The U.S. Geological Survey (USGS) conducts an inter-laboratory comparison study semiannually. This project provides a variety of Standard Reference Samples (SRSs) for laboratory quality assurance testing and are available for internal quality control. The majority of samples are prepared with water from Colorado streams and spiked with reagent grade chemicals to measurable concentrations.
Schedule of Events
Benefits of Participation
Frequently Asked Questions
SRSs Available from our Inventory
Answer Sheets and Method Codes
Standard Reference Sample Listing
Round Robin Sample Concentration Ranges
Active Labs (participating within last 2 years)
NUTRIENTS * TRACE
ELEMENTS * MAJOR IONS * PRECIPITATION * MERCURY
The project began in 1962 with a single sample containing major constituents that was prepared from distilled water and reagent grade chemicals. Twenty-three USGS laboratories participated in the determinations of six analytes. Since that time, objectives of the project have been to accomplish the following:
Approximately one hundred and twenty-five USGS and non-USGS laboratories are actively participating (from 40 states) in the project and six standard reference sample types are available (Trace Element, Major Ion, Precipitation, Mercury, Low-level Nutrient, and Regular-level Nutrient). If you would like to enroll, please contact the SRS Project Chief.
This project is typically no open to international laboratories. U.S. Federal, State, municipal, and university laboratories can participate even though they do not provide data to the USGS. Laboratories can compare their results to other labs based on the deviation (z-value) from the median and percent difference. Laboratories may order previously made SRSs by contacting the SRS Project Chief.
Benefits of Participation
SRS Project Chief
U.S. Geological Survey
Quality Systems Branch
Denver Federal Center, Bldg. 95
P.O. Box 25046, MS 401
Denver, CO 80225-0046
Jim Simmons, Branch Chief, Quality Systems Branch (303) 236-1835
If you can not fully access the information on this website, please
contact the SRS Project Chief .
To order samples for the current inter-laboratory comparison, please visit our order page. To order previously prepared SRSs, please email the SRS Project Chief. View the list of available SRSs from our inventory.
All samples are in the dissolved phase.
Trace element sample (500 mL): chlorinated with sodium hypochlorite and acidified with HNO3 (pH<2; filtered to 0.2 um) Major ion sample (500 mL): chlorinated with sodium hypochlorite (filtered to 0.2 um) Precipitation (low ionic-strength) sample (500 mL): typically non-preserved snowmelt (filtered to 0.1 um) Nutrient (low-level) sample (60 mL; dilute 1:10): must remain chilled (filtered to 0.1 um) Nutrient (regular-level) sample (250 mL): must remain chilled (filtered to 0.1 um) Mercury sample (250 mL): concentration <0.1 ug/L; acidified with HCl (0.4% [v/v]; filtered to 0.2 um)
June 2, 2022
|invitation to participate in the inter-laboratory comparison||December 5, 2022|
July 22, 2022
|sample order deadline for participating laboratories||January 20, 2023|
July 25 - August 5, 2022
|mail out samples to laboratories||January 23 - February 3, 2023|
September 23, 2022
|data entry deadline||March 24, 2023|
October 3, 2022
|results made available on the web||April 3, 2023|
Answer Sheets and Method CodesThe answer sheets below were created to help laboratories collect analytical results for electronic data entry. These forms are not to be used for data submittal. A listing of the SRS method codes has also been provided for your assistance.
Answer sheets for | Trace Sample | Major Sample | Precipitation Sample | Mercury Sample | Nutrient Samples |
SRS Method Codes are used when entering data and are included in the results reports.
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