Heavy Metals (Ph.Eur. 2.4.8 Method F)

[Katrine]

I have some trouble with the Heavy Metals analytical method, as
described in Ph.Eur. 2.4.8 Method F.

It states that:
"The test is invalid if the reference solution does not show a brown
colour compared to the blank solution or if the monitor solution is
not comparable with the reference solution."

Well, neither solution is more colored than the blank solution!

Are there any of you there have this experience?

Katrine.

[Bob M]

Colour can be produced by precipitation of sulphur. This occurs if
oxidants used in digestion are not completely destroyed prior to
addition of sulphide solution. Reference uses heat are you heating
blank sample sufficiently.
I had a similar problem with a natural raw material the material had
Iodine which was converted to iodate during digestion I eventually
found that the only way to get rid of the iodate was the addition of a
small amount 0.05 mls of hydrazine hydrate to the nessler tube prior
to the sulphide soln addition.

Bob M

Post by Katrine
I have some trouble with the Heavy Metals analytical method, as
described in Ph.Eur. 2.4.8 Method F.
"The test is invalid if the reference solution does not show a brown
colour compared to the blank solution or if the monitor solution is
not comparable with the reference solution."
Well, neither solution is more colored than the blank solution!
Are there any of you there have this experience?
Katrine.