Process for determining the particle size distribution of an aerosol and apparatus for carrying out such a process

Abstract

The present invention provides, for the first time, a process that meets the needs of the drug industry for measuring the particle size of nebulised aerosols simultaneously or one after another by the laser diffraction method and the cascade impactor method which is known in the art. In this way it is possible to bring the reliability of the results of the laser diffraction process according to the invention into conformity with that of the cascade impactor, and thereby obtain a process which combines the advantages of the rapid laser diffraction process with the accuracy of the otherwise time-consuming cascade impactor method. In addition to the process, apparatus for carrying out the process are also disclosed.

Description

BACKGROUND OF THE INVENTION [0001] The invention relates to a process for determining the size distribution of the particles contained in an aerosol, especially the particles of a pharmaceutical formulation. [0002] The invention also relates to an apparatus for carrying out such a process. [0003] Within the scope of the invention the term “pharmaceutical substance” refers to the active ingredient of a medicament which is usually also known as a drug or active substance. [0004] The term “pharmaceutical formulation” is to be interpreted broadly, to cover formulations in the form of solutions, suspensions and powders, in particular. In a solution formulation the pharmaceutical substance is dissolved in a solvent, whereas in a suspension or powder formulation the pharmaceutical substance is present in solid form. Whereas in a suspension formulation it is mixed with a suspension agent and the pharmaceutical substance is contained in this suspension agent in the form of suspended particle...

AI Technical Summary

Benefits of technology

[0060] The present invention provides a process for determining the particle size distribution in an aerosol. In particular, the present invention provides a process that is less time-consuming and costly (unlike the cascade impactor method), and does not present the problems associated with either the scattered light method or the laser diffraction process. In summary, the process of the present invention comprises the following steps:

Problems solved by technology

The analysis, i.e. the evaluation of the measurements made with the cascade impactor, is extraordinarily time-consuming and labour-intensive.

Thus, as a rule, only a few measurements can be done per day and there is a considerable time span between the actual measuring and the results of the measurements becoming available.

The particles contained in the aerosol flow obstruct the laser beams, with the result that the light beams are diffracted on the particles.

However, a disadvantage of the laser diffraction method is the fact that, unlike the impactor method, this process is carried out in an unconditioned atmosphere, particularly in an unsaturated atmosphere.

Precisely in the case of aerosols in which the particles are in the form of drops of liquid there is consequently a danger of at least partial evaporation of the liquid aerosol particles.

A disadvantage of the scattered light method is that a small measuring volume has to be defined, e.g. with sides 100 :m long, because only one particle may ever stop in the measuring volume if clear scattered signals are to be obtained.

In practice the scattered light method has proved to be inferior to the laser diffraction method as its results are less reliable.

Moreover, the scattered light method, like the laser diffraction method, is carried out in an unconditioned atmosphere with the disadvantages mentioned above.

To sum up, it can be said of the prior art that the cascade impactor is highly time-consuming and costly because of its complicated analysis, whereas the scattered light method and also the laser diffraction process, while offering comparatively fast processes, suffer from the evaporation effect owing to the fact that the measurement is carried out in an unconditioned atmosphere.

These last two processes are, moreover, carried out on an undefined free flow and thus yield results which are only reliable up to a point.

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