Proficiency Testing (PT)

aka Reference Samples

• How to Contact Approved PT Providers
• Specific PT Provider Approvals (by test category and test)
• Special Wisconsin PT Requirements
• Wisconsin-specific PT Grading Rules
• Enforcement related to non-Drinking Water PT failures
• Enforcement related to Drinking Water PT failures
• PT Sample Guidance Document
• Blind Standards (vs. Reference/PT Samples)

Reference samples, or proficiency testing (PT) samples, are an integral part of the Wisconsin Laboratory Certification program. Certified and registered laboratories are responsible for ensuring that they meet all of the requirements for the analysis of reference samples. Laboratories are required to pass at least one sample every year for each test where a reference sample is required. A list of Wisconsin's approved PT providers is available. The status of acceptable providers may change. Contact the LabCert program for updated reference sample information.

PT Samples We Cannot Accept

Certain sources and types of reference samples available from the accepted providers are not acceptable for certification and registration. Examples of unacceptable studies are ERA UST samples and "Real World" matrix samples. If you have questions, be sure to contact the Laboratory Certification and Registration Program before ordering the samples.

General Reference Sample Requirements:

Wisconsin has several specific reference sample requirements, which are described below:

• The study date for the results submitted with applications must be no older than 6 months prior to the date the application is received by the WDNR.
• Results reported from unapproved methods will not be accepted.
• For multi-analyte (e.g., organic) tests, the samples must contain a minimum number of analytes (refer to the Table below).
• Samples for semivolatiles by GC/MS (BNAs) must contain analytes from at least four of the following groups: polynuclear aromatic hydrocarbons, nonpurgeable chlorinated hydrocarbons, phthalates, haloethers, nitroaromatics and isophorone, nitrosamines, or benzidines and must also contain phenols.
• Samples for PAHs by liquid chromatography must be at the appropriate concentration levels. Fluorescing analytes (all but the first four or five analytes to elute) should be prepared with true values in the 1-10 ppb range. For the UVdetectable analytes, the true value may be higher.
• True values cannot be released to the lab before the results are reported.
• Outliers cannot be included in acceptance limit calculations.
• Calculated acceptance limits cannot be broader than ± 2.78 standard deviations.
• Acceptance limits are generally calculated based upon the results submitted by all labs in a study. Acceptance limits cannot be broader than 2.78 standard deviations. If an insufficient number of labs participate in a study, results may be graded based upon fixed limits or regression equations developed by the EPA, the Wisconsin State Laboratory of Hygiene, or another approved reference sample provider.

Minimum Number of (Spiked) Analytes Required for Multi-Analyte Reference Samples