[2lrigbal]

I have been working with and doing research in journal articles and books to find a method, or step by step procedure to use in determining As and Se concentration by hydride generation.  So far, I have found some useful infomation, but not enough to get this method to work for me. 

I am using an MHS 15 in conjunction with an AAnalyst 400 spectrometer.  I am currently working with As.

I am trying both 2% HCl and 2%HNO₃ to make my blank and calibration standards. I am also reducing these by 2 methods:

group 1: reduction by adding 2 mL L-cysteine per 10 mL sample/solution.
group 2: reduction of As by adding 1 mL KI + L(+)-ascorbic acid per 10 mL sample/solution
Wait 30 minutes for reduction. 
While I am waiting, I make up a fresh batch of 3% NaBH₄ in 1%NaOH sol'n to be used as a reductant.
15 minutes prior to running, I heat the quartz cell.
I add 10mL 1.5% HCl diluent to the reaction flask and add 10uL of the 1ppm calibration standard which should give reading in the ppb range. 
I wait the 20 second prereaction purge time and depress the plunger on the MHS 15 while the method for As is up and running on the AA400.
All recommended conditions are used for wavelength, etc, but I am getting no readings whatsoever.

I am having a lot of trouble with this, and the manual is vague.  I also do Hg determinations using the same (but separate) machine (so it is not contaminated, it is new... I thought that might be the problem because SnCl₂ is used for that).  The recommended conditions for Hg determinations is not spot on either.  There have been several modifications to make it work right, so I am thinking there are several modifications that must be done in order for As and Se determinations to work as well.

Does anyone have a method developed for this technique?  Any suggestions on what I could try or what I am doing wrong?  I have not been able to find the answers in any book, journal article, user's maunal, or through support tech.  If anyone has a developed method, please *delete me*

Thanks!

[2lrigbal]

Also, the quartz cell I am using is open on the ends.  Someone suggested that I use a quartz cell with windows, but when I spoke with tech support she was certain that I would not use a cell with windows.  Can anyone verify whether I should use windows or not?  Also, I don't know why the last part of my first post said *delete me* but really, I really could used any information. 

Thanks

[2lrigbal]

Another note and question pertaining to my quest to get my hydride generation technique to work.

First, I am using the recommended EDL lamps.  Second, I am using batch mode technique rather than flow injection (which is what I wanted, but I got this instead).

Therefore, my gas flow needs to be adjusted.  I have the tank pressure set at 36 Psi, which is what was recommended. There is an internal knob in the machine that needs to be adjusted so that at the SnCl2 setting, there is a gas flow of 1100mL/minute.  This is the same gas that provides the pressure to dispense the reductant, or for these  measurement purposes, DI water. 

Does anyone know of an equation that might relate the gas (Ar) flow rate and amount of water dispensed so that I might be able to adjust my machine appropriately?   I did a search on gas flow rate, but I couldn't narrow down the search enough, and my search left me with a lot of extra information that does not help me.   That or I'm not sure what exactly to do the search on. 

Thanks