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Internal Quality Assurance Requirements for the Analysis of Dioxins in Environmental Samples


The degree of agreement of a measured value with the true or expected value of the quantity of concern (Taylor, 1990).

Blind Sample
A sample submitted for analysis whose composition is known to the submitter but unknown to the analyst. A blind sample is used to test the proficiency of a measurement process (Taylor, 1990).

Calibration Standards
a set of solutions containing known amounts of native and carbon-13-labelled PCDDs and PCDFs. These solutions are used to establish the relationship between PCDD/PCDF concentration and MS detector response over the expected range of sample concentration.

Calibration Verification Standard
A calibration standard solution of intermediate level concentration (e.g., CS3), used to assess whether the initial calibration is still valid.

Certified Reference Material
A stable, homogeneous, and well characterized reference material, one or more of whose property values are certified by repetitive analysis by several operators and different methodologies in one or more qualified laboratories of known precision and accuracy. This material is used to assess the accuracy of a measurement process.

a member of a family of compounds that differ from each other only in terms of numbers and locations of common substituent atoms, or groups of atoms, on the parent compound. There are 75 PCDD and 135 PCDF congeners.

Control Sample
A reference material of known composition that is analyzed concurrently with test samples to evaluate the accuracy and/or precision of a measurement process (Taylor, 1990).

Column Performance Test Mixture
a solution whose components allow for performance testing of a specific Gas Chromatograph (GC) column in terms of some column characteristic that is critical to data quality. Chromatographic resolution of 2,3,7,8-TCDD and 2,3,7,8-TCDF from neighbouring isomers is assessed using such test mixtures.

Glassware Proof Rinse
The composite final solvent rinse of each piece of glassware intended for use in processing a batch of samples. Proof rinse samples are analyzed before sample processing begins.

A subset of congeners whose members are isomers one to another. For example, both 1,2,3,4-TCDD and 2,3,7,8-TCDD belong to the TCDD homologue group, whereas 1,2,3,7,8-P5CDD belongs to the P5CDD homologue group.

Instrumental Detection Limit
the smallest concentration/amount of analyte, in a solution containing only the analyte(s) of interest, that produces an instrumental response which satisfies all analyte detection and identification. criteria.

Internal Standard Quantitation
a quantitation procedure that corrects target analyte concentration data for processing losses, as well as normal variations in operator and instrument performance, in a single calculation. To use this procedure, samples must be spiked with known amounts of surrogate compounds (i.e., internal standards) before processing and a Relative Response Factor must be determined for each target analyte.

A member of a group of compounds that differ from each other only in terms of the locations of a specified number of common substituent atoms, or groups of atoms, on the parent compound. For example, there are 22 possible isomers of TCDD.

Method Blank
media (e.g., filter, solvent, water) spiked with surrogates and processed in an identical manner to actual test samples.

Method Detection Limit (MDL)
The smallest test sample concentration/amount of analyte that produces an instrumental response which satisfies all analyte detection and identification criteria when the sample is processed and analyzed according to the requirements of a specified test method. Reported MDL values reflect the composite effect of sample-related variables as well as method-related variables.

The degree of agreement between the data generated from repetitive measurements under specified conditions. It is generally reported as the standard deviation (SD) or relative standard deviation (RSD).

Quality Assurance (QA)
A system of activities whose purpose is to provide the producer or user of a product with the assurance that the product meets a defined standard of quality. The system consists of two separate but related activities, quality control and quality assessment (Taylor, 1990).

Quality Control (QC)
The overall system of activities whose purpose is to control the quality of a product so that it meets the needs of users (Taylor, 1990).

Recovery Standards
Selected compounds that are added to sample extracts immediately before instrumental analysis so that surrogate (internal standard) recoveries can be calculated. The two labelled compounds that serve as recovery standards for PCDD/PCDF analysis also serve as markers for identifying specific congeners on the basis of relative retention time.

Relative Response Factor (RRF)
The quotient of a target analyte response factor (instrument response per unit weight) divided by the response factor for its corresponding labelled surrogate. An RRF value remains constant over the range of concentration for which instrument response is linear.

2,3,7,8-Substituted Congener
A dioxin or furan congener with a minimum of four chlorine substituents at the 2,3,7, and 8 positions on the parent compound. There are seven 2,3,7,8-substituted PCDD congeners and ten 2,3,7,8-substituted PCDF congeners.

Compounds whose compositions and chemical properties are nearly identical to those of target analytes, but which are distinguishable from target analytes by some means of detection (e.g., MS). Isotopically-labelled dioxin and furan congeners are used as surrogates for their native analogues. Using surrogate compounds as internal standards allows target analyte data to be corrected for whatever degree of analyte loss has occurred during the course of sample processing.

Window Defining Mixture
A solution containing the earliest and latest eluting congeners within each homologous group of target analytes on a specified GC column.
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