Critical examination of the quantification of aromatic compounds in three standard reference materials

Three standard reference materials from the National Institute of Standards and Technology (NIST), namely, SRM 1597 coal tar, 1582 crude oil, and 1580 shale oil, were investigated in detail to determine the concentration of polycyclic aromatic sulfur heterocycles using gas chromatography with the atomic emission detector in the carbon- and sulfur-selective modes. Coelution problems were found to be common, and the use of two capillary gas chromatographic columns with stationary phases of widely differing polarity was necessary for the separation of the important analytes phenanthrene, anthracene, dibenzothiophene, and the naphthothiophenes. On the commonly used nonpolar stationary phases, phenanthrene and dibenzothiophene coelute with the isomeric naphthothiophenes and this leads to too high concentrations being measured for the two major analytes and must be corrected for. For (sulfur and oxygen) heterocycles, individual response factors must be used if the flame ionization detector is employed. The NIST values were obtained without regard to those factors. This is done here for the three SRMs, and it is shown that the adjusted NIST values agree very well with the GC/AED values. It is suggested that the (noncertified) NIST values for several polycyclic aromatic compounds (PACs) should be reexamined. Very probably many other determinations of PACs might suffer from the same shortcomings.