Measurement sampling intervals, long

The nonexponential decays impose limits on the shortest value of r) that can be measured. If we assume that the relaxation function can be determined accurately from 2 x Hr6 s to 100 s, then the limit will be determined by the condition that the function 2(t) should have a value at least as large as 1/e2 of its intercept value at the shortest reliable sampling interval. The value of P strongly affects the value of (r), but for = 0.5, the average relaxation time is two times the value of r. A practical limit for the shortest value of r) is 10-5 s. The average relaxation time is determined by the longest time part of the relaxation function, so that it is probably safe to calculate (r) even when most of the relaxation function is not measureable, as long as the final approach to the baseline is clearly observed. 

The longest value of ( r ) that can be reliably measured is determined by the longest sampling interval in the correlator times the number of channels, the dark count in the photomultiplier tube, the long term stability in the laser, and whether full correlation or clipping is employed. At present 100 s is a practical maximum for measured values of (r). In order to determine a relaxation time of 100 s, it is desirable to measure the correlation function for at least 1000 relaxation times. This means that run times of 105 s are required. This places severe requirements on the long term stability of all parts of the system. Routine measurements of (r) are probably better restricted to 10 s. 

Most techniques for polymer composition measurement require long sampling intervals, i.e. either the analysis requires a long dissolution, heating, or reaction time, or manpower or equipment limitations preclude more frequent analysis. 

Quite often a compound is rather unstable in aqueous solution. Hence the long exposure to liquid required for traditional solubility measurements will cause decomposition, and the resulting solubility results will be unreliable. In this particular case a method known as Nogami s method may be used. If a solution experiment is carried out as a dissolution experiment with samples taken at equal time intervals, 8, it can be shown [20] that when the amount dissolved at time t + 8 is plotted versus the amount dissolved at time t, a straight... 

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