Spinach result, analysis

It is worth mentioning that certified reference data were not available for the elements aluminum, titanium, vanadium, boron, nickel, and phosphorus at the time of analysis. This is a frequent problem in multielement analyses. It is diflBcult to obtain standard biological reference materials similar to the samples being analyzed with more than but a few certified analytical results. The lack of standard reference material limits quality assurance review of the data and diagnosis of analytical problems. The recent issue of new standards such as spinach leaves and brewers yeast will improve the material variety. Certification of more elements in the existing standards will also greatly assist the analyst. 

The Cs-137 measurements included 350 individual measurements in 119 data sets from 76 participants, after the elimination of outliers 343 individual values in 118 data sets of 75 laboratories remained, i.e. there were only 2% outliers. The general mean was 7.6% less than the reference value. The repeatability and reproducibility coefficients of variation were 4.7% and 9.5%, respectively. The slightly increased value of the repeatability coefficient of variation compared to the other y-nuclides probably results from the lower specific activity of this nuclide in the spinach powder. This nuclide is routinely recorded and evaluated in all laboratories that measure environmental media. The cesium-137 analysis is facilitated by the presence of an interference-free gamma line at 662 keV and the high emission probability of 85%. 

Overall, spinach powder seems to be well suited as a medium for interlaboratory comparisons. The quality of gamma spectrometric measmement of the y-nuclides K-40,1-131, Cs-134 and Cs-137, relevant for environmental monitoring, is good. However, we still foimd a broad range of results for Sr-90 analysis. 

A more detailed analysis have been done for mitochondria from non-green tissues (sycamore cells, mung bean) and for spinach chloroplasts since in these Organelles the different membranes have been purified and the membrane fractions properly characterized. The plant cell contains several other membranes such as golgi membranes, tonoplast, endoplasmic reticulum and plasmalemma. However none of these membranes have been as thorougly characterized and purified as mitochondrial and plastid membranes, thus leading to contradictory results which are mostly due to the presence of contaminating membranes. Therefore, such membranes will not be considered in this short discussion. 

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