Natural Science Forum / Chemistry / General Chemistry / July 2008

Hi everyone,

I would like to optimize a Mercury Cold-Vapors analytical method which
isn't efficient to my opinion because we get broad and flat peaks.

Anyone would know what could cause theses very broad peaks whatever the
concentration I'm using for calibration (I usually use 0.1, 1, 5 and 10
PPB)? I suspect a kinetics problem.

AAS model: Buck 210 VPG with Graphite furnace and Cold-Vapor generation
options.

Argon flow : about 0,4 LPM

Reductant, SnCl2 10% w/v (10 grams of SnCl2 into 30 ml HCl, then I add about
1 gram of Mossy Tin, then I complete to 100 wih deionized water). Injected
into the reaction flask with a syringe and through a septum.

ACIDIFICATION SOLUTION: 20% v/v H2SO4 + 15% HCl diluted with deionized
water.

All our SAMPLES, STANDARDS AND BLANKS are being diluted with "preserved
water" : 0.2% HNO3 + 2ml / L Feldman solution (20%w/v K2CrO4 into 50%v/v
HNO3, in such a way we get a 0,04%w/v dichromate concentration in all
blanks, standards and samples)

For the reaction, we use 25ml of the sample, add 25 ml of the acidification
solution and add deionized water until volume reaches the 125 ml mark (to
make sure argon will bubble through the solution).

The moisture collector in-between the reaction flask and the quartz cell is
made of a plastic tube filled with 2-3 Kim-Wipes. No Magnesium perchlorate
is being used.

Anyone have an idea on what I should do to get nice and sharp peaks? Don,t
tell me to increase gas flow, I've already tried it!:)

Regards,

Daniel Picard, P.Chem.
Lab Manager
Aqua-Mac inc.
Montréal (Quebec)