CALIBRATION AND QUALITY CONTROL:
10. Zero the microbalance before all weighings. Use the same microbalance for weighing filters
before and after sample collection. Calibrate the balance with National Institute of Standards
and Technology Class S-1.1 or ASTM Class 1 weights.
11. The set of replicate samples should be exposed to the same dust environment, either in a
laboratory dust chamber [6] or in the field [7]. The quality control samples must be taken with
the same equipment, procedures and personnel used in the routine field samples. Calculate
precision from these replicates and record Sr
on control charts. Take corrective action when the
precision is out of control [6].