Question & Answer Section

Q What tolerance is allowed between results obtained with manual and automatic sampling?
A There are no official tolerances for the variability associated with manual and automatic sampling. This should be evaluated on a case-by-case basis. When results are not highly variable, one possible approach is to use two concurrent runs with the same sampling intervals and six units for each, using manual and automated sampling methods. Compare the results obtained from each with the criteria used for intermediate precision. If the results are highly variable (i.e., the relative standard deviation [RSD] is above 20% in the earlier time points and about 10% in the later time points), perform the comparison by pulling the sample from the vessel simultaneously by manual and automated procedures for each time point. Be warned that the hydrodynamic effects of the probe will not be obtained with simultaneous sampling. Attention should be paid to the volume correction in the second case. More information can be found in the paper: Gray, V. A.; Brown, C. K.; Dressman, J. B.; Leeson, L. J. A new general information chapter on dissolution. Pharm. Forum. 2001, 27 (6), 3432–3439.