Apr. 8, 2010  9  US 2010/0087650 Al  TABLE 11  TABLE 13  TABLE 12  TABLE 14  % of cisatracurium  No. Buffer  pH  besylate at T = 0  % of cisatracuriwn  besylate after 24 hours  %  degradation  NH4 •cH3COo-1CH3COOH 3.5  54.7  52.9  3.3  2  NH 4  •cH 3 COO-/HCOOH  3.5  54.6  54.3  0.5  3  Na•CH 3 Coo-JCH 3 COOH  3.5  54.5  52.5  3.7  4  Na•No 3 -/HNO 3  3.0  54.5  54.5  0  5  K•H $_{2}$PO 4  3.0  54.7  53.7  1.8  6  CaBriHBr  3.5  54.4  54.4  0  7  diethylamine/CH 3 COOH  3.5  54.7  53.2  2.7  8  triethylamine/CH 3 COOH  3.5  54.4  52.1  4.2  9  Na•ClO 4 /HC1O 4  Atracurium besylate is precipitated in the  presence of a  Cl0$_{4 }$ ion  % area of the cis-cis isomer  Time  H= 1  H=2  (hours)  RT  D,%  4°C.  D,%  RT  D,%  40  C.  0  54.9  54.9  54.8  54.8  6  50.2  8.6  53.9  1.8  54.5  0.5  54.8  26  38.8  29.3  52.8  3.8  53.8  1.8  54.7  D,%  0  0.2  RT= room temperature, D = degradation  D  =  Xo  - X6/26  x lOO  Xo  D=  Xo-X21  xlOO  Xo  pH  Time, hours  3.0  3.5  4.0  4.5  5.0  5.5  0.0  53.4  53.6  53.4  53.9  53.6  53.6  10.0  51.3  51.0  50.5  49.9  46.1  40.8  21.0  50.0  49.2  47.9  46.2  38.4  27.8  % degradation*  6.4  8.2  10.3  14.3  28.4  48.1  Anion removal(%)  Cis-cis isomer recovery (%)  No. Buffer  Step 1  Step 2  Step 3  Step 1  Step 2  Step 3  20 mM NH 4 +CH 3 COo-;  91.5  11.5  2.9  0.2  66.35  0.1  CH 3 COOH, pH= 3.5  A graph depicting the stability of the lR-cis, lR’-trans isomer  at different pH values is provided in FIG.  7,  which demon› strates that at pH 3, after 20 hours the% area of the lR-cis,  1 ’R-cis isomer is only slightly reduced while at pH 5.5 the%  area of the 1 R-cis, 1 ’R-cis isomer is significantly reduced.  [0076]  The degradation (D) according to the data presented  in Table 12 was calculated as follows:  wherein, Xa=% of cisatracurium at Ta, and X$_{21 }$=% of cisa› tracurium at after 24 hours.  *The buffer used was the Na•CH 3 COO-/CH 3 COOH buffer at 3 different pH  values, that is pH values of3.0, 4.6 and 5.5. The values in the table are repre› sented as  % of cisatracurium besylate.  A sample solution of (lR,l’R)-atracurium besylate (10  mg/ml) was prepared using two buffer solutions at pH values  of 1.0 and 2.0 and analyzed on the C18 stationary phase by  gradient elution [20 mM  KN0$_{3 }$ buffer (at pH corresponding  to sample preparation)-methanol]. The stability of the  sample solution at the mentioned pH values was demon› strated at room temperature and at 4 °  C., as depicted in Table  13.  wherein, Xa=% of cisatracurium at Ta, and  X$_{6126}$ =%  of cisa› tracurium at after 6 or 26 hours.  Example  7  [0077]  This example demonstrates a method for purifica› tion of the cisatracurium solution from the buffer’s mixture by  Solid Phase Extraction (SPE).  [0078]  A series of the sample solutions of (lR,1 ’R)-atracu› rium besylate isomer mixture (55% cis-cis; 35% cis-trans and  6% trans-trans isomer) was prepared in diluents containing  different buffers (varying by the nature of the cation and the  anion). The diluents consisted ofa mixture of90% buffer and  10% methanol. The sample solutions were purified using SPE  C18 cartridge.  [0079]  The evaluation of the buffer anions was carried out  by HPLC. The cations were evaluated indirectly. The recov› ery of the isolate (IR cis,1 ’R-cis isomer) and anions was  checked after each step of the SPE method, which comprises  the steps of:  [0080]  1) successive transferring of the sample solution and  water through the sorbent;  [0081]  2) elution of the sample with methanol; and  [0082]  3) washing the sorbent with methanol.  The results of this study are summarized in the Table 14. 