Govert W. Somsen

CE-MS for metabolomics: developments and applications in the period 2014-2016.

This review provides an update of the state‐of‐the‐art of CE‐MS for metabolomic purposes, covering the scientific literature from July 2008 to June 2010. This review describes the different analytical aspects with respect to non‐targeted and targeted metabolomics and the new technological developments used in CE‐MS for metabolomics. The applicability of CE‐MS in metabolomics research is illustrated by examples of the analysis of biomedical and clinical samples, and for bacterial and plant extracts. The relevant papers on CE‐MS for metabolomics are comprehensively summarized in a table, including, e.g. information on sample type and pretreatment, and MS detection mode. Future considerations such as challenges for large‐scale and (quantitative) clinical metabolomics studies and the use of sheathless interfacing and different ionization techniques are discussed.

Relevance and use of capillary coatings in capillary electrophoresis–mass spectrometry

Over the last two decades, coupled capillary electrophoresis (CE)–mass spectrometry (MS) has developed into a generally accepted technique with a wide applicability. A growing number of CE-MS applications make use of capillaries where the internal wall is modified with surface coating agents. In CE-MS, capillary coatings are used to prevent analyte adsorption and to provide appropriate conditions for CE-MS interfacing. This paper gives an overview of the various capillary coating strategies used in CE-MS. The main attention is devoted to the way coatings can contribute to a proper CE-MS operation. The foremost capillary coating methods are discussed with emphasis on their compatibility with MS detection. The role of capillary coatings in the control of the electroosmotic flow and the consequences for CE-MS coupling are treated. Subsequently, an overview of reported applications of CE-MS employing different coating principles is presented. Selected examples are given to illustrate the usefulness of the coatings and the overall applicability of the CE-MS systems. It is concluded that capillary coatings can enhance the performance and stability of CE-MS systems, yielding a highly valuable and reproducible analytical tool.

The Trehalose 6-Phosphate/SnRK1 Signaling Pathway Primes Growth Recovery following Relief of Sink Limitation

The T6P/SnRK1 mechanism of growth regulation responds to sink growth restriction and recovery following low-temperature limitation. Trehalose 6-P (T6P) is a sugar signal in plants that inhibits SNF1-related protein kinase, SnRK1, thereby altering gene expression and promoting growth processes. This provides a model for the regulation of growth by sugar. However, it is not known how this model operates under sink-limited conditions when tissue sugar content is uncoupled from growth. To test the physiological importance of this model, T6P, SnRK1 activities, sugars, gene expression, and growth were measured in Arabidopsis (Arabidopsis thaliana) seedlings after transfer to cold or zero nitrogen compared with sugar feeding under optimal conditions. Maximum in vitro activities of SnRK1 changed little, but T6P accumulated up to 55-fold, correlating with tissue Suc content in all treatments. SnRK1-induced and -repressed marker gene expression strongly related to T6P above and below a threshold of 0.3 to 0.5 nmol T6P g−1 fresh weight close to the dissociation constant (4 µm) of the T6P/ SnRK1 complex. This occurred irrespective of the growth response to Suc. This implies that T6P is not a growth signal per se, but through SnRK1, T6P primes gene expression for growth in response to Suc accumulation under sink-limited conditions. To test this hypothesis, plants with genetically decreased T6P content and SnRK1 overexpression were transferred from cold to warm to analyze the role of T6P/SnRK1 in relief of growth restriction. Compared with the wild type, these plants were impaired in immediate growth recovery. It is concluded that the T6P/SnRK1 signaling pathway responds to Suc induced by sink restriction that enables growth recovery following relief of limitations such as low temperature.

Quality of original and biosimilar epoetin products.

ABSTRACTPurposeTo compare the quality of therapeutic erythropoietin (EPO) products, including two biosimilars, with respect to content, aggregation, isoform profile and potency.MethodsTwo original products, Eprex (epoetin alfa) and Dynepo (epoetin delta), and two biosimilar products, Binocrit (epoetin alfa) and Retacrit (epoetin zeta), were compared using (1) high performance size exclusion chromatography, (2) ELISA, (3) SDS-PAGE, (4) capillary zone electrophoresis and (5) in-vivo potency.ResultsTested EPO products differed in content, isoform composition, and potency.ConclusionOf the tested products, the biosimilars have the same or even better quality as the originals. Especially, the potency of originals may significantly differ from the value on the label.

CE-MS for metabolomics: Developments and applications in the period 2010-2012: CE and CEC

CE‐MS has emerged as a powerful technique for the profiling of (highly) polar and charged metabolites in biological samples. This review provides an update of the most recent developments in CE‐MS for metabolomics covering the scientific literature from July 2010 to June 2012. The present paper is an update of two previous review papers covering the years 2000–2010 (Electrophoresis 2009, 30, 276–291; Electrophoresis 2011, 32, 52–65). Emerging technological developments used in CE‐MS for metabolomics are discussed, such as the use of novel interfacing techniques for coupling CE to MS. Representative examples illustrate the applicability of CE‐MS in the fields of biomedical, clinical, microbial, plant, environmental and food metabolomics. Concerning targeted and non‐targeted approaches, a comprehensive overview of recent CE‐MS‐based metabolomics studies is given in a table. Information on sample type and pretreatment, capillary coatings and MS detection mode is provided. Finally, general conclusions and perspectives are provided.

Recent developments in coupled SPE‐CE

This article presents an overview of coupled SPE‐CE systems that have been reported in the literature between April 2007 and June 2009. The use of in‐line and on‐line SPE‐CE is covered in this review. Special attention is paid to the use of monoliths and molecularly imprinted polymers in coupled SPE‐CE systems. Application‐oriented research is discussed in which in‐line and on‐line SPE‐CE systems have been used in biomedical, pharmaceutical, environmental and food analysis. The SPE‐CE studies are presented in tables, including information on sample type, SPE sorbent, detection and LOD. Finally, some future developments that may increase the applicability of coupled SPE‐CE are highlighted.

Developments in coupled solid-phase extraction-capillary electrophoresis 2013-2015.

This article presents an overview of the design and application of coupled SPE–CE systems that have been reported in the literature between January 2011 and June 2013. The present paper is an update of three previous review papers covering the years 2000–2011 (Electrophoresis 2008, 29, 108–128; Electrophoresis 2010, 31, 44–54; Electrophoresis 2012, 33, 243–250). The use of in‐line and on‐line SPE–CE approaches is described in this review. Emerging technological developments, such as the use of in‐line frit‐free SPE and chip‐based SPE for extraction of sample components prior to CE analysis, are outlined. Selected examples illustrate the applicability of SPE–CE in biomedical, pharmaceutical, and environmental analysis. A complete overview of recent SPE–CE studies is given in table format, providing information on sample type, SPE sorbent, coupling mode, detection mode, and LOD. Finally, some general conclusions and future perspectives are provided.

Capillary electrophoresis-time of flight-mass spectrometry using noncovalently bilayer-coated capillaries for the analysis of amino acids in human urine

A capillary electrophoresis‐time of flight‐mass spectrometry (CE‐TOF‐MS) method for the analysis of amino acids in human urine was developed. Capillaries noncovalently coated with a bilayer of Polybrene (PB) and poly(vinyl sulfonate) (PVS) provided a considerable EOF at low pH, thus facilitating the fast separation of amino acids using a BGE of 1 M formic acid (pH 1.8). The PB–PVS coating proved to be very consistent yielding stable CE‐MS patterns of amino acids in urine with favorable migration time repeatability (RSDs <2%). The relatively low sample loading capacity of CE was circumvented by an in‐capillary preconcentration step based on pH‐mediated stacking allowing 100‐nL sample injection (i.e. ca. 4% of capillary volume). As a result, LODs for amino acids were down to 20 nM while achieving satisfactory separation efficiencies. Preliminary validation of the method with urine samples showed good linear responses for the amino acids (R2 >0.99), and RSDs for peak areas were <10%. Special attention was paid to the influence of matrix effects on the quantification of amino acids. The magnitude of ion suppression by the matrix was similar for different urine samples. The CE‐TOF‐MS method was used for the analysis of urine samples of patients with urinary tract infection (UTI). Concentrations of a subset of amino acids were determined and compared with concentrations in urine of healthy controls. Furthermore, partial least squares–discriminant analysis (PLS–DA) of the CE‐TOF‐MS dataset in the 50–450 m/z region showed a distinctive grouping of the UTI samples and the control samples. Examination of score and loadings plot revealed a number of compounds, including phenylalanine, to be responsible for grouping of the samples. Thus, the CE‐TOF‐MS method shows good potential for the screening of body fluids based on the analysis of endogenous low‐molecular weight metabolites such as amino acids and related compounds.

Liquid chromatography-Fourier-transform infrared spectrometry

Over the past years the coupling of liquid chromatography (LC) and Fourier-transform infrared spectrometry (FT-IR) has been pursued primarily to achieve specific detection and/or identification of sample constituents. Two approaches can be discerned in the combination of LC and FT-IR. The first and simpler approach is to use a flow cell through which the effluent from the LC column is passed while the IR spectra are continuously recorded. The second approach involves elimination of the LC solvent prior to IR detection using an interface which evaporates the eluent and deposits the analytes onto a substrate. This paper provides a general overview of flow-cell based IR detection and briefly discusses early solvent-elimination interfaces for LC-FT-IR. A more comprehensive description is given of interface systems which use spraying to induce rapid eluent evaporation, and which basically represent the state-of-the-art in LC-FT-IR. Finally, the interface systems suitable for reversed-phase LC are summarized and the perspectives of LC-FT-IR are discussed. The overview indicates that flow-cell LC-FT-IR has rather poor detection limits but can be useful for the specific and quantitative detection of major constituents of mixtures. Solvent-elimination techniques, on the other hand, provide much better sensitivity and enhanced spectral quality which is essential when unambiguous identification of low-level constituents is required.

Influence of the BGE composition on analyte response in CD‐mediated NACE‐MS

The influence of the BGE composition, including the addition of a single‐isomer sulfated β‐CD derivative, on the ionization performance of the model compound carvedilol in NACE‐ESI‐MS was studied using an alternative infusion method. This approach employs voltage‐induced infusion of the BGE containing the analyte, and takes into account the effects of variations in EOF and effective analyte mobility on the ESI‐MS intensity. First, the optimal composition of the sheath liquid for CE‐MS in terms of signal abundance and stability was determined. The BGE ammonium formate, acetate, and camphorsulfonate were found to have similar effects on analyte ionization. Addition of single‐isomer sulfated β‐CD derivatives (available as sodium salt) to the BGE revealed that the anionic CD derivatives did not give rise to the same ionization suppression effect. This result can be attributed to differences in the dissociation state of these sodium salts. Finally, it is shown that information about chiral selectivity can also be obtained with the applied infusion method.