Determination of Nutritional and Toxic Metals in Black Tea Leaves Using Calibration Free LIBS and ICP: AES Technique

Quantitative and qualitative analyze of toxic and nutritional elements existing in different kinds of black tea (Camellia Sinensis) leaves available in Pakistan was conducted with calibration free/laser-induced breakdown spectroscopy (CF/LIBS). A Q-switched Nd:YAG laser employed to create micro-plasma on the tea sample surfaces. The quantitative analysis accomplished by studying the spectral emissions of plasma using a dedicated spectrometer. Iron, magnesium, sodium, potassium, calcium, aluminum, and zinc were measured as essential nutrients, while chromium, copper, manganese, nickel, and lead as toxic metals. In order to get precise and reliable analysis, the LIBS setup was optimized by performing various parametric dependence studies. The Boltzmann plot method was adopted for calculation the plasma temperature its average values are between ~ 7500 and 9000 K for all kinds of tea leaves. To find out the electron number density (Ne), the Stark broadened line of atmospheric hydrogen pea (Hα) was chosen and was found between 1.13 × 1017 cm−3 and 1.61 × 1017 cm−3. The laser-generated micro-plasma was optically thin, and the effect of self-absorption in spectral emission lines was found negligible. The LIBS results were verified by means of inductively coupled plasma/atomic emission spectroscopy (ICP/AES). The findings obtained using LIBS and ICP techniques displayed an excellent agreement which exhibit that LIBS is very good to for spectro-chemical analysis of food products.