Analysis of Dioxins by Gas Chromatography/Resonance-Enhanced Multiphoton Ionization/Mass Spectrometry Using Nanosecond and Picosecond Lasers

Abstract

Dioxins in a soil sample were measured using gas chromatography/resonance-enhanced multiphoton ionization/time-of-flight mass spectrometry coupled with different types of laser sources. The fourth-harmonic emission (266 nm) of a nanosecond Nd:YAG laser (1 ns) provided low ionization efficiency, especially for highly chlorinated dioxins/dibenzofurans (CDDs/CDFs). The ionization efficiency was improved using the fourth-harmonic emission (266 nm) of a picosecond Nd:YAG laser (4 ps), due to shorter singlet excited-state lifetimes. It was, however, difficult to efficiently ionize hepta-CDD and octa-CDD/CDF, because of their shorter lifetimes, which were induced by stronger spin-orbit coupling that led to efficient relaxation of the excited molecule to triplet levels. The ionization efficiency was substantially improved using the fifth-harmonic emission (213 nm) of the picosecond Nd:YAG laser (4 ps), in which the analyte molecule that was relaxed to triplet levels was efficiently ionized using a photon with sufficient energy for ionization, although the pulse energy obtained at 213 nm was only one-third of the pulse energy obtained at 266 nm. The limits of detection achieved for 17 toxic polychlorinated dibenzo-p-dioxins/polychlorinated dibenzofurans (PCDDs/PCDFs) were 0.41-45 pg. The analytical instrument developed in the present study performed sufficiently well for the practical trace analysis of dioxins in soil samples.

Analysis of Persistent Organic Pollutants at Sub-Femtogram Levels Using a High-Power Picosecond Laser for Multiphoton Ionization in Conjunction with Gas Chromatography/Time-of-Flight Mass Spectrometry

“…However, it has been reported that the ionization efficiency can be significantly improved by replacing the fourth-harmonic emission with the fifth-harmonic emission (or the simultaneous use of both emissions) of a picosecond Nd:YAG laser. 36 Thus, a compact picosecond laser (33 × 18 × 46 cm) with a high average power would be useful for the practical trace analysis of DXNs in environmental samples, and probably in human blood as well. …”

Rapid Analysis of Gasoline-Contaminated Soil Using Multiphoton Ionization/Time-of-Flight Mass Spectrometry

“…The sample was heated at 230 C by a heater, and rapidly introduced into a linear-type TOFMS using air as the carrier gas. The MPI/TOFMS used in the present study has been reported in detail elsewhere, 19,20 and is now commercially available (HGK-1; Hikari-GK, Fukuoka, Japan). The fourth harmonic emission of a nanosecond Nd:YAG laser (266 nm, 4 ns, ~50 μJ, 10 Hz, GAIA II; Rayture Systems) was used as an ionization laser.…”

Unexpected Signals in Gas Chromatograph/Multiphoton Ionization/Time-of-Flight Mass Spectrometer Designed for the Detection of Negatively Charged Species

“…The second peak is too early to be a fragment ion. The third peak has a flight time twice as long as the flight time of peak (2). It should be noted that this peak cannot be assigned to a dimmer of the compound providing peak (2), since, in time-of-flight mass spectrometry, the flight time is not proportional to the mass of the analyte, but is proportional to the square root of the mass of the analyte.…”

“…When combined with gas chromatography, it is possible to detect and measure more than several hundred components at the femtogram level. [1][2][3] Since chlorinated and nitro aromatic hydrocarbons, such as dioxins and nitropyrenes, have extremely short excited-state lifetimes, it is necessary to use a femtosecond laser, because of its high efficiency of ionization. 1,3 However, the cost of such lasers is one of the most important issues in laser spectrometry, and the use of a lower-cost laser would be highly desirable in practical applications.…”