Field Quality Control Sample - Blind Duplicates

Modified on: Wed, 19 Dec, 2018 at 8:00 AM

A Blind Duplicate is a second sample collected at the same time and location, under the same conditions and submitted in separate containers.

Samples are homogenized where possible (i.e. alternate filling of sample and its blind duplicate for waters and bowl mixing for soils).  Samples are submitted to the laboratory without identifying them as duplicates.  VOCs in soil should not be homogenized.

Frequency and Purpose

Minimum of 1 field duplicate per sample set (per site).

Evaluates analytical precision, field precision and sample homogeneity. Has limited use for samples that cannot be homogenized (i.e. VOCs in soil). Field duplicates are Optional for effluents known to be highly stable and homogenous. Mandatory for unstable heterogeneous effluents and all environmental samples.

Application and Regulatory Criteria

It should be expected that the relative percent difference (see RPD) is larger than the laboratory duplicate samples.

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