Yining Zhao

Characterization of triglycerides in vegetable oils by silver-ion packed-column supercritical fluid chromatography coupled to mass spectroscopy with atmospheric pressure chemical ionization and coordination ion spray.

Characterization of triglycerides in vegetable oils was achieved by silver-ion packed-column supercritical fluid chromatography (SI-pSFC) with mass spectrometric detection. Hyphenation was made using commercially available liquid chromatography-mass spectrometry (LC-MS) interfaces without any modification. A make-up fluid was delivered through a T-piece placed before or after the SFC restrictor by means of a high pressure pump. Atmospheric pressure chemical ionization (APCI) and coordination ion spray (CIS) with silver ions were used as ionization modes. Compared to UV detection, the sensitivity was increased by a factor of 100. Both ionization modes are generating similar structural information. Molecular ions [M-H]+ or [M-Ag(-)] are observed in the mass spectra with exception of the saturated triglycerides for which only CIS gives intense molecular ions. The position at which the fatty acids are esterified to the glycerol backbone can be elucidated by pSFC-APCI although it remains speculative whether this is valid for highly unsaturated triglycerides because reference compounds are not available to proof this.

Chemiluminescence-based detection: principles and analytical applications in flowing streams and in immunoassays

The present paper provides the principles of chemiluminescence (CL) and its powerful applications in analytical chemistry, mainly in the area of flow injection analysis, column liquid chromatographic and capillary electrophoretic separating systems, and its potential in immunoassays. CL is light produced by a chemical reaction. The most common advantages of chemiluminescent reactions are the relatively simple instrumentation required, the very low detection limits and wide dynamic ranges, which have contributed to the interest of CL detection in flow injection analysis, high performance liquid chromatography, including miniaturized systems, and, most recently, the exploding area of capillary electrophoresis. The latter powerful microanalytical separation technique offers high numbers of theoretical plates and relatively short analysis times requiring only small sample volumes, the migrating system comprising aqueous buffer solutions. In non-isotopic immunoassays, covering a great variety of applications in human and veterinary medicine, forensic medicine, agriculture and food industry, the radioisotope is replaced by a fluorescence or chemiluminescent label. The use of CL as a detection principle permits quantitative determination of various compounds at low concentrations. Disadvantages of the CL-based technique may include lack of sufficient selectivity and sensitivity to various physicochemical factors.

Speciation of six arsenic compounds using capillary electrophoresis-inductively coupled plasma mass spectrometry

Capillary electrophoresis (CE) was used to separate four anionic {arsenite [As(III)], arsenate [As(V)], monomethylarsonic acid and dimethylarsinic acid} and two cationic forms (arsenobetaine and arsenocholine) of As in a single run. At sufficiently high concentrations, the determination of these compounds could be accomplished by means of UV detection. The determination of low concentrations (<10 µg l –1 ) of these compounds of interest was accomplished by coupling CE on-line with inductively coupled plasma mass spectrometry (ICP-MS). To accomplish this coupling, a microconcentric nebulizer was used. The modifications necessary to make a conventional CE system compatible with ICP-MS, the optimization of the operation parameters and of sample stacking conditions together with the effect of the sheath liquid and of an induced laminar flow are discussed. The analytical figures of merit of the method were assessed and the limit of determination (based on the peak height of a peak for which the signal-to-noise ratio is 10:1) was found to be 1-2 µg l –1 As for each species. The recovery for the compounds of interest was determined using a spiked mineral water sample. Samples of mineral water, soil leachate and urine were analyzed with the CE-ICP-MS combination.

Quantitation of 8-prenylnaringenin, a novel phytoestrogen in hops (Humulus lupulus L.), hop products, and beers, by benchtop HPLC-MS using electrospray ionization

Summary8-Prenylnaringenin (8-PN), a potent phytoestrogen, present in hops (Humulus lupulus L.), hop products, and most beers, exhibits an estrogenic activity greater than that of any of the known phytoestrogens. A sensitive, selective, and robust analytical method, based on HPLC-MS (High Performance Liquid Chromatography—Mass Spectrometry) using atmospheric pressure electrospray ionization, has been developed for systematic investigation of the development and the localization of this estrogenic trait in the hop plant, as well as for quantitative determination of 8-PN in hop varieties, hop products, and beers. Excellent linearity was obtained in the range of 3.7–2,200 μg L−1 (γ=0.9999, n=7) and the limit of detection wasca 1 μg L−1. Recoveries were between 93.8% (110 μg L−1) and 96.5% (370 μg L−1) for hop products, and between 63.4% (18.5 μgL−1) and 72.8% (37 μg L−1) for beers. Good precision was achieved with relative standard deviations of less than 5% within-day (n=6) and less than 10% from-day-to-day (n=18).

Chemiluminescence detection coupled to liquid chromatography for the determination of penicillamine in human urine

Abstract An on-line liquid chromatography (LC) chemiluminescence detection system is proposed for the determination of penicillamine in human urine. Ion-pair reversed-phase LC using octane sulphonic acid as ion-pairing reagent allows the separation of penicillamine from the urine matrix. The Chemiluminescence reaction of penicillamine with Ce(IV) in sulphuric acid sensitized by quinine is suggested for sensitive penicillamine detection in a post-column mixing set-up. The Chemiluminescence response was linearly related to the concentration of penicillamine in the range 2.0–2000 μmol 1−1 (r = 0.9994, peak height, and 0.9997 peak area, n = 10) with a detection limit ( S N = 3) of 1.0 μ mol 1 −1 (100 pmol per injection). Relative standard deviations were less than 5% (n = 10) for 10–50 μmol 1−1. The excretion rates of penicillamine in human urine of three volunteers after oral penicillamine administration were determined in the present study.

Considerations concerning interaction characterization of oligopeptide mixtures with vancomycin using affinity capillary electrophoresis-electrospray mass spectrometry

In the past few years affinity capillary electrophoresis (ACE) has proven to be a powerful tool to study molecular interactions. In ACE the change in electrophoretic mobility between a free and a complexed ligand with a receptor dissolved in the background electrolyte is observed. It provides an accurate way to calculate binding or dissociation constants and, when coupled to mass spectrometry, it forms a promising method to analyze solution‐based combinatorial libraries. We report a model study on the macrocyclic antibiotic vancomycin using a 36‐component library of tetrapeptides of the type 9‐fluorenylmethoxycarbonyl (Fmoc)‐L‐Asp‐L‐Asp‐D‐Xaa‐D‐Xaa. The mass spectrometry conditions were optimized by fine‐tuning the background electrolyte and sheath flow composition to achieve optimal sensitivity in the negative ionization mode. Different types of capillaries were also evaluated on their potential to screen combinatorial libraries. The library components that show the strongest interaction were identified. The dissociation constants of a mixture of six compounds with a broad affinity range were simultaneously established by Scatchard analysis on ACE‐MS.

Photolysis of hop-derived trans-iso-α-acids and trans-tetrahydroiso-α-acids: product identification in relation to the lightstruck flavour of beer

The photolysis of hop-derived trans-iso-alpha-acids (2a-c; naturally occurring bitter compounds present in beer) and of trans-tetrahydroiso-alpha-acids (5a-c; semi-synthetic advanced hop products) was investigated at 300 nm in methanol. The complex photoreaction mixtures were separated by high-performance liquid chromatography (HPLC) using diode array detection and the major photoreaction products were identified by HPLC-mass spectroscopy. The main part of the mixture consisted of compounds, which originated from recombination of radicals derived from Norrish Type I photocleavage of the acyloin moiety in both trans-iso-alpha-acids and trans-tetrahydroiso-alpha-acids. The results confirm the intermediacy of radicals that were previously identified by time-resolved electron paramagnetic resonance and they bear relevance to the formation of the lightstruck flavour that is generated when beer is exposed to light. Additionally, new photoproducts were found that are formed by photochemical reactions hitherto undiscovered in hop chemistry, including photoenolization of trans-isohumulone (2a) leading to trans-alloisohumulone (13a) and a retro oxa-di-pi-methane rearrangement in trans-isohumulone (2a) and trans-tetrahydroiso-alpha-acids to humulone (1a) and tetrahydro-alpha-acids (23a-b), respectively.

Analysis of jojoba oil by LC-coordination ion spray-MS (LC-CIS-MS).

The intact wax esters in jojoba oil were analyzed by microbore LC-MS. Neither atmospheric pressure chemical nor electrospray ionization (APCI and ESI) provided ions. Excellent ionization was obtained by adding post column Ag + ions. With this technique, called coordination ion spray MS (CIS-MS), the molecular ion could be unequivocally elucidated and, by applying a collision induced dissociation (CID) voltage of 290 V, the acidic and alcoholic part of the different wax esters could be identified. Ion formation and fragmentation are discussed. Unsaturation in the alcohol or acid chain is not a prerequisite for obtaining [M+Ag] + ions but fragmentation only occurs when the chains are unsaturated.

Determination of chlormequat residues in pears and pear concentrates by benchtop LC-ESI-MS

SummaryA fast, simple and robust method for the routine determination of chlormequat (CCC) in pears and pear concentrates is described. The method is based on sample clean-up using an SPE strong cationic exchange (SCX) cartridge followed by analysis on a benchtop liquid chromatograph coupled to an atmospheric pressure electrospray ionisation mass spectrometer (LC-ESI-MS). The instrument is equipped with a weak cationic exchange (WCX) column. For quantification, ionsm/z 122 and 124, representing the chloro isotopes of the molecular ion, are monitored. Recoveries for chlormequat at three levels (50, 100, 250 ppb) from pears are in the range of 81–85%, and from pear concentrates in the range of 90–93%. The dynamic range covers concentrations from 10 to 500 μg kg−1 (ppb) with a correlation coefficient of r=0.999. During validation, the reproducibility (RSD) for the standard solution is found to be 4.3% (n=8; within one day) and 6.0% (n=16, day-to-day), the limit of detection (LOD) is 3 ppb (3 S/N) and the limit of quantitation (LOQ) is 10 ppb. Residue levels in pears purchased from a local supermarket in December 1998 and January 1999 were as high as 8 mg kg−1 (8 ppm). The method can also be applied to the determination of CCC in other fruits and concentrates e.g. apples and grapes.

Chemiluminescence determination of tiopronin and its metabolite 2-mercaptopropionic acid in human urine by HPLC coupled with flow injection

SummaryIn previous pharmacokinetic studies tiopronin, a drug used for effective treatment of cystinuria and rheumatoid arthritis, and its metabolite 2-mercaptopropionic acid were analysed by conventional liquid chromatography with pre- and post-column derivatization and UV detection. Now a novel HPLC-coupled chemiluminescence-flow-injection analysis (CL-FIA) method has been developed for the determination of tiopronin and 2-mercaptopropionic acid in urine. The method is based on chemiluminescence from a Ce(IV) oxidation system sensitized by quinine, as proposed earlier by this group, and flow-injection analysis. The method, which has the advantages of high sensitivity and selectivity, simple sample treatment and prompt production of results, has also been preliminarily adapted for pharmacokinetic study of tiopronin in urine.