Challenges in Compound identification. The presence of isobars, isomers, and in source fragments complicate the identification of chemicals in HRMS data, sometimes even leading to these analytes to be excluded from HRMS analysis. Several cases tramadol (due to tramadol's higher metadata scores). Using standards, the first peak (12.2 min) was ultimately assigned to be O-desmethylvenlafaxine, while the second peak (12.4 min) was tramadol. In order to quantify both compounds, the peaks had to be manually integrated to avoid integrating the two peaks as one compound.