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Staphylococcus aureus produces enterotoxins, which are causative agents of foodborne intoxications. Enterotoxins are single-chain polypeptides and have a molecular weight of about 26-28 kDa. The consumption of food contaminated with Staphylococcus aureus enterotoxins results in the onset of acute gastroenteritis within 2-6 h. The objective of this study was the development of a new method for the quantification of Staphylococcal enterotoxin B (SEB) in food matrices. Tryptic peptide map was generated and nine proteolytic fragments were clearly identified (sequence coverage of 35%). Among these, three specific tryptic peptides were selected to be used as surrogate peptides and internal standards for quantitative analysis using an isotopic tagging strategy along with analysis by LC-MS/MS. The linearity of the measurement by LC-MS/MS was evaluated by combining mixtures of both isotopes at 0.1, 0.2, 0.5, 1.0 and 2.0 ¹H/²H molar ratios with a slope near to 1, values of R² above 0.98 and %CV obtained from six repeated measurement was below 8%. The precision and accuracy of the method were assessed using SEB spiked in chicken meat homogenate samples. SEB was fortified at 0.2, 1 and 2 pmol/g. The accuracy results indicated that the method can provide accuracy within a 84.9-91.1% range. Overall, the results presented in this manuscript show that proteomics-based methods can be effectively used to detect, confirm and quantify SEB in food matrices., (Copyright © 2011 John Wiley & Sons, Ltd.)

A highly specific and sensitive method using high performance liquid chromatography coupled with diode-array detection and ion-trap mass spectrometry (HPLC-DAD-MS(n)) was developed for study of the constituents of flavonoid extract of jujube seeds and the metabolites in rat plasma, urine, and feces samples after oral administration of flavonoid extract of jujube seeds. Two major flavonoids (spinosin and 6'''-feruloylspinosin) with content >60% in the flavonoid extract of jujube seeds were detected and confirmed by comparison with the reference standards. Furthermore, five metabolic components in plasma, seven in urine, and four in feces were detected and elucidated. The scientific and plausible biotransformation pathways of the main components in flavonoid extract of jujube seeds were also proposed, together with presentation of clues for potential bioactive mechanisms. This convenient HPLC-DAD-MS(n) method could be used to identify the chemical components of flavonoid extract of jujube seeds as well as their metabolites, and to reveal their possible metabolic mechanism of action in vivo.

A novel fast high-performance liquid chromatography (HPLC) method coupled with diode array detection (DAD) and time-of-flight mass spectrometry (TOF/MS) was developed for qualitative and quantitative analysis of Radix Astragali products. The potential of fast HPLC on 1.8-microm particles was compared with the performance of HPLC on conventional 5-microm particles columns. Significant advantages of fast HPLC include high-speed chromatographic separation, four times faster than HPLC with conventional columns, and great enhancement in sensitivity with limits of detection low to 0.001 ng. With dynamic adjustment of fragmentor voltage in TOF/MS, an efficient transmission of the ions was achieved to obtain the best sensitivity and abundant fragmentation. By accurate mass measurements within 5 ppm error for each molecular ion and subsequent fragment ions, a reliable identification and differentiation of six major saponins including two groups of isomers and twelve main isoflavonoids was described here for the first time. For quantitative analysis by fast HPLC-TOF/MS, linearity of response over two orders of magnitude was demonstrated (r(2)>0.99) for all analytes. Intra-day reproducibility was below 3% RSD and inter-day values were below 5% RSD. A good correlation (slope=1.1108, r(2)=0.9853) was observed for accuracy test. It is concluded that the fast and sensitive HPLC-DAD-TOF/MS is powerful in qualitative and quantitative analysis of complex herbal medicines in terms of time savings, sensitivity, selectivity, precision, accuracy as well as increasing sample throughout and lowering solvent consumption.

A sensitive and reliable high-performance liquid chromatography-mass spectrometry (HPLC-MS) was developed and validated for simultaneous quantification of five main bioactive components, i.e., calycosin-7-O-beta-D-glucoside, ononin, astragaloside IV, astragaloside I and ferulic acid in rat plasma after oral administration of Danggui Buxue Tang (DBT) extract. Plasma samples were extracted with solid-phase extraction (SPE) separated on an Inertsil ZORBAX C(18) column and detected by MS with electrospray ionization (ESI) interface in negative selective ion monitoring (SIM) mode. Calibration curves offered linear ranges of two orders of magnitude with r(2)>0.99. The method had the lower limit quantification of 0.55, 0.46, 1.07, 1.12 and 4.6 ng/mL for calycosin-7-O-beta-D-glucoside, ononin, astragaloside IV, astragaloside I and ferulic acid, respectively, with precision less than 10%. The RSD of intra- and inter-day variations ranged from 2.10% to 6.19% and 2.37% to 6.72%. This developed method was subsequently applied to pharmacokinetic studies of the five compounds in rats successfully.