Analysis of As, Pb and Cd in elute from tea

Introduction

Hazardous metallic elements from the soil accumulating in tea leaves is a health concern for people in Japan and Europe, where a large amount of tea leaves are imported and consumed. In the total reflection X-ray florescence (TXRF) method, sample preparation is easy: an aliquot of liquid is simply pipetted onto a carrier. Multi-elements quantification is available using the internal standard method without the need to prepare calibration curves. This note describes the analysis of hazardous elements such of As, Pb and Cd in the elute from tea leaves.

Measurement and results

The tea leaf sample was heated at 95°C for 10 min. Ten µL of 5 mg/L of a Ga solution and 20 µL of 100 mg/L of an Ag solution were added as internal standards to 970 µL of the elute. Gallium was used for the analysis of elements whose X-ray energies are below 18 keV, such as As and Pb. Silver was used for the analysis of elements like Cd, whose X-ray energies are in the high-energy range, above 18 keV. Ten µL of solution was pipetted onto a quartz glass carrier and dried under reduced pressure conditions. Analytical results of the elute are shown in Table 1.

Several hundred mg/L of K, and sub mg/L to several mg/L of Ti, Mn, Fe, Zn and Rb were detected as inorganic components. As, Pb, and Cd, the hazardous elements of concern, were not detected. Figure 1 shows the spectra obtained from the elute samples to which Pb and Cd solution were added. Resulting concentrations after adding were 20 and 50 µg/L for Pb, 0.5 and 1.0 mg/L for Cd. The LLDs for As, Pb and Cd were calculated to be 1.7, 6.4 and 112 µg/L respectively. Thus, TXRF is expected to be applied to liquid sample analysis. 

Figure 1:  Pb and Cd spectra of the elute from tea leaves.  (a) Pb solution added to 20 and 50 µg/L, (b) Cd solution added to 0.5, and 1 mg/L.

Table 1:  Analytical values of the elute from tea leaves (Unit: mg/L) 

*: Not detected