Instrumental Limits Of Quantification Research Articles

Fast separation liquid chromatography–tandem mass spectrometry for the confirmation and quantitative analysis of avermectin residues in food

A new residue analytical method for the confirmation and quantification of avermectin residues in food is described in this article. This method allows a fast analysis for the determination of avermectin residues, abamectin (ABM), ivermectin (IVM), emamectin benzoate (EMA) and doramectin (DOR) by liquid chromatography–tandem mass spectrometry (LC–MS/MS). Separation was performed using a short column of 1.8 μm particle size.The hybrid quadrupole/linear ion trap (QqQ LIT) system via the linearly accelerating (LINAC) high-pressure collision cell, allows the MS detection in multiple reaction monitoring (MRM) mode operating in fast scan acquisition times. The effect of reduced dwell times on mass spectral quality and sensitivity is evaluated in this study. For quantitative purposes, the influence of dwell time on S/N ratio and peak area was observed. ABM, IVM, EMA and DOR show an increased trend of peak area and S/N ratio, when dwell times are of 50 ms against 10–20 ms, suited when the number of compounds to be analyzed is higher. The sensitivity achieved by using the LC–MS/MS system is enough for the confirmation of avermectin residues in the selected commodities (salmon muscle and pepper) at trace concentration levels (sub-μg/kg and μg/kg) and therefore a sample pre-concentration step was not necessary. The instrumental limits of quantification (ILQ) are in the range of 0.15–5 ppb. Samples were extracted by solid–liquid extraction (SLE) procedure using acetonitrile, and cleaned-up using alumina. The average recoveries obtained were acceptable (80–95%). The calibration curves were linear over the working range from ILQs to 500 μg/kg. For the quantitative analysis, matrix-matched calibration and dilution of SLE extracts was proven as reliable alternative to compensate matrix-effects and for its feasible application in routine analysis.

A simple and rapid ion-pair HPLC method for simultaneous quantitation of 4-nitrophenol and its glucuronide and sulfate conjugates

Because of its simple and well characterized metabolic profile, 4-nitrophenol is widely used as a model substrate to investigate the influence of drug therapy, disease, nutrient deficiencies and other physiologically altered conditions on conjugative drug metabolism in animal studies. For simultaneous determination of 4-nitrophenol (PNP), 4-nitrophenyl-β- d-glucuronide (PNP-G) and 4-nitrophenyl-sulfate (PNP-S) in samples generated in rat small intestine luminal perfusion experiments, an ion-pair HPLC assay coupled with UV detection was set up. The RP-HPLC separation was achieved with a methanol–water mixture (50:50, v/v) containing 0.01 M tetrabutyl-ammonium-bromide with UV detection of the analytes at 290 nm. The isocratic system was operated at ambient temperature and required less than 7 min of chromatographic time. The method provided good enough within-day precision, between-day precision and linearity in the target concentration ranges of 6–1200 μM (PNP) and 2.5–100 μM (PNP-G and PNP-S). The instrumental limit of quantification for PNP-G and PNP-S was found to be 2.7 μM and 2.1 μM, respectively. The assay was applied for determination of PNP, PNP-G and PNP-S in rat small intestine perfusates.

A multiresidue analytical method using solid-phase extraction and high-pressure liquid chromatography tandem mass spectrometry to measure pharmaceuticals of different therapeutic classes in urban wastewaters

An analytical method with two extraction steps has been developed and validated for the simultaneous determination of 30 pharmaceuticals belonging to various therapeutic categories in urban wastewater. The aim was to boost the little available information on drugs’ fates in sewage treatment plants (STPs) and in the receiving surface water. Aqueous samples were divided into two aliquots, each extracted by a different solid-phase extraction (SPE) method and analysed by reversed-phase liquid chromatography tandem mass spectrometry (HPLC–MS–MS). Recoveries of the pharmaceuticals were mostly greater than 70% and the overall variability of the method was below 8%. The instrumental quantification limit (IQL) varied between 30 and 400 pg injected, and the limits of quantification (LOQ) were in the low ng/L range. Nineteen pharmaceuticals were detected in concentrations between 0.5 and 2000 ng/L in effluents collected from several STPs in Italy. Atenolol, ciprofloxacin, furosemide, hydrochlorothiazide, ofloxacin, ranitidine and sulphamethoxazole were the most abundant compounds. The present analytical method was useful to check for pharmaceuticals in various Italian STPs and to identify the most abundant compounds.

Trace determination of fluoroquinolone antibacterial agents in urban wastewater by solid-phase extraction and liquid chromatography with fluorescence detection.

Fluoroquinolones (FQs) are among the most important antibacterial agents (synthetic antibiotics) used in human and veterinary medicine. An analytical method based on reversed-phase liquid chromatography with fluorescence detection was developed and validated for the simultaneous determination of nine FQs and the quinolone pipemidic acid in urban wastewater. Aqueous samples were extracted using mixed-phase cation-exchange disk cartridges that were subsequently eluted by ammonia solution in methanol. Recoveries were above 80% at an overall precision of better than 10%. Instrumental quantification limits varied between 150 and 450 pg injected. The presented method was successfully applied to quantify FQs in effluents of urban wastewater treatment plants. The two most abundant human-use FQs, ciprofloxacin and norfloxacin, occurred in primary and tertiary waste-water effluents at concentrations between 249 and 405 ng/L and from 45 to 120 ng/L, respectively. The identity of FQs in urban wastewater was confirmed by recording full fluorescence spectra and liquid chromatography directly coupled to tandem mass spectrometry. These results indicate that conventional environmental risk assessment overestimates FQ concentrations in surface waters by 1 to 2 orders of magnitude.