A transient signal acquisition and processing method for micro-droplet injection system inductively coupled plasma mass spectrometry (M-DIS-ICP-MS)

Abstract

An optimal signal acquisition and processing method for use with intermittent small-sized sample introduction techniques, such as the micro-droplet injection system (M-DIS), was investigated. This type of system is expected to play an important role in environmental and medical fields by enabling analysis of single cells or nanoparticles. A model signal was formed based on an analog signal that was acquired using an inductively coupled plasma mass spectrometer coupled to the M-DIS. Using this model signal, signal-to-noise ratios (SNRs) were evaluated in the cases where the sampling interval and the integration time of the detector were equal, where the analog signal from the detector was acquired using an analog recorder, and where the analog signal from the detector was acquired digitally using a digital oscilloscope. The behavior indicated by the simulation results was different in each case and gave optimal filter time constants of approximately 1.40, 0.99 and 1.36 times the full width at half maximum value, respectively. The characteristics of the three cases were discussed based on their SNRs, and it was found that the highest SNR for the transient signal would be obtained when the analog signal was acquired digitally using a high sampling frequency and a digital filter with an optimal time constant (288 μs in this study). In this case, the sodium limit of detection of 85 ag was obtained using a raw droplet signal when the sampling frequency was 10⁷ Hz and the moving average time constant was 288 μs.