INTERFERENCE OF EMULSIFIERS WITH PRESERVATIVES VIII 85 SORBIC Acre TESTS It has been thought that the discrepancy between our results and those reported by others using sorbic acid, could be in the medium employed. Both magnesium and ferrous iron have been suggested as forming sorbates less soluble than the free acid. However, magnesium sorbate is far more water soluble than sorbic acid itself. In experiments made with Jaag medium with and without these two ions, no difference in growth was observed. When deionized water served as the medium, the addition of these ions in the concentration found in Jaag medium showed no effect on preservative action. Though Lach (4) has found sorbic acid to be less complexed by poly- glycols than the p-hydroxybenzoates, our work to date, using mainly niger as the test organism does not confirm this. Furthermore, one of us (M. G. deN.) has found that at a pH above 5.0, sorbic acid is a poor pre- servative even in the absence of nonionics in Jaag medium. against niger. 0.1% cationic only* 0.1% cationic plus 2% G-3720' 0.1% MPt 0.15% MP 0.2% MP Ethyl Hyamine Roccal Cetab 10X ++++ ++++ ++++ + ++ _ _ ++++ Figure 4.--Twelve Month Growth of •/. niger in 2% Mixture of Cationic (20%) in G-3720 with Methyl p-Hydroxybenzoate * No other preservative. t Methyl p-hydroxybenzoate. 12 Months Tween 80 q- q- q- G-3720 q- q- G-3810 G-1425 q- q- Figure 5.--Growth •/. niger, in Jaag Medium, 2% Nonionic 0.2% MP* * Methyl p-hydroxybenzoate. MISCELLANEOUS OBSERVATIONS Of the many preservatives tested, we found benzoic, sorbic and dehydro- acetic acids very sensitive to pH in their antimicrobial activity. Ethyl vanillate and the parabens had a fairly wide pH spectrum. In general, we found that the greater the number of moles of ethylene oxide in the ether or ester chain, the greater the inactivation of pre- servative. These data are based on tests of a series of ethoxylated nonyl phenols, glyceryl monostearate, stearic acid and cetyl alcohol. We found •lspergi//us growing slightly in 0.2 per cent formaldehyde (100 per cent basis) in Jaag medium containing 2 per cent G-3720. Similar

86 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS tests with lower concentrations of formaldehyde showed, as would be expected, heavier growth, but in no case was it more than moderate. At the end of one series of tests using Jaag medium, Atspergillus and methyl p-hydroxybenzoate in concentrations of 0.1, 0.15, and 0.2 per cent, we added 0.1 per cent of a commercial perfume compound dissolved by 2 per cent G-3720 to the group. In two months tubes preserved with 0.1 per cent methyl p-hydroxybenzoate showed a very heavy growth. At a concentration of 0.15 per cent methyl p-hydroxybenzoate, a heavy growth took place in one year. At a concentration of 0.2 per cent methyl p- hydroxybenzoate no growth was discernible at the end of one year. It was of interest to note the profound effect of the nonionic G-3720 on the growth of At. niger in Jaag medium containing Duponol C. At 0.1 per cent concentration of Duponol C alone, tubes were free of growth at the end of one year. When 0.1 per cent G-3720 was added, moderate growth was observed in five months. At a concentration of 0.3 per cent G-3720, and 0.1 per cent Duponol C, heavy growth occurred in four days. When the sodium alkyl sulfate was ethoxylated with 11/2 to 2 moles ethylene oxide, moderate growth was readily noticeable in three weeks. Based on a suggestion made in Geneva in 1957, we used five materials because their main action was fungicidal. Jaag medium was made with 2 per cent G-3720 and variable amounts of the fungicides with the fol- lowing results. Vancide 89 (5) showed a very heavy growth in a 0.01 per cent concentra- tion in thirty days. Isothan Q-15 (6) in 0.1 per cent concentration showed a heavy growth in twenty days. Salicylanilide 0.1 per cent took one hundred fifty days to give a very heavy growth. Rotax (7) 0.1 per cent gave a moderate growth in one hundred twenty days, while TMTD (8) 0.1 per cent has shown no growth for nine months. We find that not only nonionics but other macromolecules inactivate preservatives when tested in Jaag medium. Thus, 0.5 per cent Carbopol 934 (9) containing 0.2 per cent methyl p-hydroxybenzoate shows moderate growth of At. niger in from two to four months depending on the alkali used in neutralizing the material. Cellosize (10) can be preserved with as little as 0.15 per cent methyl p-hydroxybenzoate against At. niger. How- ever, 2 per cent tragacanth in Jaag medium shows slight growth of At. niger in five months in the presence of 0.2 per cent methyl p-hydroxybenzo- ate. Methocel 1500 (11) gives moderate to heavy growth of At. niger in concentrations of 0.1 to 0.2 methyl p-hydroxybenzoate. PVP, two types, shows moderate growth of At. niger in 0.2 per cent methyl p-hydroxy- benzoate after five months. We now have indications that the presence of around 8 per cent ethyl alcohol in the preserved nonionic medium, may retard inactivation of the preservative toward At. niger.