Rapid Limit Tests for Metal Impurities in Pharmaceutical Materials by X-ray Fluorescence Spectroscopy Using Wavelet Transform Filtering

• Published in: Analytical chemistry (Washington) Vol. 83; no. 3; pp. 1061 - 1068
• Main Authors: Arzhantsev, Sergey, Li, Xiang, Kauffman, John F
• Format: Journal Article
• Language: English
• Published: Washington, DC American Chemical Society 01-02-2011
• Subjects: Analytical chemistry; Calibration; Chemistry; Exact sciences and technology; Fluorescence; Mass spectrometry; Metals, Heavy - analysis; Signal to noise ratio; Spectrometric and optical methods; Spectrometry, X-Ray Emission - instrumentation; Spectrometry, X-Ray Emission - methods; Studies; Time Factors; Ultraviolet Rays; Wavelet transforms; United States > US; Trace analysis; Filtering; Arsenic; Impurity; Noise; Sample; Use; X ray spectrometry; Calibration; Laboratory; Metal; X ray analysis; Signal; Analysis method; Wavelet transformation; Filter; Detection limit; Chromium; Lead; X ray fluorescence spectrometry; Poison; Mercury; Signal to noise ratio
• ISSN: 0003-2700; 1520-6882
• DOI: 10.1021/ac1028598

We introduce a new method for analysis of X-ray fluorescence (XRF) spectra based on continuous wavelet transform filters, and the method is applied to the determination of toxic metals in pharmaceutical materials using hand-held XRF spectrometers. The method uses the continuous wavelet transform to filter the signal and noise components of the spectrum. We present a limit test that compares the wavelet domain signal-to-noise ratios at the energies of the elements of interest to an empirically determined signal-to-noise decision threshold. The limit test is advantageous because it does not require the user to measure calibration samples prior to measurement, though system suitability tests are still recommended. The limit test was evaluated in a collaborative study that involved five different hand-held XRF spectrometers used by multiple analysts in six separate laboratories across the United States. In total, more than 1200 measurements were performed. The detection limits estimated for arsenic, lead, mercury, and chromium were 8, 14, 20, and 150 μg/g, respectively.