Enantiodetermination of R,S-3,4-methylenedioxypyrovalerone in urine samples by high pressure in-line solid-phase extraction capillary electrophoresis-mass spectrometry.

This study presents for the first time an in-line solid-phase extraction capillary electrophoresis-mass spectrometry (SPE-CE-MS) method for the enantiodetermination of drugs of abuse in urine samples. The enantioseparation of R,S-3,4-methylenedioxypyrovalerone (R,S-MDPV) was achieved with a 10 mM ammonium acetate BGE (pH 7) that contained 0.5% (m/v) of sulphated-α-CD as chiral selector. At these pH conditions, this CD was negatively charged, which prevented its entrance into the mass spectrometer since it migrates in the opposite direction. To improve sensitivity, an in-line SPE-CE-MS method using high pressure for sample introduction (i.e. 20 min at 3 bars) was developed. Furthermore, the conditioning procedure and the first part of the electrophoretic separation were performed by switching off the nebulizer gas and the ionization source voltage to avoid non-volatile contaminant arrival into the mass spectrometer. The developed methodology was validated by analyzing urine samples, which required a very simple liquid-liquid extraction (LLE) sample pretreatment. Linearity ranged from 30 to 250 ng mL-1, limit of detection (LOD) was 10 ng mL-1, relative standard deviation (RSD) values were below 10.5% in terms of intra-day and inter-day precision and the relative error values were below 9% for peak areas accuracy.

Field-amplified sample injection combined with CE for the enantiodetermination of cathinones in urine samples.

This work presents a capillary electrophoresis methodology for the enantiodetermination of cathinones in urine employing a liquid-liquid extraction sample pretreatment. The cathinones were enantioseparated by adding a mixture of 8 mM 2-hydroxypropyl ß-cyclodextrin and 5 mM ß-cyclodextrin to the background electrolyte, which consists of 70 mM of monosodium phosphate aqueous solution at pH 2.5. Field-amplified sample injection was used as preconcentration strategy to improve the sensitivity. We studied various parameters that affect this stacking strategy, in particular, the sample solvent and its pH, the presence or absence of a low conductivity solvent plug introduced before the sample injection, the nature and volume of this plug, and the voltage and time of the electrokinetic injection of the sample. The optimum conditions were achieved by injecting a plug of isopropanol:H2 O 50/50 at 50 mbar for 5 s prior to the electrokinetic injection of the sample prepared in an aqueous solution of HCl 10-6  M. The sensitivity enhancement factors were from 562 to 601 in terms of peak area and from 444 to 472 in terms of peak height. The method was validated by analyzing spiked urine samples, obtaining a linear range of 25 to 1000 ng/mL and limits of detection ranging from 15 to 45 ng/mL.

Enantioselective determination of cathinones in urine by high pressure in-line SPE-CE.

This work presents a strategy based on the in-line coupling of SPE and CE for the chiral determination of cathinones (R,S-mephedrone, R,S-4-methylephedrine, and R,S- methylenedioxypyrovalerone) in urine samples, using a sample pretreatment based on liquid-liquid extraction. The chiral separation of the compounds is achieved by adding a mixture of 8 mM 2-hydroxypropil ß-CD and 5 mM ß-CD to the BGE, which consists of 70 mM of monosodium phosphate aqueous solution at pH 2.5. Oasis HLB was the selected sorbent for the in-line SPE device, and to reduce analysis time and LODs, several parameters affecting the in-line SPE system were evaluated, such as pressure and time of sample injection and dimensions of the SPE device. The highest preconcentration factors were achieved by using 3 bar of injection pressure for 20 min with an in-line SPE device of 2 mm length and 150 µm of i.d. The developed method was applied to determine the presence of the compounds in spiked urine samples. The LODs obtained were between 3 and 8 ng/mL, and these levels were below the usual concentrations at which these drugs are present in urine from cathinone abusers. Thus, the optimized method has the potential to be applied for toxicological and forensic purposes.