Frequently Asked Questions

wavy line rule

bullet What is the cost and volume of the samples?

No cost but we have some restrictions (based on Round Robin participation). See new policy on the list of available samples.
Trace: 500 mL
Major: 500 mL
Precip: 500 mL
Mercury: 220 mL
Nutrient (low): 60 mL (dilute 1:10)
Nutrient (reg): 250 mL

bullet How often is the inter-laboratory comparison study performed?

invitation to order samples mid December mid June
distribution of samples early February early August
analytical results due late March late September
report generation early April early October

bullet Who can participate in the Standard Reference Sample round robin studies?

U.S. Federal, State, municipal, and university laboratories can participate. This project is not open to international laboratories. Labs must enroll before participating. Please contact me at

bullet Why canít I log into the data entry page?

Your username (lab#) and password, that were assigned to you at enrollment, are to be entered with no spaces and lower case. Your lab number should replace the pound (#) sign.

bullet When will the inter-laboratory comparison results be released?

Results are displayed on the website within a week of the data entry deadline. Publications are no longer produced.

bullet Are the Standard Reference Sample's filtered and are they appropriate for unfiltered sample analyses?

The water is passed through a series of filters to 0.2 um and UV sterilized throughout the preparation process. A filtered aqueous reference material has the entire mass of analyte in the dissolved phase, so the unfiltered-sample analysis and the filtered-sample analysis of the reference material should yield the same concentration. However, the digestion step for a raw sample is not evaluated because there are no particulates to extract. Note that the calibration standards and internal quality-control samples used for the unfiltered-sample analysis also have no particulate phase.

bullet Why aren't unfiltered reference samples available?

Unfiltered samples are not prepared because of analyte concentration instability due to microbial activity and phase changes over time. Also, there isn't a good way to accurately split a large volume sample into 100's of individual bottles that would be consistent/representative of the whole. Variability would be too high for a reference sample. It is assumed that most of the deviation between the laboratory result and the target value (most probable value) is due to the laboratory process, not the SRS itself. Therefore, an unfiltered sample would not be reliable to measure laboratory performance.

bullet How should the mercury sample be prepared for analysis?

Follow your normal method SOP, but do an in-bottle oxidation, rather than first taking a subsample, to ensure a representative aliquot.