I analyzed Pb along the trajectory of wounds in deer meat some time ago. I tried both acid digestion with HNO3 and tissue solubilization with tetra methyl ammonium hydroxide, which both worked satisfactory. I guess your low reproducibility comes from dry ashing, which I must confess I did not try. You may also consult:

http://quimica.udea.edu.co/~carlopez/cromatoion/smpleabostron.pdf

According to my opinion, dry ashing preparation is not the best pretreatment method. Part of both of analytes is lost. Try the same with a chemical modifier during dry ashing step (e.g. Mg(NO3)2 or microwave pretreatment of the sample.

J. A. Stratis

I had same problem.I solved Cd problem. but i haven't solve Pb problem yet, I am going on trying.

My methode for Cd : I use microwave digetion for samples with nitric acid and hydrogen peroxide. And I use 10 ppm palladium for matrix modifier. 20 micro litre sample + 5 micro litre matrix modifier.

My graphite furnace methode for Cd is attached.

if you have problem or you want to discuss something, you can write me.

We have good and reproducible results of Cd and Pb determination by ETAAS after acid digestion (HNO3 + H2O2) in microwave oven. Dry ashing we have used in some cases with adding Mg(NO3)2 and some drops od HNO3, but we preferewet method. For GFAAS we use the same matrix modifier and temperature programme as Fikret Suvari; sometimes we use for Pb determination also NH4H2PO4 matrix modifier. Matrix modifiers for GFAAS and Cd and Pb we use in all cases.

Thank you all for your advice and opinion. I have voted up all your answers because they were quite helpful. I think that this discussion was very useful. Most importantly, I managed to fix the problem with the accuracy of the method by changing the method of sample preparation (primarily) to wet digestion and by modifying graphite furnace program.

i work with vegetables, i have no problem with Pb, the calibration curve is 3 ppb to 10 ppb but i have correction zeeman. Digestion is by microwave. i have noticed the clean glassware is main issue on reproducibility. prepare the curve and QC fresh, same day. I use NH4H2PO4 + Mg(NO3)2 (dissolve 10g NH4H2PO4 in deionized water and make up to 100mL. Dilute 1 mL of this solution and 0.1 mL of Mg stock solution to 10 mL with deionized water).

Mg stock solution = ( 10g/L Mg)

My problem is with Arsenic the spike was not expected. the problem is spike low (60%) i have tried with two different matrix modifiers, two furnace program and spike after digestion with microwave and the problem is the same, the QC is ok, laboratory blank is ok, spike blank is ok, but spike sample is low ¿Do you work with As? or somebody help me! :)

It may be the contamination with the sample at drying process. I also face same problem in Pb in fish. From the beginning we unable to obtain close results between triplicates. Because of the waste burning ash contaminated. Be careful with such issues. And try with the alternate wavelength