Method Blank

A method blank is a laboratory control sample that is free of the target parameters and any substances that may interfere with that analysis, typically deionized water or purified san.  The method blank is processed through the entire analytical method including any extraction, digestion or any other preparation procedure.

Frequency and Purpose

Mandatory: 1 per analytical batch run

Monitors laboratory background levels of target analytes and laboratory artifacts.

Application and Regulatory Criteria

Used for all analytical parameters with a few exceptions such as pH.  In general, target analytes should be less than (<) the reporting detection limit (RDL).  However, detectable levels of the analyte <2x the RDL may be reported without corrective action.  Higher levels usually require repeat of the batch for the impacted analytes.

Recommended Actions

Unless stated otherwise, sample data is not corrected for blank concenrations.  If the level of the blank is less than 10% of the sample concentration or the sample concentration is significantly below the regulatory limit, this level of contamination would not be considered significant and would not affect data usability.  Analytes present in the blank but not detected in the sample can be ignored.