Evaluation of on-line solid-phase extraction capillary electrophoresis–mass spectrometry with a nanoliter valve for the analysis of peptide biomarkers

Abstract

On-line solid-phase extraction capillary electrophoresis-mass spectrometry (SPE-CE-MS) is a powerful technique for high throughput sample clean-up and analyte preconcentration, separation, detection, and characterization. The most typical design due to its simplicity and low cost is unidirectional SPE-CE-MS. However, in this configuration, the sample volumes introduced by pressure depend on the dimensions of the separation capillary and some matrix components could be irreversibly adsorbed in its inner walls. Furthermore, in many cases, the requirements of on-line preconcentration are incompatible with the background electrolyte necessary for an efficient separation and sensitive MS detection. Here, we present SPE-CE-MS with a nanoliter valve (nvSPE-CE-MS) to overcome these drawbacks while keeping the design simple. The nvSPE-CE-MS system is operated with a single CE instrument and two capillaries for independent and orthogonal SPE preconcentration and CE separation, which are interfaced through an external and electrically isolated valve with a 20 nL sample loop. The instrumental setup is proved for the analysis of opioid and amyloid beta peptide biomarkers in standards and plasma samples. NvSPE-CE-MS allowed decreasing the limits of detection (LODs) 200 times with regard to CE-MS. Compared to unidirectional SPE-CE-MS, peak efficiencies were better and repeatabilities similar, but total analysis times longer and LODs for standards slightly higher due to the heart-cut operation and the limited volume of the valve loop. This small difference on the LODs for standards was compensated for plasma samples by the improved tolerance of nvSPE-CE-MS to complex sample matrices. In view of these results, the presented setup can be regarded as a promising versatile alternative to avoid complicated matrix samples entering the separation capillary in SPE-CE-MS.

Recent developments in capillary and microchip electroseparations of peptides (2019–mid 2021)

“…In these reviews, the application of various procedures for sample clean-up are described, such as (ultra)filtration, SPE, solid-phase microextraction, liquid-liquid extraction, and several electro-driven techniques. Special reviews and articles deal with the particular sample clean-up techniques, such as online SPE with a nanoliter valve for analysis of opioid and Aβ peptide biomarkers in standards and plasma samples [64], two-dimensional affinity capture and separation platform for the isolation and enrichment of biopeptides and other biomarkers, potentially applicable for analysis of liquid biopsies [65], in-capillary immunopreconcentration with circulating biofunctionalized magnetic beads [66], and online electro-driven sample-stacking techniques [67]. The latter electro-driven procedures comprise field-amplified sample stacking [68], field-enhanced or field-amplified sample injection [68][69][70] large volume sample stacking [71], transient-ITP (t-ITP) [69,72], electrokinetic supercharging (EKS) [68,69], dynamic pH barrage junction and pH-mediated stacking [73], and electromembrane extraction [74].…”

Sensitivity enhancement in capillary electrophoresis and their applications for analyses of pharmaceutical and related biochemical substances

“…Online SPE‐CE‐MS was applied for the analysis of peptide biomarkers by Gascon et al. [125]. The technique could provide LODs 200 times lower than conventional CE‐MS [125].…”

“…Detection and interaction study of CSMNPs could be realized with 350-fold sensitivity improvement [124]. Online SPE-CE-MS was applied for the analysis of peptide biomarkers by Gascon et al [125]. The technique could provide LODs 200 times lower than conventional CE-MS [125].…”

“…Online SPE-CE-MS was applied for the analysis of peptide biomarkers by Gascon et al [125]. The technique could provide LODs 200 times lower than conventional CE-MS [125]. An online three-step stacking strategy combining FESI, sweeping, and micelle to solvent stacking was developed to determine trace amounts of 1-dodecyl-3-methylimidazolium hydrogen sulfate, in complex biological samples.…”

Applications of capillary electrophoresis in the fields of environmental, pharmaceutical, clinical, and food analysis (2019–2021)

“…Therefore, the use of sample pretreatment techniques prior to analysis with CE is necessary [2][3][4]. Different online microextraction techniques for concentrating the target analytes in the complex samples before sample injection were reported such as SPE [5][6][7], solid-phase micromembrane tip extraction (SPMMTE) [8], and magnetic SPE (MSPE) [9], and so forth. Preconcentration techniques during or after sample injection were also used such as fieldamplified sample stacking (FASS) [10], field-amplified sample injection (FASI) [11], large volume sample stacking (LVSS) [12] and transient isotachophoresis (tITP) [13,14], etc.…”