Application of Hadamard transform to gas chromatography/nonresonant multiphoton ionization/time-of-flight mass spectrometry

The technique of Hadamard transform was successfully coupled with GC/nonresonant multiphoton ionization/TOFMS, for the first time. 1,4-Dichlorobenzene and the fourth harmonic generation (266 nm) of a Nd:YAG laser were employed as a model sample and an ionization laser, respectively. A Hadamard-injector coupled with a capillary-based supersonic jet nozzle (capillary-injector) was also developed in this study. The Hadamard-injector was used to obtain the chromatogram, which was encoded by successive sample introduction based on Hadamard codes, and the capillary-injector was used for injection of GC-elutes into TOFMS. Compared with a conventional single injection method, the S/N ratios were substantially improved after inverse Hadamard transformation of the encoded chromatogram. Under optimized conditions, when Hadamard matrices of 103 and 255 were used, the S/N ratios of the signals for 1,4-dichlorobenzene (concentration level, 4 mg/1 mL ACN) were substantially improved to 4.1- and 6.6-fold, respectively, and those improvements are in good agreement with those obtained by theory (5.1- and 8.0-fold).