Short interval method

In the short-interval method, one computes a value of the rate constant (/q u) for each successive pair of data points. The arithmetic average of the rate constants computed in this manner is assumed to be a representative value of the rate constant. However, it can be shown that when the time interval between experimental observations is constant, the short-interval method for computing k is equivalent to rejecting all but the first and the last measurements The intermediate observations might just as well have not been made. 

Since usually the reference electrode is not equipped with a capillary probe (see Fig. 2-3), there is an error in the potential measurement given by Eq. (2-34) in this connection see the data in Section 3.3.1 on IR-free potential measurement. The switching method described there can also be applied in a modified form to potential-controlled protection current devices. Interrupter potentiostats are used that periodically switch off the protection current for short intervals [5]. The switch-off phase is for a few tens of microseconds and the switch-on phase lasts several hundred microseconds. 

Repeatability is defined as precision under conditions where independent test results are obtained with the same method on identical test material in the same laboratory by the same operator using the same equipment within short intervals of time. The replicate analytical portion for testing can be prepared from a common field sample containing incurred residues. This approach is used extremely rarely. Normally, repeatability is estimated by the relative standard deviation ofrecoveries, which should be lower than 20% per commodity and fortification levels according to SANCO/825/00. In justified cases, higher variability can be accepted. 

Repeatability (r) is the value below which the absolute difference between two single test results obtained with the same method on identical test material, under the same conditions (same operator, same apparatus, same laboratory and a short interval of time) may be expected to lie, with a specified probability in the absence of other indications, a probability of 95% is used. 

Repeatability Precision under repeatability conditions, i.e. conditions where independent test results are obtained with the same method on identical test items in the same laboratory by the same operator using the same equipment within short intervals of time. 

A suitable method of calculation is to divide the period of flow into a number of short intervals so that conditions change only slightly during each interval. One method of doing this is to specify the length of each time interval and calculate the mass of gas flowing from the tank in that interval. From this the mass of gas remaining in the tank can be calculated and hence the pressure at the end of the interval determined. Conditions for the next interval can then be calculated from this pressure. 

Often a chemical being tested is both toxic as weft as potentially carcinogenic. When competing toxicity causes extreme differences in mortality or there is clustering effect in tumor prevalence in a very short interval of time, none of the adjusted methods works. One then must use biological intuition to evaluate the tumor data. 

The methods used to prepare monodisperse colloids aim to achieve a large number of critical nuclei in a short interval of time. This induces all equally sized nuclei to grow simultaneously, thus producing a monodisperse colloidal product. 

Repeatability Repeatability is a measure of the precision under the same operating conditions over a short interval of time, that is, under normal operating conditions of the analytical method with the same equipment. It is sometimes referred to as intra-assay precision. 

Closeness of agreement between test result and accepted reference value Closeness of agreement between independent test results obtained under stipulated conditions Precision under conditions where independent test results are obtained with same method on identical test items in same laboratory by same operator using same equipment within short intervals of time Precision under conditions where independent test results are obtained with same method on identical test items in same laboratory but by different analysts using different equipment over extended period of time Precision under conditions where test results are obtained with same method on identical test items in different laboratories with different operators using different equipment 1... 

Repeatability should be obtained by the same operator with the same equipment in the same laboratory at the same time or within a short interval using the same method. 

A second approach is to use [lsO]bicarbonate and to follow the incorporation of lsO into a carboxylated substrate. If C02 is the primary substrate only two labeled oxygen atoms enter the compound, whereas if HC03 is the reactant three are incorporated.287 A third technique is measurement of the rate of incorporation of C02 or bicarbonate in the carboxylated product. Over a short interval of time, e.g., 1 min, different kinetics will be observed for the incorporation of C02 and of bicarbonate.288 Using these methods, it was established that the product formed in Eq. 13-46 and the reactant in Eq. 13-47 is C02. However, the carboxylation enzymes considered in the next section use bicarbonate as the substrate. 

The start of the reaction must be pinpointed exactly and accurately. A stop-watch is adequate for timing conventional rates for faster reactions electronic devices are used. If spectroscopic methods of analysis are used it is simple to have flashes at very short intervals, e.g. 10 6 s, while with lasers intervals of 10 12 s are common. Recent advances give intervals of 10 15 s. 

Since equation (5.27) can hardly be integrated in quadratures, calculations are carried out with the use of different approximate methods. For example, the piecemeal-analytical method may successfully be employed.332 It is based on dividing the examined time range into a finite number of sufficiently short intervals and the subsequent application of equation (5.29) to each of them. Equation (5.27) can be transformed into a transcendental equation239 which is then solved by numerical methods. 

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