Which statement best describes a Single Blind Sample?

• A. An external QA sample identified as QA to the lab, but parameter concentrations are unknown to personnel.
• B. An external QA sample whose concentrations are known to the laboratory staff.
• C. A production sample disguised as QA sample.
• D. A blank spike in water.

Answer: (A)

Single blind samples are external QA materials where the lab personnel do not know the true concentrations of the analytes, while the QA program knows them. This setup keeps the testing process unbiased because the analysts can’t tailor their approach or expectations to the expected result. The best statement captures this by describing an external QA sample identified as QA to the lab with concentrations hidden from the staff. Knowing the concentrations would remove the blind aspect and could influence how results are interpreted or reported, while a disguised production sample or a blank spike describes different QC scenarios that don’t reflect the single blind QA purpose.