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User Benefits Application News Fig. 1 Image of Sample 33 As, 48 Cd, 50 Sn, 80 Hg, 82 Pb Elements Table 2 Standard Samples Fig. 2 Calibration Curves One test method for heavy metals in food products is the color reaction (staining) method, but because that method cannot identify metals (elements) or is influenced by the sample components, AA (atomic absorption spectrophotometry), ICP-AES (inductively coupled plasma atomic emission spectrometry) or ICP-MS (inductively coupled plasma mass spectrometry) is used for elemental analysis. However, sample preparation for these test and analysis methods requires a lot of work, such as component extraction with reagents and acidic cleavage, and in the case of the staining method, individual differences in judgment have become an issue in production process and quality control. For this reason, we propose a method using energy dispersive X-ray fluorescence spectrometry (EDXRF), which enables simple analysis in the entire process from sample preparation to measurement and judgment. In general, quantitation by EDXRF at levels below 1 ppm is difficult, as shown in Table 1, because these values are around or below the limit of quantitation. However, in the case of powdered milk, the standard values for the powder form before dissolution in hot water are about 7.7 times higher than the values shown in Table 1. This means that a screening analysis to determine whether the concentration is below the standard value or not is possible with EDXRF, which can analyze powders as-is. Since the sensitivity of the ALTRACE for heavy metal elements was substantially improved in comparison with the conventional EDXRF (EDX-7000) by installing a high output X-ray tube, it is now possible to analyze samples with same sensitivity as the conventional instrument in only 1/10 the measurement time. Introduction ALTRACE realizes the same analysis sensitivity as the conventional instrument (EDX-7000) in 1/10 the measurement time. Improved workability can be expected, as continuous analysis of up to 48 specimens is possible. Simple screening analysis of heavy metals without complex sample preparation is possible because it is only necessary to set the sample in the sample holder. Screening Analysis of Trace Heavy Metals in Powdered Milk Yuki Tamura Energy Dispersive X-ray Fluorescence Spectrometer ALTRACE Table 1 Tolerances of Heavy Metals, Etc. in Voluntary Standards for Baby Food *1 Arsenic Total mercury Lead Cadmium Tin 0.5 or less *2 0.1 or less 0.3 or less 0.2 or less 10 or less [ppm] *1 The concentration shows the value when prepared according to the method shown on the product label. *2 For products containing seaweed and seafoods, 1.0 or less. Excerpted from the voluntary standards of the Japan Baby Food Council. After dripping an atomic absorption standard solution in powdered milk, the sample materials were frozen and crushed. Table 2 shows the concentrations of the standard samples. Certification of the samples was done by ICP-MS measurement. Sample 7 was included here for correction of overlap of Pb with As. Standard Samples [ppm] Sample As Hg Pb Cd Sn 1 ND *1 ND ND 0.002 0.004 2 0.205 0.190 0.195 0.202 0.204 3 0.495 0.495 0.485 0.499 0.488 4 1.00 1.03 0.990 1.02 0.932 5 5.05 4.62 4.88 5.04 5.23 6 10.0 8.55 9.54 9.98 10.2 7 – *2 – 4.98 – – *1 ND: Below the limit of detection. *2 – : Not measured. The samples were introduced into sample containers lined with polypropylene film (thickness: 5 μm), and simple compression was applied. Fig. 1 shows an image of a sample. Sample Preparation Fig. 2 shows the calibration curves and Table 3 shows the calibration curve accuracy. For As, correction for overlap by Pb was applied (coexisting element correction, dj method), and to lessen the variations of the X-ray intensity, which are considered to be caused by the sample filling condition in sample preparation, the sample particle diameter, and other factors, correction was carried out using an internal standard for X-ray scattering. Excellent results were obtained for the accuracy of the calibration curves in Fig. 2, as the results were 0.2 ppm or less in all cases (Table 3). Calibration Curves 48 Cd 33 As Standard value (ppm) Measured intensity ratio Standard value (ppm) Measured intensity ratio 80 Hg 50 Sn Standard value (ppm) Measured intensity ratio Standard value (ppm) Measured intensity ratio 82 Pb Standard value (ppm) Measured intensity ratio
Application News www.shimadzu.com/an/ Shimadzu Corporation © Shimadzu Corporation, 2024 For Research Use Only. Not for use in diagnostic procedures. This publication may contain references to products that are not available in your country. Please contact us to check the availability of these products in your country. The content of this publication shall not be reproduced, altered or sold for any commercial purpose without the written approval of Shimadzu. See http://www.shimadzu.com/about/trademarks/index.html for details. Third party trademarks and trade names may be used in this publication to refer to either the entities or their products/services, whether or not they are used with trademark symbol “TM” or “”. Shimadzu disclaims any proprietary interest in trademarks and trade names other than its own. The information contained herein is provided to you "as is" without warranty of any kind including without limitation warranties as to its accuracy or completeness. Shimadzu does not assume any responsibility or liability for any damage, whether direct or indirect, relating to the use of this publication. This publication is based upon the information available to Shimadzu on or before the date of publication, and subject to change without notice. First Edition: Nov. 2024 01-00803-EN X-ray Fluorescence Spectra of Measured Elements Conclusion ALTRACE is a trademark of Shimadzu Corporation or its affiliated companies in Japan and/or other countries. Fig. 3 shows a comparison of the X-ray fluorescence spectra of the 1 ppm standard sample and blanks of As and Cd acquired with ALTRACE and EDX-7000 (excerpted from Application News No. X260). In the case of As, a clear difference between the added samples and the blank can be detected by both instruments, but for Cd, only ALTRACE can detect a clear difference in the peaks. The greatly improved sensitivity of ALTRACE can be understood from the peak shape, particularly in the measurements of Cd, Sn and other high energy band elements. Excellent results were obtained for both the calibration curves and the analysis results of powdered milk. EDXRF is useful for production process and quality control, as it is possible to measure samples directly in powder form or with only simple sample preparation, and thanks to its simple instrument handling and excellent repeatability, there are virtually no individual differences in results and judgments. The sensitivity of ALTRACE for heavy metal elements was substantially improved by installing a high power X-ray tube, enabling highly accurate management in a shorter time, thereby contributing to improved throughput. <Related Application News> 1. Screening Analysis of Trace Heavy Elements in Powdered Milk by EDXRF, Application News No.X260 Limit of Detection Table 5 shows the limits of detection calculated from the theoretical statistical variation. The data for the EDX-7000 are excerpts from Application News No. X260. Sensitivity equal to or higher than that of the EDX-7000 can be obtained with ALTRACE, even when the measurement time is greatly shortened to about 1/10 of the conventional level. Table 3 Accuracy of Calibration Curves [ppm] Element 33As 80Hg 82Pb 48Cd 50Sn Accuracy 0.08 0.08 0.11 0.12 0.11 ALTRACE Fig. 3 X-ray Fluorescence Spectra (Blue: As, Cd 1 ppm, Red: Blank) Measurement time: ALTRACE (As 600 s, Cd 600 s) EDX-7000 (As 3600 s, Cd 7200 s) Table 4 shows the analysis conditions. Analysis Conditions Table 4 Analysis Conditions Instrument ALTRACE Elements As, Cd, Sn, Hg, Pb Analysis group Calibration curve method Detector SDD X-ray tube Rh target Tube voltage 50 [kV] (As, Hg, Pb) 65 [kV] (Cd, Sn) Tube current Auto [μA] Primary filter #5 (As, Hg, Pb), #1 (Cd, Sn) Atmosphere Air Integration time 600 [s] x 2 Ch Dead time Max. 40 [%] EDX-7000 Table 5 Limits of Detection [ppm] Element 33As 80Hg 82Pb 48Cd 50Sn Analytical line AsKα HgLα PbLβ1 CdKα SnKα Instrument ALTRACE LOD *1 0.029 0.069 0.059 0.075 0.131 Measurement time 600 s 600 s Instrument EDX-7000 LOD 0.047 0.069 0.074 0.237 0.573 Measurement time 3600 s 7200 s *1 LOD: Limit of detection; 3 times the theoretical statistical variation obtained from the calibration curve. Results of Screening Analysis Assuming a solution prepared by dissolving 13 g of powdered milk in hot water to make up a total of 100 g is used as the standard concentration when ingested, the value obtained by multiplying the standard values in Table 1 by the dilution factor of 7.69 (100÷13) is set as the reference value in the powder form. The result is “OK” if the total of the quantitative value and error (judgment value) is less than the reference value. Table 6 shows the result of a screening analysis of sample 4 in Table 2. From this result, it can be understood that determination at the 1 ppm level is sufficiently possible with ALTRACE. Table 6 Result of Screening Analysis of Standard Sample (1 ppm) Heavy metal, etc. (analyte element) Arsenic (As) Total mercury (Hg) Lead (Pb) Cadmium (Cd) Tin (Sn) Judgment OK Not OK OK OK OK ① Quantitative value 1.00 1.01 0.97 1.02 1.00 ② Standard deviation σm 0.020 0.020 0.017 0.022 0.044 ③ Calibration curve accuracy σc 0.08 0.08 0.11 0.12 0.11 ④ Error 2 × √( ② 2 + ③ 2 ) 0.158 0.162 0.215 0.237 0.232 ⑤ Determination value ① + ④ 1.16 1.17 1.19 1.26 1.23 ⑥ Reference value 3.8 0.76 2.3 1.5 77 Note: Error was obtained using the following expression: Error = × σ 2 + σ 2 : With coverage factor set to 2 σ : Calibration curve accuracy σ : Measurement repeatability (standard deviation) Measurement time: 600 s Measurement time: 3600 s Measurement time: 600 s Measurement time: 7200 s
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