I have been recently asked to join a project dealing with measurements of nutrients and trace elements (e.g. Mn, Cd, Cr, Cu, V etc.) in fruits. This is not my greatest area of expertise, thus I am sorry if my question may look trivial. When peeling and/or cutting the fruits, would it make a difference if I would use a stainless steel knife or a glass (porcelain) knife? I have been told by some other people in my department that any contact with metal during the preparation of the samples will alter the final results. Is this true? And, if yes, which is the magnitude and for what elements? I would like also to have any reference to papers dealing with this topic.
The question you ask is not trivial. Contamination from sample preparation is often the most overlooked source of error in trace metal analysis. The concentration ranges for the elements of interest also may bias perceptions of potential contamination. A cutting process that may show no apparent sign of contamination when the element of interest is at low ppm level may have cause a significant level of contamination when you are working at low ppb levels so be careful when reviewing the literature as to the concentration ranges. As instrumentation has improved so have detection limits. We have seen evidence of contamination from both stainless steel and ceramic knives in the analysis of vegetation samples. You can also look at the blades before and after processing the samples for any signs of physical damage or wear. Analysis of all element possible (depending on the analytical technique you are planning to use) can also provide more insight into potential contamination issues. Depending on how hard the fruit samples are, you might also want to test plastic knives as well. One additional test you can do is to compare the data on a sample processed finely vs coarsely with the same blade and see if there is any significant difference in the trace element data. Depending on the acidity of the fruit you may also get leaching from the surface of the blades.
Here is a reference to an older paper "Sample preparation (cleaning, drying, homogenization) for trace element analysis in plant matrices" B. Markert The Science of the Total Environment 176 (1995) 45-61. as a starting point.
Hi. It depends on the amount of the element present in the matter (sample etc.) if the concentration is greater than, say, 50 ppm, then using a clean clean clean steel knife would not affect the concentration (absorbed into the standard deviation). For lower concentrations please used a titanium knife (you would have to (to have) one made specially (there is no titanium in the body and plants except plants that are used for metal remediation). But then you would be sure that there is no contamination. We use a normal scalpel, but the blade is made of pure titanium. In any event having the this knife and the blades made will ensure not contamination.
Save your sample from all kind of contamination prior to analysis. You may cut or peel of your sample with quartz glass or teflon blades. But before peeling, dip the teflon or quartz blade dipped in deionized water for 24 hours.
- Badges
- Science topic
- Similar topics
- Geoscience
- Asia
- India