How should the LLOQ for total Xylenes be reported, i.e., a sum of the LLOQ for the 3 isomers?
Unless a separate integration for total xylenes is performed, the xylene isomer LLOQs should be added together. Similarly, when reporting total xylenes, the results of m&p xylene and o-xylene should be added together.
It is important to point out that m- and p-xylene are difficult to chromatographically separate under the conditions described in methods 8015 and 8260, while separation of the o-xylene peak from m+p-xylenes is easier to achieve. If both m- and p-xylenes are present in a mixed stock solution at the same concentration, then the calibration range for the peak representing m- and p-xylene would be twice as high as for other target analytes. Along with their corresponding lower limit of quantitation (based on the low standard concentration).
Other category: 8000 Series