PubMed · 8432034
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L E Preshaw. 1993. The reference range as a control.. https://pubmed.ncbi.nlm.nih.gov/8432034/
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The use of a programmed temperature vaporiser (PTV) with a packed liner was evaluated for the injection of large volumes (up to 100 microl) of plasma extracts in a gas chromatograph. Solvent purity, which is essential when large volumes are injected into the GC system, was determined. Special attention was paid to the purity of the solvents used for the solid-phase extraction (SPE) procedure. For this SPE method, ethyl acetate was used as the extraction and reconstitution solvent, and thus the purity of the ethyl acetate was critical, especially when a non-selective GC detector was applied. The liquid capacity and inertness of different packed liners were investigated. The liner packed with ATAS "A" (modified Chromosorb-based material with special treatment) was found to be the most suitable for the analysis of the tested drugs. Good linearity in response for variations in volume and concentration was observed. A comparison was made between the applicability of flame ionisation detection (FID) and mass-selective detection (MSD). When 50-microl volumes of plasma extracts were injected with the PTV, the detection limits for secobarbital, lidocaine, phenobarbital and diazepam were about 50-times lower than when 1-microl volumes were injected. The detection limits of the tested compounds in plasma for injection of 50-100 microl plasma extract are 5-10 ng/ml for GC-FID whereas plasma concentrations of 250 pg/ml can be detected using the selected ion monitoring (SIM) mode of a MSD. For non-selective GC-FID, the background from a 50-microl injection was substantially larger than with 1-microl injection as a result of co-injected plasma matrix components and solvent impurities. These background effects were less with GC-MSD in the total ion current mode and virtually absent with GC-MSD in the SIM mode.
A review of subject literature suggests management strategies for the treatment of dyspepsia to be characterised by marked differences. In some strategies the possibility of indirect Helicobacter pylori testing (e g, breath tests) is ignored and endoscopy recommended as the only appropriate investigation; only those with verified disease are treated, and the risk of antibiotic overuse is minimised. In other strategies, indirect H pylori testing is recommended for younger patients (< 45 years of age) without alarming symptoms, either to select patients for endoscopy or to eradicate the infection (i.e., irrespective of whether the patient has peptic ulcer disease or not, on the grounds that the risk of having or developing such disease is thus minimised. The article consists in discussion of the different strategies, and suggests a choice of investigations tailored to the needs of the individual patient to be preferable to dogmatic adoption of either approach, though endoscopy should be available without delay if required. Moreover, the accuracy of the various indirect H pylori tests needs to be considered. To be acceptable for use in primary care, it is suggested that recommendations regarding interventions for the various disorders associated with dyspepsia should be characterised by reasonably comparable risk levels. An algorithm with alternative strategies suited to available facilities and the patient's needs and wishes is also presented.