I am often too blunt and harsh in my technical [and other] opinions. I
apologize for any trampled feelings from my earlier email. I just cannot
fathom how the optimized Monier -Williams method can give positive results -
even in the 1 - 10 ppm range for fresh ocean caught shrimp. The method in
my experience has a couple of critical points to control from false
positives and/or low recoveries. 1 - the condensers must be chilled to at
least 14C throughout the reflux. 2 - the nitrogen used to carry the sulfur
dioxide over to the trap must be oxygen free - we go to the extreme of using
an alkaline pyrogallol solution trap that the nitrogen is bubbled thru
before going to the evolution apparatus. 3 - always use the Barium
precipitation finish after titration to double check the titration is really
measuring sulfuric and not just some other volatile acid component 4 - in
line with the previous make sure the sample does not char during reflux - we
find this especially easy to have during the initial heating if one is not
careful.
You may wish to contact Dr. Charles Warner at the US FDA who has worked
extensively with this methodology as he may have some insights as well. His
contact info is email: CWarner@bangate.fda.gov phone:(202) 205-4912
Again I am sorry for being too blunt and critical - it truly was not my
intention to be so - just a flaw in my mannerisms.
regards and good luck with this
Ernest Jerry Oliveras, Jr.
Laboratory Director & President
ANRESCO, Inc.
1370 Van Dyke Avenue
San Francisco, CA 94124
www.anresco.com
800-359-0920 x18
FAX: 415-822-6615
cell: 415-378-1600
alternate email: anresco@pacbell.net
-----Original Message-----
From: tilak [mailto:tilakr@sify.com]
Sent: Tuesday, May 20, 2003 1:57 PM
To: seafood@ucdavis.edu
Cc: phowgate@rsc.co.uk; Jerry; info@foodfocus.com
Subject: discussion re-sulphites in shrimps
Dear SEAFOOD LISTERS,
MY SINCERE THANKS FOR EVERYBODY WHO SENT
IN THEIR INFORMATIVE COMMENTS.
REGARDING SOME QUERIES-
THE SHRIMP SAMPLES MENTIONED WERE ALL FRESHLY CAUGHT FROM SEA AND
ESTUARIES.
METHOD OF ANALYSIS-AOAC OFFICIAL METHOD,17th
Edition-OPTIMISED MONIER-WILLIAM'S.
RESIDUAL SULPHITE VALUES WERE 1 to 10 ppm range.
we bow our heads in shame to my esteemed
colleague Mr.Jerry Oliveras's comment that he find our humble observations
'highly dubious'.I remember his valuable contributions in enlightening us
on several important topics. we are taking the criticism from a senior
lister who is heading a prestigious lab,in it's true spirit and
will strive for more perfection in further tests.
EVERYBODY,HAVE AGOOD DAY.
r,tilak makkiseril
cochin,India
This archive was generated by hypermail 2b29 : Wed May 21 2003 - 11:25:12 PDT