Two-dimensional alignment of differential mobility spectrometer data

Alignment of data is critical for analysis involving the comparison of multiple files. Analytical sensor data resulting from complex chemical mixtures can often be mis-aligned due to time-varying biases resulting from mechanical instrument variability. In addition to the necessity for time alignment, data from the micromachined differential mobility spectrometer (DMS) may be slightly shifted when comparing various data sets due to the effect of heat and flow variations on the compensation voltage (Vc). Thus, the data in this dimension can also benefit from alignment. We present here a method for the alignment of both dimensions (scans and Vc) of pyrolysis-DMS data, using a single file as reference. The Vc dimension is first aligned with respect to the reference file; this is a rigid shift and no interpolation is performed. This is an advantage as the Vc dimension has physical meaning and should not be altered by interpolation. The time (or scans) dimension is then aligned with respect to the reference by identifying common landmarks and interpolating according to a piecewise linear function calculated based on the amount of shift between the two files. The effect of a slight change in flow in the Vc dimension is examined using the nitrogen reactant ion peaks as a standard signal. This method is useful for further data processing in which multiple files are to be directly compared, and it could also be useful for two-dimensional alignment of data from other sensor modalities.