Archive for February, 2014

Sample Preparation Guidelines for ED-XRF Analysis (preparing for accuracy)

X-Ray Fluorescence spectrometers offer a very simple, fast, and relatively inexpensive analysis method in laboratory and production facilities.  However, no matter how good an XRF analyzer is, sample preparation may be the most important step in the analysis of liquids, powders, and solids.  Simple steps in sample preparation must be consistently implemented whenever an analysis is performed to insure repeatable and reliable measurements.

XRF Standards DiscussionThe key to sample preparation is that the sample must be homogenous at the time of analysis.  The following offers basic guidelines but contact Eastern Applied to discuss your applications and obtain method sheets with detailed sample preparation information.

The primary points to keep in mind for any sample preparation include:

Proper Film Handling: making sure you have the right film for your sample and preparing the cup correctly (tight film, etc) go along way in analyzer performance

Cleanliness: avoid contamination of sample material by taking precautions in sample preparation (i.e. don’t prepare cups in advance, use proper gloves, never re-use materials, etc).

When liquid samples need to be analyzed, the Hitachi EA-1200VX would be the first analyzer to review.  It has ability for the analysis of petrochemicals and other liquids, so these techniques are commonly discussed.

It is a best practice to measure liquid samples immediately after sample preparation because, while liquid samples are typically the easiest to make homogenous, they may not stay that way for long or evaporate quickly causing false results.  Other liquids may attack the sample cup film causing leakage or wicking of the liquid into your XRF analyzer, which may cause severe damage to the electronics and a large repair bill.

Choose carefully when selecting the sample cup materials and look for XRF sales associates that offer this knowledge and support. In some applications, it may be suggested to incorporate secondary cup systems into the XRF to prevent accidental spills from damaging the analyzer.

Solid samples, like rocks and soil, are not homogenous and require a more involved preparation in order to obtain the best data possible.  Solid sample materials must first be ground and mixed into a powder.  At this point, they can be placed directly into a sample cup similar to that used with a liquid sample.  This technique usually is followed by simply tapping the sample cup to level and compress the powder after filling.

The precision and reproducibility of results from sample to sample may vary when simply measuring the grinded powder because the density may vary and finer grain will separate, causing layers to form and reducing the homogeneity of the sample.  The best method is to press the powders into “pucks” using consistent pressure and dies designed to do this (ask us about pellet press options).  Sample spinning incorporated into your XRF may also help to improve the consistency of the powders whether pressed or not.

For more information contact Eastern Applied Research for tips on sample preparation, the proper equipment, and to make certain you utilize the correct ED-XRF instrument for your material analysis goals.

More Information: Hitachi Elemental Analyzers referred to above