Qualitative and quantitative comparison of different commercially available 1-84 parathyroid hormone proteins to the WHO international standard 95/646 using orthogonal methods

Relative quantitation methods rely on the use of reference substances to determine the content of samples. The aim of this study was to compare 1-84 parathyroid hormone (PTH) standards from different manufacturers to the WHO international standard 95/646. CE and LC with UV detection were investigated as quick and inexpensive quantitation methods, with an emphasis on selectivity between intact 1-84 PTH and its oxidized forms. Both methods were fully validated according to ICH Q2R1. Moreover, method performance was also evaluated according to guidelines defining the maximum allowable measurement uncertainty (MU) of a biological parameter from its intraindividual variation (CV_I), as well as the proportion of that MU devoted to the reference material. This study highlighted the fact that some 1-84 PTH standards have a content that is actually twice as high as the one stated on the label, which was confirmed by an amino acid analysis investigation. Our approach offers a quick and inexpensive way to estimate the content of 1-84 PTH standards.

Development and validation of a fast and reliable method for the quantification of glucagon by liquid chromatography and tandem mass spectrometry

INTRODUCTION

The quantitation of glucagon remains a challenging immunoassay, mainly due to cross-reactivity. A sensitive, rapid and specific intact glucagon method is therefore necessary for quality routine analysis. A tandem mass spectrometry method to fulfill this objective is described in this work.

METHODS

Glucagon was extracted from plasma employing a mixed-mode anion exchange solid-phase extraction. Sample stability was assessed in K2-EDTA and P800 tubes at different temperatures. We compared our method to two different immunoassays. FDA and EMA guidelines were followed for validation. An external quality control program served for comparison with other laboratories.

RESULTS

Assay imprecision was below 4%. Recoveries were within 95-103%. LoQ was 8.75 pg/mL. Total analytical CV was 2.91%. Samples were found stable at 4 °C for less than 4 h. Diasource® RIA disagreed with our method. Mercodia® ELISA provided a closer agreement, also proven by external quality control samples.

CONCLUSIONS

A rapid and specific LC-MS/MS method for glucagon quantitation has been developed, validated and is suitable to routine care. The simplicity and the good performances in terms of time and specificity, could open the possibility to establish a standardized method for glucagon.

Capillary Electrophoresis-Mass Spectrometry at Trial by Metabo-Ring: Effective Electrophoretic Mobility for Reproducible and Robust Compound Annotation

Capillary zone electrophoresis-mass spectrometry (CE-MS) is a mature analytical tool for the efficient profiling of (highly) polar and ionizable compounds. However, the use of CE-MS in comparison to other separation techniques remains underrepresented in metabolomics, as this analytical approach is still perceived as technically challenging and less reproducible, notably for migration time. The latter is key for a reliable comparison of metabolic profiles and for unknown biomarker identification that is complementary to high resolution MS/MS. In this work, we present the results of a Metabo-ring trial involving 16 CE-MS platforms among 13 different laboratories spanning two continents. The goal was to assess the reproducibility and identification capability of CE-MS by employing effective electrophoretic mobility (μeff) as the key parameter in comparison to the relative migration time (RMT) approach. For this purpose, a representative cationic metabolite mixture in water, pretreated human plasma, and urine samples spiked with the same metabolite mixture were used and distributed for analysis by all laboratories. The μeff was determined for all metabolites spiked into each sample. The background electrolyte (BGE) was prepared and employed by each participating lab following the same protocol. All other parameters (capillary, interface, injection volume, voltage ramp, temperature, capillary conditioning, and rinsing procedure, etc.) were left to the discretion of the contributing laboratories. The results revealed that the reproducibility of the μeff for 20 out of the 21 model compounds was below 3.1% vs 10.9% for RMT, regardless of the huge heterogeneity in experimental conditions and platforms across the 13 laboratories. Overall, this Metabo-ring trial demonstrated that CE-MS is a viable and reproducible approach for metabolomics.