2022 Volume 43 Issue 2 Pages 67-71
This fundamental study was conducted to increase the multiplicity of frequency division in multiplex high-performance liquid chromatography-mass spectrometry (HPLC-MS). Virtual chromatograms were used to investigate the high efficiency separation, i.e., the peak with a narrow band in time-domain chromatograms. They revealed that the peak induces the broad signals in the frequency-domain power spectrum obtained from the Fourier transform (FT) of the chromatogram. For a high performance separation of N = 50 000 and 200 000, a minimum modulation frequency of 22.5 and 45 Hz, respectively, are required for 4HPLC-1MS. The high-frequency modulation was successfully achieved by increasing discharge rate with modifying the electric circuit in the modulation system. In addition, a higher sampling rate in MS is required for a higher modulation frequency to achieve successful FT analytical results. In other words, the sampling frequency must be increased by a factor of five for a given modulation frequency. Using a laboratory-made four channel interface, the simultaneous sample introductions in infusion mode was achieved with various modulation frequencies. The signal separation in the frequency region was successfully achieved for modulation frequencies up to 30 Hz with a sampling rate of 160 Hz.