[plateeny]

I have coffee sample for metal analysis of As, Pb and Cd. I have digested the sample in HNO3 at 70 degree, I have prepared 3 samples one of them spiked with 50 ppb of three metals, ICP-OES  was used for determination, the unspiked sample I got nothing and the spiked I got less than 50 ppb of three metals, so can advice for another  analysis method. 

[Ida Isotope]

I'm not sure if I understand what exactly you are asking....are you asking for a method to analyze?

I would suggest an infrared spectometer but I'm not sure if it would pick up those metals?

Anybody know?

[Sam (NG)]

I'm not sure if I understand what exactly you are asking....are you asking for a method to analyze?

I would suggest an infrared spectometer but I'm not sure if it would pick up those metals?

Anybody know?

No you wouldn't.  An FTIR spectrometer only allows you to detect changes in dipole moments.  Even if the metals were covalently bonded to something, the stretching vibration of the bond would be so low wavenumber that you wouldn't be able to detect it with most IR spectrometers.  Besides, the chances of getting a quantitative measurement of the amount of each metal in the sample from this method are very low.

I'm afraid that I would have used ICP-MS myself to find that out, but I'm not an analytical chemist.  Maybe there's something that you can change in the way that you prepare your samples that will allow you to use ICP.

[marquis]

Can you give more information on the sample preparation? 

Often, a wet ash is done on samples of this type.  You would measure one gram of sample into a vycor and the add sulfuric and nitric acid.  Slowly heat the sample until it is well charred.  Then ash until the sample has no organic material. 

After cooling, you would do the nitric acid digestion.
 
Is this how you did the acid digestion?  Otherwise, the metals could get caught up in the organic matrix.

This will handle lead and probably cadmium.  Haven't done arsenic with AA.  Often, for arsenic, arsenic trihydride (arsine) analysis is done.  This is a touchy and potentially very dangerous, so use caution if you try it.