Thermo Scientific 42i Instruction Manual page 323

Standards for Trace Level Analyzers
Geysitech Commands
ppb range, primarily due to the dark current of the photomultiplier tube,
note due to impurities in the zero gas source.
In conclusion, tests by the United States Environmental Agency, Tennessee
Valley Authority, Battelle National Labs, and THERMO FISHER
SCIENTIFIC's Engineering Department have demonstrated that Trace
Level analyzers are readily calibrated at the low concentration levels require
for sub-ambient monitoring. Although extra care is required, primarily in
zero air generation, users familiar with normal compliance requirements
should be able with minimal additional effort to obtain valid concentration
data.
Thermo Fisher Scientific Model 42i Trace Level Instruction Manual E-3