QCS (Quality Control Standards)

formerly known as "Blind Standards"

What is a QCS?

A QCS is a "reference" sample obtained from an external source, whose validated concentration is known to the facility supervisor, but is unknown to the lab analyst/technician.

NR149 definition:
s. NR 149.03 (57) “Quality control standard” or “QCS” means a solution or sample containing method analyte of known concentration, accompanied by specified analytical acceptance limits, and obtained from a source external to the laboratory and different from the source of calibration standards. These samples are distinguished from proficiency test samples in that the acceptance limits are provided with the sample, rather than after analysis. Quality control standards are used to check either laboratory or instrument performance.

Back to Top

What's the difference between QCS and PT samples?

No need to use an "approved provider"

Unlike PT samples, QCS do not have to be purchased from an approved provider. The only specification is that the samples obtained have a theoretical "true" value, and statistically determined acceptance criteria.

Rapid performance feedback

Also unlike PT samples, whose results are typically not received for 45 dasys (or longer), the acceptance criteria for QCS are immediately available to the analyst. The exception to this is those PT providers that offer a "rapid response" type of PT program. QCS can --and should--be used at any time there is concern about the control of a specific analysis. Having immediate access to the validated concentrations allows the analyst/technician to take immediate action to identify and correct the problem. These types of samples are important indicators of quality due to the real-time feedback on analytical performance obtained.

Back to Top

What's a second source standard and how does it compare to QCS?

A second source standard is a standard that is different from the standard used to prepare calibration standards. Second source standards are either standards purchased from an entirely different manufacturer, or from the same manufavcturer, but with obtained or prepared from two unique "lots". NR 149 or individual analyutical methods establish acceptance criteria for second source satnadrds. A laboratory can prepare its own second source standrads.

NR149 definition:
s. NR 149.03 “Second source standard” means a standard procured from a supplier or manufacturer different from the supplier or manufacturer of a laboratory’s calibration standards, or a standard obtained from the same supplier or manufacturer of a laboratory’s calibration standards from a lot verifiably different from the lot of the calibration standards.

Back to Top

Can I make my own QCS samples?

No. By definition, QCS must be "obtained from a source external to the laboratory and different from the source of calibration standards".

Back to Top

Parameters that require analysis of QCS in lieu of PT samples

[NR 149.22 (3)] Laboratories performing the following analytical techniques for metals analysis in aqueous and solid matrices shall analyze quality control standards 3 times per year at evenly spaced intervals in lieu of analyzing proficiency testing samples:
  1. Flame atomic absorption spectrophotometry.
  2. Colorimetric, for analytes other than hexavalent chromium.
  3. Ultra-low level metals

Back to Top

How often must they be analyzed?

Section NR 149.48(5)(a)specifies that Laboratories that do not use second source standards to verify the accuracy of initial calibrations shall analyze QCS

Note: Analysis of quality control standards is not required for tests, such as pH, which are performed using instruments calibrated by tuning them to conform to a universally accepted scientific law or scale. These tests are also exempt from initial calibration verification with a second source standard.

Back to Top

What must I do if I get unacceptable results for a QCS?

  1. Take corrective action
  2. Within 30 days, analyze and obtain acceptable results on either:
    • another QCS, or
    • a processed second source standard.
Laboratories shall evaluate the results of known quality control samples against the acceptance criteria supplied by the provider. If the results of known quality control samples exceed the acceptance limits issued by a provider, the laboratory shall take corrective action and demonstrate within 30 days, through analysis of another known quality control sample or processed second source standard, the effectiveness of the corrective action taken.   NR 149.48(5)(b)

Back to Top

Exemptions from requirement to analyze QCS

Laboratories that do not use second source standards to verify the accuracy of initial calibrations shall analyze quality control standards. Note that this exemption does not apply if analysis of QCS is required by the analytical method which you reference. Basically a lab is exempt from analyzing QCS as directed by NR 149 if second source standards are analyzed as per NR 149.44 (6)(i).

Automatic exemption from NR 149-directed QCS analyisis is also granted for pH analysis, DO and BOD analysis, as well as any analyses performed using ion selective electrodes.
Laboratories shall verify all initial instrument calibrations after they are generated but before they are used to quantitate any samples, with a second source standard, unless either of the following conditions exists:
1. An instrument is calibrated by tuning it to conform to a universally accepted scientific law or scale, as is the case with pH meters, ion selective electrodes and dissolved oxygen meters.
2. The laboratory analyzes quality control standards for the analyte or analyte group involved and evaluates them as specified in s. NR 149.48 (5).    NR 149.44 (6)(i)

Back to Top

Last Revised: Tuesday November 18 2008