combinatorial natural product discovery methodology that uses a viral vector system to transfer secondary metabolite-related enzymes from C. roseus to tobacco cell cultures. Using high-resolution separation techniques, including HPLC, CE and MS, they describe the analysis of secondary metabolite patterns.
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Non-Discriminating Analytical Pyrolysis — A Novel Tool for Studying Environmental SamplesConventional pyrolysis can cause defunctionalization of polar structural moieties carrying functional groups, which leads to biased results.
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The Benefits of Including Certified Reference Materials in a Collaborative TrialThis article assesses the advantages of including certified reference materials in collaborative method validation studies in food analysis. A recently conducted collaborative trial on the determination of acrylamide in bakery and potato products is described to illustrate this.
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A Geometric Approach to Robustness Testing in Analytical HPLCThe authors describe a new approach for verifying robustness testing in HPLC.
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Non-Discriminating Analytical Pyrolysis — A Novel Tool for Studying Environmental SamplesConventional pyrolysis can cause defunctionalization of polar structural moieties carrying functional groups, which leads to biased results.
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Method Development and Validation for Phenol and Nitrophenols in Tap Water by HPLC using a Monolithic ColumnAn isocratic HPLC method for the determination of phenol and nitrophenols (4-nitrophenol, 2-nitrophenol, 4,6-dinitro-o-cresol and 2,4-dinitrophenol) has been developed and validated using 2-chlorophenol as internal standard (IS) and a monolithic column in tap water samples. Prior to HPLC, the method requires solid-phase extraction (SPE) using polymeric Lichrolut EN cartridges. The method development involved the study of methanol and acetonitrile as organic modifiers, pH and flow-rate using a Chromolith RP-18e (150 mm × 4.6 mm I.D.) column. After comparing the performance of the separations obtained with both organic modifiers, the optimum separation of these compounds was achieved using 50 mM acetate buffer (pH 5.0)-acetonitrile (80:20, v/v) as mobile phase, 3 mL min-¹ flow-rate and UV detection at maximum absorbance wavelength. Under these conditions, all analytes were separated (Rs > 2.0) in an analysis time of less than 3.5 min and the most important validation parameters were evaluated. The recoveries obtained in the accuracy test for all phenols studied were in the 90–112% range using a preconcentration factor of 40, and the intraday and interday precisions [expressed as coefficient of variation (CV)] were smaller than 15%. Finally, the proposed method was applied to wastewater samples from several industries.
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De Novo Formula Generation with "Sub-ppm" Confidence using Compass OpenAccess and the micrOTOFAccurate mass measurements are a key element of chemical characterization. However, the accepted mass accuracy tolerance of 3–5 ppm can still leave significant ambiguity in the proposed chemical formula. Consequently a further input from other analytical techniques such as NMR or MS/MS, along with some judgment based on the synthetic history is often required to arrive at a confident formula assignment.
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Forensic Drug Screening by LC–MS Using Accurate Mass MeasurementBecause of progress in liquid chromatography/time-of-flight mass spectrometry (LC/TOF-MS) instrumentation, data processing and reporting, the measurement of compounds' accurate masses is becoming routine practice in screening analysis based on target databases. As such databases of monoisotopic masses can be easily updated with recent data from the literature; rapid characterization of new compounds and metabolites is possible without the need for primary reference standards. This approach has already been established in comprehensive toxicological urine screening and in analysis of drugs-of-abuse in seized street drug samples. Currently, a mass accuracy within 5 ppm can be routinely achieved, and confirmation via a numerical isotopic pattern match (SigmaFit) is provided by a new generation LC/TOF-MS instrument.
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Classifying Chromatographic Systems by ClusteringIt would help to have a restricted set of chromatographic systems (CS) that together serve as potential starting points in method development.
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On-line Supercritical Fluid Extraction-Capillary Gas Chromatography for the Analysis of DieselDirect coupling of SFE with GC has advantages over the off-line alternative.
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Analysis of Combinatorial Natural Products by HPLC and CEIn this article the authors report on a combinatorial natural product discovery methodology that uses a viral vector system to transfer secondary metabolite-related enzymes from C. roseus to tobacco cell cultures. Using high-resolution separation techniques, including HPLC, CE and MS, they describe the analysis of secondary metabolite patterns.
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Preparative Chromatography with Improved LoadabilityThe authors show that the loadability and throughput of ionizable compounds can be enhanced by using hybrid packings.
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A GC–MS Purge-and-Trap Method Comparison Study for MTBE Analysis in GroundwaterThis article describes a study that assesses the ability of commercially available GC–MS methods to meet project criteria for MTBE in groundwater matrices.
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The Application of Multiplexed Microemulsion Electrokinetic Chromatography for the Rapid Determination of log POW Values for Neutral and Basic CompoundsThis article illustrates the use of multiplexed microemulsion electrokinetic chromatography with UV detection to develop a rapid approach for obtaining log POW values of neutral and basic compounds.
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Influence of Na+- and K+- Concentration in Solvents on Mass Spectra of Peptides in LC/ESI–MSIn this article, the authors examine the concentration-dependent influence of Na+- and K+ ions on mass spectra of peptides, with human gastrin as a model peptide using LC/ESI–MS as the selected ionization technique.
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Influence of Na+- and K+- Concentration in Solvents on Mass Spectra of Peptides in LC/ESI–MSIn this article, the authors examine the concentration-dependent influence of Na+- and K+ ions on mass spectra of peptides, with human gastrin as a model peptide using LC/ESI–MS as the selected ionization technique.
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Determination of Diethylene Glycol in Sorbitol Solutions Used for Pharmaceutical FormulationsIngestion of DEG-adulterated glycerin excipients in pharmaceuticals and personal care products, such as toothpaste, mouth wash and medicinal syrups has caused systemic alcohol intoxication, acidosis and subsequent multiorgan failure that have led to hundreds of fatalities of children and adults.
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Optimizing Flavour Analysis Using Modern Heart-Cutting MDGCThis review discusses recent technological advances in classical heart-cuttting two-dimensional gas chromatography (GC–GC). These developments are then illustrated by application to analysis of important flavour compounds at trace levels in very complex matrices
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New Chromatography Columns and Accessories for 2015Volume 33 Number 4Pages 234-247This is our annual review of new liquid chromatography (LC) columns and accessories introduced at Pittcon and throughout the previous year. This year, Michael Swartz, former author of our "Innovations in HPLC" and "Validation Viewpoint" columns, steps in as a guest columnist to write the review.
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Ahuja Award Session Demonstrates the Significance of Analytical Extraction TechniquesProf. Emanuela Gionfriddo of the University of Toledo, in Ohio, is the recipient of the ACS Analytical Division 2023 Satinder Ahuja Award for Young Investigators in Separation Science, which was presented to her at Pittcon 2023. The purpose of this award is to recognize and encourage outstanding contributions to the fields of analytical chemistry by a young analytical scientist based on or more of the following criteria: conceptualization and development of unique instrumentation for separations; development of novel and important separation methods or methodologies; elucidation of theory or fundamental processes involved in separations; and other significant contributions to the furtherance of separation science role in the use of chemical instrumentation. Read more about this award session here.
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Standardizing Proteomics: Results of a Collaborative StudyA multilaboratory collaborative study organized by the Human Proteome Organization demonstrated that participating laboratories had difficulty in identifying components of a simple protein mixture.
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Lloyd R. Snyder (1931-2018): A Personal TributeLloyd Snyder was one of perhaps ten “founding fathers” of high performance liquid chromatography (HPLC), with seminal publications in most areas, including adsorption (normal phase), reversed phase, isocratic, gradient, and preparative chromatography; plus solvent, temperature, and column selectivity. With nine books, several hundred publications, and an h-index of 83, he was one of the most widely cited chromatographers and received many of the most prestigious awards in separation science.
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Characterization of Allergens in Cosmetics by GC×GC–TOF-MS with Variable-Energy Electron IonizationThe detection and quantitation of allergens in complex cosmetics extracts using two-dimensional gas chromatography–time-of-flight mass spectrometry (GC×GC–TOF-MS) is described. In particular, variable-energy electron ionization is shown to enhance both the sensitivity and selectivity of analyses by generating mass spectra containing structurally significant fragment ions with an improved molecular ion signal.
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An Introduction to OPLC Operation and ApplicationsThis article describes the basis of OPLC and its instrumentation, and provides brief details of recent applications for which this technique is suited.
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Parallel Chromatography — Double Your MoneyIn this month's instalment, the authors cover the topics of column-switching techniques and parallel chromatography for LC?MS?MS methods, and describe the time benefits that can be achieved using such systems. An example set-up is presented and the authors outline the various steps required to perform such analyses routinely.
