Separation of very hydrophobic analytes by micellar electrokinetic chromatography. I. Optimization of the composition of the sample solution for the determination of the aromatic ingredients of sassafras and other essential oils of forensic interest

Abstract

A micellar electrokinetic chromatographic method using UV and (UV)LIF detection in-line was developed for the determination of aromatic constituents, mainly allylbenzenes in essential oils. The method optimization included the optimization of the composition of the separation electrolyte using ACN and urea to reduce retention factors and CaCl(2) to widen the migration time window. In addition, it was necessary to optimize the composition of the sample solution which included the addition of a neutral surfactant at high concentration. With the optimized method, the determination of minor constituents in essential oils was possible despite of the presence of a structurally related compound being in a molar ratio excess of 1000:1. The use of UV and LIF-detection in-line enabled the direct comparison of the two detection traces using an electrophoretic mobility x-axis instead of the normal time-based scale. This simplifies the assignment of signals and enhances repeatability. The method developed was successfully applied to the determination of minor and major constituents in herbal essential oils, some of them being forensically relevant as sources of precursors for synthetic drugs.

Separation of very hydrophobic analytes by micellar electrokinetic chromatography. III. Characterization and optimization of the composition of the separation electrolyte using carbon number equivalents

“…Those parameters (Table 2) were selected which have been proven in previous studies [27] to make possible the separation of very hydrophobic analytes (log P OW = 3-4) with a conventional surfactant. The separation electrolytes studied are all based on 1.875 mmol/L Na 2 B 4 O 7 and 60 mmol/L SDS.…”

“…In a previous paper investigating the separation of hydrophobic analytes by MEKC with conventional surfactant [27] the separation of aromatic ethers in essential oils of forensic interest containing safrole as main constituent is described (safrole is precursor for the clandestine synthesis of (3,4-methylenedioxymethamphetamine) [27,28]. MEKC has been chosen for the separation of these analytes because this technique provides good selectivity and a high peak capacity and can handle large differences in the concentrations of main and minor components.…”

“…In order to describe and to predict retention factors at different volume fractions of an organic modifier in the mobile phase, a second descriptor the polarity index q i was introduced which is a measure of polar interactions. In order to determine n ce and q i , it is necessary to measure k dependent on the volume fraction of the organic modifier for the solute and for the homologous calibration series.In a previous paper investigating the separation of hydrophobic analytes by MEKC with conventional surfactant [27] the separation of aromatic ethers in essential oils of forensic interest containing safrole as main constituent is described (safrole is precursor for the clandestine synthesis of (3,4-methylenedioxymethamphetamine) [27,28]. MEKC has been chosen for the separation of these analytes because this technique provides good selectivity and a high peak capacity and can handle large differences in the concentrations of main and minor components.…”

Separation of very hydrophobic analytes by MEKC. II. Carbon number equivalents as analyte descriptors – influence of the composition of the separation electrolyte

“…In the first publication of this series [11] we have investigated the determination of allylbenzenes in essential oils used for the clandestine production of 3,4-methylenedioxymethamphetamine (MDMA). In order to obtain baseline separation of these very hydrophobic analytes, a thorough optimization of the composition of the separation electrolyte was necessary.…”

Comparative Analysis of the Chemical Profiles of 3,4‐Methylenedioxymethamphetamine Based on Comprehensive Two‐Dimensional Gas Chromatography–Time‐of‐Flight Mass Spectrometry (GC × GC‐TOFMS)*

“…For the profiling of MDMA precursors, Huhn et al. (7,8) developed a micellar electrokinetic chromatographic method using ultraviolet and laser induced fluorescence detection. GC methods are also commonly applied for impurity profiling of MDMA (9–17).…”