Chromatography-atmospheric Pressure Ionization Mass Spectrometry Research Articles

Nontargeted Screening Using Gas Chromatography-Atmospheric Pressure Ionization Mass Spectrometry: Recent Trends and Emerging Potential.

Gas chromatography–high-resolution mass spectrometry (GC–HRMS) is a powerful nontargeted screening technique that promises to accelerate the identification of environmental pollutants. Currently, most GC–HRMS instruments are equipped with electron ionization (EI), but atmospheric pressure ionization (API) ion sources have attracted renewed interest because: (i) collisional cooling at atmospheric pressure minimizes fragmentation, resulting in an increased yield of molecular ions for elemental composition determination and improved detection limits; (ii) a wide range of sophisticated tandem (ion mobility) mass spectrometers can be easily adapted for operation with GC–API; and (iii) the conditions of an atmospheric pressure ion source can promote structure diagnostic ion–molecule reactions that are otherwise difficult to perform using conventional GC–MS instrumentation. This literature review addresses the merits of GC–API for nontargeted screening while summarizing recent applications using various GC–API techniques. One perceived drawback of GC–API is the paucity of spectral libraries that can be used to guide structure elucidation. Herein, novel data acquisition, deconvolution and spectral prediction tools will be reviewed. With continued development, it is anticipated that API may eventually supplant EI as the de facto GC–MS ion source used to identify unknowns.

In-vitro metabolism of isotetrandrine, a bisbenzylisoquinoline alkaloid, in rat hepatic S9 fraction by high-performance liquid chromatography-atmospheric pressure ionization mass spectrometry.

The objective of this study was to investigate the in-vitro metabolism of isotetrandrine, a bisbenzylisoquinoline alkaloid, using rat hepatic S9 fraction and to profile and identify its metabolites using high-performance liquid chromatography-atmospheric pressure ionization mass spectrometry (HPLC-MS) and tandem mass spectrometry (MS/MS). Isotetrandrine was incubated at a concentration of 100 microg mL(-1) with male rat hepatic S9 fraction in the presence of an NADPH generating system (Tris buffer, pH 7.4, 37 degrees C). Samples were removed at 60 min after reaction initiation. Unchanged isotetrandrine (approximately 63% of the sample) and four metabolites were profiled, characterized and tentatively identified using solvent extraction, methyl derivatization, and HPLC-MS and MS/MS techniques. Isotetrandrine metabolites were mainly formed via two main pathways, N-demethylation and isoquinoline ring oxidation. The first pathway produced a major metabolite, N-desmethyl isotetrandrine (approximately 16% of the sample). The second pathway produced three minor oxidized metabolites, hydroxy-isotetrandrine (approximately 6% of the sample), oxo-isotetrandrine (approximately 7% of the sample), and oxohydroxy-isotetrandrine (approximately 7% of the sample). Diazomethane treatment of these metabolites did not produce any methyl derivatives and therefore the hydroxylated sites of the metabolites were tentatively assigned at the heterocyclic moieties of the isoquinoline rings. In conclusion, isotetrandrine is substantially metabolized in this in-vitro rat hepatic system.

Determination of atractyloside in Callilepis laureola using solid-phase extraction and liquid chromatography–atmospheric pressure ionisation mass spectrometry

Determination of atractyloside in Callilepis laureola using solid-phase extraction and liquid chromatography–atmospheric pressure ionisation mass spectrometry

Highly Sensitive Screening Method for Nitroaromatic, Nitramine and Nitrate Ester Explosives by High Performance Liquid Chromatography—Atmospheric Pressure Ionization—Mass Spectrometry (HPLC-API-MS) in Forensic Applications

A highly sensitive screening method based on high performance liquid chromatography atmospheric pressure ionization mass spectrometry (HPLC-API-MS) has been developed for the analysis of 21 nitroaromatic, nitramine and nitrate ester explosives, which include the explosives most commonly encountered in forensic science. Two atmospheric pressure ionization (API) methods, atmospheric pressure chemical ionization (APCI) and electrospray ionization (ESI), and various experimental conditions have been applied to allow for the detection of all 21 explosive compounds. The limit of detection (LOD) in the full-scan mode has been found to be 0.012-1.2 ng on column for the screening of most explosives investigated. For nitrobenzene, an LOD of 10 ng was found with the APCI method in the negative mode. Although the detection of nitrobenzene, 2-, 3-, and 4-nitrotoluene is hindered by the difficult ionization of these compounds, we have found that by forming an adduct with glycine, LOD values in the range of 3-16 ng on column can be achieved. Compared with previous screening methods with thermospray ionization, the API method has distinct advantages, including simplicity and stability of the method applied, an extended screening range and a low detection limit for the explosives studied.

Determination of atractyloside in Callilepis laureola using solid-phase extraction and liquid chromatography–atmospheric pressure ionisation mass spectrometry

A selective analytical method based on high-performance liquid chromatography, combined with atmospheric pressure ionisation mass spectrometry, was developed for the detection of atractyloside. The analysis was performed on an Xterra Phenyl column utilising a gradient elution profile and a mobile phase consisting of 10 mM aqueous ammonium acetate buffer–methanol–acetonitrile. The calibration curve of the method (1 ng/ml–160 μg/ml) was best described by a second order polynomial function ( r 2 = 0.998) but displayed good linearity in the range of 100 ng/ml–1 μg/ml ( r 2 = 0.999). The limit of detection for the atractyloside standard was determined and found to be 100 pg/ml and the limit of quantification of atractyloside in tuber matrix was found to be 250 pg/ml. The relative standard deviation of the method was on average below 5% ( n = 8). The method was successfully applied to the analysis of Callilepis laureola tubers and unknown powdered samples for the presence of atractyloside.

Determination of flumethasone in calf urine and serum by liquid chromatography–tandem mass spectrometry

Corticosteroids can be illegally administered to cattle as growth promoting agents to improve meat production. We developed a liquid chromatography–atmospheric pressure ionization mass spectrometry–mass spectrometry (LC–MS–MS) method able to identify and quantify flumethasone, one of the most potent fluorinated synthetic corticosteroid, in serum and urine from treated calves. The analyte was purified from urine (conjugated and free, following enzymatic hydrolysis) and from serum by C 18 solid-phase and liquid–liquid extractions, then analyzed by LC–MS–MS monitoring the product ions of an abundant precursor (SRM in negative ionization mode). Results on flumethasone residues in biological fluids in three calves treated at different levels are presented. This method allowed the detection of flumethasone in bovine urine and serum at the 30-pg/ml level.

Determination of Imidacloprid and Benzimidazole Residues in Fruits and Vegetables by Liquid Chromatography–Mass Spectrometry after Ethyl Acetate Multiresidue Extraction

A simple and sensitive method based on liquid chromatography-atmospheric pressure ionization-mass spectrometry is described for the determination of 4 benzimidazole pesticides (carbendazim, thiabendazole, benomyl, and thiophanate-methyl) and imidacloprid in vegetables and fruits. Food samples were typically extracted with ethyl acetate to draw the analytes into the organic phase. No cleanup step was necessary before injection into the liquid chromatographic (LC) system with electrospray mass spectrometric detection. The analytes were separated on a reversed-phase C8LC column. Limits of detection for the compounds were in the microg/L range. Results are reported for validation studies with fortified pear and tomato samples and for residues of the target compounds found in the pesticide residue monitoring program during 1998.

Detection of Metabolites Using High‐Performance Liquid Chromatography and Mass Spectrometry

This unit provides a discussion of high-pressure liquid chromatography-atmospheric pressure ionization mass spectrometry (LC-API-MS) for separation, detection, and identification of products from xenobiotic metabolism. It includes an introduction and important technical information for electrospray and atmospheric pressure chemical ionization methods as well as scan modes. Emphasis has been placed on each method as related to phase I and phase II metabolite identification and there are listings of specific applications (and references) to reduce method development time.

Application of spectral libraries for high-performance liquid chromatography–atmospheric pressure ionisation mass spectrometry to the analysis of pesticide and explosive residues in environmental samples

The coupling of high-performance liquid chromatography (HPLC) and atmospheric pressure ionisation mass spectrometry (API-MS) seems to be the method of choice if good separation and selective detection of semi-volatile, thermolabile, and polar substances is required. Libraries of mass spectra will make the identification of unknown substances in complex environmental samples easier and more user-friendly. Unfortunately, existing GC–MS libraries are not applicable to HPLC–API-MS analysis. Thus, new and extensive mass spectral libraries were constructed. Several investigations of chromatographic (composition and salt concentration of the eluent) as well as mass spectrometric (orifice voltage) parameters and a few applications of real environmental samples are used to discuss the possibilities and limits of these libraries.

Analysis of low-molecular-mass inorganic and organic anions by ion chromatography–atmospheric pressure ionization mass spectrometry

Different nonvolatile mobile phases have been tested for the combination of ion-exchange chromatography combined with mass spectrometric detection of anions and organic acids. Buffer systems based on carbonate, sulfate, oxalate and citrate as the eluting species have been used. Among these, citrate proved to be the most versatile eluent allowing the separation of anions with absolute detection limits between 0.4 and 0.7 ng and of organic acids with detection limits between 0.4 and 4 ng in the non-suppressed mode. In the suppressed eluent mode iodate, bromate and chlorate could be separated using sodium carbonate as the mobile phase resulting in detection limits of 50 pg. The method was applied to the analysis of water samples containing oxyhalides originating from ozonization. Additionally, organic acids were separated by chromatographic separation techniques like reversed-phase, ion-pair or ion-exclusion chromatography and the compatibility with mass spectrometry was investigated with special respect to sensitivity of this detection mode.

Poor reproducibility of in-source collisional atmospheric pressure ionization mass spectra of toxicologically relevant drugs

The purpose of the study was to examine the intra- and interlaboratory reproducibility of mass spectra obtained with liquid chromatography–atmospheric pressure ionization mass spectrometry (LC–API-MS) both in electrospray (ESI) and atmospheric pressure chemical ionization (APCI) modes. Toxicologically relevant drugs of different polarity were selected as test substances: morphine-6-glucuronide, 6-monoacetylmorphine, codeine, lysergic acid diethylamide, methylenedioxymethamphetamine. The study was performed in two laboratories using identical instruments and in one using a slightly different instrument. Basic instrument settings and mobile phase were identical in all laboratories. Mass spectra of drugs were taken at four collision energy voltages and using mobile phase of different composition (four concentration levels of acetonitrile and of ammonium formate buffer). The experiments demonstrated that mass spectra of given drugs, obtained in identical conditions with identical instruments, may show very different degrees of fragmentation. Mass spectra obtained with different instruments differed profoundly not only in the degree of fragmentation, but also different fragments and adducts were observed. Short-term intralaboratory reproducibility of mass spectra was satisfactory. On the other hand, the long-term experiments showed different degrees of fragmentation of APCI-generated mass spectra at nominally identical fragmentation energy. The changes in the composition of the mobile phase (concentration of organic modifier or buffer molarity) did not affect the reproducibility of fragmentation to any relevant degree.The study showed that the interlaboratory exchange and use of mass spectrum library, generated by single-quadrupole LC–API-MS instruments, is hardly feasible at the moment, even under very carefully standardized conditions.

Speciation of organo-tin compounds using liquid chromatography–atmospheric pressure ionisation mass spectrometry and liquid chromatography–inductively coupled plasma mass spectrometry as complementary techniques

A liquid chromatographic method for the determination of dibutyltin (DBT), tributyltin (TBT), diphenyltin (DPhT) and triphenyltin (TPhT) in sediments has been developed, which is compatible with both atmospheric pressure ionisation (API) mass spectrometry and inductively coupled plasma (ICP) mass spectrometry. As a result of this development both techniques may be used for the complementary speciation of organo-tin compounds. The chromatographic system comprises of a Kromasil-100 5 μm C18 (150×2.1 mm) column and a mobile phase of 0.05% triethylamine in acetonitrile–acetic acid–water (65:10:25), at a flow-rate of 0.2 ml min−1. The optimisation of the LC–API-MS conditions is discussed, together with the analysis of a real sediment sample for DBT and TBT using selected ion monitoring (SIM).

Liquid chromatography-atmospheric pressure ionization mass spectrometry for the determination of chloro- and nitrophenolic compounds in tap water and sea water

Liquid chromatography coupled to atmospheric-pressure ionization mass spectrometry (LC-API-MS) with negative ion detection was studied for the determination of a variety of phenolic compounds in environmental waters. An isocratic mobile phase of 0.05% acetic acid-acetonitrile (50:50, v/v) was used. The influence of post-column addition of different bases on the sensitivity of the detection in electrospray (ES) was studied. The [M-H] − ion was the base peak for all the compounds using both ES and atmospheric-pressure chemical-ionization (APCI) ion sources. Moreover, abundant structural information was obtained by increasing the extraction voltage. Detection limits for standard solutions ranging from 2 to 13 ng injected for LC-ES-MS and from 0.02 to 20 ng for LC-APCI-MS were obtained. Good reproducibilities (day-to-day and run-to-run) were observed. The optimum LC-ES-MS and LC-APCI-MS conditions thus determined were used for a quantitative analysis of some phenolic compounds in spiked tap water and sea water samples.

Determination of mono- and disulphonated azo dyes by liquid chromatography–atmospheric pressure ionization mass spectrometry

Liquid chromatography–atmospheric pressure chemical ionization (APCI) mass spectrometry (MS) with positive (PI) and negative (NI) modes of operation and liquid chromatography–high flow pneumatically assisted electrospray (ES) mass spectrometry with negative mode were used for the determination of the disulphonated azo dyes Acid Red 1, Mordant Red 9, Acid Red 13, Acid Red 14, Acid Red 73, Acid Yellow 23, Direct Yellow 28 and Acid Blue 113 and of the monosulphonated azo dyes Mordant Yellow 8, Mordant Black 11 and Mordant Black 17. High fragmentation was observed when using APCI with losses of one or two SO3Na groups, either attached to one ring or two different rings. Losses of Na and 2Na are common to all techniques used. High flow ES was the most sensitive technique for all the dyes studied, except for Mordant Red 9, with a linear range varying from 1–3 to 700–800 ng. APCI using negative ion mode was one order of magnitude less sensitive than ES, with a linear range varying from 50–70 to 2000–3000 ng, whereas positive ion mode APCI-MS showed the poorest linear range and sensitivity. The determination of Direct Yellow 28 and Acid Blue 113 in water samples was also reported by preconcentrating 500 ml of water with solid-phase disk extraction followed by LC–high flow pneumatically assisted ES-MS.

Quantification of S-Carboxymethyl-R-Cysteine in Human Plasma by Highperformance Ionexchange Liquid ChromatographyAtmospheric Pressure Ionization Mass Spectrometry

Quantification of S-Carboxymethyl-R-Cysteine in Human Plasma by Highperformance Ionexchange Liquid ChromatographyAtmospheric Pressure Ionization Mass Spectrometry

Quantification of S-Carboxymethyl-R-Cysteine in Human Plasma by Highperformance Ionexchange Liquid ChromatographyAtmospheric Pressure Ionization Mass Spectrometry

Quantification of S-Carboxymethyl-R-Cysteine in Human Plasma by Highperformance Ionexchange Liquid ChromatographyAtmospheric Pressure Ionization Mass Spectrometry

Determination of Thyreostats in Thyroid and Urine Using High-performance Liquid Chromatography–Atmospheric Pressure Chemical Ionisation Mass Spectrometry

A method using liquid chromatography–atmospheric pressure ionisation mass spectrometry is described for the determination of five thyreostats in urine and thyroid tissue. Samples were extracted with ethyl acetate and the extracts were cleaned up on silica solid-phase cartridges. They were then concentrated and injected into the LC–MS system, monitoring the [M + H] + ions for each compound. Additional fragment ions for confirmation purposes could be obtained by increasing the cone voltage on the LC–MS system. Detection limits were in the region of 25 ng g - 1 and recoveries ranged from 41% for the more hydrophilic compounds such as thiouracil to above 100% for the more hydrophobic compounds such as propyl- or phenylthiouracil.

Application of liquid chromatography-atmospheric pressure ionization mass spectrometry in natural product analysis evaluation and optimization of electrospray and heated nebulizer interfaces

A representative set of 46 secondary metabolites of plant and microbial origin was examined with electrospray and atmospheric pressure chemical ionization MS in both positive and negative ion mode, in order to evaluate the applicability of atmospheric pressure ionization LCMS as a tool for rapid identification and dereplication of bioactive compounds in the drug screening process. MS characteristics of different compound classes were determined on the basis of quasi-molecular ion and other adduct ion responses observed with the two LCMC interfaces. Interface parameters and LC mobile phase composition were optimized and an analytical protocol applicable to a wide range of secondary metabolites is proposed.

Determination of triamcinolone acetonide in equine serum and urine by liquid chromatography-atmospheric pressure ionization mass spectrometry.

Urine and serum samples collected from four standard-bred mares after 30-mg intraarticular administrations of triamcinolone acetonide were analyzed using combined high-performance liquid chromatography-atmospheric pressure ionization mass spectrometry. Maximum triamcinolone acetonide concentrations of 32.3, 14.8, 24.3, and 29.4 ng/mL in the urine and 2.7, 1.9, 2.3, and 2.5 ng/mL in the serum samples were observed. The peak concentrations of the drug were detected approximately 22 h (urine) and 12 h (serum) after administration. The drug elimination profiles for both urine and serum are presented and discussed.

Compositional analysis of the phenylthiocarbamyl amino acids by liquid chromatography-atmospheric pressure ionization mass spectrometry with particular attention to the cyst(e)ine derivatives

An approach presented recently for the high-performance liquid chromatographic determination of dl- and l-cystines and cysteines as phenylthiocarbamyl (PTC) derivatives has been completed (i) with the determination of d-cystine/cysteine, (ii) by a study relating to the spectral characteristics of the PTC cystine/cysteine derivatives performed with diode-array detection and (iii) by the fragment analysis of the PTC-cyst(e)ine derivatives, applying the extremely soft conditions of the liquid chromatography-atmosphere pressure ionization mass spectrometry (LC-API-MS). In accordance with earlier experiences it has been repeatedly demonstrated that cystines and cysteines can be determined on the basis of two or four derivatives, with the same retention times and molar responses, without any special pretreatment, furnishing a simple possibility for the determination of the total cystine/cyteine in protein hydrolysates. The UV spectra of all four PTC derivatives provided by diode-array-detected purity parameters (PuP) showed that the corresponding PTC derivatives of dl-l- and d-cystine and -cysteine are identical and homogeneous, and do not show any characteristic differences. On the basis of the fragmentation patterns of seventeen PTC-amino acids and those of six PTC-cyst(e)ines, obtained under the very soft conditions of the LC-API-MS procedure, it can be stated that two characteristic PTC derivatives are formed: (i) the main product (“a” and “b” diastereoisomers, >80% of the total), shown to be the fragment of m/ z = 255, a monomeric cysteine derivative, and (ii) the other characteristic constituent (“c” and “d” stereoisomers, <20% of the total), consisting of a fragments of m/ z = 255 and its oxidised form of m/ z = 287.