Determination Of Dead Time Research Articles

Practical equation for deadtime determination in X-ray counting systems

A practical equation is presented to determine the deadtime τd in conventional X-ray counting systems when the amount of deadtime is greater than that which can be accounted for by non-extended deadtime theory. The use of this equation to determine the deadtime increases the practical range over which conventional X-ray detection systems can be used.

Updating of the OECD Test Guideline 107 “partition coefficient N-octanol/water”: OECD Laboratory Intercomparison Test on the HPLC method

As a result of testing experience several OECD member countries proposed the updating of the OECD Test Guideline 107 and the inclusion of the HPLC method. The OECD Updating Panel reviewed all comments and drafted an improved and for OECD member countries widely acceptable version of the HPLC test method. Before finally adopting the HPLC test method a validation by means of an OECD Laboratory Intercomparison Test was necessary. The most important determinants for a reliable experimental result were shown to be the choice and the number of reference substances, whereas the dead-time determination, the use of a guard column, the choice of the analytical column, and the temperature have little or no effect on the result. Using an appropriately buffered methanol/water eluent with a water content of at least 25 % and at least six reference substances with well-established partition coefficients covering the value to be determined, the log P OW of the test substance can be obtained within ± 0.5. A list of recommended reference substances was elaborated. At the same time the calculation methods of Hansch/Leo, Rekker, and Hansch/Fujita were reviewed by the participating laboratories and recommended for inclusion in OECD Test Guideline 107.

Mathematical dead time determination and calculation of the constants of the n‐alkane retention time curve on OV polymethyl phenylsilicone stationary phases in gas chromatography

AbstractThe column dead time and the constants of the n‐alkane retention time curve in gas‐liquid chromatography are calculated by the Wentworth iterative method on series of OV polymethylphenylsilicones with an increasing percentage of phenyl substituent. The values obtained are in good agreement with those calculated by the methods of Gröbler and Kaiser and with the experimental ones reported in the literature for stationary phases studied at 120°C and 150°C. The scatter of experimental retention times of n‐alkanes and tM and b and c and Kováts retention indices are calculated.

Determination of dead times for inverse gas chromatography: Measurements by use of methane

Determination of dead times for inverse gas chromatography: Measurements by use of methane

Use of retention plots of n-alkyl benzenes for determining dead times in liquid and gas chromatography

The retention behaviour of the homologous series of n-alkylbenzenes from toluene to hexylbenzene has been examined in reversed-phase liquid chromatography (RPLC) and in gas chromatography (GC) using columns of varying polarity. The series was found to be inappropriate for the mathematical estimation of dead time in GC. The series ethylbenzene to hexylbenzene provided a reasonable estimate of system hold-up volume in RPLC when compared with the retention volume for uracil. However, when toluene was included in the estimation procedure erroneous results were obtained and it is therefore suggested that the use of the alkylbenzene series is unwise in dead time determination in both chromatography systems.

Evaluation of procedures for the estimation of dead time

In order to determine the exact retention of compounds in gas chromatographic studies some method of determining the column dead time must be employed. This paper reviews direct measurement techniques using methane injection as well as mathematical determination of dead-time from retention data for n-alkanes. A critical evaluation of these procedures is made along with recommendations concerning the choice of evaluation method to be adopted by the chromatographer.

Some remarks on the determination of dead time by the two sources method

The condition n12τ≲0.1 usually prescribed in measuring the dead time τ of an electronic chain is too drastic. Indeed, if the recurrence is increased by a factor n, the measurement duration of τ is n3 times smaller. Even if n12τ=0.1, the exact formula giving τ, n12τ =1−(1−2n12τap)1/2, where τap= (n1+n2−n12)/2n1n2, is needed for an accuracy of 1%. These conclusions have been verified experimentally.