Trace elements in western Canadian hard red spring wheat (Triticum aestivum L.): levels and quality assurance.

A monitoring program was conducted for trace elements in Western Canadian Hard Red Spring wheat (Triticum aestivum L.). Samples were selected from harvest survey samples submitted by producers from crop districts in Manitoba, Saskatchewan, and Alberta for 1996, 1997, and 1998 crops. The analytical quality control measures used in these surveys are described along with the results for Cd, Cu, Fe, Mn, Se, and Zn. Accuracy and precision for the analyses fell within the acceptable control limits. Year-to-year variations in grain chemistry were small for Cd, Mn, Se, and Zn, but Cu and Fe contents showed 12 and 9% decreases, respectively, over the 3 years. The overall variability for the plant-essential trace elements-Cu, Fe, Mn, and Zn-was low compared with that for Cd and Se. The spatial variation in crop chemistry across the Canadian Prairie wheat-producing region was greater than the year-to-year variations. Soil properties were major factors in controlling Cd and Se levels in grain.

Comparison of closed-vessel and focused open-vessel microwave dissolution for determination of cadmium, copper, lead, and selenium in wheat, wheat products, corn bran, and rice flour by transverse-heated graphite furnace atomic absorption spectrometry.

A method is described for the determination of Pb, Cd, Cu, and Se in cereal samples. An atomic absorption spectrometer equipped with a transverse-heated graphite furnace with Zeeman background correction was used for all determinations. Sample preparation was performed by closed-vessel microwave digestion using nitric acid and focused openvessel microwave digestion using nitric acid-hydrogen peroxide. Both techniques were evaluated by using 15 cereal reference materials and comparing results with certified or reference values for each element. Cereal reference standards obtained from the Community Bureau of Reference (Europe), the National Institute of Standards and Technology (USA), the National Institute for Environmental Studies (Japan), the National Research Centre for Certified Reference Materials (People's Republic of China), and the Canadian Grain Commission were used. Application of a series of t-tests, conducted according to Sidak's modified Bonerroni t-procedure, showed that both techniques yielded accurate results for cereal reference materials. Some differences from certified and reference values, however, were found for each element.

Gas-liquid chromatography and flame photometric detection of phosphine in wheat.

A screening method using gas-liquid chromatography with flame photometric detection has been developed for determining phosphine in wheat. Phosphine is measured as the sum of physically bound intact phosphine and that derived from residual aluminum phosphide. Wheat is extracted in a closed, partially evacuated glass system by refluxing with 10% sulfuric acid. Liberated gases are swept into a gas-collection flask fitted with rubber septa to permit gas sampling. Aliquots of collected gas are injected into a gas chromatograph. Phosphine is quantitated by peak area as determined by an electronic integrator. Recoveries varied with concentration: 67% was recovered at 0.10 ppm and 98% was recovered at 19 ppm. For concentrations less than 1.5 ppm, the coefficient of variation was 9.95%. Using flame photometric detection, phosphine concentrations as low as 0.04 ppm were easily determined in wheat.