FAQs, OPT-DIS

Can the OPT-DISS be used in conjunction with Apparatus 4? Yes!
It is not necessary to use fiber optic probes with the OPT-DISS for Apparatus 4. LEAP offers a flow through cuvette option for this application. OPT-DISS software can calculate %Dissolved for closed loop operation with App. 4.

Is it possible to use traditional dip probes with the OPT-DISS? Yes! LEAP can use a wide range of traditional dip probes. LEAP however does caution use due to potential hydrodynamic turbulence possibilities.

What are the advantages/disadvantages of second derivative baseline corrections? Second derivatives are used to correct for curved baselines. However, applying second derivatives reduces the signal-to-noise ratio by a factor of 100. This reduction is partially offset by simultaneously applying a smoothing algorithm, but care must be taken in determining the degree of smoothing or data (and results) will be distorted. The more straightforward single, dual, and average-over-range wavelength corrections are preferred. Second derivatives (always applied with smoothing) can distort the data.

Is the system USP compliant? Yes. As with any automated procedure, it is necessary to show equivalence to manual procedures. LEAP has verified that their sampling method (fiber optics via the ARCHTM) do not adversely affect solution hydrodynamics. Single-wavelength, average over range, dual-wavelength correction and even second derivative baseline correction is adequate in many cases to account for light scattering effects due to solution turbidity.

How is it possible to obtain accurate results without filtration? Direct, in situ UV measurements with the OPT-DISS system are only potentially affected by solution turbidity -- not particulates. If, with your manual, off-line UV method, you were only filtering to remove particulates that would release active into your measurement cuvettes, then the in situ measurements would accurately reflect the concentration of active in the vessel without having to correct for turbidity effects. In fact you would be avoiding the possible detrimental effects of filtration such as removing leachable materials from the filter and/or adsorbing active drug ingredient onto the filter.

But my solutions are highly turbid. In that case you apply one of the available absorbance background correction techniques to account for a shifting baseline due to light scattering from particulates. The baseline correction also accounts for instrument drift. You still avoid the downside of filtration. Additionally, by eliminating filtration, method validation time is shortened because there is no need to conduct a filtration validation study.