Performance of a Robotic Weighing System and Quality Practices for Gravimetric Mass Measurements

Abstract

Gravimetric analysis is an essential baseline measurement for air quality monitoring networks to monitor particulate matter and to track adherence to the National Ambient Air Quality Standards. The Clean Air Act requires the state and local agencies to monitor and report particulate matter concentrations as a part of their air monitoring requirements. Highthroughput gravimetry laboratories need to be capable of weighing thousands of filter-based samples each month while maintaining strict quality control requirements set by the Federal Reference Method for the determination of particulate matter in ambient air.Here, we present an evaluation of the performance of a robotic weighing system and review quality control measures applicable to gravimetric mass measurements. Results from this study show robotic weighing is better able to control static effects common to manual weighing. Electrostatic charges are increased with each human movement during the manual weighing process and, as indicated here, can occur suddenly and be difficult to detect. This study provides insights into the ability of robotic weighing to mitigate this effect and suggests new quality practices to detect and track the static effect.

An evaluation of mass absorption cross-section for optical carbon analysis on Teflon filter media

“…The arm movements were closely monitored using the weighing results. Our results showed that the RWS showed a high degree of precision and accuracy with no significant drift and with negligible effect of static electricity, and imparted no contamination onto the filters (Presler-Jur et al, 2016).…”

“…Being able to estimate BC from Teflon filters thus enhances the ability to expand the spatial scale of estimated EC measurements at a lower cost than thermal OC/EC analysis, if, for example, it is performed routinely on these network filters. The ability to automate such measurements on Teflon filters using a robotic weighing system (RWS) (Presler-Jur et al, 2016) while also measuring gravimetric mass provides exceptional value by generating concurrent BC data at reduced human labor effort relative to multiple manual measurements. Further, the ability to analyze archived filters enables expanding the temporal extent of estimated EC data.…”

“…Measurements of b att were performed using a Magee Scientific SootScan model OT21 transmissometer (Magee Scientific Corporation, Berkeley, CA). The OT21 system used in this study is a modified version that is incorporated into an MTL Corporation AH-225 Precision Weighing System (Minneapolis, MN), an RWS that is designed to provide automated, accurate, gravimetric mass measurements on a large scale (Presler-Jur et al, 2016). This inline version of the OT21 system is hereafter referred to as the Robotic OT21 to distinguish it from the benchtop Magee Scientific SootScan model OT21 transmissometer (Benchtop OT21).…”

“…Both OT21s are located in a climate-controlled walk-in environmental chamber in the RTI International Gravimetry Laboratory that is tightly controlled for temperature and relative humidity to meet federal requirements for gravimetric analysis. More information about the RWS and the environmental chamber can be found in Presler-Jur et al (2016).…”

Filter Processing and Gravimetric Analysis for Suspended Particulate Matter Samples

“…Automated weighing systems have been used in which filters are loaded into cassettes and robotically moved to and from the microbalance for automatic weighing (Presler-Jur et al 2016). While weights have been shown to be comparable to those derived from manual weighing, there is little technician time saved as the filters must be transferred from the Petri slide to the cassettes and back again.…”