XRF Analyses and Sample Preprocessing

X-Ray Fluorescence Analysis (XRF) is a nondestructive physical method used for chemical elemental analysis of materials in the solid or liquid state. The specimen is irradiated by photons or charged particles of sufficient energy to cause its elements to emit (fluoresce) their characteristic x-ray line spectra.The detection system allows determining energies of the emission lines and their intensities. Elements in a specimen are identified by their spectral line energies or wavelengths for qualitative analysis, and intensities are related to concentrations of elements providing opportunity for quantitative analysis. Computers are widely used in this field, both for automated data collection and for reducing the x-ray data to weight-percent and atomic-percent chemical composition or area-related mass. Email:marketing@medicilon.com.cn web:www.medicilon.com

XRF Measurements XRF measurements were conducted four different ways to examine the effect of sample processing and XRF settings. First, an initial screening was conducted, followed by material isolation screenings by hand and in-stand, and lastly cryomilled materials were measured. By hand refers to measurements made while holding the XRF analyzer in hand and manually pulling a trigger. Measurements can also be made in-stand where the analyzer is docked in a stationary stand and remotely activated. Cryomilling refers to the process of reducing a sample to very small particle sizes by employing cryogenic temperatures and a mechanical mill. Further details on each of the measurements are included below. All samples were measured in Niton’s TestAll® mode. Initial Screening All components of each individual item underwent an initial 30-second handheld XRF screening. Components were defined as items with different colors or base materials including materials not meant to be handled, e.g., stuffing from pillows or comforters. During the initial screening, subcomponents were measured while still attached to the original product, i.e., not isolated. Data collected were merged with the spreadsheet constructed during sample cataloguing, using the unique alphanumeric number. During the initial screening effort, 30 items were randomly selected for duplicate analyses. Duplicates were performed for approximately the same amount of time as the original analysis. Here and throughout the project, duplicate (and triplicate) analyses were performed by taking an additional reading immediately after the original analysis without moving the analyzer. Sample Selection Seventy-two sample components were selected for further XRF screening and laboratory analysis of metal analytes. To determine which products to further analyze, results from the initial 30-second screening were reviewed for a range of concentrations and analytes. Items were selected for metals analysis if the XRF indicated an appreciable amount of one of the metals of interest. A range of concentrations for each element were selected from near XRF limits of detection (LODs) to several thousand ppm. Products from both the high and low end of the concentration spectrums were included to gauge performance at both ends. Additionally, a mix representing all material types (plastics, metals, textiles), product types (play toy, apparel, bedding, food ware) and retailers were selected from the products exhibiting detections. Each sample selected was analyzed for all seven elements of interest. Sixty-eight samples were selected for PBDE analysis, based on bromine content detected during the screening phase. In addition to high concentration samples (primarily recycled electronics), approximately 20 samples with low or no detected bromine were analyzed for PBDEs to examine the possibility of false negatives. Material Isolation Screening After samples were selected for screening, the specific component of interest was isolated from the product. This was done in order to remove interfering materials which may have confounded the initial XRF screening. Components were removed with clean (nitric- and acetone-rinsed) stainless steel tools including scissors, saws, and a handheld rotary tool. The isolated material was re-examined by the XRF for 60 seconds by handheld measurements and for 60 seconds using the XRF bench-top stand. Materials were folded or stacked when necessary to provide a thickness of at least 0.5 cm. A subset of the samples forwarded to the laboratory was measured in 30, 60, and 90 second increments to assess precision across different timeframes. These measurements were carried out during the isolated material XRF screenings both by hand and in the stand. Cryomilling Plastic samples were shipped to Toy Testing Inc. where they were cryomilled following established laboratory guidelines (Toy Testing Lab, 2010). Milled samples were returned to Ecology and measured by XRF in the stand (hereafter referred to as “powder” analysis). Samples that could not be milled by the laboratory (fabrics, foams, and metals) were cut into small pieces (<1 cm) and forwarded to the laboratory. Cryomilling could not be done on foam products because small pieces of foam clump together even under extremely low temperature. Fabric pieces were also not suitable for cryomilling because the mill uses a ball bearing in the vessel to grind the sample; fabric pieces can bind together and be packed by the ball rather than pulverized. Metal materials are also not compatible with cryomilling because metal substrates would damage the cryo vessel.