After elemental analysis of the samples, carbon content of the charcoal was 102 (several repetitions were made, but obtained the same values), the equipment was tested with other samples of wood obtained coherent results (the equipment is working well). How can I adjust the elemental composition values since the sum of C,H,N,O and ash should be 100?
What is your blank peak area immediately after measuring the charcoal? If your combustion is limiting, then you may have residual organic that may persist between aliquots. Also test the linearity of the sample size vs peak area by running several repeats of the same sample at different mass. If this is all ok, then you need to question the reference material against which you are calibrating because >100% seems impossible. Again - check linearity by measuring standards of different mass. Last test - check the linearity/calibration of your balance because your symptom might point to a problem here.
If the CHNS analyzer doesn't work properly, you can verify the results by the TOC analyzer or you can check it by EDX analysis.
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