Gas Chromatography
Joseph Chamberlain in The Analysis of Drugs in Biological Fluids, 2018
The two methods of chromatography described earlier employ relatively simple and cheap equipment, and also have in common the fact that the final chromatogram is a complete picture of the separated components. Gas chromatography (Figure 6.1), although depending on the same basic separation principles, is characterized by continuous detection of the components eluting from the column, and the chromatogram is the recorded trace rather than the paper or the thin-layer plate (Figure 6.2). In gas chromatography the compounds to be separated are partitioned between a stationary phase, usually a high-boiling liquid coated onto an inert support (such as celite, diatomaceous earth, firebrick, etc.) and the gaseous carrier gas. The variable parameters affecting separation in gas chromatography are: (1) the temperature of the column, usually maintained in a thermostated oven; (2) the flow rate of the carrier gas; and (3) the nature of the stationary phase. Although gas-solid chromatography has been described (where the absorption of solute onto a solid surface is the separation determinant), this technique has not found general application in the analysis of drugs.
Current Perspectives and Methods for the Characterization of Natural Medicines
Rohit Dutt, Anil K. Sharma, Raj K. Keservani, Vandana Garg in Promising Drug Molecules of Natural Origin, 2020
Chromatography is a major method for the separation of bioactive products from natural resources. This technique works based on the distribution of molecules in different phases. The natural compounds are distributed into two different phases, i.e. stationary phase and mobile phase. Based on the relative distribution of the chemical constituents, the constituents are separated. Chromatography is functioning by different methods: (i) column/adsorption chromatography; (ii) partition chromatography; (iii) paper chromatography; (iv) thin-layer chromatography; (v) gas-liquid chromatography; (vi) gas-solid chromatography; and (vii) ion-exchange chromatography. The parameters such as retention factor, selectivity, efficiency, retention time, and peak area are investigated for the structural characterization of marine products based on chromatography. Different types of chromatography techniques employed in the isolation and characterization of phytochemicals and marine constituents are tabulated in Table 2.1.
Adulteration of Essential Oils
K. Hüsnü Can Başer, Gerhard Buchbauer in Handbook of Essential Oils, 2020
Gas chromatography is one of the most widely deployed methods in analytical chemistry to investigate organic sample material due to its simple ease of use, the ready availability of sophisticated inexpensive instrumentation, and the large amount of qualitative and quantitative information that can be retrieved if the appropriate configuration is employed. Especially the high separation efficiency for volatiles makes GC very suitable to investigate complex mixtures and sample matrices. But for some applications, the separation performance is not sufficient when it comes to very complex mixtures like odors, flavors, crude oil products, and foodstuff. Co-elution with other analytes or sample matrix elements causes problems in detection and quantitation especially when the analytes differ greatly in their concentration. This problem can be solved by cutting out the co-eluting part of the chromatogram and a subsequent second chromatographic separation of the excised effluent preferably on a stationary phase of different polarity. This technique, called heart-cutting or two-dimensional GC (2D GC or GC-GC), is done with the help of a diverting valve or a Deans switch. The sought-after substances are then resolved in the second GC column.
A randomized trial comparing omega-3 fatty acid plasma levels after ingestion of emulsified and non-emulsified cod liver oil formulations
Published in Current Medical Research and Opinion, 2019
Nelly Conus, Nicola Burgher-Kennedy, Frans van den Berg, Gurleen Kaur Datta
The present study had multiple strengths, including the use of a closely matched non-emulsified formulation that provided similar doses of DHA and EPA as the test formulation (both formulations contained 10% cod liver oil and 10% cod oil), which was expected to limit any potential dose-related effects on DHA and EPA concentrations. In addition, efforts were made to limit the participants’ dietary intake of omega-3-rich foods before and during the study period. Use of a crossover design limited inter-subject variability by allowing subjects to serve as their own control group, and the study used a robust statistical analysis plan. Variations between the formulations (e.g. different volumes used in the emulsified and non-emulsified formulations and doses of vitamin A) were not expected to impact DHA and EPA pharmacokinetics. Moreover, an identical volume of apple juice was consumed with both formulations after dosing to reduce differences in post-dose stomach volume. It is also worth noting that some prior studies in this area have used gas chromatography19,22,23, but the decision to use liquid chromatography in the current study was based on the assumption that it is a validated methodology and, as such, would provide accurate results. The tests were also performed in an ISO-certified laboratory.
Serum and plasma amino acids as markers of prediabetes, insulin resistance, and incident diabetes
Published in Critical Reviews in Clinical Laboratory Sciences, 2018
C. Gar, M. Rottenkolber, C. Prehn, J. Adamski, J. Seissler, A. Lechner
Modern gas and liquid chromatography of amino acids are still conducted primarily on ion-exchange and reverse-phase columns [49,50], but now usually coupled with high resolution mass spectrometry (MS) to analyze the effluent [49,51–55]. Gas chromatography is used less frequently today because it is only suitable for volatile yet thermo-stable molecules. Instead, high performance liquid chromatography (HPLC) is used widely in the metabolomics field. It maintains high sensitivity and quantitative reproducibility without a mandatory need for chemical derivatization [51]. Stationary phases can now be manufactured from very small particles of about 2 µm diameter that enhance specificity and sensitivity with a higher peak capacity compared to standard HPLC columns. This technique is usually recognized as ultra-high performance liquid chromatography (UHPLC) [56–59].
Real-time quantitative monitoring of in vitro nasal drug delivery by a nasal epithelial mucosa-on-a-chip model
Published in Expert Opinion on Drug Delivery, 2021
Hanieh Gholizadeh, Hui Xin Ong, Peta Bradbury, Agisilaos Kourmatzis, Daniela Traini, Paul Young, Ming Li, Shaokoon Cheng
Organ-on-chip technology has enhanced in vitro studies of drugs by providing physiologically relevant microenvironments that closely match the corresponding organs of interest, with the ultimate goal of reducing the drug development time and improving the success rate of clinical trials. These miniature devices are cost-effective as they enable high throughput drug screening and drug response to be tested with low reagent consumption [1]. Moreover, organ-on-chips can facilitate the screening of biological and chemical parameters in the cellular microenvironment by incorporating sensing technologies [2]. This can offer in situ monitoring alternatives to conventional assays and simplified assays without the need for sample collection and preparation and by using significantly less reagents. Electrochemical analytical methods are potential techniques that can be incorporated into organ-on-chip devices to enable in situ analyte detection. However, the conventional techniques such as high-performance liquid chromatography (HPLC) and gas chromatography, known for highly precise and selective measurements, are time-consuming due to sample preparation/derivatization and require large volumes of organic solvents, which results in their high cost of use [3]. Despite the progress in organ-on-chips technology, there remains a scarcity of knowledge of how organ-on-chip devices can be effectively extended as in situ sensing platforms for the quantitative monitoring of pharmaceutical compounds transport across the cell layers in drug delivery assessments.
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