A modified HPLC method for the determination of ochratoxin A by fluorescence detection

A high-performance liquid chromatographic method (HPLC) with fluorescent detector is described for the determination of ochratoxin A (OTA). A mobile phase consisting of acetonitrile:water:acetic acid (99:99:2, v/v/v) was used for the resolution of the compound on a C(18) Hypersil column. The retention time for OTA and diflunisal which was used as an internal standard (IS) were 11.7 and 12.8 min, respectively. The method is selective, reliable, reproducable with relative standard deviation (RSD) of 1.70 and linear in the range of 2.5 x 10(-9)-1.5 x 10(-8) M OTA. The limit of detection (LOD) and limit of quantification (LOQ) were 2.5 x 10(-10) M corresponding to 0.1 ng mL(-1) and 8.2 x 10(-10) corresponding to 3.3 ng mL(-1), respectively. Recovery studies were 81.2 +/- 1.9 (SD). The method was applied for analysis of OTA in wheat, corn, red pepper, cheese and wine. The proposed method can be used for the routine analysis of OTA in food and animal feed.     

Spectroscopic study on thermal reaction and desorption of sulfur/Rh(1 0 0) induced by oxygen-containing molecules

The surface reaction and desorption of sulfur on Rh(1 0 0) induced by O₂ and H₂O are investigated with X-ray photoelectron spectroscopy (XPS) technique. The Rh(1 0 0) sample covered with atomic sulfur is prepared by means of the exposure to H₂S gas, and subsequently the sample is annealed under O₂ or H₂O atmosphere. The XPS results show that atomic sulfur adsorbed on Rh(1 0 0) reacts with O₂ and desorbs from the surface at 473 K or more. On the other hand, atomic sulfur can not be removed from Rh(1 0 0) surface by H₂O at any temperature.