Acid-Soluble Internal Capsules for Closed-Face Cassette Elemental Sampling and Analysis of Workplace Air

Abstract

Airborne particles that are collected using closed-face filter cassettes (CFCs), which are used widely in the sampling of workplace aerosols, can deposit in places other than on the filter and thereby may not be included in the ensuing analysis. A technique for ensuring that internal non-filter deposits are included in the analysis is to collect airborne particles within an acid-soluble internal capsule that, following sampling, can be dissolved along with the filter for subsequent elemental analysis. An interlaboratory study (ILS) was carried out to evaluate the use of cellulosic CFC capsule inserts for their suitability in the determination of trace elements in airborne samples. The ILS was performed in accordance with an applicable ASTM International standard practice, ASTM E691, which describes statistical procedures for investigating interlaboratory precision. Performance evaluation materials consisted of prototype cellulose acetate capsules attached to mixed-cellulose ester filters. Batches of capsules were dosed with Pb-containing materials (standard aqueous solutions, and certified reference material soil and paint). Also, aerosol samples containing nine target analyte elements (As, Cd, Co, Cr, Cu, Fe, Pb, Mn, and Ni) were generated using a multiport sampler; various concentrations and sampling times were employed to yield samples fortified at desired loading levels. Triplicates of spiked capsules at three different loadings were conveyed to each volunteer laboratory; loading levels were unknown to the participants. The laboratories were asked to prepare the samples by acid dissolution and to analyze aliquots of extracted samples by atomic spectrometry in accordance with applicable ASTM International Standards. Participants were asked to report their results in units of μg of each target element per sample. For the elements investigated, interlaboratory precision and recovery estimates from the participating laboratories demonstrated the utility of the cellulosic capsule inserts for the measurement of sampled trace elements.

Interlaboratory evaluation of cellulosic acid-soluble internal air sampling capsules for multi-element analysis

“…These results are consistent with previous reports entailing elemental analysis of soluble capsules for use as cassette inserts. (3, 11) …”

“…Of the 33 elements evaluated in the ILS, 30 were found to satisfy the NIOSH criterion for method accuracy. Based on this work and the results of related laboratory and field studies, (3,11) a new NIOSH procedure (Method no. 7306) will soon be promulgated describing the use of soluble cassette inserts for sampling and analysis of metals and metalloids in workplace atmospheres.…”

“…(2) An effective technique for ensuring that internal non-filter deposits are included in the analysis is to collect airborne particles within an acid-soluble internal capsule which, following sampling, can be dissolved along with the filter for subsequent elemental analysis. (3) In this project, an interlaboratory study (ILS) was carried out to evaluate the use of cellulosic CFC internal capsules for their suitability in the determination of trace elements in airborne samples from workplaces.…”

“…A principal aim of this work was to carry out an ILS to evaluate the analytical suitability of cellulosic internal capsules for their use with traditional plastic air sampling cassettes. In an effort to complement previously-reported results for soluble internal capsules fortified with fewer metals and metalloids, (3) it was deemed important to obtain performance data for many more elements that are of concern for workplace exposure monitoring. The ILS entailed fortifying the cellulosic capsules with various loadings of metals and metalloids of interest and sending them to volunteer laboratories for analysis.…”

New Methods for Personal Exposure Monitoring for Airborne Particles

“…Another innovation in inhalable sampling is the use of Accu-cap filters (SKC Inc.), which consist of an acid-soluble cellulose acetate capsule attached to filter media (e.g. mixed-cellulose ester, PVC) [18, 19]. The Accu-cap allows quantification of all particles that enter the traditional 37-mm closed-face cassettes, including those caught on the filter and those that would have deposited on the walls of the cassette.…”