Site-selective electron nuclear double resonance in the exchange-narrowed regime of the ESR in conducting solids.

Electron nuclear magnetic double resonance on conduction electrons reveals the hyperfine interaction hidden by the fast electron spin exchange. We used the Overhauser shift technique to investigate the electron spin density of the conduction band of gallium oxide, beta-Ga(2)O(3). Due to the monoclinic structure, the conduction band of beta-Ga(2)O(3) is anisotropic and it is dominated by contributions from the two nonequivalent Ga sites. The large quadrupole couplings of the two gallium isotopes (69)Ga and (71)Ga (both with I = 3/2) are completely resolved in our double-resonance experiments. This resolved quadrupole interaction allows the determination of the electric field gradients at both gallium sites with high precision and high sensitivity. The resolved quadrupole splitting is the key to the site-selected determination of the hyperfine interaction. The concepts behind these double-resonance techniques are rather general and should be applicable in similar semiconductor systems.

A novel method for continuous online glucose monitoring in humans: the comparative microdialysis technique.

The aim of this study was to prove the feasibility of continuous subcutaneous glucose monitoring in humans using the comparative microdialysis technique (CMT). The performance of the CMT was determined by comparing tissue glucose values with venous or capillary blood glucose values in healthy volunteers and type 1 diabetic subjects. The CMT is a microdialysis-based system for continuous online glucose monitoring in humans. This technique does not require calibration by the patient. Physiological saline with glucose (5.5 mM) is pumped in a stop-flow mode through a microdialysis probe inserted into the abdominal s.c. tissue. Tissue glucose concentration is calculated by comparing the dialysate and perfusate glucose concentrations. The time delay due to the measurement process is 9 min. We tested the CMT on six healthy volunteers and six type 1 diabetic patients for 24 h in our clinical setting. Comparisons were made to HemoCue analyzer (Angelholm, Sweden) capillary blood glucose measurements (healthy volunteers) and to venous blood glucose concentration determined with a Hitachi analyzer (diabetic patients). The mean absolute relative error of the CMT glucose values from the blood glucose values was 17.8+/-15.5% (n = 167) for the healthy volunteers and 11.0+/-10.8% (n = 425) for the diabetic patients. The mean difference was 0.42+/-1.06 mM (healthy volunteers) and -0.17+/-1.22 mM (diabetic patients). Error grid analysis for the values obtained in diabetic patients demonstrated that 99% of CMT glucose values were within clinically acceptable regions (regions A and B of the Clarke Error Grid). The study results show that the CMT is an accurate technique for continuous online glucose monitoring.

Comparative studies on the detection of mycotoxins in barley using enzyme immunoassays.

Barley samples (n = 128) from Central Canada (Manitoba) of the 1993 and 1994 crop years were analysed using enzyme immunoassays for the detection of the mycotoxins deoxy-nivalenol, 3-acetyldeoxynivalenol, 15-acetyldeoxynivalenol, and zearalenone. For this study enzyme immunoassays, which were developed at the Lehrstuhl für Hygiene und Technologie der Milch as well as a commercial testkit (Ridascreen® DON, specific for deoxynivalenol and its acetylated derivatives) were used. In addition, some samples were analysed by using a combination of HPLC and enzyme immunoassay (immunochromatography). Results obtained by the enzyme immunoassays for these samples were compared with other analytical data on mycotoxin contamination (analysed by GC/MS) and with the mycological conditions, respectively.

First survey on the natural occurrence of Fusarium mycotoxins in Bulgarian wheat.

Wheat for human consumption (140 samples) was collected after harvest from all regions of Bulgaria. The 1995 crop year was characterized by heavy rainfall in the spring and summer months. The internal mycoflora of wheat samples was dominated by Fusarium spp. and Alternaria spp., and storage fungi were rarely present. The samples were analysed for contamination with Fusarium mycotoxins deoxynivalenol (DON), 3-acetyldeoxynivalenol (3-AcDON), 15-acetyldeoxynivalenol (15-AcDON), T-2 Toxin (T-2), diacetoxyscirpenol (DAS), and zearalenone (ZEA), using enzyme immunoassay methods. DON and ZEA were the predominant toxins, with a contamination frequency of 67% and 69%, respectively. The average levels of these toxins in positive samples were 180 micrograms/kg (DON) and 17 micrograms/kg (ZEA), maximum concentrations were 1800 micrograms kg-1 and 120 micrograms kg-1, respectively. Acetyl derivatives of DON, namely 3-AcDON and 15-AcDON, were found in 2.1% and 0.7% of the samples, at at maximum level of about 100 micrograms kg-1. Only one sample was positive for T-2 (55 micrograms/kg), DAS was not detected. This is the first report about the natural occurrence of a range of Fusarium mycotoxins in wheat for human consumption in Bulgaria.

Natural contamination of Manitoba barley by 3,15-diacetyldeoxynivalenol and its detection by immunochromatography.

Contamination of Canadian barley samples by 3,15-diacetyldeoxynivalenol was detected by enzyme immunoassays combined with liquid chromatography-mass spectrometry. This is the first reported natural occurrence of this mycotoxin. The barley was infected mainly with Fusarium graminearum. Deoxynivalenol, 3-acetyldeoxynivalenol, and zearalenone were also found.