What is the purpose of performing a zero check during instrument calibration?

• A. To set the instrument to its maximum reading.
• B. To adjust for humidity.
• C. To verify the sample collection times.
• D. To ensure the instrument reads zero concentration in clean air, checking for offset drift.

Answer: (D)

Zero checks establish the baseline of an instrument by ensuring that, when exposed to clean air with no analyte, the reading sits at zero. This tests for offset drift or bias in the sensor or electronics. If the baseline isn’t truly zero, all subsequent measurements will carry that bias, making readings inaccurate until the offset is corrected. By verifying zero before moving on to span calibration, you confirm that the instrument’s starting point is accurate and stable.

Setting to a maximum reading isn’t what this step does, and adjusting for humidity isn’t the purpose of a zero check. Verifying sample collection times relates to how samples are taken, not the instrument’s baseline reading.