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Table 5 Get acquainted with blanks

From: Wrangling environmental exposure data: guidance for getting the best information from your laboratory measurements

Approach (see Additional file 4 for example of this approach with real data):
1. Summarize results across all chemicals by blank type (e.g., field blank, solvent method blank, matrix blank, etc.), with non-detects set to zero. For chemicals with no detects in blanks, the MRL will equal the lab reporting limit and none of the subsequent steps in Tables 6 or 7 are needed.
For chemicals detected in blanks:
2. Visualize levels in blanks by blank type. Set non-detects to ½ lab reporting limit and plot by analytical batch.
 □ Consider whether blank detects are consistent across batches. Note whether detects seem to occur mostly in one type of blank which could indicate a source of contamination in the lab or field.
   If a particular source is suspected, we investigate (talk to lab, look at field logs, etc.).
3. Visualize levels in blanks by blank type along with field samples by analytical batch. Set non-detects to ½ lab reporting limit.
 □ Note whether blanks are in range of the samples.
 □ If field samples have been randomized into batches, check if variation in sample results correlates with blank results by batch. Note: we still go through this step even when we were not able to randomize field samples, but it is more challenging to distinguish whether contamination is driving differences in sample results in a particular batch or whether other explanations are more likely (e.g., all samples in one batch were collected in a different season or from a particular study site).