title: Analysis of pesticides by gas chromatography/multiphoton ionization/mass spectrometry using a femtosecond laser.
abstract: Gas chromatography/multiphoton ionization/time-of-flight mass spectrometry (GC/MPI/TOFMS) was utilized for analysis of a standard mixture sample containing 49 pesticides and 4 real samples using the third-harmonic emission (267 nm) of a femtosecond Ti:sapphire laser (100 fs) as the ionization source. A sample of a standard mixture of n-alkane was also measured for calibration of the retention time indices of the pesticides. Two photons are required for the excitation of n-alkane due to an absorption band located in the far ultraviolet region (140 nm). The n-alkane molecule in the excited state was subsequently ionized either directly or by absorbing another photon because of a high ionization potential. Due to a large excess of energy, the molecular ion was decomposed and formed many fragment ions. Compared to n-alkanes, most of the pesticides were softly ionized by the femtosecond laser; one photon was used for excitation and another was used for the subsequent ionization. The pesticides with no conjugated double bond had a lower ionization efficiency. The present analytical instrument was applied to several samples prepared from a variety of vegetables and a single fruit after pretreatment with solid-phase extraction. Three pesticides were found in these samples, although some of them were not detected by conventional GC/EI/MS-MS due to insufficient sensitivity and selectivity.
authors.affiliation: Department of Applied Chemistry, Graduate School of Engineering, Kyushu University, Nishi-ku, Fukuoka, Japan.
authors.forename: Adan
authors.initials: A
authors.lastname: Li
authors.forename: Tomoko
authors.initials: T
authors.lastname: Imasaka
authors.forename: Tomohiro
authors.initials: T
authors.lastname: Uchimura
authors.forename: Totaro
authors.initials: T
authors.lastname: Imasaka
mesh_terms: D005638:Fruit / Q000737:chemistry*; D008401:Gas Chromatography-Mass Spectrometry / Q000379:methods*; D007834:Lasers; D010575:Pesticides / Q000032:analysis*; D012680:Sensitivity and Specificity; D014675:Vegetables / Q000737:chemistry*
chemical_list: D010575:Pesticides