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.

What is claimed is  
     
         1 . In a process for determining the size distribution of particles in an aerosol used to administer pharmaceutical formulations to the lung—which process uses either the laser diffraction or the scattered light method, the improvement which comprises adding a conditioning agent to the carrier medium of the aerosol to a given degree of saturation, mixing the conditioned carrier medium with a pharmaceutical formulation for administration, introducing the conditioned carrier medium with pharmaceutical formulation into at least one measuring cell in order, and determining the size distribution of the particles in such cell or cells.  
     
     
         2 . The process as recited in  claim 1 , wherein the pharmaceutical formulation is a solution, with active pharmaceutical substance or substances dissolved in a solvent.  
     
     
         3 . The process as recited in  claim 2 , wherein the solvent is used as the conditioning agent.  
     
     
         4 . The process as recited in  claim 1 , wherein the pharmaceutical formulation is a suspension with active pharmaceutical substance or substances in the form of particles in a liquid or gaseous medium.  
     
     
         5 . The process as recited in  claim 4 , wherein the liquid or gaseous medium is used as the conditioning agent.  
     
     
         6 . The process as recited in  claim 1 , wherein the pharmaceutical formulation is a powder comprising one or more active pharmaceutical substance.  
     
     
         7 . The process as recited in  claim 6 , wherein water is used as the conditioning agent.  
     
     
         8 . The process as recited in  claim 1 , wherein the carrier medium is air.  
     
     
         9 . An apparatus for determining the size distribution of particles contained in an aerosol comprising: 
 a conditioning device ( 24 ) for saturating a carrier medium with a conditioning agent according to a given saturation level,    a metering device ( 26 ) for the aerosol,    a mixing chamber ( 25 ) for mixing the conditioned carrier medium and the metered aerosol to produce a conditioned aerosol, and    at least one measuring cell ( 23 ) into which the conditioned aerosol is introduced in order to carry out a measurement of the particle size distribution of the aerosol by a laser diffraction process or a scattered light method.    
     
     
         10 . The apparatus as recited in  claim 9 , characterised in that each measuring cell has at least one entry window ( 21 ) for the entry of a light beam from a light source and at least one exit window ( 22 ) for the exit of the scattered light from the light beam.  
     
     
         11 . The apparatus as recited in  claim 10 , characterised in that each entry window ( 21 ) is tilted relative to the incident light beams from the light source.  
     
     
         12 . The apparatus as recited in  claim 10 , characterised in that each exit window ( 22 ) is tilted relative to the emergent light beams.  
     
     
         13 . The apparatus as recited in  claim 10 , characterised in that each entry window ( 21 ) and each exit window ( 22 ) are tilted at identical—but opposite—angles relative to the incident light beams.  
     
     
         14 . The apparatus as recited in  claim 10 , characterised in that each entry window ( 21 ) and each exit window ( 22 ) are constructed to be removable.  
     
     
         15 . The apparatus as recited in  claim 10 , characterised in that each entry window ( 21 ) and each exit window ( 22 ) are less than about 2 mm thick.  
     
     
         16 . The apparatus as recited in  claim 10 , characterised in that each entry window ( 21 ) and each exit window ( 22 ) are arranged opposite one another.  
     
     
         17 . The apparatus as recited in  claim 10 , characterised in that each exit window ( 22 ) and each entry window ( 21 ) of each measuring cell ( 23 ) are arranged substantially at right angles to one another.