66o 
Titration  of  Certain  Alkaloids. 
5  Am.  Jour.  Pharm. 
1      Sept.,  1921. 
quinine  hydrochloride  titrated  in  this  way  gave  99.79  per  cent.  In 
the  same  way  quinine  acid  hydrochloride  or  sulphate  may  be  titrated 
with  standard  alkali  until  an  orange  color  corresponding  to  a  Ph  of 
about  5.15  is  obtained  with  methyl  red  solution.  A  sample  of 
quinine  acid  hydrochloride  titrated  in  this  way  gave  97.3  per  cent. 
The  end  points  are  not  quite  so  sharp  with  quinine  as  with  mor- 
phine, but  with1  a  little  practice  quite  reliable  results  can  be  obtained. 
This  method  of  titration  may  be  applied  to  tinct.  quinin.  ammon.  for 
the  combined  determination  of  quinine  and  ammonia  in  the  follow- 
ing manner: — 25  cc.  of  the  tincture  are  run  into  50  cc.  N/2  hydro- 
chloric acid,  brom-phenol  blue  is  added,  and  the  liquid  titrated  back 
with  N/2  alkali  until  a  pale  greenish-yellow  color  is  obtained.  Let 
a  =  No.  of  cc.  N/2  alkali  used.  Methyl  red  is  then  added  to  the 
solution  and  the  titration  continued  with  N/10  alkali  until  the  pink 
color  of  the  methyl  red  disappears  and  only  the  blue  color  of  the 
brom-phenol  blue  remains. 
Commercial  samples  of  quinine  salts  tested  in  1  per  cent,  solution 
gave  the  following  values  for  Ph  : 
The  B.  P.  and  U.  S.  P.  employ  cochineal  for  the  titration  of 
the  alkaloids  obtained  from  belladonna. 
Squire's  "Companion"  (nineteenth  edition)  states  that  "atropine 
may  be  readily  determined  by  titration,  using  cochineal  or  iodeosin 
as  an  indicator/'  Atropine  sulphate  is  stated  to  be  neutral  to  litmus 
paper. 
Allen's  "Commercial  Organic  Analysis,"  Vol.  V,  page  296, 
states  that  commercial  atropine  sulphate  is  often  faintly  alkaline, 
and  keeps  better  when  so  made. 
In  order  to  determine  the  Ph  of  a  i  per  cent,  solution  of  atro- 
pine hydrochloride,  a  known  weight  of  pure  atropine  was  dissolved 
Let  b  —  No.  of  cc.  N/10  alkali  used. 
W/v  quinine  sulphate  B.  P.  =  b  X  0-1763. 
W/v  ammonia  =  50  —  (a  +  — )  X  0.034. 
Quinine  hydrochloride 
Quinine  acid  hydrochloride 
Quinine  acid  sulphate 
Ph. 
6.2 
3-7 
3-6 
THE  TITRATION  OF  ATROPINE. 
