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Use of Linear Retention Indices in GC-MS Libraries for Essential Oil Analysis
Published in K. Hüsnü Can Başer, Gerhard Buchbauer, Handbook of Essential Oils, 2020
Emanuela Trovato, Giuseppe Micalizzi, Paola Dugo, Margita Utczás, Luigi Mondello
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).
Basics Of Gas Chromatography Mass Spectrometry System
Published in Raquel Cumeras, Xavier Correig, Volatile organic compound analysis in biomedical diagnosis applications, 2018
William Hon Kit Cheung, Raquel Cumeras
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.
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.
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.
RF-energised intracoronary guidewire to enhance bipolar ablation of the interventricular septum: in-silico feasibility study
Published in International Journal of Hyperthermia, 2018
Juan J. Pérez, Ana González-Suárez, Andre d’Avila, Enrique Berjano
Figure 1 shows the physical study set-up, which consists of an interventricular septum ablation using two irrigated-tip electrodes placed on opposing sides of the septal wall surface and an endovascular metallic guidewire (0.35 mm diameter) placed inside the septal wall. Both irrigated-tip electrodes and the guidewire could be connected to a programmable switch controller to allow selecting “bipolar”, “guide” and “time-division multiplexing” (TDM) ablation modes. The bipolar mode consists of applying energy between both irrigated-tip electrodes, one of which is active and the other dispersive, whereas the guidewire remains passive (non RF-energised). The guide mode consists of applying RF energy only, using the metal zone of the guidewire, while both irrigated-tip electrodes act as dispersive electrodes. Finally, TDM mode consists of combining bipolar and guide mode once a second. In TDM mode, the bipolar pattern is activated for a fraction of the time (90%) and the RF-energised guidewire for the remainder (10%) of each second. In this way the switching frequency between patterns is 1 Hz, i.e. in a given second the bipolar ablation is conducted for the first 900 ms and RF-energised guidewire in the remaining 100 ms.