Surface-activated chemical ionization ion trap mass spectrometry in the analysis of drugs in dilute urine samples. Part II: analysis of morphine and other street drugs

A system consisting of cation-exchange chromatography, combined surface-activated chemical and electrospray ionization, and ion-trap analysis for the analysis of 8-oxo-7,8-dihydro-2'-deoxyguanosine in urine

RATIONALE

8-Hydroxy-2'-deoxyguanosine has served as a biomarker for oxidative damage to DNA from different types of biological samples, and various techniques have been used to analyze it. In particular, liquid chromatography coupled to mass spectrometry has been used to identify 8-hydroxy-2'-deoxyguanosine in urine samples. Usually, a triple quadrupole analyzer and multiple reaction monitoring have been employed for its detection. Only a few studies have used a less expensive ion-trap analyzer instead.

METHODS

We have developed a new liquid chromatography/mass spectrometry procedure that incorporates cation-exchange chromatography in conjunction with surface-activated and electrospray ionization with an ion trap analyzer for the mass spectral step.

RESULTS

The combination of two ionization sources reduced the matrix effect arising from in-source reactions, thus increasing the sensitivity to levels comparable with those obtained by triple quadrupole analyzers.

CONCLUSIONS

This new method for 8-hydroxy-2'-deoxyguanosine detection provided increased sensitivity and reduced chemical noise, using a less expensive, stable and accurate mass spectrometric technology.

Surface-activated chemical ionization combined with electrospray ionization and mass spectrometry for the analysis of cannabinoids in biological samples. Part I: analysis of 11-nor-9-carboxytetrahydro-cannabinol

Recently, electrospray ionization mass spectroscopy (ESI-MS) has been widely used for the identification of drugs of abuse and their metabolites in biological samples. However, the sensitivity and selectivity of this technique are commonly inadequate for the analysis of tetrahydrocannabinol (THC) and its metabolites at very low levels, such as those sometimes required in forensic and clinical-legal applications. We coupled electrospray ionization and surface-activated chemical ionization (ESI-SACI) to various types of mass analyzers (ion trap, triple quadrupole and orbitrap) (ESI-SACI-MS) to improve the detection of 11-nor-9-carboxy-tetrahydrocannabinol (THC-COOH), the most common marker of THC abuse. The benefits of this approach in terms of sensitivity and selectivity compared with a common ESI-MS approach are clearly demonstrated.

Atmospheric pressure thermospray ionization using a heated microchip nebulizer

When a standard atmospheric pressure chemical ionization (APCI) or atmospheric pressure photoionization (APPI) ion source is used without applying the corona discharge or photoirradiation, atmospheric pressure thermospray ionization (APTSI) of various compounds can be achieved. Although largely ignored, this phenomenon has recently gained interest as an alternative ionization technique. In this study, this technique is performed for the first time on a miniaturized scale using a microchip nebulizer. Sample ionization with the presented microchip-APTSI (microAPTSI) is achieved by applying only heat and gas flow to a nebulizer chip, without any other methods to promote gas-phase ionization. To evaluate the performance of the described microAPTSI setup, ionization efficiency for a set of test compounds was monitored as the microchip positioning, temperature, nebulizer gas flow rate, sample solution composition, and solvent flow rate were varied. The microAPTSI mass spectra of the test compounds were also compared to those obtained with ESI and APCI. The microAPTSI produces ESI-like spectra with low background noise, favoring the formation of protonated or deprotonated molecules of compounds that are ionizable in solution. Multiple charging of peptides without in-source fragmentation was also observed. Unlike ESI, however, the microAPTSI source can tolerate the presence of mobile phase additives like trifluoroacetic acid (TFA) without significant ion suppression. The microAPTSI source can be used with standard mass spectrometer ion source hardware, being a unique alternative to the present interfacing techniques.

Development and applications of surface-activated chemical ionization

This review regards the recently developed ionization source named surface-activated chemical ionization (SACI) that employs an interaction with a surface placed at low voltage for the activation of the ionization of sample molecules to increase the sensitivity in the analysis of various compounds of biological and clinical interest. These results are due to the strong chemical noise decrease and the increase of ionization efficiency. This ionization source has been employed for the analysis of various compounds of different molecular mass and polarity (addicted and pharmaceutical drugs, amino acids, steroids, peptides, and proteins). The SACI development theoretical mechanism, benefits, disadvantages, applications, and future developments are reported and discussed.

Recent studies of the electrospray ionisation behaviour of selected drugs and their application in capillary electrophoresis–mass spectrometry and liquid chromatography–mass spectrometry

This review is concerned with recent studies of electrospray ionisation-mass spectrometry (ESI-MS) of selected small molecular mass drugs and their application in qualitative and quantitative analytical methods using the techniques liquid chromatography mass spectrometry (LC-ESI-MS) and capillary electrophoresis mass spectrometry (CE-ESI-MS). The publications reviewed are taken from the Web of Knowledge database for the year 2006. The drugs have molecular mass less than 1000 Da and are chosen according to selected drug classifications in which they give ESI signals primarily as [M+H]+ ions. The drug classifications are antibiotics/antibacterials, steroids, anti-tumour drugs, erectile dysfunction agents, anti-epileptic drugs, antiasthmatic drugs, psychoactive drugs and miscellaneous drugs. Details are given on the fragmentations, where available, that these ionic species exhibit in-source and in ion trap, triple quadrupole and time-of-flight mass spectrometers. Analytical methods for the detection and determination of these small molecular mass drug molecules are also discussed, where appropriate, under the particular drug classifications. Analytical information on, for example, sample concentration techniques, separation conditions, recoveries from biological media and limits of detection/quantitation (LODs and LOQs) are provided.

Surface-activated chemical ionization ion trap mass spectrometry for the analysis of cocaine and benzoylecgonine in hair after extraction and sample dilution

Surface-activated chemical ionization (SACI) was employed for the analysis of cocaine and its metabolite, benzoylecgonine, extracted from hair. Following decontamination and acid hydrolysis procedures on the hair sample, the sample solution was diluted (1:10) and directly analyzed by liquid chromatography/surface-activated chemical ionization multiple collisional stage single reaction monitoring mass spectrometry (LC/SACI-MS(3)-SRM) without solid-phase extraction (SPE) pre-purification and concentration procedures. To increase the selectivity of the method, MS(3) was chosen instead of the less selective MS/MS. This data was compared with that achieved using gas chromatography/mass spectrometry (GC/MS), the reference method used by the Italian Government Institute of Health protocol. The limits of detection (LODs) were 0.003 ng/(mg hair) for cocaine and 0.02 ng/(mg hair) for benzoylecgonine and the limits of quantitation (LOQs) were 0.01 ng/(mg hair) for cocaine and 0.04 ng/(mg hair) for benzoylecgonine. The squared correlation coefficient (R(2)) of the calibration curve was 0.9887-0.9980 for cocaine and 0.9987-0.9997 for benzoylecgonine. The percent accuracy error was 2-5% for both cocaine and benzoylecgonine using the LC/SACI-MS(3)-SRM approach, whereas it was higher for benzoylecgonine (20-25%) using the LC/SACI-MS/MS-SRM approach compared with the GC/MS data due to hair matrix contamination. In both cases, high precision was achieved (1-3% precision error), which confirmed the stability of the developed methods.

Surface-activated chemical ionization and high-flow gradient chromatography to reduce matrix effect

The new atmospheric pressure chemical ionization source, named surface-activated chemical ionization (SACI), has been used in conjunction with high-flow gradient chromatography to reduce the matrix effect. This high-flow gradient chromatography approach avoids the co-elution of analyte and biological matrix compounds that leads to a reduction in quantitation errors due to matrix effect. However, this approach cannot be employed with the classical electrospray ionization (ESI) source that usually works at low eluent flow (< 300 microL/min). SACI can work at high eluent flow (100-2000 microL/min) and can be employed in conjunction with high-flow gradient chromatography. The reduction in matrix effect in tacrolimus analysis in protein-precipitated blood samples, an important immunosuppressive agent for renal transplantation, is presented and discussed.