Analyzing Lead in Wheat Noodles

The Codex Alimentarius needs a maximum level of lead to be less than 0.2 mg/kg in cereal grains (Codex Standard 193-1995). This article examines the capabilities of the Epsilon 3XLE, a benchtop energy dispersive X-ray fluorescence spectrometer as a tool for inspecting lead in wheat noodles. The XRF technique is an interesting analytical method for the food industry due to the simple sample preparation involved, coupled with quick measurements of elements. It enables analysis close to production lines.

Instrumentation

Measurements were recorded using a PANalytical Epsilon 3XLE EDXRF spectrometers. These instruments are equipped with a 50 kV silver anode X-ray tube, a helium facility, 6 beam filters, a high-resolution SDDultra silicon drift detector, a 10-position removable sample changer and a sample spinner.

Sample Preparation

Noodles were grounded to a fine powder using a ball mill (Retsch MM400). To create the calibration samples, known amounts of lead were added into 5 g samples of the fine noodle powder. The samples were then transferred into loose powder sample cups with a 3.6-µm thick Mylar foil.

Measurement Procedure

Five calibration samples were used to set up calibration. Table 1 shows the measurement condition used for measuring lead. An air atmosphere was used to perform analyses and the total measurement time per sample was 15 minutes. The intensities for lead were measured with a region of interest (ROI) calculation using intensities from the Lα and Lβ lines. Figure 1 shows the spectrum for one of the calibration samples.

Table 1. Measurement conditions

Condition kV µA Medium Filter Meas. time (s) Elements
<Ni-Mo> 50 200 Air Ag 900 Pb

Zoomed-in spectrum of lead in noodles obtained using the condition. <Ni-Mo/>

Figure 1. Zoomed-in spectrum of lead in noodles obtained using the condition. <Ni-Mo>

Calibration Results

Shown in Figure 2 is the calibration plot for lead in noodles, applying the condition given in Table 1. A good correlation between the chemical concentrations and the measured intensities is shown by the calibration plot. The calibration data for the noodle samples is summarized in Table 2.

Calibration graph for lead in noodles.

Figure 2. Calibration graph for lead in noodles.

Table 2. Calibration details

Element Concentration range (mg/kg) RMS* (mg/kg) Correlation LLD (mg/kg)
Pb 0 - 100 0.28 0.9999 0.06

(* RMS: The most accurate calibration have the smaller RMS values)

Precision

In order to test the repeatability, the 2 mg/kg calibration sample was measured as an unknown, for 10 times consecutively. Table 3 shows the average concentration, RMS (1 sigma standard deviation) and the relative RMS of the repeat measurements for lead. The individual results for the 10 measurements are graphically displayed in Figure 3. The results show excellent precision.

Table 3. Results of the repeatability test of lead in noodles

Element Average conc. (mg/kg) RMS (mg/kg) Rel. RMS (%)
Pb 2.4 0.04 1.6

Graphical representation of the repeatability results.

Figure 3. Graphical representation of the repeatability results.

Conclusion

The data presented in this article clearly shows that an Epsilon 3XLE EDXRF spectrometer is a suitable tool for analyzing lead in wheat noodles, with detection limits meeting those laid down by the Codex Alimentarius with analysis time taking 15 minutes.

The repeatability results demonstrate the robustness and stability of the Epsilon 3XLE. The excellent detector resolution coupled with high sensitivity and powerful software contributes to the precision and accuracy of the results.

This information has been sourced, reviewed and adapted from materials provided by Malvern Panalytical.

For more information on this source, please visit Malvern Panalytical.

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