ABSTRACT
A certified reference material (CRM) for trace elements in acidified sea water, NMIA MX014, has been produced by the National Measurement Institute Australia (NMIA). The CRM consists of natural coastal sea water with 12 elements (As, Cd, Co, Cr, Cu, Fe, Hg, Mn, Ni, Pb, Se and V) fortified to levels relevant to environmental regulatory testing in Australia ranging from 0.4 to 22 µg/kg. Certified values for these 12 elements were assigned using reference methods developed at NMIA, using either isotope dilution or standard addition with ICP-MS measurement. Specialised sample preparation (coprecipitation) and ICP-MS optimisation (online dilution, collision/reaction chemistry, high mass resolution) were used to negate the effect of the high level of dissolved solids. Multiple confirmatory experiments were performed in order to verify that ICP-MS spectral interferences were eliminated and to estimate the measurement uncertainty contribution from method precision and method trueness. Extensive homogeneity and stability testing was performed and the measurement uncertainty of certified values includes contributions from between-bottle homogeneity, short-term stability, medium-term stability and long-term stability. Special attention was paid to the stability of Hg due to well-known preservation problems. Acidified sea water matrix was satisfactory for stabilising Hg at 0.4 µg/kg for at least 4 years. Relative expanded uncertainties (k = 2) for the 12 certified values were between 1 and 11 %. NMIA MX014 is intended for use as a reference material for analytical method validation and quality control for quantification of trace elements in saline water and other similar sample types.
ABSTRACT
Using a statistical approach, sampling plans for the semiquantitative detection of genetically modified (GM) canola within a bulk seed sample can be developed and tailored to meet different GM thresholds, costs, and confidence limits. This is achieved by changing the number of subsamples analyzed, the number of seeds per subsample, and the percentage of positive results allowed. These sampling plans must be devised carefully, taking into account the detection capability of the analytical assay. This is particularly important in the case of InVigor (a registered trademark of Bayer CropScience) canola, for which expression levels of the introduced protein in seed are very low. Lateral flow assays and enzyme-linked immunosorbent assays (ELISA) were both investigated for their suitability as a qualitative assay using a subsampling approach. On the basis of an ELISA, several sampling plans have been devised and validated to provide at least 99% confidence that bulk seed samples containing at least 0.9% (w/w) InVigor canola will be detected. Although the term "seed" is used throughout this paper to refer to the canola, the term "seed" is to be taken to include both seed and the canola seed (grain) that is harvested by the farmer/grower.
