are you as familiar with Energy Dispersive X-Ray?. ICAP is a detructive test and there are several non destructive Xray and EDX (with flourescence spec) techniques used to focus in on metal ratios.
What if you have a chondrite?? They are so heterogeneous in composition you could be like the blind wise men touching the elephant.(Its a metal, stone and silicate mix but like a rice pudding you also gotta find the raisins and the cinnamon to analyse)
ICAP is ok but mteorites are arranged in crytal axes that are defined by their Widdmenstaten figuews. SO if you get one that hs rpidly cooled, the Ni and Fe form totally different bars in the "W" figures.
I think you need to learn some more about how many types of meteorites there are and how they present themselves.
A meteorite is cut and polished to show its structure (If its a metal Fe/Ni one). An energy dispersive x ray (EDAX) can be run acrocc a line on the cut surface and youd get back ratios of Ni/Fe along that line. You can then PLOT the ratios by running several lines and then modelling their relative yields of metal.
(Many meteorites will contain other metals too. By doing an ICAP, you may miss these (unless you take huge samples of the meteorite and take it down in Aqua regia and then dealing with the insolubles in another way (silica based-use HF)
An EDAX wont give you ppb levels but in an Fe/Ni meteorite, why are we doing ppb (or even PPM level analyses??)