Real-time PCB Gas Monitoring
System (MOHMS-21GP)
SHINSAKU DOBASHI* 1
YOSHIHIRO DEGUCHI*1
MASAHARU KIRA* 2
RYUICHIRO TANAKA* 3
YOSHINORI IZAWA*3

This report describes the technical characteristics and measurement results of a real time PCB gas monitoring
system (MOHMS-21GP) developed by Mitsubishi Heavy Industries, Ltd. (MHI). The characteristics of the gas directintroduction type laser ionization TOFMS (Time of Flight Mass Spectrometry), which indicates the measuring principle of this device, are described. A detecting sensitivity of 0.01 mg/m3N, equivalent to 1/15 of the limit specified byregulatory requirements, was achieved. The measurement test results obtained using the exhaust gas from a PCB
disposal plant (MHI) are also presented.
However, since conventional analysis methods require twoor three days to analyze a sample, the development of areal-time analytical method has been eagerly sought. Inorder to meet this need, MHI has developed a PCB gas
monitoring system (MOHMS-21GP) using laser ionization
TOFMS (time of flight mass spectrometry). This system
is capable of measuring PCB gas in one minute with asensitivity of 0.01 mg/m3N (equivalent to 1/15 of the limit
specified by law). MHI has verified the applicability ofthis system to the exhaust gas and the atmosphere of thework environment in PCB disposal processes, in the MHI’s
PCB disposal plant.

1. Introduction
PCB (Polychlorobiphenyl), which had been widely used
as insulating oil for condensers and other equipment up
to 1970s, is suspected at present of being one relative ofenvironmental chemical adversely influencing organisms
and environment(1). Thus, in order to make all domestically existing PCBs completely harmless, the Japanese
PCB Treatment Special Equipment Law came into force
from June 2002. One result of this new law is that theconstruction of PCB disposal plants is being accelerated.
In order to dispose PCBs completely, it is essential to monitor the concentration of PCB at all times, so as to prevent
any PCB leakage and to ensure the safety of personnel.

2. Characteristics of PCB gas monitoring system
Table 1 shows the specification of the PCB gas monitoring system (MOHMS-21GP). As shown in the table,
this system is characterized by its capability of measuring PCBs with a sensitivity of 0.01 mg/m3N.
The measuring principle used for this monitoring system is known as the gas direct-introduction type laser
ionization TOFMS method. Fig. 1 shows the measuring

Table 1 Specifications of PCB gas monitoring system (MOHMS-21GP)
Trade name

MOHMS - 21 GP
Gas direct-introduction type laser ionization
TOFMS method

Measuring principle
Lower limit of quantitative
analysis of PCB

0.01 mg /m3N

Measuring time

One minuteLaser

Ion trapping device

Vacuum chamberDetector

GasPCB(1) Laser ionization technology
Selective separation of PCB(2) Ion-trapping technology
Concentration of PCB(3) TOFMS technology
Real-time quantitative analysis of PCB

Fig. 1 Measurement process of PCB gas monitoring system (MOHMS-21GP)
After PCB ions are generated by irradiation with a laser and the PCB ions are concentrated in an ion trap,
PCB is identified and quantitatively analyzed by TOFMS.

*1 Nagasaki Research & Development Center, Technical Headquarters*2 Machinery Headquarters*3 Nagasaki Shipyard & Machinery Works
1

Mitsubishi Heavy Industries, Ltd.
Technical Review Vol.40 No.5 (Oct. 2003)

Controlcomputer
TOFMS deviceLaser device

Vacuum pump

Generator of PCB
standard sample gas

Fig. 2 Photograph of PCB gas monitoring system (MOHMS-21GP)
The PCB gas monitoring system consists of a laser device, TOFMS device, vacuum pump,control computer, and a generator of PCB standard sample gas.

principle of this system(2)-(5). As can be seen in the figure, the system introduces the sample gas directly into
the vacuum chamber, where (1) laser ionization (2), (2)ion-trapping, (3) TOFMS(2) are performed to identify andquantitatively analyze PCBs concentration.
Gas contains many molecules other than PCB. Inorder to monitor trace amounts of PCB contained in gas
while on-line, it is essential to be able to separate andconcentrate PCBs in a short time. Accordingly, the following three technologies has been developed and been
proven successful in overcoming this essential requirement. The most important characteristic of thisdevelopment is the capability of measuring PCB to a highlevel of sensitivity, while maintaining the analysis accuracy of PCB even in the exhaust gas and the atmosphereof the work environment.
(1) Laser ionization: Extensive original research work
has made it possible to determine the optimum laserirradiating condition (wavelength: 266 nm, laser pulse
duration: 100 picoseconds) for selectively ionizing
PCBs and to separate PCBs selectively.
(2) Ion-trapping: Extensive research work has also madeit possible to develop effective methods for concentrating PCBs and highly sensitivity.
(3) TOFMS: Real-time quantitative analysis of PCBs has
been made possible by combining the benefits of mass
spectrometry into the process.
These developed technologies enable for this system
to analyze trace amounts of PCBs, while maintaining ahigh level of selectivity in one minute, even in the ex-haust gas and the atmosphere of the work environment
containing various kinds of molecules.

3. Composition of PCB gas monitoring system
Fig. 2 shows the photograph of the PCB gas monitoring system. This system consists of a TOFMS device, alaser device, vacuum pumps, a generator of PCBs standard sample gas, and a control computer.
The TOFMS device is kept at a vacuum of approximately 10 -7 Torr, which makes mass spectrometry
possible by TOFMS, in which is vacuumed using avacuum pump (turbo molecular pump). The laser device
irradiates UV light (wavelength of 266 nm and a pulse
time length of 100 picoseconds) to achieve the highly efficient ionization of PCB. The generator of PCBs standard
sample gas makes it possible to use for the correction of
the PCBs concentration.
In this system, PCBs reference sample gas with a concentration of 0.001 to 1 mg/m3N (the concentration of PCB
introduced varies according to the number of chlorine
atoms in the PCB molecule) can be introduced, with thevapor of the PCB standard sample mixed together withbalance gas (nitrogen gas). The control computer controls the operation of the system, and sends the datawith the computed results to the central control room of
the PCB disposal plant.
The gas sampling line can be switched using automatic switching valves so that it can be connected tomany different sampling points in the PCB disposal
plant. In the MHI’s PCB disposal plant, a total of fiveMitsubishi Heavy Industries, Ltd.
Technical Review Vol.40 No.5 (Oct. 2003)

2sampling points are provided in the exhaust gas line of
the PCB hydrothermal decomposition process and thelines of atmosphere of the work environment in the PCB
container treatment process so that PCB levels in eachgas sample can be monitored.

this monitoring system has a good correlation with theresults analyzed using the conventional method, withan accuracy within 30% of the standard deviation. As
a result, it could be verified that a sensitivity of 0.01
mg/m 3 N equivalent to 1/15 of the limit, 0.15 mg/m 3 N
specified in statutory regulations, can be perfectlyachieved.

4. Measuring results of PCB

Results measured with
PCB gas monitoring system (mg/m3N)

3 chlorine PCB
2 500
2 000
1 chlorine PCB
4 chlorine PCB

1.0E-03

1.0E-04
1.0E-03 1.0E-02 1.0E-01 1.0E+00
Results analyzed using GC-MS method (mg/m3N)

1.0E+00

1.0E-01

1.0E-02

1.0E+00

1.0E-01

1.0E-02

1.0E+00
1.0E-03
1.0E-02
1.0E-01
Results analyzed using GC-MS method (mg/m3N)

5000175

1.0E-02(b) 3 chlorine PCB

2 chlorine PCB

1 000

1.0E-01

1.0E+00
1.0E-03
1.0E-02
1.0E-01
Results analyzed using GC-MS method (mg/m3N )

3 000

1 500

1.0E+00(a) 2 chlorine PCB

Results measured with
PCB gas monitoring system (mg/m3N)

Signal intensity of PCBs (A.U.)

3 500

Results measured with
PCB gas monitoring system (mg/m3N)

4.1 Evaluation of measuring sensitivity of PCB
Fig. 3 shows the results obtained by measuring PCBs
introduced from the PCB standard sample gas, applying laser ionization TOFMS method. The PCB standard
sample KC-300 (Kaneka Corporation) was used as thesample, which contains 2, 3, and 4 chlorine PCBs as
the main components. The measuring time was oneminute. The concentrations of these PCBs were determined by analysis [gas sampling + GC-MS (GasChromatography Mass Analysis)]. As a result, concentration values of 0.20, 0.69, and 0.16 mg/m 3 N wereobtained for the 2, 3, and 4 chlorine PCBs, respectively.
The x-axis and y-axis in Fig.2 indicate mass number
and signal intensities, respectively. As can be seen fromthe figure, it could be confirmed that the 2, 3, and 4chlorine PCBs can be measured to an excellent degree.
The theoretical detection limits converted by S/N = 3
are 0.0001 mg/m 3N (about 100 pptv) for 2 chlorine PCB,0.00048 mg/m3N (about 40 pptv) for 3 chlorine PCB, and
0.00080 mg/m 3N (about 60 pptv) for 4 chlorine PCB, respectively.
Fig. 4 shows the evaluation test results for accuracies obtained by analysis (gas sampling + GC-MS). The
x-axes in the figures indicate the results analyzed using the GC-MS method, while the y-axes indicate themeasured results of the concentration of PCB obtainedusing the PCB gas monitoring system (MOHMS-21GP).
As shown in the figures, it can be confirmed that themeasured results of the concentration of PCB using(c) 4 chlorine PCB
Fig. 4 Comparison of analysis results by the method(gas sampling + GC-MS)
As a result of measurements of reference gas sample using thePCB gas monitoring system (MOHMS-21GP), it could be confirmedthat the measurements have a good correlation with those obtainedusing the conventional method, with an accuracy that is within 30%of the standard deviation.

200225250
275
300
Mass number
Fig. 3 Measured result of PCB standard sample (KC-300)
It could be confirmed that PCB can be measured without noise
signal and with an excellent sensitivity using this system.

Mitsubishi Heavy Industries, Ltd.
Technical Review Vol.40 No.5 (Oct. 2003)

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4.2 Measured results of actual gas from PCB
disposal plant
4.2.1 Comparison with GC-MS method
Fig. 5 shows a comparison of both results of measurements obtained with the PCB gas monitoring system(MOHMS-21GP) and results obtained by analysis (gassampling + GC-MS) for the exhaust gas examined fromthe PCB disposal plant (MHI). The x-axis in the figuresindicates measurement time, while the y-axis indicatesmonitored PCB concentrations. In the gas measurements,
both the PCB gas monitoring system and GC-MS method
must conform with each other in both low concentrations
and high concentrations of PCBs. As can be seen from thefigure, it could be confirmed that the results measured
using the MOHMS-21GP conform with the results obtained with the GC-MS method, for both high and low
concentrations and high concentrations of PCB.
As noted above, since it could be confirmed that PCB

measurement is possible even in actual gas containing
main gases mixed with various substances, it could beverified that use of the PCB gas monitoring system(MOHMS-21GP) is practical.
4.2.2 Measurement test results of the gas in thePCB disposal plantFig. 6 shows an example of the exhaust gas and theatmosphere of the work environment measurement results of the PCB disposal plant (MHI). The exhaust gas
from the PCB hydrothermal decomposition process andthe atmosphere of the work environment in the PCB container treatment process were analyzed using the PCBgas monitoring system (MOHMS-21GP). The results ofthe analysis are shown in the figure. The x-axis of thefigure indicates the measuring time, while the y-axis
indicates the concentration measured using MOHMS21GP. As can be seen from the figure, it was confirmedthat the concentration of PCB in the environmental gas,
which is remarkably lower than the 0.15 mg/m3N specified by statutory regulations, can be measured in realtime. As a results, it could be verified that the MOHMS21GP is a very useful tool for being able to check whether
a PCB disposal process is performed safely and well; thatis, the MOHMS-21GP is a very useful device for ensuring safety in a PCB disposal process.

Concentration of PCBs (mg/m3N)

0.30
0.25
Results analyzed using
GC-MS method :0.001 mg/m3N
0.20

5. Conclusion

0.15
Gas sampling time

The technical characteristics and measurement test
results of a PCB gas monitoring system (MOHMS-21GP)
were indicated, and the effectiveness of real time measurement of PCB was verified. The following major
results could be verified.
(1) The gas direct-introduction type laser ionizationTOFMS method was applied as a real time PCB gas

0.10
Measurements obtained using
PCB gas monitoring system

0.05
0.00

0246Time (h)81012(a) Measurement of the exhaust gas containing low concentration PCB
0.20

Results analyzed using
GC-MS method : 0.21 mg/m3N

Concentration of PCB (mg/m3N)

Concentration of PCBs (mg/m3N)

0.30
0.25
0.20
0.15

Measurements obtained using
PCB gas monitoring system

0.10
0.05

0.15

0.10

0.05

0.00

Gas sampling time

PCB concentration in gas,
specified by statutory regulation0100200300400500

Time (h)

0.00
00.2

0.4

0.6
Time (h)0.811.2

Fig. 6 Measured result of the gas in the PCB disposal plant
It could be confirmed that the concentration of PCB in the gas,
which is lower than 0.15 mg/m3N specified by statutory regulation,
can be measured in real time during an actual PCB disposal process.
Accordingly, it could be verified that the PCB gas monitoring system(MOHMS-21GP) is a very useful tool capable of checking whether
a PCB disposal process is safely and excellently performed.
In other words, the MOHMS-21GP is a very useful device forensuring safety during a PCB disposal process.

(b) Measurement of the exhaust gas containing high concentration PCB
Fig. 5 Comparison with measured results of the exhaust gas
using conventional method
Results measured using the PCB gas monitoring system were found to
be in good agreement with results measured using the conventional
method in both low and high concentration zones of PCB.

Mitsubishi Heavy Industries, Ltd.
Technical Review Vol.40 No.5 (Oct. 2003)4

monitoring system. As a result, a measuring sensitivity of 0.01 mg/m3N PCB could be fully achieved.
(2) The PCB gas monitoring system (MOHMS-21GP) was
capable of measuring PCB levels without being influenced by main gas components and coexistent varioussubstances, even under the exhaust gas and the atmosphere of the work environment conditions fromthe PCB disposal plant (MHI). Accordingly, theMOHMS-21GP could be evaluated as being a very
useful tool for confirming the safety and excellent
operation of a PCB disposal plant.
As mentioned above, the PCB gas monitoring system
is believed to play an important role in ensuring safety
in PCB disposal procedures. Further details can be obtained by contacting the Environmental Solution
Department, Machinery Headquarters, MHI (Tel.81-36716-3735).

Shinsaku Dobashi

The authors would like to thank Executive Acting
Director M. Morita of National Institute for Environmental Studies for his in-depth guidance on measurement
instruments, and Professor D. M. Lubman of the University of Michigan for his extensive advice on thedevelopment of TOFMS measuring technology.
References(1) Japan Industrial Waste Management Foundation, PCB Shorigijutsu Gaido-bukku (The Guidebook of PCB Treatment Technology in Japanese), Gyou-sei (1999)(2) D. M. Lubman, Lasers and Mass Spectrometry, Oxford University Press (1990)(3) Deguchi, Y. et al., Dioxin Measurement Method using Laser
Spectroscopy (in Japanese), Nensho Kenkyu (Journal of theCombustion Society of Japan) No.119 (2000) pp.37-40(4) Kira, M. et al., PCB Monitoring System using Laser Ionization TOFMS Method, The Collected Papers of The 13th
JSWME Meeting (2002) pp.775-777(5) R. D. March, Quadrupole Storage Mass Spectrometry, JOHNWILLEY & SONS (1989)

Yoshihiro Deguchi

Masaharu KiraRyuichiro Tanaka

Yoshinori Izawa

Mitsubishi Heavy Industries, Ltd.
Technical Review Vol.40 No.5 (Oct. 2003)

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