mid - distillate hydrocarbon fuels , preferably having initial boiling points above 350 ° f ., are separated e . g . by prep - hplc into non - aromatic and aromatic fractions which are used to set 0 % aromatics and 100 % aromatics on an nir spectrophotometer . from nir aromatic band absorbances of unknown samples , their percent aromatics is determined using this two - point calibration and the beer - lambert equation . preferred nir bands of 1650 - 1700 and 2120 - 2256 exhibit excellent correlation with aromatics content . also similar techniques measure sulfur through correlation with the benzothiophenic band and its overtones and combination bands , or possibly directly .