Chromatography-atmospheric Pressure Ionization Mass 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.

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.

Adduct formation in quantitative bioanalysis: effect of ionization conditions on paclitaxel

Quantitative analysis of target compounds with liquid chromatography atmospheric pressure ionization mass spectrometry is sometimes hampered by adduct formation. In these situations, cationization with alkali metal ions instead of proton addition is often observed in the positive ion mode. This work studies the process of adduct formation and investigates potential strategies to control this phenomenon. Paclitaxel, a pharmaceutical chemotherapeutic agent, was used as a model compound. Electrospray (ESI), atmospheric pressure chemical ionization (APCI) and sonic spray ionization (SSI) are evaluated and compared. The work was performed on two different instruments, allowing the evaluation of different ionization behavior for different source design for electrospray, if any. Different mobile phase additives were compared, including acetic acid, formic acid, ammonium formate, and a range of primary amines. Continuous infusion was used for a fast screening, to detect optimal conditions. These were then further investigated in detail by LC-MS. The results indicate that electrospray is the more sensitive interface for this compound on the investigated apparatus. Unacceptable quantitative data were acquired without additives in the mobile phase. Generally, additives increased the reproducibility significantly. A response of mainly one ion was achieved with dodecylamine/acetic acid and acetic acid/sodium acetate. The data also point out the importance of evaluating adduct formation for compounds prone to this phenomenon during method development, especially in view of accurate quantitation.

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.

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).

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.

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.

Assay of nicergoline and three metabolites in human plasma and urine by high-performance liquid chromatography—atmospheric pressure ionization mass spectrometry

A method for the simultaneous determination of nicergoline and three of its metabolites in human plasma and urine has been developed using high-performance liquid chromatography—atmospheric pressure ionization mass spectrometry. Nicergoline and its metabolites were extracted from the plasma and urine samples with chloroform and separated on a reversed-phase ODS column. The eluents were led to the atmospheric pressure ionization interface and then analysed in the selected-ion monitoring mode. The detection limits of nicergoline and three of its metabolites were ca. 2 ng/ml in plasma and ca. 10 ng/ml in urine, at a signal-to-noise ratio of 4.

Analysis of underivatized glycosphingolipids by high-performance liquid chromatography/atmospheric pressure ionization mass spectrometry

Analytical conditions for underivatized glycosphingolipids by using high-performance liquid chromatography atmospheric pressure ionization mass spectrometry ( HPLC API-MS ) were investigated. The analysis was performed by using an ordinary reversed-phase column (4.6 × 150 or 4.6 × 250 mm) at a flow rate of 1 ml/min. The glycosphingolipids could be characterized from the HPLC API-MS in terms of molecular weight, ceramide composition, and partial oligosaccharide sequence. In order to obtain an adequate spectrum the amount of material needed is in the range of a few micrograms of lipid. By selected ion monitoring the sensitivity of the method allowed characterization of only 60 ng of glycosphingolipid. The method will be very useful in the characterization of small quantities of glycosphingolipids from biological samples.