874 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS Aerosols Containing Insoluble Material Aerosols containing a solid material of known particle size were pre- pared. Sulfadiazine Calcomites © and Microcrystals* were employed in this phase of the study and formulated as follows: Sulfadiazine Calcomites or Microcrystals Span 85* Ethanol, anhydrous Blancophor AW High Concn. Propellant 12/11 (50: 50) 0.5 10.0 20.0 0. 064 69.436 The sulfadiazine was placed in a mortar with the Blancophor and 1nixed with the Span 85. Propellant 11 was added and mixed with the powders. This slurry was then placed into an aerosol container and chilled. Pro- pellant 12 was added by the cold process and the container was then fitted with a metered valve. By means of an oral adapter, approximately 12- 15 sprays were dispensed into the sampling chamber of the Cascade Im- pactor. The results are shown in Tables IV and V and represent the average of three results of each powder. Table IV Particle Size Distribution of Sulfadiazine Calcomites Aerosol Diameter of Mass of Collected Cumulative Mass Cumulative Weight Particle (/•) Material (g) (g) Per Cent 2 0.6864 0.6864 13.61 4 1.9024 2.5888 51.70 8 2.3163 4.9051 97.95 16 0.1009 5.0060 100.00 32 ......... DISCUSSION OF RESULTS The fluorometric method of analysis has been used for many sub- stances which have the property of being fluorescent. Tracer studies have also been conducted by the addition of a fluorescent dye to a known system. Since the intensity of the fluorescent light emitted by a sample * Sulfadiazine Calcomites (American Cyanamid Corp., N.Y.), 99% of the particles are less than 10tz and 95% are less than 4tz. Microcrystals, 99.7% of the particles less than 10tz and 50% less than 5tz. • Sorbitan Sesquioleate, Atlas Chemical Industries, Wilmington, Del.

PARTICLE SIZE DETERMINATION Table V Particle Size Distribution of Sulfadiazine Microcrystals Aerosol 875 Diameter of Mass of Collected Cumulative Mass Cumulative Weight Particle (u) Material (g) (g) Per Cent 1 0.3803 0.3803 11.87 2 1.0309 2.0612 44.66 4 1.5309 3.5427 75.45 8 1.3127 4.8553 100.00 16 ......... 32 ......... under constant input light intensity is directly proportional to the con- centration of the fluorescent comp,ound, these substances can be used as tracers (6). The use of one such fluorescent compound for this purpose has been shown in this paper. As can be seen in Fig. 2, the initial con- centration of the material must be carefully selected so that in the range of concentration used, fluorescence becomes indicative of concentration. Concentrations of Blancophor above 0.05% were noted to produce only slight increase in fluorescence with an increase in concentration. For this reason, 0.05% was the maximum concentration of Blancophor used in this study. Two hair spray aerosols, having a different particle size distribution, were studied by both the weight-by-difference and fluorometric methods of analysis. Table III gives a comparison of the results. It can be noted that the particle size distribution as determined by the fluorometric method tends to give slightly higher cumulative weight per cent than that given by the other method. This could possibly be due to the greater ac- curacy of fluorometric analysis. To convert per cent fluorescence to cumulative weight per cent, the assumption was made that if a 5-ml sample could be recovered from the aerosol product and its fluorescence determined, the reading would be 72% (as shown in Table II and Fig. 2). By adding a sufficient amount of dye to the aerosol to produce a 0.05% by weight solution, this assumption becomes valid. The amount of dye deposited on each slide is then equal to Known concn. o[ dye in sample X fluorescence o[ slide Fluorescence of sample or 0.05 x fluorescence o[ slide 72