Customer Information

Western Ag Innovation performs quality control analysis on all PRS® Probe batches after the regeneration process to ensure that we only send out clean PRS® Probes to our clients. Method blanks can be used to test for possible contamination after the PRS® Probes are shipped out to the researcher for use. The pricing for blank analysis is the same price as other samples to be analyzed. It is best to decide at the beginning of the study if and how many method blanks will be needed, and include the number of blanks in your overall sample number.

Method blanks cannot be used to correct sample values. The reason is that method blanks are saturated with easily-displaced counter-ions while ions adsorbed during burial are more strongly held. As an extreme example, we soaked PRS® Probes in tap water for one hour and found that K and Mg on blank probes increased from 1 to 28 mg/m2 and 3 to 100 mg/m2, respectively, but K on sample probes declined from 222 to 104 mg/m2 and Mg was unchanged (360 vs. 346 mg/m2). The method blanks were useful to show contamination, but the impact on sample values is dependent on relative ion activities and strengths of adsorption.

It is important to treat blank samples with extreme care. The importance of handling blanks properly is essential because it can determine if the blank values are usable or not. Soil in the bag, dirty fingers and other factors can lead to variability and background noise on the blanks. Also, higher supply rate values on the blanks are known to occur when PRS® Probes have been stored in a dry state for extended periods of time. The reason for this is that the membrane shrinks on desiccation and causes shedding. This shedding may add ammonium to the sample as the anion membranes uses quaternary ammonium as the functional group for adsorption. Therefore, it is important to treat method blanks carefully when using them in a study. Keep the method blanks clean and store them in moist refrigerated conditions to prevent the membrane from drying out and becoming contaminated. Do not touch the membrane with your fingers especially if they are dirty. Be sure to wash all blank PRS® Probes with the same DI water used on the field samples.

Recommended procedures for blanks

  1. Do not touch the membrane of the PRS® Probes with your hands. This goes for all samples, but especially blanks. This is particularly important in the field when the hands are covered with soil. PRS® Probes taken out to the field are bound to get somewhat contaminated before insertion into the soil. This however is not as important because the amount of contaminant adsorbed on the membrane should be insignificant relative to what will be adsorbed in the soil. However, contamination on blank probes may show up in blank probe data.
  2. Do not use the PRS® Probes that have been contaminated in any way as blanks. For example do not use left over PRS® Probes at the bottom of the bag, that have been taken out to the field and soil has collected at the bottom.
  3. Be sure to treat the blank PRS® Probes as closely as possible to the other samples. Wash them with the same DI water as the other PRS® Probes.
  4. Make sure all PRS® Probes are kept moist (when not in field) and in sealed plastic bags. Higher supply rate values on the blanks are known to occur from PRS Probes that have been stored in a dry state for extended periods. Note: Often a moist membrane will be slightly rippled. When a membrane is completely dry the membrane will be very tight and stretched inside the PRS® Probe casing.
  5. We suggest taking out random PRS® Probes and putting them aside as sample blanks before going in the field. Place them in a sealed plastic bag; this would be the best way to keep them from being contaminated. Then take them out to the field and treat them to the same conditions as the other PRS® Probes. Bring the blanks back to the lab when all samples are placed in the field and put the blank samples in the refrigerator to keep them cool. Make sure bags are sealed properly so that membrane remains moist. When collecting the samples for analysis from the field, wash all PRS® Probes (field and blanks) with the same DI water.