Analysis of therapeutic peptides in human urine by combination of capillary zone electrophoresis–electrospray mass spectrometry with preparative capillary isotachophoresis sample pretreatment

The presented study deals with the off-line coupling of preparative isotachophoresis (pITP) with on-line combination of capillary zone electrophoresis with electrospray mass spectrometric detection (CZE–ESI–MS) used for the analysis of therapeutic peptides (anserine, carnosine, and buserelin) in complex matrix (urine). Preparative capillary isotachophoresis, operating in a discontinuous fractionation mode in column-coupling configuration, served as a sample pretreatment technique to separation, and fractionation of mixture of therapeutic peptides present in urine at low concentration level. The fractions isolated by pITP procedure were subsequently analyzed by capillary zone electrophoresis with electrospray mass spectrometric detection. Acetic acid at 200 mmol L−1 concentration served as background electrolyte in CZE stage and it is compatible with MS detection in positive ionization mode. In pITP fractionation procedure, sodium cation (10 mmol L−1 concentration) as leading ion and beta-alanine as terminating ion (20 mmol L−1 concentration) were used. While using CZE–ESI–MS, the limits of detection were 0.18 μg mL−1 for carnosine, 0.17 μg mL−1 for anserine and 0.64 μg mL−1 for buserelin in water and 0.19 μg mL−1 for carnosine, 0.50 μg mL−1 for anserine and 0.74 μg mL−1 for buserelin in 10 times diluted urine, respectively. The cleaning power of pITP sample pretreatment was proved as the peptides provided the higher MS signals at lower concentration levels resulting from the minimized matrix effects. The quality of obtained MS/MS spectra was very good so that they can provide information about the structure of analytes, and they were used for verification of the analytes identities. The pITP pretreatment improved the detection limits of the analyzed therapeutic peptides at least 25 times compared to the CZE–ESI–MS itself.

► CZE–ESI–MS analysis of 3 therapeutic peptides (anserine, buserelin, carnosine).
► pITP sample pretreatment of human urine samples.
► LODs after pITP pretreatment were improved at least 25 times.