This study used five handheld material-identity verification systems (TruScan, Ahura Scientific, Wilmington, MA, see Figure
1). These instruments use Raman spectroscopy as the analytical technique and contain a 785-nm NIR external cavity-stabilized,
thermoelectrically cooled laser as the light source. The laser typically operates at 300 mW output and automatically adjusts
if necessary to avoid detector saturation. These instruments also include a single-pass dispersive spectrometer, a cooled
CCD detector array, and dielectric edge filters for Rayleigh rejection. Each instrument has an integrated barcode reader
for selecting methods and capturing sample lot/batch/other identifiers. Table I shows specifications for the TruScan Raman
material identity verification system.
Figure 1: TruScan handheld material identity verification system based on Raman spectroscopic technology.
Acquiring a spectrum is facilitated by using an auto-acquisition mode that monitors incoming data in real time and automatically
adjusts the control settings (e.g., laser power, exposure time, number of exposures) such that spectra of comparable statistical
resolving power are achieved from one measurement to the next. This adaptive approach to spectroscopy ensures consistent statistical
performance of the instrument and embedded decision algorithms regardless of operating conditions.
Four of the instruments (hereafter called reference devices) were used to acquire reference spectra for the 198 materials
included in this study (see sidebar, "Materials tested"). To obtain the reference spectra, a reference sample of each material
contained in a borosilicate glass vial (Kimble Glass, Vineland, NJ) was placed at the correct distance from the device's laser
aperture using a vial-holder accessory. All data acquisition was performed in auto-mode. For test spectra, most analyses are
complete in less than one minute. Reference-grade spectra used for method development are also generated using an auto-mode;
however, these spectra have higher standards for signal-to-noise ratio than a standard test spectrum and therefore require
a longer data acquisition time. Most auto-mode reference spectra are acquired in less than 30 min. The scans that did not
auto-terminate within 45 min were manually stopped at 45 min to prevent photobleaching.
Reference spectra can be transferred between TruScan devices using a compact flash card or a standard web browser that addresses
the device via a TCP/IP connection. Using these approaches, the reference spectra were transferred from the four reference
devices to the test device. Once all of the reference spectra had been transferred to the test device, the TCP/IP utility
WebAdmin was used to generate a new method for each of the 198 materials using only one reference spectrum for each method.
In the context of the TruScan device, methods are analytical tasks based on stored reference spectra that the instrument's
software executes to determine whether a material's identity can be verified.
To challenge the methods, a test sample of each material was placed in a borosilicate glass vial, and the vial was inserted
into the test device's vial holder. For each test sample, a spectrum was acquired using auto-mode. The onboard processor then
evaluated the spectrum acquired for each test material against the method developed for that material, and also against all
the methods created for the rest of the 198 materials, for a total of 39,204 evaluations of test spectra against methods.
In addition to the pass and fail results normally presented by the test device, the p-value was recorded for each test sample–method evaluation pair.