Page 430 - Instrumentation Reference Book 3E

Further reading 413
The exponential dilution technique is a valu- introduced to the dilution vessel by injection with
able calibration method especially suitable for use a valve or syringe, the accuracy and precision of
at very low concentrations. It is also valuable for the entire calibration curve resulting from the dilu-
studying or verifying the response of a detector tion is limited by the accuracy and precision ofthe
over a range of concentrations. However, it initial injection.
should be noted that strict adherence to a known
exponential law for the decay of concentrations in
the vessel depends on the attainment of theoret-
ically perfect experimental conditions which can- 18.7 Further reading
not be achieved in practice.
Changes in the flow rate of the diluent gas or in Cooper, C. J. and A. J. De Rose, “The analysis of gases
the temperature or pressure of the gas in the by chromatography,” Pergarnon Series iiz Analytical
Chenzistry, Vol. 7. Pergamon, Oxford (1983)
dilution vessel anc imperfect or non-instant- Cullis, C. F. and J. 6. Firth (eds): Detection and Meas-
aneous mixing in the vessel lead to unpredictable urement of Hazardous Gases, Heinemann, London
deviations from the exponential decay law. (1981)
Deviations also occur if the determinand is lost Grob, R. L. (ed.), Modern Practice of Gas Chronqoto-
from the system by adsorption on the walls of the graplzy, Wiley, Chichester, UK (1977)
vessel. Since the technique involves extrapolation Jeffery, P. F. and P. J. Ipping, Gus Annlysis by Gas
from the known initial concentration of the deter- Chromatography, International Series of Mono-
minand in the diluting gas, any deviations are graphs in Analytical Chemistry, Vol. 17, Pergamon,
Oxford (1972)
likely to become more important at the Sevcik, J., Detectors in Gas Chronzatograplzy, Journal of
later stages of the dilution. If possible it is there- Chromatography Library, Vol. 4, Elsevier. Amster-
fore advisable to restrict the range of the dilution dam (1976)
to two or three orders of magnitude change in Also review articles in Analytical Chemistry. and man-
concentration. Where the gas to be diluted is ufacturers’ literature.