The instrument parameters were optimized. The configurations and operation of the MPT ion source were stated in detail in our previous work . Microwave power was set to 50 watt, and the reflected power was reduced to almost 0 watt by adjusting the tuning piston of the microwave plasma torch tube. Stable argon plasma could be obtained when the flow rate of working gas (Ar) was 0.4 L/min and flow rate of carrier gas (Ar) was 1.2 L/min. In order to reduce the measurement error caused by the uneven distribution of active ingredient in tablets, the contact area of about 0.5 cm2 between plasma torch and the sample was controlled by adjusting the angle and distance of desorption (h).