The U.S. Geological Survey (USGS) conducts an inter-laboratory comparison study semiannually. This program provides a variety of Standard Reference Samples (SRSs) for laboratory quality assurance testing and are available to purchase for internal quality control. The majority of samples are prepared with water from Colorado streams.

Information: Fact Sheet Schedule of Events Frequently Asked Questions SRS's Available for Purchase Answer Sheets and Method Codes Branch of Quality Systems Contacts Standard Reference Sample Price List Participating Laboratories in the SRS Project Links: Branch of Quality Systems USGS Laboratory Evaluation Project USGS Privacy Statement | Disclaimer | Accessibility

NUTRIENTS * TRACE ELEMENTS * MAJOR IONS * PRECIPITATION *  MERCURY

The program 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 program have been to accomplish the following:

• Evaluate and improve the performance of participating laboratories;
• Provide a library of carefully prepared, homogeneous, stable reference materials to laboratories;
• Identify analytical problem areas;
• Identify quality assurance needs with respect to environmental analyses and develop new reference materials to meet these needs; and
• Ascertain the accuracy and precision of analytical methods

Over one hundred and fifty USGS and non-USGS laboratories are participating in the program and six standard reference sample types are available (Trace Element, Major Ion, Precipitation, Mercury, Low-level Nutrient, and Regular-level Nutrient).

This program is not 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 can purchase previously made SRS by calling the number below.

Contacts

Other numbers:
Mark Nilles, Branch Chief (acting), Branch of Quality Systems (303) 236-1878
Brooke Connor, Laboratory Evaluation Project Chief, Branch of Quality Systems (303) 236-1877
B.J. North, System Administrator, Branch of Quality Systems (303) 236-1820 - COMPUTER SUPPORT

If you can not fully access the information on this website, please contact Mark Woodworth .

Price List

All samples are currently $40 (includes shipping). We cannot accept checks or PO's; we can only accept credit cards or USGS standard vouchers. To order samples for the current inter-laboratory comparison, please visit our order page. To order previously prepared SRSs, please call (303) 236-1875. View the list of available SRSs from our inventory.

All samples are in the dissolved phase (filtered to 0.2 um).

Trace element sample (500 mL): chlorinated with sodium hypochlorite and acidified with nitric acid	$40.00
Major ion sample (500 mL): chlorinated with sodium hypochlorite	$40.00
Precipitation (low ionic-strength) sample (500 mL): typically non-preserved snowmelt	$40.00
Nutrient (low concentration) sample (60 mL; dilute 1:10): concentrations <0.5 mg/L	$40.00
Nutrient sample (250 mL): concentrations >0.5 mg/L	$40.00
Mercury sample (250 mL): concentration <0.1 ug/L; acidified with hydrochloric acid	$40.00

Event Schedule

Answer Sheets and Method Codes

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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