Search

An isotope pattern deconvolution (IPD) quantification method has been applied for the determination of five substances (amphetamine, benzoylecgonine, cocaine, methamphetamine and MDMA) in wastewater for the application in wastewater-based epidemiology (WBE). A previously validated method that used a calibration curve for quantification was modified to apply IPD. The two approaches were compared in terms of analytical uncertainty in recovery studies of quality control samples, i.e. six wastewater samples from different geographical origins spiked at two concentration levels. Both methods were reliable as they passed (z-score < 2) in an interlaboratory exercise. After 60 individual determinations, IPD provided 11 results outside recovery limits (70-120%) while the previous method produced 31 adverse results. All mean values for IPD were accurate whereas 6 out of 10 results showed RSD values higher than 30% or recoveries outside limits when using the former method. Moreover, the calculated method bias for the latter doubles that of IPD, which, in turn, makes the combined uncertainty (u(c)) much higher. Consequently, a simple change of data treatment-IPD quantification methodology-resulted in a lower uncertainty of the estimated illicit drug concentration, one of the main steps contributing to the final uncertainty in the normalized daily drug consumption through WBE. The current study demonstrated that the employment of IPD can also be very interesting for future applications of WBE, especially when matrix effects are high, complicating accurate quantification. In addition, when a high number of samples and/or compounds need to be analysed, IPD is faster than calibration and, eventually, cost-effective when isotopically labelled internal standard is highly expensive.

A Liquid Chromatography coupled to tandem mass spectrometry (LC-MS/MS) based method have been developed for the determination of the main estrogen compounds -estrone (E1) and 17β-estradiol (E2)- in human serum. Two isotope dilution mass spectrometry (IDMS) quantification procedures have been used: a classical calibration curve-based method were compared to a recently developed isotope pattern deconvolution (IPD) method. IPD is based on isotopic abundance measurements and multiple linear regression. Validation was performed in terms of intra-assay repeatability (n = 5), inter-assay reproducibility (n = 9) and accuracy using spiked steroid-free serum at 5 concentration levels and 3 certified reference materials. Both methodologies meet EMEA requirements yielding recoveries between 79-106% and coefficient of variations of 1.7-8.3% along all experiments. Limits of quantification as low as 5 ng/L were achieved. 40 real samples were analysed for comparison purposes showing a great correlation between calibration and IPD concentration values. Real samples were also quantified by routine immunoassay analysis, which showed a significant proportional bias of 2.55 for E1 and good correlation for E2. While methods were considered suitable for routine or countercheck analysis within the context of hospital's needs, IPD has demonstrated to be faster and cost saving., (Copyright © 2019 Elsevier B.V. All rights reserved.)

In this work, a method for the separation of triacylglycerols (TAGs) present in human milk and from other mammalian species by reversed-phase high-performance liquid chromatography using a core-shell particle packed column with UV and evaporative light-scattering detectors is described. Under optimal conditions, a mobile phase containing acetonitrile/n-pentanol at 10 °C gave an excellent resolution among more than 50 TAG peaks. A small-scale method for fat extraction in these milks (particularly of interest for human milk samples) using minimal amounts of sample and reagents was also developed. The proposed extraction protocol and the traditional method were compared, giving similar results, with respect to the total fat and relative TAG contents. Finally, a statistical study based on linear discriminant analysis on the TAG composition of different types of milks (human, cow, sheep, and goat) was carried out to differentiate the samples according to their mammalian origin.