COMPARISON OF CONTAINERIZED LIQUID SAMPLING DEVICES IN STRATIFIED LIQUIDS:
James D. Hoover, Ph.D.
Scott R. Somers, MS
Advanced Concepts & Design, Inc.
Independent testing was conducted to determine systematic differences in sampler performance between the Drum Thief, COLIWASA, and AC&D’s Liquid Samplers in containerized sampling of stratified liquids. Phase I (design-related errors) measured the devices’ collection ability in varying ratios of oil and water. Phase II (operator-related errors) explored the variability that exists from personnel interface. Both phases revealed statistically significant differences in the accuracy, precision, spillage, and sampling time among the devices tested. Researchers noted that although profile-based sampling has been ongoing for 20-30 years, this is the first review that compares data quality as a function of device design and usability.
The performance of the AC&D Liquid Samplers exceeded that of the other devices in all categories of evaluation. Nearly all aspects of sampling performance were dominated by the differences in the design and function of this new device. Among the devices tested, sampler performance with the AC&D devices was found to be the least dependent upon user factors, including experience, and received the highest rating for “ease-of-use”. The research concludes that the utility of the AC&D Liquid Sampler can improve profiling-based sampling tasks, in addition to operator safety and workforce productivity.
EXPERIMENTAL DESIGN AND TEST METHODS
This study evaluated three types of liquid sampling devices used for the sampling of stratified liquids from containers, such as drums. Conditions of stratified liquid sampling were chosen because most data quality issues in containerized liquid sampling involve representative sampling of segregated liquids. The devices evaluated were the Drum Thief, the COmposite LIquid WAste SAmpler (COLIWASA-inner closure), and a new product, the Advanced Concepts & Design (AC&D) Liquid Samplers. These liquid sampling devices were chosen on the basis of recognition by the regulatory and standards community as appropriate for profile sampling. Two different sizes of units were tested, small (250-mL) and large (1-L).
Test Conditions and Outputs
All samples were collected under controlled laboratory conditions simulating the sampling of stratified liquids from 55-gallon waste drums. In Phase I, measured volumes of oil and water were placed into 34” acrylic cylinders to known stratified conditions (5:95, 10:90, 30:70, 50:50, 70:30, 90:10 and 95:5). A single operator then sampled each ratio, an equivalent number of times using each sampling device (n=216). The output from Phase I compared known vs. actual for each ratio and graphed accordingly, Figures 1-2. During Phase II tests, 52 individuals collected samples with each of the sampling devices from drums having a 50:50 oil:water ratio (n=250). Various outputs were assessed, such as sample precision, accuracy, spillage, time, and an exit survey was conducted that asked for the participants’ perspective of each sampling device, Figures 3-6.
Nearly all aspects of liquid sampling performance differed depending upon with the type of device used. Systematic sampling errors were attributable to the inherent design of the devices and the extent to which device operation was affected or influenced by the user. The magnitude of sampling error and spillage with some devices also appears to depend on the viscosity and proportions of the liquids.
The findings suggest that traditional sampling methods and tools used to collect profile samples are highly variable and suffer from design and operator interface concerns. The Drum Thief and COLIWASA suffer from variable accuracy and precision, as well as the other indices recorded. Sampling error with the Drum Thief was due to the surface tension effects caused by variable viscosities, whereas the COLIWASA’s error was mainly attributed to the inner-closure design, which restricted and causes poor fluid flow during insertion. AC&D Liquid Samplers have been designed to account for these error sources, yielding more precise, compliant and defensible data.
Phase I: Design-Related Error
The collection of 216 data points were used to generate Figures 1 and 2, for both small (250-mL) and larger (1-L) sample volumes, respectively. The graphs represent the significant error that is present when using traditional Drum Thief and COLIWASA methods. For example, in Figure 2 at the 30:70 oil:water stratification, the error associated with the COLIWASA is 35% as compared to an error of 5% with AC&D Liquid Samplers.
Phase II: Operator-Related Error
Figures 3-6 represents the findings of 52 individual during the collection of 250 samples at a single stratification (50:50) oil:water. Among the measured outputs were precision and accuracy, spillage (as an indicator of safety and cross contamination), time (as a measure of productivity), and “ease-of-use”.
Advanced Concepts and Design, Inc. welcomes any comments about this research paper. For further information about the AC&D Liquid Samplers or to request other reviews, please call 800/404-9559 or visit us online at www.coliwasa.com.