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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.

Fact Sheet
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)

Quick Links:
Quality Systems Branch
U.S. Geological Survey

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Standard Reference Sample Project
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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.

bullet Benefits of Participation

Note: All samples are in the dissolved phase (filtered to 0.1 to 0.2 um) so bottle aliquots are homogeneous. Creating an unfiltered SRS cannot be prepared without very high variability.

bullet Contacts

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

Other numbers:
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 .

bullet Sample List

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)

bullet Event Schedule

FALL 2024
June 5, 2024
invitation to participate in the inter-laboratory comparison December 4, 2023
July 19, 2024
sample order deadline for participating laboratories January 19, 2024
July 22 - August 2, 2024
mail out samples to laboratories January 22 - February 2, 2024
September 20, 2024
data entry deadline March 22, 2024
September 30, 2024
results made available on the web April 1, 2024

bullet Answer Sheets and Method Codes

The 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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