This system surveys the stability of a substance in a liquid. Prepares mixtures in desired proportions and sends samples to the detector at certain intervals to measure the quantity and stability of a certain substance. Has a UV/Vis detector with 5 mm light path flow cell. Because some impurities may cause the marker to deteriorate, fuel oil marker is added to ethanol samples in a certain proportion when working with bioethanol. The stability is surveyed with quantification in 6 hour intervals for a 48 hours period. 10 or 20 ml vials can be used for sample preparation. Sampling intervals can be customized and set to minutes, hours or days. While previously prepared samples are waiting to be analyzed, new samples can be added to the sequence list.