Avoid the Pitfalls:
One of the major mistakes made with this method is not paying attention to precision on your readings. XRF is one of the few instruments that actually shows reading uncertainty. Use this to your advantage in 2 ways:
Assume your target cleanup level is 100ppm:
- Analyze your sample until the error is satisfactory. During initial sampling of your grid to determine the plume of contamination, continue measurement until your instrument provides reasonable certainty:
100ppm + - 50ppm after 30 seconds is not reasonable certainty and requires a longer sampling time. Continue sampling until the precision on the instrument (+/- error) provides certainty well over the range of your action level. 100ppm + - 20ppm falls within the acceptable level of precision (20%) according to Method 6200.
- Stop sampling if certainty has been met. Save time by doing the math as you go:
2300ppm +- 500ppm after 20 seconds can be stopped since it is clearly over your action level even if you subtract the whole of the uncertainty: 2300 – 500 = 1800ppm.
Some sites are more naturally homogeneous than others when considering particle size of your sample. Since XRF is affected by particle size, it is important to take steps to eliminate this affect. By grinding your sample with a mortar and pestle and passing it through a sieve, you create particle sizes that are homogeneous and much more XRF friendly.
Don’t waste your time sieving down to the smallest µm sieve (i.e. 125 µm) if you obtain good data from sieving through a 250 µm sieve or if the improvement in data is less than 20%. The Ziploc approach often saves time and delivers reasonable enough results depending on your DQOs. Analyze directly into the bag once the large chunks are removed.
Avoiding the pitfalls:
- Be certain to fill your XRF sample cup at least ¾ of the cup full. XRF analyzers are calibrated for infinite thickness so if you do not have a thick enough sample to analyze, it will skew your results in an undesired manner.
- Since XRF is nondestructive, send the same sample cup you analyzed with your XRF to the lab for analysis. This ensures the closest possible corroboration of XRF results to lab results.
When used appropriately, Method 6200 can save time and money on sending all samples to the lab and waiting for the results. Cut down sending 100 samples to 10 and enjoy the speed in which your project is completed. Ask us any lingering questions you may have about Method 6200 now!
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