Investigation of commercial sorbents for the analysis of opioid peptides in human plasma by on‐line SPE‐CE

Abstract

In this study, we investigated the performance of several commercial sorbents (Sep-pack) C18, (t)C18, C8 and (t)C2, Oasis HLB, Isolute ENV+, Strata-X and Oasis MCX) for the determination of opioid peptides by solid-phase extraction coupled on-line to capillary electrophoresis (SPE-CE). First, standard solutions were analyzed in order to achieve the lowest LOD and the best electrophoretic separations using UV detection. The best results were obtained using C18, C8 and (t)C2 sorbents, which were examined for the analysis of spiked human plasma samples. A double-step sample clean-up pretreatment, which consisted of precipitation with acetonitrile and filtration, was needed to prevent saturation of the on-line SPE microcartridge. The filtration step was critical to obtain optimum analyte recovery and to clean up the sample matrix. A range of centrifugal filters and filtration conditions were tested and the recoveries of the sample pretreatment were evaluated by CE-ESI-MS. The LODs attained through SPE-CE-UV were approximately ten-fold better with C18 than with C8 and (t)C2. The 0.1 microg/mL LODs achieved by C18-SPE-CE-UV were further improved until we could detect 1 ng/mL concentrations of opioid peptides in plasma samples by C18-SPE-CE-ESI-MS, due to the outstanding selectivity of the MS detection.

Transient isotachophoresis in on‐line solid phase extraction capillary electrophoresis time‐of‐flight‐mass spectrometry for peptide analysis in human plasma

“…However, due to the specific features of both instrumental set-ups, it was convenient to run some experiments to finely tune those conditions [34,36]. We analyzed a 10 mg/mL standard mixture of the opioid peptides by CE-TOF-MS and tITP-CE-TOF-MS.…”

“…proteins) before SPE-CE-TOF-MS or SPE-tITP-CE-TOF-MS. The sample pretreatment consisted of precipitation with acetonitrile followed by filtration using Amicon centrifugal devices of 3 kDa cut-off cellulose acetate filters (YM-3) (Millipore, Billerica, MA, USA) [23,24,34].…”

“…A SPE microcartridge (7 mm L T  250 mm id  360 mm od fused-silica capillary, Polymicro technologies) containing C18 sorbent from Sep-Pak cartridges (Waters, Milford, MA, USA) was inserted at 7.5 cm from the inlet of the separation capillary column as described elsewhere [22][23][24]34]. The SPE-CE columns were first conditioned by consecutive flushes of water (1 min), methanol (1 min), water (1 min) and BGE (3 min) at 930 mbar.…”

An update for human blood plasma pretreatment for optimized recovery of low-molecular-mass peptides prior to CE-MS and SPE-CE-MS

“…Thus, for example, centrifugal filtration is often applied to desalt and concentrate high M r protein fractions, hence recoveries are often evaluated in terms of the retentate and no attention is given to the low M r peptides in the filtrates . In a previous work, we proposed a double‐step pretreatment for the analysis of low M r peptides (namely opioid peptides) in human blood plasma by CE–MS and SPE–CE–MS that consisted of precipitation with acetonitrile followed by centrifugal filtration . Peptide recovery for the precipitation step was good when the volume ratio between acetonitrile and plasma was 6:1 v/v (49, 91, and 102% for dynorphin A (1–7) (Dyn A, Tyr‐Gly‐Gly‐Phe‐Leu‐Arg‐Arg, M r 867.4715), endomorphin 1 (End 1, Tyr‐Pro‐Trp‐Phe‐NH 2 , M r 610.2904), and methionine enkephalin (Met, Tyr‐Gly‐Gly‐Phe‐Met, M r 573.2257), respectively) .…”

“…In a previous work, we proposed a double‐step pretreatment for the analysis of low M r peptides (namely opioid peptides) in human blood plasma by CE–MS and SPE–CE–MS that consisted of precipitation with acetonitrile followed by centrifugal filtration . Peptide recovery for the precipitation step was good when the volume ratio between acetonitrile and plasma was 6:1 v/v (49, 91, and 102% for dynorphin A (1–7) (Dyn A, Tyr‐Gly‐Gly‐Phe‐Leu‐Arg‐Arg, M r 867.4715), endomorphin 1 (End 1, Tyr‐Pro‐Trp‐Phe‐NH 2 , M r 610.2904), and methionine enkephalin (Met, Tyr‐Gly‐Gly‐Phe‐Met, M r 573.2257), respectively) . The first step of protein precipitation was enough before CE–MS, but not before C 18 ‐SPE–CE–MS that required the subsequent centrifugal filtration step for an improved sample matrix clean‐up.…”