Signal enhancement in desorption nanoelectrospray ionization by custom-made inlet with pressure regulation.

The efficiency of desorption/ionization becomes more critical as the sampled surface area decreases. Desorption electrospray and desorption nanoelectrospray belong to ambient ionizations and enable direct surface analysis including mass spectrometric imaging. Lateral resolution in tens of micrometers was demonstrated for desorption nanoelectrospray previously, but sensitivity of the surface scan can be an issue. For desorption electrospray, the drag force in the source is driven by the flow of used gases and vacuum suction. Ion signal intensity can be improved by controlling the nebulizing gas flow rate or auxiliary pumping of a closed compartment in front of the mass spectrometer inlet. Because nanoelectrospray generates charged droplets without the assistance of a nebulizing gas, only vacuum suction drives the gas flow. In this study, the effect of pressure drop between the atmospheric and evacuated region of a mass spectrometer on the ion signal intensity was investigated for desorption nanoelectrospray. A modification of the commercial inlet was designed. An auxiliary pump was directly connected to an inner compartment of the modified mass spectrometer inlet through a needle valve that enabled the regulation of the reduced pressure. Adjustment of the pressure drop significantly increased signal intensity (more than one order of magnitude in some cases). To a lesser extent, the temperature of a heated capillary (an integral part of the inlet) also influenced the signal intensity. The applicability of desorption nanoelectrospray equipped with pressure regulation was demonstrated by the analysis of synthetic cathinones or a pill of paracetamol. Because pressure in the inlet depends on the diameters of orifices and the power of vacuum systems of mass spectrometers, the effect of the pressure regulation can be different for different instruments. Nevertheless, the presented results confirmed the importance of pressure drop-driven transport for desorption nanoelectrospray efficiency and can encourage its new applications.

Determination of residual solvents in isobutylboronic acid: Masking derivatization improves stability of GC column.

Masking derivatization was introduced for the determination of residual solvents in samples containing a volatile reactive matrix component(s). Isobutylboronic acid, used in the last step of Bortezomib synthesis, represents a compound passing to the gas phase and deteriorating a chromatographic column during a headspace analysis. The masking derivatization with 1,8-diaminonaphthalene allowed a simple and straightforward conversion of isobutylboronic acid to a stable nonvolatile derivative and thus prevented gas chromatography column deterioration. The method was successfully validated according to the guidelines of International Committee for Harmonization (Q3C (R6) Guideline for Residual Solvents) and international pharmacopoeias (Ph. Eur., USP) and approved by Teva Czech Industries for routine application.

Analysis of new psychoactive substances in human urine by ultra-high performance supercritical fluid and liquid chromatography: Validation and comparison.

New psychoactive substances represent serious social and health problem as tens of new compounds are detected in Europe annually. They often show structural proximity or even isomerism, which complicates their analysis. Two methods based on ultra high performance supercritical fluid chromatography and ultra high performance liquid chromatography with mass spectrometric detection were validated and compared. A simple dilute-filter-and-shoot protocol utilizing propan-2-ol or methanol for supercritical fluid or liquid chromatography, respectively, was proposed to detect and quantify 15 cathinones and phenethylamines in human urine. Both methods offered fast separation (<3 min) and short total analysis time. Precision was well <15% with a few exceptions in liquid chromatography. Limits of detection in urine ranged from 0.01 to 2.3 ng/mL, except for cathinone (5 ng/mL) in supercritical fluid chromatography. Nevertheless, this technique distinguished all analytes including four pairs of isomers, while liquid chromatography was unable to resolve fluoromethcathinone regioisomers. Concerning matrix effects and recoveries, supercritical fluid chromatography produced more uniform results for different compounds and at different concentration levels. This work demonstrates the performance and reliability of supercritical fluid chromatography and corroborates its applicability as an alternative tool for analysis of new psychoactive substances in biological matrixes.

Carbon fiber brush electrode as a novel substrate for atmospheric solids analysis probe (ASAP) mass spectrometry: Electrochemical oxidation of brominated phenols.

A carbon fiber brush electrode (CFBE) was newly designed and used as a substrate for both controlled potential electrolysis and atmospheric solids analysis probe (ASAP) mass spectrometry. Electropolymerized and strongly adsorbed products of electrolysis were directly desorbed and ionized from the electrode surface. Electrochemical properties of the electrode investigated by cyclic voltammetry revealed large electroactive surface area (23 ± 3 cm2) at 1.3 cm long array of carbon fibers with diameter 6-9 µm. Some products of electrochemical oxidation of pentabromophenol and 2,4,6-tribromophenol formed a compact layer on the carbon fibers and were analyzed using ASAP. Eleven new oligomeric products were identified including quinones and biphenoquinones. These compounds were not observed previously in electrolyzed solutions by liquid or gas chromatography/mass spectrometry. The thickness around 58 nm and 45 nm of the oxidation products layers deposited on carbon fibers during electrolysis of pentabromophenol and 2,4,6-tribromophenol, respectively, was estimated from atomic force microscopy analysis and confirmed by scanning electron microscopy with energy-dispersive X-ray spectroscopy measurements.

Simple area determination of strongly overlapping ion mobility peaks.

Coupling of ion mobility with mass spectrometry has brought new frontiers in separation and quantitation of a wide range of isobaric/isomeric compounds. Ion mobility spectrometry may separate ions possessing the identical molecular formula but having different molecular shapes. The separation space in most commercially available instruments is limited and rarely the mobility resolving power exceeds one hundred. From this perspective, new approaches allowing for extracting individual compound signals out of a more complex mixture are needed. In this work we present a new simple analytical approach based on fitting of arrival time distribution (ATD) profiles by Gaussian functions and generating of ATD functions. These ATD functions well describe even distorted ion mobility peaks of individual compounds and allow for extracting their peaks from mobilograms of mixtures. Contrary to classical integration, our approach works well with irregular overlapping peaks. Using mobilograms of standards to generate ATD functions, poorly separated compounds, e.g. isomers, with identical mass spectra representing a hard to solve task for various chemometric methods can be easily distinguished by our procedure. Alternatively ATD functions can be obtained from ATD profiles of ions unique to individual mixture components (if such ions exist) and mobilograms of standards are not required. On a set of hyaluronan-derived oligosaccharides we demonstrated excellent ATD repeatability enabling the resolution of binary mixtures, including mixtures with minor component level about 5%. Ion mobility quantitative data of isomers were confirmed by high performance liquid chromatography.

Fast separation of selected cathinones and phenylethylamines by supercritical fluid chromatography.

The chromatographic behaviour of eleven synthetic cathinones and four phenylethylamines under supercritical/subcritical fluid conditions was investigated. Four stationary phases with sub-2µm particles (Waters Acquity UPC(2) BEH silica, BEH 2-ethylpyridine, CSH Fluoro-Phenyl, and HSS C18SB) were evaluated in terms of isomer resolution, chromatographic peak shape, and analysis time. Methanol, water, formic acid, ammonium hydroxide, ammonium acetate, and ammonium formate were mixed with carbon dioxide to test their influence on analyte retention and peak shapes. Methanol and ammonium cations were essential for successful separations. Efficient separations of four isomeric pairs (R>1), and most of the remaining analytes, were achieved in less than 3.3min on BEH and Fluoro-Phenyl columns with gradient of methanolic ammonium hydroxide in CO2. Drugs were detected by positive electrospray ionization-triple quadrupole mass spectrometry in selected reaction monitoring mode. Added detection specificity and faster separation of isomers on the BEH column using a steep gradient and high flow rate reduced analysis time of the mixture of 15 drugs to 1.6min.