Abstract
The current practice for the determination of personal exposures to airborne dusts involves the aspiration of known quantities of air through membrane filters held in filter holders. The two-piece, 37-mm polystyrene cassette is the most typically used filter holder. Two potential major errors exist with filter-based air-sampling methods. The first error is caused by potential sample loss on the inside of the cassette top during the sample's collection and shipment back to the laboratory for analysis. A second error is caused by sample loss during the removal of the filter from the cassette prior to analysis. The potential for sample loss creates a third problem that is specific to gravimetric methods. A small linear range exists for gravimetric methods between their limit of quantitation and filter capacity. A new filter cartridge device was developed and evaluated to estimate the concentration of airborne total dusts over a larger linear range while eliminating negative bias errors associated with both sample losses on the inside of the cassette's top during sampling and with sample losses during filter removal and handling. Additionally, the new device is designed to be disposable, inexpensive, easy to handle in the laboratory, and totally compatible with the commonly used 37-mm polystyrene cassette. The new filter cartridge device is made from a filter and a cylindrical cap insert sealed together to form an enclosure. The cartridge is designed to fit snugly inside a 37-mm polystyrene cassette top between the backup pad and the inside of the cassette top. The completed cartridge weighs about 190 mg. Its mass can be determined gravimetrically to 0.05 mg. A unique identification number is engraved onto the top surface of each cartridge. This number can be used by both the field and laboratory staffs handling the cartridge. The mean difference between preweight and postweight masses of 70field blank cartridges was calculated as −0.07 mg with a standard deviation of 0.04 mg. The limit of detection for the cartridge method was calculated as 0.12 mg; the limit of quantitation for the cartridge method was calculated as 0.2 mg. Although capacity is a function of the type of dust collected, based on actual field samples, the capacity of the cartridge may be 50 mg or more.