Positive-ion Atmospheric Pressure Chemical Ionization Research Articles

Atmospheric pressure ionization for gas chromatography-high resolution mass spectrometry determination of polychlorinated naphthalenes in marine sediments

In this work, the performance of the atmospheric pressure chemical ionization (APCI) and photoionization (APPI) was assessed to develop a new selective and sensitive gas chromatography-high resolution mass spectrometry (GC-HRMS) method for the determination of polychlorinated naphthalenes (PCNs) in sediment samples. The capability of both APCI and APPI sources for the ionization of PCNs was investigated, showing the formation of the molecular ion and the [M‒Cl+O]‒ ion in positive and negative ion modes, respectively. Positive ion APCI provided high responses using high corona ion current, while the use of high vapour pressure dopant-solvents, such as toluene in positive mode and diethyl ether in the negative mode, was required to achieve high ionization efficiencies in APPI. The performance of the two API sources in the PCN determination by GC-HRMS were compared and the best results were achieved using the GC-APPI(+)-HRMS (Orbitrap) system. The GC-APPI(+)-HRMS (Orbitrap) method was applied to the characterization of Halowax mixtures and the analysis of marine sediments collected near to the coastal area of Barcelona (NE, Spain), demonstrating a great detection capability with low method limits of detection (0.2–1.6 pg g−1 dry weight), good precision (RSD <15%) and trueness (relative error <13%). Total PCN concentrations ranged from 0.35 to 5.0 ng g−1 dry weight and the presence of related compounds, such as polychlorinated biphenyls (PCBs), was also detected by combining positive and negative ion modes, providing complementary information to better monitor of all PCN congener groups. The results presented here show the feasibility of the GC-APPI-HRMS method for the suitable determination of PCNs.

MOFs-derived N-doped carbon matrix superacid-catalyzed hydrocracking of a residue from thermal dissolution of Hefeng subbituminous coal

An active, low-cost, and recyclable catalyst was prepared by impregnating trifluoromethanesulfonic acid (TFMSA) onto metal-organic frameworks (MOFs)-derived N-doped carbon matrix nanoparticles. The residue (RTD) from thermal dissolution (TD) of Hefeng subbituminous coal in methanol was subjected to further TD and catalytic hydrocracking (CHC) over the catalyst, i.e., TFMSA/MOFs at 300 °C in cyclohexane. Detailed molecular compositions of the soluble portions from TD (SPTD) and CHC (SPCHC) were characterized with a Fourier transform infrared spectrometer, gas chromatograph/mass spectrometer (GC/MS), and positive-ion atmospheric pressure chemical ionization orbitrap mass spectrometer (PIAPCIORMS). The results show that 15.60% of organic matter in RTD was converted to a soluble portion by the CHC, whereas the yield of SPTD is only 1.04%. According to the analysis with GC/MS, SPCHC is rich in alkyl-substituted benzenes, while most of the GC/MS-detectable compounds in SPTD are alkyl-substituted arenols, alkyl-substituted cyclenones, and phenylalkanones in addition to alkyl-substituted benzenes. The analysis with PIAPCIORMS shows that both the number and yields of basic nitrogen-containing species were dramatically reduced after the CHC. These facts indicate that TFMSA/MOFs effectively catalyzed the cleavage of Car–Calk bridged bonds connecting some aromatic rings (ARs) and side chains on some ARs in RTD to obtain soluble compounds. Di(1-naphthyl)methane and 2-(benzyloxy)naphthalene were used as coal-related model compounds (CRMCs) and their CHCs were investigated to further explore the catalysis of TFMSA/MOFs in the CHC of RTD. As a result, TFMSA/MOFs effectively catalyzed the cleavage of Car-Calk and C-O bonds in the CRMCs under moderate conditions. TFMSA/MOFs can be easily separated by using an external magnetic field and the recovered TFMSA/MOFs is still highly active for the CHC of DNM.

Identification of organic hydroperoxides and peroxy acids using atmospheric pressure chemical ionization–tandem mass spectrometry (APCI-MS/MS): application to secondary organic aerosol

Abstract. Molecules with hydroperoxide functional groups are of extreme importance to both the atmospheric and biological chemistry fields. In this work, an analytical method is presented for the identification of organic hydroperoxides and peroxy acids (ROOH) by direct infusion of liquid samples into a positive-ion atmospheric pressure chemical ionization–tandem mass spectrometer ((+)-APCI-MS/MS). Under collisional dissociation conditions, a characteristic neutral loss of 51 Da (arising from loss of H2O2+NH3) from ammonium adducts of the molecular ions ([M + NH4]+) is observed for ROOH standards (i.e. cumene hydroperoxide, isoprene-4-hydroxy-3-hydroperoxide (ISOPOOH), tert-butyl hydroperoxide, 2-butanone peroxide and peracetic acid), as well as the ROOH formed from the reactions of H2O2 with aldehydes (i.e. acetaldehyde, hexanal, glyoxal and methylglyoxal). This new ROOH detection method was applied to methanol extracts of secondary organic aerosol (SOA) material generated from ozonolysis of α-pinene, indicating a number of ROOH molecules in the SOA material. While the full-scan mass spectrum of SOA demonstrates the presence of monomers (m∕z = 80–250), dimers (m∕z = 250–450) and trimers (m∕z = 450–600), the neutral loss scan shows that the ROOH products all have masses less than 300 Da, indicating that ROOH molecules may not contribute significantly to the SOA oligomeric content. We anticipate this method could also be applied to biological systems with considerable value.

Mass spectrometric elucidation of triacylglycerol content of Brevoortia tyrannus (menhaden) oil using non-aqueous reversed-phase liquid chromatography under ultra high pressure conditions

A non-aqueous reversed phase high performance liquid chromatography method was developed, and optimized for triacylglycerol analysis in a Brevoortia tyrannus (menhaden) oil sample. Four columns were serially coupled to tackle such a task, for a total length of 60cm of shell-packed stationary phase, and operated under ultra high pressure conditions. As detection, positive-ion atmospheric pressure chemical ionization mass spectrometry was used to attain identification of the analyzed sample components. A number of 137 triacylglycerols containing up to 19 fatty acids, with 14–22 carbon atom alkyl chain length and 0–6 double bonds, were positively identified in the complex lipidic sample. This is the first work that reports an extensive characterization of the triacylglycerol fraction of menhaden oil.

Analysis of Daphnane Orthoesters in Poisonous Australian Pimelea Species by Liquid Chromatography−Tandem Mass Spectrometry

Cattle grazing in arid rangelands of Australia suffer periodic extensive and serious poisoning by the plant species Pimelea trichostachya, P. simplex, and P. elongata. Pimelea poisoning (also known as St. George disease and Marree disease) has been attributed to the presence of the diterpenoid orthoester simplexin in these species. However, literature relating to previous studies is complicated by taxonomic revisions, and the presence of simplexin has not previously been verified in all currently recognized taxa capable of inducing pimelea poisoning syndrome, with no previous chemical studies of P. trichostachya (as currently classified) or P. simplex subsp. continua. We report here the isolation of simplexin from P. trichostachya and the development of a liquid chromatography-mass spectrometry/mass spectrometry (LC-MS/MS) method to measure simplexin concentrations in pimelea plant material. Simplexin was quantified by positive-ion atmospheric pressure chemical ionization (APCI) LC-MS/MS with selected reaction monitoring (SRM) of the m/z 533.3 > 253.3 transition. LC-MS/MS analysis of the four poisonous taxa P. trichostachya, P. elongata, P. simplex subsp. continua, and P. simplex subsp. simplex showed similar profiles with simplexin as the major diterpenoid ester component in all four taxa accompanied by varying amounts of related orthoesters. Similar analyses of P. decora, P. haematostachya, and P. microcephala also demonstrated the presence of simplexin in these species but at far lower concentrations, consistent with the limited reports of stock poisoning associated with these species. The less common, shrubby species P. penicillaris contained simplexin at up to 55 mg/kg dry weight and would be expected to cause poisoning if animals consumed sufficient plant material.

Improved Abundance Sensitivity of Molecular Ions in Positive-Ion APCI MS Analysis of Petroleum in Toluene

Positive-ion atmospheric pressure chemical ionization (APCI) Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) analyses of petroleum sample were performed with higher sensitivity by switching the solvent composition from toluene and methanol or acetonitrile to a one-component system consisting only of toluene. In solvent blends, molecular ions were more abundant than were protonated ions with increasing percentages of toluene. In 100% toluene, the double-bond equivalence (DBE) distributions of molecular ions obtained by APCI MS for each compound class were very similar to those obtained in dopant assisted atmospheric pressure photo ionization (APPI) MS analyses. Therefore, it was concluded that charge-transfer reaction, which is important in toluene-doped APPI processes, also plays a major role in positive-ion APCI. In the DBE distributions of S(1), S(2), and SO heteroatom classes, a larger enhancement in the relative abundance of molecular ions at fairly specific DBE values was observed as the solvent was progressively switched to toluene. This enhanced abundance of molecular ions was likely dependent on molecular structure.

The Use of APCI-MS with HPLC and Other Separation Techniques for Identification of Carotenoids and Related Compounds

The heat labile carotenoids cannot be analyzed by gas chromatography (GC) and GC-mass spectrometry (GC- MS). The only useful method appears to be high-performance liquid chromatography (HPLC) with UV/visible (UV/Vis) or mass spectrometric detection (LC-MS). Reversed-phase HPLC (RP-HPLC) is a preferred method, which is frequently used with C18 stationary phase, usually with gradient elution. In contrast to other ionization techniques, xanthophylls and carotenes form both molecular ions and protonated molecules during positive ion APCI (atmospheric pressure chemical ionization). APCI is an ideal method of ionization for low- to medium-polar compounds, which include also carotenoids and related compounds. Since their molecular mass does not exceed 2000 amu even in the case of glycosides or esters with fatty acids, this method is exceedingly suitable for their analysis. The review summarizes the data on its use for this group of compounds.

Triacylglycerols profiling in plant oils important in food industry, dietetics and cosmetics using high-performance liquid chromatography–atmospheric pressure chemical ionization mass spectrometry

Optimized non-aqueous reversed-phase high-performance liquid chromatography method using acetonitrile–2-propanol gradient elution and the column coupling in the total length of 45 cm has been applied for the high resolution separation of plant oils important in food industry, dietetics and cosmetics. Positive-ion atmospheric pressure chemical ionization mass spectrometry is used for the unambiguous identification and also the reliable quantitation with the response factors approach. Based on the precise determination of individual triacyglycerol concentrations, the calculation of average parameters important in the nutrition is performed, i.e. average carbon number, average double bond number, relative concentrations of essential, saturated, monounsaturated and polyunsaturated fatty acids. Results are reported in the form of both chromatographic fingerprints and tables containing relative concentrations for all triacylglycerols and fatty acids in individual samples. In total, 264 triacylglycerols consisting of 28 fatty acids with the alkyl chain length from 6 to 26 carbon atoms and 0 to 4 double bonds have been identified in 26 industrial important plant oils.

Comprehensive Analysis of Vitamin E Constituents in Human Plasma by Liquid Chromatography−Mass Spectrometry

The present paper describes the development and validation of a normal-phase liquid chromatography-mass spectrometry (NP-HPLC-MS) method for the screening and quantification of vitamin E constituents in human plasma and food matrixes. Liquid-liquid extraction combined with isotope dilution was applied to extract the lipophilic target analytes. Baseline separation of alpha-tocopherylacetate, alpha-tocopherol, alpha-tocotrienol, alpha-tocopherylquinone, beta-tocopherol, gamma-tocopherol, beta-tocotrienol, gamma-tocotrienol, delta-tocopherol, and delta-tocotrienol was achieved utilizing a normal-phase amine column operated with n-hexane and 1,4-dioxane as solvents. Detection was achieved by positive-ion atmospheric-pressure chemical ionization (APCI). Key features of the method are lower limits of detection, 3-51 nmoles/L; lower limits of quantification, 8-168 nmoles/L; linearity coefficients, 0.9778-0.9989; linear ranges, 0.01-29 micromol/L; recoveries, 53-92%; accuracies, 99-103%; intraday precisions, 2-17%; interday precisions, 5-18%; and suppression values, 0-29%. Fragmentation of tocopherols was studied by tandem mass spectrometry, and a fragmentation scheme for tocotrienols/tocopherols is postulated. Neutral-loss and precursor-ion scan experiments were performed for targeted discovery of oxidation products of tocopherols in human blood and fish oil, the latter being an important food component. The presented data suggest that this method will help to expand the number of quantified/discovered vitamin E constituents detected in food products and analyzed during human/animal trials in order to give a more comprehensive picture to nutritionists about the fate of vitamin E.

Effects of functional groups on the fragmentation of dyes in electrospray and atmospheric pressure chemical ionization mass spectra

Electrospray ionization (ESI) is most suitable for dyes with an ionic or very polar character, while atmospheric pressure chemical ionization (APCI) suits better those dyes and pigments with low to medium polarity. The negative-ion mode of ESI is used for anionic dyes such as (poly)sulfonated and/or (poly)sulfated variants, where the series of deprotonated molecules enables an easy determination of molecular weights and the number of acid groups. The positive-ion APCI or ESI mass spectra of non-ionic and cationic dyes and pigments provide typical molecular adducts [M + H] +, [M + Na] + and [M + K] + used for the molecular assignment. The first-order mass spectra often suffer from the lack of fragment ions, which can be solved by using multistage tandem mass spectra (MS n ) measured with an ion trap analyzer. The effects of various functional groups on the fragmentation behavior are described herein. The detailed understanding of fragmentation paths enables the correlation among particular functional groups and the fragmentation patterns. The presented approach is applicable for the structural analysis of complex mixtures using HPLC/MS/MS techniques with volatile ion-pairing agents.

High‐throughput adaptation for the quantitation of total folate in human red blood cells by LC‐MS/MS

We adapted an LC-MS/MS method for measuring whole blood folate (J. Ag. Food Chem., 2005;53:–7394) to high-throughput platform for rapid sample processing and analysis in a 96-well format. Briefly, whole blood was fortified with [13C6]pABA internal standard and treated with 12.1 N hydrochloric acid at 110 °C for four hours, causing release of the folates from the whole blood and subsequent hydrolysis to para-aminobenzoic acid (pABA). The hydrolysate was diluted and cleaned-up using a C18 SPE 96-well plate; and the pABA isotopomers were eluted with ethyl acetate/hexane before methylation with methanol and trimethylsilyldiazomethane. The methyl-pABA derivatives were detected and quantified by positive-ion atmospheric pressure chemical ionization (APCI) LC-MS/MS. An isocratic mobile phase of acetonitrile-water (70:30) on a C18 analytical column was used with a post-column reagent of 0.025% formic acid. The limit of quantitation for folate was 56 nmol/L. Results obtained by this method, an LC-MS/MS method, and chemiluminescence were compared for fifteen blood samples obtained from healthy volunteers. This method provided enhanced sample throughput (n = 192/day) compared to previously reported GC/MS and LC-MS/MS methods and is a good candidate for clinical studies where accuracy is needed to assess folate nutritional status. Supported by NIH DK 45939.

Quantitation of Total Folate in Whole Blood Using LC-MS/MS

An accurate method for measuring whole blood total folate using liquid chromatography with tandem mass spectrometry is described and compared to GC/MS and a chemiluminescence assay. Whole blood from normal adults (n = 15) was fortified with a [(13)C(6)]para-aminobenzoic acid (pABA) internal standard and treated with 12.1 N hydrochloric acid at 110 degrees C for 4 h to hydrolyze all folates to pABA. Contaminants in the hydrolysate were adsorbed onto a C18 SPE cartridge. The eluate containing the folate catabolite pABA was partitioned into ethyl acetate and methylesterified with trimethylsilyldiazomethane. The methyl-pABA derivatives were quantified by positive-ion atmospheric pressure chemical ionization (APCI)LC-MS/MS. An isocratic mobile phase of acetonitrile-water (70:30) (v/v) on a C18 analytical column was used with a postcolumn reagent of 0.025% formic acid. The limit of quantitation for folate was 56.6 nmol/L RBC, and the limit of detection was 22.6 nmol/L RBC. Folate levels as determined by LC-MS/MS correlated well with the chemiluminescence assay and a GC/MS method. This new LC-MS/MS method provides enhanced sample throughput (n = 36 per day) as compared to GC/MS methods. LC-MS/MS will enable accurate measurements of red blood cell (RBC) folate in nutrition surveys and clinical trials.

Determination of β-Agonist Residues in Bovine Urine Using Liquid Chromatography-Tandem Mass Spectrometry

A multiresidue method was developed and validated to screen bovine urine samples for 10 beta-2-adrenergic agonistic drugs--brombuterol, cimaterol, clenbuterol, clenpenterol, isoxsuprine, mabuterol, ractopamine, ritodrine, salbutamol, and tulobuterol--at the 2 microg/L level. The method is also quantitative in the range of 1 to 4 microg/L for all analytes except salbutamol. The procedure uses enzymatic digestion, liquid-liquid extraction, and cleanup on solid-phase extraction columns, followed by detection using a liquid chromatograph-tandem quadrupole mass spectrometer operated in the positive-ion atmospheric pressure chemical ionization multiple-reaction monitoring mode. Method validation included assessment of recoveries, repeatabilities, linearity of responses, decision limits, and detection capabilities. Overall average recoveries ranged from 70-91%; recoveries were generally lower for salbutamol. The decision limits ranged from 0.4-1.0 microg/L, and detection capabilities from 0.6-1.7 microg/L.

Ion‐pairing high‐performance liquid chromatography‐mass spectrometry of impurities and reduction products of sulphonated azodyes

AbstractAn HPLC separation method with triethylammonium acetate mobile phase additive developed for the analysis of impurities in polysulphonated azo dyes provides good separation selectivity and compatibility with electrospray ionisation (ESI) mass spectrometry. The negative‐ion ESI mass spectra containing only peaks of deprotonated molecules [M–H]– for monosulphonic acids, [M–xH]x–, and sodiated adducts [M–(x + y)H + yNa]x– for polysulphonic acids allow easy molecular mass determination of unknown impurities. Based on the knowledge of the molecular masses and of the fragment ions in the MS/MS spectra, probable structures of trace impurities in commercial dye samples are proposed. To assist in the interpretation of the mass spectra of complex polysulphonated azodyes, additional information can be obtained after chemical reduction of azodyes to aromatic amines. The structures of the non‐sulphonated reduction products can be determined by reversed‐phase HPLC/MS with positive‐ion atmospheric pressure chemical ionisation and of the sulphonated products by ion‐pairing HPLC/MS with negative‐ion ESI.

Identification of acylated xanthone glycosides by liquid chromatography–atmospheric pressure chemical ionization mass spectrometry in positive and negative modes from the lichen Umbilicaria proboscidea

The xanthoside composition of the crude extract of Umbilicaria proboscidea (L.) Schrader was characterized using LC–UV diode array detection and LC–atmospheric pressure chemical ionization (APCI) MS methods. The presence of acylated xanthone- O-glucosides was determined by both positive and negative ion LC–APCI-MS methods. Based on UV and MS spectral data and NMR spectroscopy, a total of 14 compounds (6- O-acylated umbilicaxanthosides A and B) were identified in U. proboscidea for the first time. In order to further develop the applicability of LC–MS techniques in phytochemical characterization, the effect of different ionization energy on fragmentation was studied using APCI. The optimal ionization conditions were achieved in positive ion APCI by using ammonium acetate buffer and in negative ion APCI by using formic acid (pH 4).

Mass spectrometric determination of ergosterol in a prairie natural wetland

Fungi are the main decomposers of plant material in an aquatic system. Levels of ergosterol, a compound generally specific to the cell membranes of fungi can be used as an indirect measure of their presence and biomass. Described is a procedure utilising reversed-phase liquid chromatography with positive-ion atmospheric pressure chemical ionization tandem mass spectrometry (LC–APCI–MS–MS) for full quantification and confirmation of ergosterol in various wetland matrices. Solid and liquid samples (0.2–1 g dry weight and 10 ml) were subjected to alkaline saponification followed by serial extraction using pentane (3×10 ml). The procedure was applicable to quantitative analysis of wetland samples with little or no clean up. Under low energy (CID) collision induced dissociation conditions the major product-ion formed from m/ z 379.4 [M+H–H 2O] + was m/ z 69.4 [(CH 3) 2CHCHCH] +. Selected reaction monitoring (SRM) of this transition along with the retention time were used to confirm that ergosterol was widely distributed at ppm levels (2.4 to 303 μg ash free dry mass (AFDM)) in matrices of decaying willow leaves, Scirpus stems (living and dead) and sediment collected at the water–sediment interface. Comparison between LC–APCI–MS–MS (SRM), LC–APCI–MS using selected ion monitoring (SIM) and liquid chromatography with ultraviolet absorption detection (LC–UV) indicated that SRM analysis was the most selective technique.

Simultaneous determination of all-trans, 9-cis, 13-cis retinoic acid and retinol in rat prostate using liquid chromatography-mass spectrometry.

Since retinoic acid (RA) and RA receptors are key developmental regulators during organogenesis, they might participate in the abnormal development of the prostate caused by early estrogen exposure. In order to test this assumption, a sensitive analytical method that can differentiate 9-cis, 13-cis, and all-trans RA in small tissue samples ( approximately 8 mg) is required. Since retinol is the metabolic precursor to RA, simultaneous quantification of retinol would also provide valuable information. Here, we report a liquid chromatography-mass spectrometry method for simultaneous determination of retinol and 9-cis, 13-cis, and all-trans RA in rat prostate. Mass spectrometric signal responses for RA were compared using positive ion atmospheric-pressure chemical ionization (APCI) and electrospray, as well as positive ion and negative ion APCI. Positive ion APCI was selected for all subsequent analysis for its better sensitivity, and to provide simultaneous determination of retinol and RA. Ventral prostate tissue samples were homogenized and extracted following simple protein precipitation without derivatization. Baseline separation of 9-cis, 13-cis, and all-trans RA standards was obtained by using a non-porous silica C18 column. Selected ion monitoring of the ions m/z 301 and m/z 269 was carried out for mass spectrometric quantitative analysis. The ion of m/z 301 corresponded to the protonated molecule of RA, whereas the ion of m/z 269 corresponded to loss of water or acetic acid from the protonated molecule of retinol or the internal standard retinyl acetate respectively. The method has a linear response over a concentration range of at least three orders of magnitude. The limit of quantitation was determined to be 702 fmol all-trans RA injected on-column. The method showed excellent intra- and inter-assay reproducibility and good recovery, and is suitable for analyzing RA and retinol in small tissue samples (approximately 8 mg).

Determination of retigabine and its acetyl metabolite in biological matrices by on-line solid-phase extraction (column switching) liquid chromatography with tandem mass spectrometry

A HPLC assay with tandem mass spectrometric detection in the positive-ion atmospheric pressure chemical ionisation (APCI) mode for the sensitive determination of retigabine [( I), D-23129] and its acetyl metabolite [( II), ADW 21-360] in plasma was developed, utilising the structural analogue (D-10328), ( III), as internal standard. Automated on-line solid-phase extraction of diluted plasma samples, based on 200-μl plasma aliquots, at pH 6.5, allowed a reliable quantification of retigabine and the acetyl metabolite down to 1 ng/ml. Injection of 500 μl of diluted plasma onto a C 2 stationary phase-based column switching system in combination with a 75 mm×4 mm reversed-phase analytical column at a flow-rate of 0.5 ml/min provided cycle times of 4 min per sample. The standard curves were linear from 1 to 1000 ng/ml using weighted linear regression analysis (1/ x 2). The method is accurate (mean accuracy ≤±10%), precise (RSD <±15%) and sensitive, providing lower limits of quantification in plasma of 1 ng/ml for retigabine ( I), and 2.5 ng/ml for the metabolite ( II) with limits of detection of 0.5 ng/ml for both analytes. Up to 200 unknowns may be analysed each 24 h per analyst.

Packed Column Supercritical Fluid Chromatography/Mass Spectrometry for High-Throughput Analysis. Part 2

A supercritical fluid chromatograph was previously interfaced to a mass spectrometer (SFC/MS) and the system evaluated for applications requiring high sample throughput using negative-mode atmospheric-pressure chemical ionization (APCI) (Ventura et al. Anal. Chem. 1999, 71, 2410-2416). This report extends the previous work demonstrating the effectiveness of SFC/MS, using positive ion APCI for the analysis of compounds with a wide range of polarities. Substituting SFC/MS for LC/MS results in substantial time saving, increased chromatographic efficiency, and more precise quantitation of sample mixtures. Flow injection analysis (FIA) also benefits from our SFC/MS system. A broader range of solvents is compatible with the SFC mobile phase compared with LC/MS, and solutes elute more rapidly from the SFC/MS system, reducing sample carryover and cycle time. Our instrumental setup also allows for facile conversion between LC/MS and SFC/MS modes of operation.

Separation and identification of various carotenoids by C30 reversed-phase high-performance liquid chromatography coupled to UV and atmospheric pressure chemical ionization mass spectrometric detection

In this paper the application of on-line HPLC–UV–APCI (atmospheric pressure chemical ionization) mass spectrometry (MS) coupling for the separation and determination of different carotenoids as well as cis/trans isomers of β-carotene is reported. All HPLC separations were carried out under RP conditions on self-synthesized polymeric C30 phases. The analysis of a carotenoid mixture containing astaxanthin, canthaxanthin, zeaxanthin, echinenone and β-carotene by HPLC–APCI-MS was achieved by scanning the mass range from m/z 200 to 700. For the characterization of a sample containing cis/trans isomers of β-carotene as well as their oxidation products, a photodiode-array UV–visible absorbance detector was used in addition between the column and the mass spectrometer for structural elucidation of the geometrical isomers. The detection limit for β-carotene in positive-ion APCI–MS was determined to be 1 pmol. In addition, an extract of non-polar substances in vegetable juice has been analyzed by HPLC–APCI-MS. The included carotenoids could be identified by their masses and their retention times.