[Qemko]

I'm currently trying to study mercury conversion by bacteria using CV-AFS. I've tried  some different  containers ( tests without using bacteria) like  glass (20ml capacity),  PP  (polypropilene) (10ml) and PVC containers (40ml). I usually use 15 or 6.3ml of muller hinton media  (a rich medium, pH=7), and inject HgCl2 to work with a concentration between 800 and 1000ppb of mercury. The vessels are placed horizontally with an orbital agitation of 120rpm and at 37ºC.
 I keep taking aliquots of 1ml at 0, 24 and 48H. The problem is the mercury levels keep falling after sample analysis, to a point that at 48 hours i only have between 30 to 50% in glass, and in polymer between 10-30%.
Can disproportionation of mercury account for these losses. I tried washing the vessels after the test with HNO3 and water (50:50) at 65% but i can only recover between 10 and 30% of mercury, therefore probably adsorbed.
Are the aliquots i take too much?
My teacher says i'm crazy, and that the error must be human (meaning, mine)., but i have already a lot of tests, that even though are not very reproductible corroborate a permanent loss of mercury. All these tests without bacteria.
Can anybody give me a hand here?!

(my teacher is freakin out! She states that she used those vessels to keep biological samples in the freezer, and that there was never a loss above 10% of mercury).

[Borek]

HgCl2

(...)

Can disproportionation of mercury account for these losses.

Disproportionation? HgCl₂ or Hg₂Cl₂?

[Qemko]

HgCl2

[Borek]

HgCl2

What disproportionation reaction do you expect?

[Qemko]

HgCl2

What disproportionation reaction do you expect?

i expect that due to the fact that i'm using a rich organic medium Hg2+ will obtain electrons and reduce itself, formaing hg(0) volatilizing from the container when i remove the samples. Of course that in a growth medium mercury will form a lot of chemical complexs with proteins and other substances. The main question remains, if i can't obtain the initial mercury concentration what is happenning to mercury. A researcher in thios field has pointed out disproportionation of mercury has the most probable cause. I just what to know if someone have obtained strange results working with mercury in bacterial detoxification experiments.

[Borek]

i expect that due to the fact that i'm using a rich organic medium Hg2+ will obtain electrons and reduce itself, formaing hg(0)

That's hardly disproportionation. Disproportionation means the same compound acts as oxidizer and reducer and the same time, like in this case:

Hg₂Cl₂ -> Hg + HgCl₂

The main question remains, if i can't obtain the initial mercury concentration what is happenning to mercury. A researcher in thios field has pointed out disproportionation of mercury has the most probable cause.

Sorry, can't be of help - just wanted to clarify terminology. I understand your problem but have no idea about what is happening. Have you tried to do the experiment using just DI water?

[Qemko]

I always use DI water   

[Borek]

DI water WITHOUT media.

[Qemko]

DI water WITHOUT media.

Well i also tried using only DI water in a separate test and didn't had such low results of mercury recuperation, even though the samples reanalysed, showed variations in mercury content.
It' one of those things..~