Analysis of some metabolites of T-2 toxin, diacetoxyscirpenol and deoxynivalenol by thermospray high-performance liquid chromatography-mass spectrometry

Detection and identification of mycotoxin metabolites is a very challenging task. In order to achieve adequate sensitivity and specificity an analytical technique must overcome serious matrix interferences. Gas chromatography-mass spectrometry (GC-MS) which has the sensitivity and specificity to detect and identify mycotoxin metabolites requires hydrolysis of conjugated metabolites as well as derivatization. Thermospray high-performance liquid chromatography-mass spectrometry (HPLC-MS) offers the sensitivity, specificity, and structural information to detect and identify some mycotoxin metabolites in fecal and urine samples without derivatization. The mycotoxins evaluated in this study include deoxynivalenol (DON), T-2 toxin, and diacetoxyscirpenol. The de-epoxy and hydroxy metabolites of each toxin and the glucuronide conjugate of DON were isolated, extracted, and analyzed to detect their occurrence in animals. The thermospray mass spectra of the toxins showed an [M + H]+ ion and numerous structurally significant fragment ions in the positive ion detection mode. Negative ion detection exhibited primarily [M + acetate]- cluster ions with less fragmentation than observed by positive ion detection. The operation of the interface in the filament-on mode greatly increased the sensitivity in both positive and negative ion detection mode. Detection limits of 50-500 pg injected on column are obtained for these toxins and their metabolites using multiple ion detection. The urine and fecal extracts from rats, hens, and cows did not interfere with the HPLC-MS analysis for the specific metabolites or the glucuronide conjugate.     

Random Copolymers of 1,5-Dioxepan-2-one

ABSTRACT

Copolymers of 1,5-dioxepan-2-one (DXO) and e-caprolactone (?-CL), δ-valerolactone (δ-VL) or L-lactide (LLA) have been synthesized and characterized. High molecular weight copolymers were obtained using stannous-2-ethyl hexanoate as catalyst in bulk. Reactivity ratios for the copolymerization of DXO and δ-VL were determined at 110°C as r_VL=0.5 and r_DXO=2.3. At high conversion, depolymerization of δ-VL occurred, resulting in lower molecular weight and variations in the copolymer composition.

Physical properties, such as crystallinity and melting temperature of the DXO-copolymers proved to be strongly dependent on the choice of comonomer and on the molar composition of the copolymers. DXO appears to be incorporated into the poly-?-caprolactone (PCL) crystals and to some extent into the poly-δ-valerolactone (PVL) crystals, resulting in a more gradual decrease in crystallinity with increasing amount of DXO.     

Application of high-performance liquid chromatography and thermospray high-performance liquid chromatography-mass spectrometry to the analysis and identification of 2',3'-dideoxyadenosine and its metabolite in biological media

Reversed-phase high-performance liquid chromatographic (HPLC) procedures are described for determining the stability of 2',3'-dideoxyadenosine (DDA) in biological fluids at therapeutic dosages. The validated methodology uses both direct injection and solid-phase extraction techniques. Deamination of DDA to 2',3'-dideoxyinosine (DDI) in plasma by adenosine deaminase was monitored by HPLC, and the identification of DDI verified by thermospray HPLC-mass spectrometry. This methodology should prove useful in future studies concerning the stability and metabolism of dideoxynucleosides.     

Secondary ion yields produced by keV atomic and polyatomic ion impacts on a self-assembled monolayer surface

A suite of keV polyatomic or 'cluster' projectiles was used to bombard unoxidized and oxidized self-assembled monolayer surfaces. Negative secondary ion yields, collected at the limit of single ion impacts, were measured and compared for both molecular and fragment ions. In contrast to targets that are orders of magnitude thicker than the penetration range of the primary ions, secondary ion yields from polyatomic projectile impacts on self-assembled monolayers show little to no enhancement when compared with monatomic projectiles at the same velocity. This unusual trend is most likely due to the structural arrangement and bonding characteristics of the monolayer molecules with the Au(111). Copyright 1999 John Wiley & Sons, Ltd.     

Fusion around the barrier for 7Li+12C

Fusion cross-sections for the ⁷Li + ¹²C reaction have been measured at energies above the Coulomb barrier by the direct detection of evaporation residues. The heavy evaporation residues with energies below 3 MeV could not be separated out from the α-particles in the spectrum and hence their contribution was estimated using statistical model calculations. The present work indicates that suppression of fusion cross-sections due to the breakup of ⁷Li may not be significant for ⁷Li + ¹²C reaction at energies around the barrier.     

Analysis of candidate anticancer drugs by thermospray high-performance liquid chromatography-mass spectrometry

Thermospray high-performance liquid chromatography-mass spectrometry was used to confirm the identity of five bulk anticancer drugs, and in some cases, to identify drug impurities. Analysis resulted in both molecular weight and structural (fragment ions) information obtained from the full scan spectra of as little as 50 ng of each drug. The technique was also used to evaluate the chromatographic specificity of corresponding ultraviolet or refractive index high-performance liquid chromatographic detection in the presence of drug degradation products.     

Processes that affect electrospray ionization-mass spectrometry of nucleobases and nucleosides

Due to the complexity of electrospray ionization processes and the many factors that affect the ion signal, optimization of electrospray ionization methods to gain ultimate sensitivity for analysis of nucleobases and nucleosides may not be straightforward. In this work, we investigated the effect of the pK _a and the gas-phase basicity of analyte and other electrolytes on the [M+H]⁺ ion signal for 11 select nucleobases and nucleosides in 50% methanol:water solution. Solution chemistry plays a role in the electrospray signal for all analytes, but gas-phase chemistry may be important for compounds with pK _a <3 depending on the solution composition. For compounds with pK _a <3, gas-phase proton transfer reactions can be promoted to increase analyte electrospray response by the addition of ammonium acetate to the solution.     

Investigation of collisional-activation decomposition process and spectra in the transport region of an electrospray single-quadrupole mass spectrometer.

The use of collisional-activation dissociation (CAD) in the electrospray transport region was evaluated for generating structural information on several pesticides and antibiotics. The collision energy used to generate the CAD spectra could be varied easily by changing the capillary/skimmer potential difference, imparting from 0 eV to above 16 eV internal energy to the near thermal ions generated by electrospray. The internal energy distribution for low-energy collisions (capillary/skimmer potential difference of 20 V) closely matches the curves generated by a triple-quadrupole mass spectrometer. Furthermore, the CAD spectra for selected compounds generated by electrospray in the transport region at a capillary/skimmer potential difference of 30-50 V closely resembled those obtained from the [M + H]+ ion by a triple quadrupole using 30 eV collision energy. The CAD of ions in the transport region resulted in 70% to 80% daughter-ion yields and minimal loss in overall ion current compared to the ion current for protonated or cationized parent molecules. The major daughter ions for 10 pg of Aldicarb and penicillin G could be detected (signal-to-noise ratio greater than 5) under full-scan CAD conditions.     

Analysis of candidate anticancer drugs by thermospray high-performance liquid chromatography-mass spectrometry and by high-resolution mass spectrometry

Thermospray high-performance liquid chromatography-mass spectrometry (TSP-HPLC-MS) and direct probe high-resolution MS was used to analyze four candidate anticancer drugs. The techniques were used to confirm the identity of the bulk drug and to identify impurities. Analysis by TSP-HPLC-MS resulted in molecular weight information from the separated components using as little as 50 ng of each drug. The high-resolution direct probe MS analysis provided additional structural information and possible empirical formulas for the parent drugs and their impurities. The use of both of these complimentary techniques proved to be very specific for the detection of the anticancer drugs and for postulating the identity of impurities.