56o 
Assay  of  Citral  in  Lemon  Oil. 
f  Am.  Jour.  Pbarm. 
\   December,  1911. 
course  of  the  analysis  until  further  addition  causes  no  marked  pink 
color  in  either  the  control  or  the  test,  after  heating  for  a  reasonable 
length  of  time  in  a  water  bath  which  is  boiling  briskly.  We  have 
found  it  best  to  add  the  rosolic  acid  solution  from  a  calibrated  i 
c.c.  pipette. 
The  end  point  is,  as  we  have  suggested,  by  no  means  sharp  and 
brings  a  large  personal  error  into  play.  After  summing  up  the 
points  of  weakness  of  this  assay,  and  adding  to  them  the  fact  that 
Citronellal  may  be  determined  and  reported  as  Citral,  we  reached 
the  conclusion  that,  as  a  means  of  roughly  approximating  the  true 
Citral  content,  the  method  was  entirely  too  involved  and  laborious. 
In  trying  to  find  a  suitable  substitute  we  have  made  some  tests 
using  the  method  outlined  by  Chace  and  also  the  one  described  by 
Hiltner. 
Chace's  fuchsin-sulphurous  acid  method  was  followed  without 
great  modification.  (We  found  it  convenient  tO'  use  a  refrigerator 
with  a  temperature  of  13°  to  13.5°  C.  and  to  make  our  compari- 
sons at  the  end  of  15  to  20  minutes.)  For  a  description  we  refer 
the  reader  to  Chace's  original  article  or  to  Leach's  Food  Inspection 
and  Analysis,  page  866.  Nessler  tubes  were  used  instead  of  a 
colorimeter,  and  varying  amounts  of  a  standard  solution  of  pure 
Citral  in  aldehyde-free  alcohol  were  employed  for  comparing  color 
values.  The  method  is  rapid  and  gives  results  which  are  in  gen- 
eral slightly  higher  than  those  given  by  the  U.  S.  P.  assay.  Unfor- 
tunately this  excellent  and  rapid  method  involves  the  use  of  alde- 
hyde-free alcohol,  a  reagent  which  cannot  be  obtained  in  a  short 
time.  This  handicaps  the  analyst  who  assays  but  few  samples  of 
the  oil  and  who  is  called  upon  to  report  quickly.  Under  these  cir- 
cumstances he  has  little  time  to  wait  until  the  aldehyde  has  been 
removed,  (We  found  that  more  than  eight  hours'  boiling  under 
reflux  and  that  considerably  more  than  5  g'ms.  of  metaphenylene 
diamine  hydrochloride  were  necessary  to  eliminate  most  of  the  alde- 
hyde in  1000  c.c.  of  95  per  cent,  grain  alcohol.  Even  then  our 
distillates  gave  a  distinct  aldehyde  reaction.) 
Hiltner's  method  with  slight  changes  has,  however,  proven  suf- 
ficiently satisfactory  to  warrant  a  brief  outline  of  the  procedure 
followed  in  this  laboratory.  A  more  detailed  description  may  be 
obtained  from  the  author's  original  paper. 
A  standard  solution  of  Citral  made  by  weighing  accurately  be- 
tween 50  and  70  mgms.  of  pure  Citral  and  making  up  to  50  c,c.  with 
