I choline chloride states the following-"Succinylcholine chloride without previous drying melts between 160" and 164"." Difficulty in obtaining this range has been expressed by some workers.
Because of this, a more intensive examination was made of the various batches of Anectinem brand succinylcholine chloride that were in the laboratory. Due to the presence of two moles of water of hydration in the official substance, it was a t first thought that the difficulty was caused by variations in the water content. However, pure samples of succinylcholine chloride were found to invariably contain 8.59.5% water (theory = 9.1% H?O) and were stable in this range. No difficulty has been found in obtaining melting ranges within 159.5-164" on these samples. While the range of melting was usually 2-3', the beginning and end of melting were sharp and except for gas bubbles, which disappeared about one degree above the end of melting, a perfectly clear melt was obtained.
Examination of several low melting samples from various commercial sources was made to see if a reason could be found for the low melting ranges.
In the case of a sample giving a very low melting range (153-156') it was found that in addition to containing 11.3y0 water, it also contained free acid amounting to 4.6y0 hydrolyzed succinylcholine chloride. Other samples giving melting ranges both within and without the limits were checked for free acid as follows: 0.1 Gm of succinylcholine chloride was transferred to a 50-ml. Erlenmeyer flask, dissolved in 5 ml. water and 1 drop of bromcresol green-methyl red mixed indicator (1) added.