Basics Of Gas Chromatography Mass Spectrometry System
Raquel Cumeras, Xavier Correig in Volatile organic compound analysis in biomedical diagnosis applications, 2018
The column film thickness and the internal diameter of the GC column will also strongly influence the retention factor (k) and the resulting resolution. The retention factor is the time required for the target analyte spent in the stationary phase relative to the mobile phase. A combination of low internal column diameter and high film thickness will results in increase retention; however, this effect is attenuated by increasing temperature (Grob and Barry, 2004; Detter-Wlide and Engewald, 2014). For highly volatile compounds increase retention is often required for optimal chromatographic separation, in such instances, it is necessary to use a column with a higher film thickness so that the compound will spend more time in the stationary phase. For high molecular weight compounds, a lower film thickness is preferred as this reduces the length of the time that the compounds are retained by the stationary phase and also reduce the effect of column bleeding at a higher temperature. GC column with a higher film thickness will inherently suffer from a higher rate of column bleed and reduces operating temperature limits.
Use of Linear Retention Indices in GC-MS Libraries for Essential Oil Analysis
K. Hüsnü Can Başer, Gerhard Buchbauer in Handbook of Essential Oils, 2020
As is well known and reported by Poole, the retention of analytes in gas chromatographic capillary columns results from the differential distribution (partition) of the solutes between the stationary liquid and the mobile gas phases (Poole, 2003). A compound's retention behavior on a specific column is characterized by three parameters: retention time (tR), retention factor (k), and relative retention (r).
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
Thin-layer chromatography is used for the characterization of natural compounds by a qualitative and quantitative manner. The major principles of thin-layer chromatography are adsorption or partition or both depending upon the adsorbent (stationary phase) and solvent (mobile phase). Silica gel, alumina, cellulose powder, kieselguhr, and Sephadex gel are used as the stationary phase. The mobile phase is carbon tetrachloride, benzene, ethyl acetate, dichloromethane, hexane, chloroform, ethanol, and water. The chemical components having an efficient affinity to stationary phase travel slower, whereas the components with a lower affinity toward the stationary phase travel faster. A stationary phase is used as a silica gel coated strip and organic solvents are play as mobile phases. The adsorbent is loaded on thin glass/sheet/plastic and it acts as a stable phase. About ~25 mm thickness coating on the glass plate was used for thin-layer chromatography. Plaster of Paris is used as a binder to makes coating of adsorbent. After the preparation of plates, all the plates are activated by keeping it in 100ºC for 3 hr. The organic solvent are spotted at the bottom of the stationary phase. The solvent or mixture of solvent is allowed to move up to the plate by capillary action. The compounds are separated with respect to its affinity, size, and charge. Retardation factor (Rf) value (distance traveled by solute/distance traveled by solvent front) is used as a characteristic parameter in thin-layer chromatography. However, the nature of adsorbent, mobile phase, the thickness of layer, temperature, and sample loading are the critical factors and it can alter the Rf value. Thin-layer chromatography separates the components into the individual by using a finely divided adsorbent (solid/liquid) spread over a plate. The technique is employed under temperature and pressure-controlled laboratory. Thin-layer chromatography provides many advantages over other chromatography, i.e., (i) non-volatile/low volatile chemical compounds able to analyzed; (ii).
Aspergillus ochraceopetaliformis SSP13 modulates quorum sensing regulated virulence and biofilm formation in Pseudomonas aeruginosa PAO1
Published in Biofouling, 2018
Subhaswaraj Pattnaik, Tanveer Ahmed, Sampath Kumar Ranganathan, Dinakara Rao Ampasala, V. Venkateswara Sarma, Siddharha Busi
The crude extract of SSP13 was subjected for HPTLC for partial separation of bioactive compounds. The crude extract was spotted onto pre-coated TLC silica gel plate (TLC silica gel 60 F254, Merck, Darmstadt, Germany) using an automated sampler (CAMAG TLC Sampler, Muttenz, Arlesheim, Switzerland). The spotted TLC plate was eluted in an elution system of dichloromethane and methanol (9:1). The developed chromatogram was air dried and visualized in a UV chamber (CAMAG TLC Visualizer) at 254 nm. The developed chromatogram was scanned for clearly resolved bands and the corresponding Rf (Retention factor) values was calculated (CAMAG TLC Scanner 4). For preliminary bioactivity study, the resolved bands were scrapped and tested against P. aeruginosa PAO1 (Zeeshan et al. 2012; Murali et al. 2017).
Sauromatum guttatum extract promotes wound healing and tissue regeneration in a burn mouse model via up-regulation of growth factors
Published in Pharmaceutical Biology, 2019
Ali Said, Fazli Wahid, Kashif Bashir, Hafiz Majid Rasheed, Taous Khan, Zohaib Hussain, Sami Siraj
It is important to know the phytochemical composition of any plant extract before evaluating its pharmacological activities. Therefore, the chemical composition of S. guttatum crude extract was evaluated. The results indicated the presence of flavonoids, saponins, phytosterols, phenols, tannins and alkaloids, but glycosides and proteins were not detected as shown in Table 2. To confirm the presence of various compounds in the extract, TLC analysis was carried out. The TLC chromatogram and retention factor (Rf) values of various compounds from A to E of the extract are shown in Figure 1. TLC chromatogram of crude extract showed various spots and Rf values as shown in Figure 1 are A (0.07), B (0.26), C (0.36), D (0.77) and E (0.84). HPLC analysis of the crude extract derived from S. guttatum showed the appearance of four major and various minor peaks (Figure 2). The major peaks appeared at retention time of 2.96, 21.5, 28.9 and 35.67 min.
Hair dye and risk of skin sensitization induction: a product survey and quantitative risk assessment for para-phenylenediamine (PPD)
Published in Cutaneous and Ocular Toxicology, 2020
Kevin M. Towle, Ruth Y. Hwang, Ernest S. Fung, Dana M. Hollins, Andrew D. Monnot
According to the EU Scientific Committee on Consumer Safety cosmetic ingredient safety evaluation guidance documents for evaluating dermal exposure to oxidative/permanent hair dyes, it is recommended to assume that 1% of the hair dye product remains on the skin as a residue post-rinsing (i.e. a retention factor), and could therefore be available for uptake23. Thus, for purposes of this assessment, a retention factor of 1% was applied to all CEL calculations. Additionally, a dermal absorption factor (DA) of 3.71% for PPD was applied to all CEL calculations. This value is based on results from an in vitro percutaneous absorption/penetration study, where human skin samples were coated with a hair dye containing [14C]-labeled PPD24. Twenty-four hours after application, 3.71% of the applied radioactivity was located in the stratum corneum, epidermis, dermis, and receptor liquid24. Lastly, the surface area of an adult human scalp has been reported to be 800 cm225.
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