Photoionization detector with sealed or windowless discharges for ppb detection of VOC’s or and or fixed gases

ABSTRACT SYMPOSIUM NAME: Advances in Sensors and Biosensors for Environmental Monitoring

ABSTRACT SYMPOSIUM PROGRAM AREA NAME: ENVR
CONTROL ID: 2976537PRESENTATION TYPE: Oral Only

TITLE: Photoionization detector with sealed or windowless discharges for ppb detection of VOC’s or and or fixed gases

AUTHORS (FIRST NAME, LAST NAME): John N. Driscoll2, Jennifer L. Maclachlan1INSTITUTIONS (ALL): 1. PID Analyzers, LLC, Centerville, MA, United States. 
2. PID Analyzers, LLC, Sandwich, MA, United States. 

ABSTRACT BODY: Abstract: The Photoionization detector (PID) with a 10.6 eV lamp and a sealed window has been shown to be 50-80 times more sensitive for aromatic hydrocarbons than the flame ionization detector (FID) but the 10.6 PID does not respond to small molecules like formaldehyde, chloro alkanes, MeOH, C2-C4 alkanes, The 11.7 PID will respond to many of these compounds with sub ppm detection limits but it has a lithium fluoride window that results in decreased transmission after absorption of the photons at 11.6 and 11.8 eV. This color center formation limits the useful lifetime to 700-800 hours on the gas chromatograph (GC). We have designed a windowless PID option that uses the same base (ion chamber) and can easily be exchanged with the sealed 10.6 eV lamp when a different application is needed. We will compare the sensitivity of a sealed 11.7 lamp with the windowless lamp. The windowless argon lamp will not have 11.7 sealed lamp transmission problem but now it becomes very important to maintain a constant (high purity) argon flow and constant discharge conditions. If we change the discharge gas from argon to helium, we will be able to have a detector with an ionization source with an energy of 20.2 eV that will be able to detect organic, inorganic and fixed gases at low ppb levels. We will compare the results for the sealed PID with the windowless PID for a number of gas mixtures.