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Measuring Ointment Firmness
MEASURING OINTMENT FIRMNESS By Walter G. Fredell*
or firmCONSISTENCY ness is of interest in many pharmaceutical and cosmetic p~epa rations. Therefore, methods of determining this property are important.. The degree of firmness indicates to some extent the ease with which an ointment or cream can be spread, and it is important to know that batches made at different times have the same spreadability. This paper presents an easily constructed device for measuring the consistency of semisolid pharmaceutical and cosmetic products. Results obtained are recorded numerically and are duplicable. The Lattice Consistency Apparatus
The lattice consistency apparatus consists of two parallel pieces of wood l inch high, 1 12 inch wide, and 18 inches long, which have semicircular grooves spaced at intervals along their length. (These grooves are easily made by clamping the two pieces of wood together to form one piece 2 x 1I 2 x 18 inches and drilling 118-inch holes at the designated intervals down the center.) The distance from the center of groove 0 to the center of groove 1 is 1I 8 inch, from 1 to 2 is 2 I 8 inch, from 2 to 3 is 3I 8 inch, increasing 1 I 8inch for each succeeding interval up to 15. The two parallel pieces are placed about six inches apart, and applicator sticks are laid across them in the grooves to form a lattice. Numerical recording of consistency
0.1 2.
3
4
5
6
Lambert Pharmacal Co., St. Louis, Missouri. Presented to the Section on Practical Pharmacy, AMERICAN PHAIUIACEUTICAL AssociATION, I950 meeting, Atlantic_City.
170
The product, in· a collapsible tube fitted with a cap in which a 1I 8-inch hole has been drilled, is extruded in a ribbon across the lattice from 0 to 15. (For some products, it is conveni~rtt to have a smaller hol~ in the cap.) Three ribbons are extruded and th~ reading of the consistency is based on at least two of the ribbons breaking bet ween the same applicator sticks. The number of the last stick which supports at least two ribbons of the product is the numerical consistency reading. Readings are n1ade one minute and five minutes after extrusion of the product across the lattice. Readings at these time intervals are made because slight differences in consistency are indicated when comparing products. To illustrate: if readings such as those in Table I were obtained on three experimental _emulsion type ointments, the readings would indicate that product A is firmer than product C, and that C is firmer than B.
Table /-Consistency Readings
Product
l minute
A B
7
7
6
6
7
6
c
7 •••••••••• 13
is taken from the numbers 1 to 15 which represent increased distances of 118 inch for each succeeding number. The scale of intervals hut not the exact measure, is illustrated in Figure I.
*
Method
14
5 minutes
15
Discussion
With most formulations on which lattice readings can be obtained, the readings show a direct relationship to the consistency of the product. As with other consistency measuring devices, there are instances when the results seem anomalous. Vol. XII, No. 3
or firmCONSISTENCY ness is of interest in many pharmaceutical and cosmetic p~epa rations. Therefore, methods of determining this property are important.. The degree of firmness indicates to some extent the ease with which an ointment or cream can be spread, and it is important to know that batches made at different times have the same spreadability. This paper presents an easily constructed device for measuring the consistency of semisolid pharmaceutical and cosmetic products. Results obtained are recorded numerically and are duplicable. The Lattice Consistency Apparatus
The lattice consistency apparatus consists of two parallel pieces of wood l inch high, 1 12 inch wide, and 18 inches long, which have semicircular grooves spaced at intervals along their length. (These grooves are easily made by clamping the two pieces of wood together to form one piece 2 x 1I 2 x 18 inches and drilling 118-inch holes at the designated intervals down the center.) The distance from the center of groove 0 to the center of groove 1 is 1I 8 inch, from 1 to 2 is 2 I 8 inch, from 2 to 3 is 3I 8 inch, increasing 1 I 8inch for each succeeding interval up to 15. The two parallel pieces are placed about six inches apart, and applicator sticks are laid across them in the grooves to form a lattice. Numerical recording of consistency
0.1 2.
3
4
5
6
Lambert Pharmacal Co., St. Louis, Missouri. Presented to the Section on Practical Pharmacy, AMERICAN PHAIUIACEUTICAL AssociATION, I950 meeting, Atlantic_City.
170
The product, in· a collapsible tube fitted with a cap in which a 1I 8-inch hole has been drilled, is extruded in a ribbon across the lattice from 0 to 15. (For some products, it is conveni~rtt to have a smaller hol~ in the cap.) Three ribbons are extruded and th~ reading of the consistency is based on at least two of the ribbons breaking bet ween the same applicator sticks. The number of the last stick which supports at least two ribbons of the product is the numerical consistency reading. Readings are n1ade one minute and five minutes after extrusion of the product across the lattice. Readings at these time intervals are made because slight differences in consistency are indicated when comparing products. To illustrate: if readings such as those in Table I were obtained on three experimental _emulsion type ointments, the readings would indicate that product A is firmer than product C, and that C is firmer than B.
Table /-Consistency Readings
Product
l minute
A B
7
7
6
6
7
6
c
7 •••••••••• 13
is taken from the numbers 1 to 15 which represent increased distances of 118 inch for each succeeding number. The scale of intervals hut not the exact measure, is illustrated in Figure I.
*
Method
14
5 minutes
15
Discussion
With most formulations on which lattice readings can be obtained, the readings show a direct relationship to the consistency of the product. As with other consistency measuring devices, there are instances when the results seem anomalous. Vol. XII, No. 3