Systems A1 and A2 both fulfilled all defined criteria and may therefore be recommended as generic EME systems for acidic analytes. Based on the data in Figure , the extraction windows of system A1 and A2 were defined as 1.8 ≤ log P ≤ 6.0 and 0.5 ≤ log P ≤ 6.0, respectively. It should be noted that the upper limit was based on one compound (telmisartan, log P = 6.1) and the exact value is therefore uncertain. Within their respective extraction windows, the average extraction recovery was 85.1% and 79.9%. Considering price, the ~10 mg liquid membrane was estimated to cost 0.079 € and 0.024 € for A1 and A2, respectively, which may be considered negligible in the total analysis cost. The analytical merits were very similar in both systems, and the overall loss of liquid membrane to the acceptor phase was also similar. System A1 however operated at almost 3-fold less current than A2. Based on these considerations, for overlapping extraction windows, system A1 is therefore recommended. The recommendation of both systems is limited to substances with an acidity corresponding to pKa ≤ 6.5. For 6.5 < pKa ≤ 9.0, A1 and A2 may be recommended, but the sample and acceptor pH should be re-optimized and any increased dissolution of the liquid membrane should be evaluated (due to phenol on thymol). No generic system can currently be recommended for weak acids with pKa > 9.0, but the authors recommend tri(pentyl) phosphate is a liquid membrane that remains unionized at elevated pH and may be the starting point for method development. Although not recommended as first choice for bases, A1 and A2 may also be applied within the extraction windows mentioned above.