Real-Time Measurements of Polychlorinated Biphenyls Using Laser Ionization Time-of-Flight Mass Spectrometry

Abstract

Polychlorinated aromatic hydrocarbons include many hazardous compounds, 1-5 such as PCBs (polychlorinated biphenyls), PCDDs (polychlorinated dibenzodioxins), PCDFs (polychlorinated dibenzofurans), polyhexachlorobenzene and pentachlorophenol. For protection from such chemicals, it is necessary to rapidly monitor their concentrations. Especially in PCB disposal plants, pollution of the surrounding environment must be strictly prevented, giving a strong imperative for the development of real-time measurement technology for PCB concentration monitoring.The conventional methods, such as GC-ECD (gas chromatograph with an electron-captured detector) and GC-MS (gas chromatograph-mass spectrometry), require extensive analysis time (several days per sample) and are not suitable for the above requirements.Recently, the development of the pulsed-laser technique has enabled us to measure aromatic hydrocarbons quite rapidly. In particular, the LI-TOFMS technique is expected to be a powerful method for on-line, selective and sensitive measurements. In the work reported here, real-time (1 min) LI-TOFMS measurements were carried out on gaseous 2 -4 chlorinated PCBs. With respect to laser ionization (as the key technology underpinning this method), in particular, the efforts to determine the laser wavelength and the pulse duration for PCB ionization resulted in the establishment of a technique having sufficient sensitivity (< 0.01 mg/Nm 3 ) for real-time PCBs measurements. Principle 2·1 Laser ionizationThe laser ionization principle used in this study is known as resonance-enhanced two-photon ionization. 6-10 A three-level ionization model (energy diagram) 27,28 is presented in Fig. 1, illustrating the principle behind this method. Here, X indicates the ground state of a molecule, R the exited state, and C the ionization potential. Molecules are excited to induce the R⇔X transition and ionized by the C←R transition. The notation "a" is the rate constant for the R⇔X transition, and "b" is that for the R←C transition. These are related to the number of photons (F) in terms of a∝F and b∝F. Notation kr is the rate constant for spontaneous emission, while knr indicates that for the nonradiative decay processes in state R. In the present study, Real-Time Measurements of Polychlorinated Biphenyls Using Laser Ionization Time-of-Flight Mass SpectrometryShinsaku DOBASHI, † Yoshihiro DEGUCHI, Takahiro KUBOTA, and Katsuhiko SHINODA Nagasaki Research and Development Center, Mitsubishi Heavy Industries Ltd., Japan Polychlorinated biphenyls (PCBs) are hazardous compounds for which there are few methods involving real-time measurement. Recently, the development of the pulsed-laser technique has enabled us to measure aromatic hydrocarbons quite rapidly. In particular, the LI-TOFMS (laser ionization time of flight mass spectrometry) technique is expected to be a powerful method for on-line, selective and sensitive measurements. In the context of developing a highly selective and sensitive technique, the effective laser wavelength and pulse du...

Automated Analysis of Persistent Organic Pollutants in the Gas Phase by Laser Ionization Mass Spectrometry

“…It was confirmed that a laser with a pulse duration of 100 ps clearly generated a stronger PCB ion signal than a 5 ns pulse laser, by a factor of more than 10. 43) New findings presented here include the e$cient trapping of laser-ionized PCB ions using the dynamic trapping time-of-flight mass spectrometry (TOFMS), as well as the simulation of electric field control conditions for e$cient trapping, and observation of the e#ectiveness of reducing the speed of the ions introduced into the trap apparatus. 41), 42) Evaluations of accuracy based on comparisons with the results of the conventional method (gas sampling/gas chromatography mass spectrometry; gas sampling/ GC-MS) demonstrated a coe$cient of variation of ῌ30῍.…”

Real-time Monitoring of Monochlorinated Benzene and Polychlorinated Biphenyls in the Gas Phase with On-line Detection: High Chemical Selectivity of Resonance-Enhanced Two-Photon Ionization

“…E-mail: shinsaku_dobashi@mhi.co.jp AREF) maintains a high internal vacuum of about 10 -8 Torr by means of turbo-molecular pumps. 8 The measurement sample is supplied to the apparatus in the form of an ultrasonic molecular beam, through the use of a pulse valve (R. M. Jordan Co., PSV) and a 5 mm diameter skimmer. The pulse valve (orifice, 0.5 mm) delivered 50 µs duration gas pulses at 10 Hz into the vacuum chamber.…”

“…The pulse duration of this laser equipment was 5 ns, with a pulse repetition rate of 10 Hz and an output of 5 mJ/pulse at 266 nm. 7,8 Measurement samples Figure 2 shows the chemical structures for monochlorinated benzene and PCBs. The m/z of MCB, 2 -4 chlorinated PCBs are 112, 222, 256 and 290, respectively.…”

“…The authors of the present study have applied laser ionization TOFMS to the measurement of chlorinated aromatic hydrocarbons, and have demonstrated the effectiveness of this method for real-time measurements. [7][8][9][10][11] The objective of the research reported here was to develop a measurement system capable of measuring chlorinated aromatic hydrocarbons quite rapidly, thus leading to the development of the laser ionization TOFMS (time-of-flight mass spectrometry) method. The laser ionization method uses resonance enhanced two-photon ionization.…”

“…The laser ionization method uses resonance enhanced two-photon ionization. 8,28,29 With respect to laser ionization, in particular, efforts to determine the laser wavelength for the ionization of aromatic hydrocarbons resulted in the establishment of a method having sufficient sensitivity (ppbV level) for real-time measurements. In the work reported here, real-time laser-ionizaion TOFMS measurements were carried out on gaseous monochlorinated benzene and 2 -4 chlorinated PCBs, a detection sensitivity at the ppbV level was achieved.…”