This paper discusses three problems linked to how to be more accurate for quantitative analysis from the perspective of the analyst in order to perform trace-level analysis of semi-volatile organic pollutants, such as organochlorine pesticides (OCPs), ploychlorinated biphenyls (PCBs) and polycyclic aromatic hydrocarbons (PAHs) in groundwater. These are namely: 1) drawing a calibration curve in one order of magnitude; 2) thoroughly preparing reference materials; and 3) avoiding false positives and false negatives. This paper analyzed one by one for the sources of these important problems, which were often overlooked, and discussed how to draw calibration curves, outlines for reference materials preparation, how to find and avoid false positive and false negative, and how to improve service quality and save cost.