The purpose of this report is to provide background information and op
erating principles about process mass spectrometry to process operator
s. Those people who make it their business to operate and maintain che
mical processes will understand the difficulty in producing a good qua
lity product on a day-to-day basis. The use of real-time process analy
sis and control has been useful in establishing and maintaining optimu
m operating parameters so that the potential for human error may be re
duced. Real-time data allows the process operators to make decisions t
o immediately correct for a problem during the process so that the pro
duct quality can be preserved. Process mass spectrometers have been us
ed in Dow Chemical for approximately 20 years in process control appli
cations. In spite of this early start, the number of applications for
process mass spectrometers in Dow has been relatively few. More recent
ly, there is renewed interest in using mass spectrometers for process
analysis because of their speed and multicomponent analysis capabiliti
es. As a result, the number of process mass spectrometers in Dow North
America has more than doubled in the last five years. This paper pres
ents the basic function of process mass spectrometry and compares proc
ess mass spectrometry with its main competitors, namely process gas ch
romatography and process infrared spectrometry.