Capillary Electrophoresis-electrospray Ionization-tandem Mass Spectrometry Research Articles

Sensitive detection of benzophenone-type ultraviolet filters in plastic food packaging materials by sheathless capillary electrophoresis–electrospray ionization–tandem mass spectrometry

While they are commonly used as ultraviolet (UV) filters in plastic food packaging materials, benzophenones (BPs) are reported as environmental endocrine disruptors, and some of them possess significant estrogenic activity. Therefore sensitive determination of the content of those UV filters in plastic polymers is of vital importance in safety assessment of food packaging materials. Here, the sheathless capillary electrophoresis–electrospray ionization–tandem mass spectrometry (CE–ESI–MS/MS) method is applied for the first time to sensitively detect BP-type UV filters in plastic food packaging materials. We investigate and optimize a variety of factors that may affect ESI–MS efficiency and CE separation. Sensitive detection of six BP-type UV filters is achieved using sheathless CE–ESI–MS/MS in conjunction with accelerated solvent extraction and solid phase extraction, with the limit-of-detection of 7 pg/mL–2.4 ng/mL. The method exhibits excellent inter/intra-day repeatability along with the advantages of efficient separation, rapid analysis, low sample consumption and high sensitivity. Six BP-type UV filters in eight different brands of plastic films obtained from supermarkets are successfully analyzed using the method. Good recoveries of 81.3–104.1% at three levels of spiked concentrations are achieved with low RSDs (n = 5) of 2.5–8.7%. Our study shows that the sheathless CE–ESI–MS/MS is a robust and reliable method for sensitive and rapid analysis of UV filters, which would be of potential application in safety assessment of plastic food packaging materials.

Highly sensitive determination of aminoglycoside residues in food by sheathless CE-ESI-MS/MS

A highly sensitive sheathless capillary electrophoresis-electrospray ionization-tandem mass spectrometry method and transient isotachophoresis was established for the determination of aminoglycoside antibiotics in milk.

Capillary-electrophoresis mass spectrometry for the detection of carbapenemases in (multi-)drug-resistant Gram-negative bacteria.

In a time in which the spread of multidrug resistant microorganisms is ever increasing, there is a need for fast and unequivocal identification of suspect organisms to supplement existing techniques in the clinical laboratory, especially in single bacterial colonies. Mass-spectrometry coupled with efficient peptide separation techniques offer great potential for identification of resistant-related proteins in complex microbiological samples in an unbiased manner. Here, we developed a capillary electrophoresis-electrospray ionization-tandem mass spectrometry CE-ESI-MS/MS bottom-up proteomics workflow for sensitive and specific peptide analysis with the emphasis on the identification of β-lactamases (carbapenemases OXA-48 and KPC in particular) in bacterial species. For this purpose, tryptic peptides from whole cell lysates were analyzed by sheathless CE-ESI-MS/MS and proteins were identified after searching of the spectral data against bacterial protein databases. The CE-ESI-MS/MS workflow was first evaluated using a recombinant TEM-1 β-lactamase, resulting in 68% of the amino acid sequence being covered by 20 different unique peptides. Subsequently, a resistant and susceptible Escherichia coli lab strain were analyzed and based on the observed β-lactamase peptides, the two strains could easily be discriminated. Finally, the method was tested in an unbiased setup using a collection of in-house characterized OXA-48 (n = 17) and KPC (n = 10) clinical isolates. The developed CE-ESI-MS/MS method was able to identify the presence of OXA-48 and KPC in all of the carbapenemase positive samples, independent of species and degree of susceptibility. Four negative controls were tested and classified as negative by this method. Furthermore, a number of extended-spectrum beta-lactamases (ESBL) were identified in the same analyses, confirming the multiresistant character in 19 out of 27 clinical isolates. Importantly, the method performed equally well on protein lysates from single colonies. As such, it demonstrates CE-ESI-MS/MS as a potential next generation mass spectrometry platform within the clinical microbiology laboratory.

Site-specific separation and detection of phosphopeptide isomers with pH-mediated stacking capillary electrophoresis-electrospray ionization-tandem mass spectrometry

This study reported a pH-mediated stacking CE coupled with ESI MS/MS method to determine the phosphorylation sites of three synthetic phosphopeptides containing structural isomers. These phosphopeptides mimic the phosphopeptides (amino acid residues 12-25) derived from the trypsin-digested products of human lamin A/C protein. The LODs were determined to be 118, 132 and 1240 fmol for SGAQASS(19)TpPL(22)SPTR, SGAQASS(19)TPL(22)SpPTR, and SGAQASS(19)TpPL(22)SpPTR, respectively. The established method was employed to analyze the phosphorylation sites of the trypsin-digested products of glutathione S-transferase-lamin A/C (1-57) fusion protein that had been phosphorylated in vitro by cyclin-dependent kinase 1. The results indicated that this method is feasible to specifically determine the phosphorylation site from phosphopeptide isomers in the trypsin-digested products of a kinase-catalyzed phosphoprotein, which should benefit the investigation of protein kinase-mediated cellular signal transduction.

Sensitive determination of d-carnitine as enantiomeric impurity of levo-carnitine in pharmaceutical formulations by capillary electrophoresis–tandem mass spectrometry

In this work, capillary electrophoresis–electrospray ionization-tandem mass spectrometry was applied to the determination of l- and d-carnitine in pharmaceutical formulations. A simple sample treatment procedure consisting of the use of a dilution or an extraction step with water was employed prior to derivatization with 9-fluorenylmethoxycarbonyl (FMOC). The method was validated in terms of selectivity, linearity, accuracy, precision and sensitivity, with a LOD of 10 ng mL −1 for each enantiomer, which was enough to detect enantiomeric impurities up to 0.002% of d-carnitine with respect to the main enantiomer ( l-carnitine). Eleven pharmaceutical formulations were analyzed including ampoules, oral solutions, sachets, and tablets. Results showed contents for carnitine comprised between 77 and 101% with respect to the labeled ones in the case of those formulations marketed with the racemate, and from 97 to 102% in those cases where the single enantiomer ( l-carnitine) was employed as active ingredient. Percentages for the enantiomeric impurity ( d-carnitine) ranging from 0.6 to 1.3% were obtained exceeding the limits established for impurities in drug products. These results corroborate the need of validated analytical methodologies enabling the quality control of pharmaceutical formulations containing carnitine.

Quantitative analysis of anionic metabolites for Catharanthus roseus by capillary electrophoresis using sulfonated capillary coupled with electrospray ionization-tandem mass spectrometry

This paper describes a practical method to quantify anionic metabolites using contemporary capillary electrophoresis-electrospray ionization-tandem mass spectrometry (CE-ESI-MS/MS). The use of sulfonated capillary permitted a simultaneous analysis of sugar phosphates, organic acids, nucleotides and coenzyme A compounds with only one CE condition. This capillary also improved the repeatability and sensitivity. MS/MS with multiple reaction monitoring (MRM) detection was utilized to achieve significant selectivity and sensitivity. Under optimized CE-ESI-MS/MS system, the detection limits of 53 metabolites at signal-to-noise ratio of 3 were between 0.040 and 8.8 mumol/l. The relative standard deviations (RSDs) for the majority anionic metabolites were better than 0.5% for migration times, and better than 10.0% for peak areas (n=6). Matrix effects by contaminants in sample solution in CE-ESI-MS/MS analysis were removed dramatically by the sample preparation method with liquid-liquid fractionation and ultrafiltration procedure. Furthermore, the developed method was successfully applied to determine anionic metabolites in a cultured cell of Catharanthus roseus. Accumulation of some metabolites including shikimate, malate, and sedoheptulose 7-phosphate by elicitation of methyl jasmonate was observed. The result would show shikimate, tricarboxylic acid and pentose phosphate pathways were activated. Our method will be useful for detailed analysis of primary metabolism dynamics.

Qualitative and quantitative analysis of amino acids by capillary electrophoresis-electrospray ionization-tandem mass spectrometry.

We describe a method to identify and quantify amino acids using capillary electrophoresis-electrospray ionization-triple-quadrupole tandem mass spectrometry (CE-ESI-MS/MS). Amino acids, including physiological amino acids, were first separated by CE under acidic pH conditions and then detected by MS/MS. To efficiently introduce the whole sample into the capillary, no electrical potential was applied to the electrospray probe until running electrophoresis. The position of the electrosprayer with respect to the MS capillary entrance drastically affected sensitivity and generation of cluster ions. MS/MS with multiple reaction monitoring (MRM) detection was performed to obtain sufficient selectivity and sensitivity. Under optimized CE-MS/MS conditions, the minimum detectable levels for 32 free amino acids normally found in proteins and other physiological amino acids were between 0.1 and 14 micromol/L with pressure injection of 50 mbar for 3 s (3 nL) at a signal-to-noise ratio of 3. For most amino acids, this constitutes a severalfold increase in sensitivity compared to CE-MS. The relative standard deviations (% RSD) for all amino acids were better than 0.4% for migration times and between 1.4% and 8.6% for peak areas (n = 10). Since amino acids exhibited characteristic MS/MS spectra, this approach is useful for the simultaneous, selective, quantitative, and reproducible analysis of amino acids in physiological and biological samples that contain various kinds of matrices. The power of the method was demonstrated by analyzing amino acids in human urine.