What analytical methods are used to quantify C, O, N, and H in a sample? A very common analytical method for detection of more than 70 elements is ICP-OES (Wikipedia page). But apparently, it's not suited for some substances (cited from this paper, section 6.2, page 12):


  The elements that are
  not usually determined by ICP/OES fall into three basic
  categories. The ﬁrst category includes those elements
  that occur either as trace contaminants in the argon gas
  used in the ICP/OES ($C$ from $CO_2$), constituents of the
  sample solvent ($C$, $O$, $H$), or as contaminants from the
  environment or atmosphere ($N$ for example). The second
  category encompasses those elements that require high
  excitation energy, such as the halogens. These elements
  could be determined with poor LOD, however. The third
  category is the family of short-lived radioactive elements
  that are commonly determined by $\gamma$-ray spectrometry.


So, apparently, when I'm working with, say carbon-based fuels, and I want to determine $C$ contents, ICP-OES would not be the method of choice, at least not the standard variety. So, what else would be the typical choice? Or are there modifications to ICP-OES, such as using very pure $Ar$, or $He$, as the plasma gas and sealing the plasma chamber from the atmosphere?
For N:

Total N = N from NO2 + N from NO3 + Total Kjeldahl N

The methods from here are:

Liquid Chromatography: NO2, NO3

Specific electrodes: NO3, Kjeldahl

Spectrophotometry: NO2

This for water including wastewater. I don't know the aplicability for other samples.

Also ICP-MS is worth researching.