Study On The Detection Method Of Pb In Tea

Objective:(1) The new method—inductively coupled plasmamass spectrometry will be established to detect lead in tea.The feasibility of thenew method was investigated comparing with the classical method--atomicabsorption spectrophotometric method. Method:(1) Pre-treatment patterns wereinvestigated for the extraction of lead from tea sample with the stability and thespiked recoveries as indexes among dry digestion, wet digestion andmicrowave digestion.(2) The best conditions of the ashing temperature,atomization temperature, matrix modifier selection and dosage wereinvestigated by comparing experiments in the atomic absorption spectrometer.(3) The best conditions of the inductively coupled plasma mass spectrometrywere investigated through the instrument itself tuning screen the optimumconditions of RF power, nebulizer argon gas flow and prism voltage etc.(4) Theparameters including the linear range, precision, accuracy and detection limit ofthe two kinds of methods were measured.(5)The paired t test was taken forverifying whether there were significant difference between the two methods.Results:(1) The best pre-treatment method was the microwave digestionmethod through the comparison of stability factor and the adding standardrecovery.(2)The best detection conditions of the lead in tea by the atomicabsorption spectrometer is: drying stage: the first step from room temperatureup to70℃with a speed of3℃/s, holding10s; The second step was in a speedof5℃/s from70℃up to90℃, holding10s; The third step was in a speed of5 ℃/s from90℃up to120℃, holding10s. Ashing stage: With a speed of250℃/s,the temperature up to750℃from120℃, holding15s,end. Atomizationstages: the temperature is heated to1500℃from750℃at a rate of1400℃/s. Select5μl0.2%ammonium dihydrogen phosphate as a matrixmodifier.(3)The best detection conditions of the lead in tea by the inductivelycoupled plasma mass spectrometry is: RF power1100W; nebulizer argon flow0.84L/min; plasma argon gas flow15.00L/min; auxiliary gas flow1.20L/min;CeO/Ce <3%, Ba++/Ba+<3%（.4）For the same batch of tea samples,therewere no significant differences in the recoveries, precision and stability of thetwo methods. Conclusion:(1)The microwave digestion method is the bestpre-treatment method for detecting lead in tea.(2)Both of the Atomic absorptionspectrometry and inductively coupled plasma mass spectrometry are accuratefor detecting lead in tea. It shows that the new method for the detection of teaby inductively coupled plasma mass spectrometry of lead is feasible.