Tested substances Tested substances to analyte ratio (w/w) K+ 16000 Na+ 4000 Al3+ 1 Mg2+ 50 Zn2+ 10 Fe3+ 2 Cu2+ 0.5 Cl- 6000 NO3- 50 Glucose 1500 Sucrose 2000 Glycine 500

Table 1: Tolerance limits of interfering substances.