Tetraethylammonium contains an impurity which alkalizes cytoplasm and reduce calcium buffering in neurons

Commercial tetraethylammonium chloride contains about 5% of the impurity triethylamine. External triethylamine raises cytoplasmic pH, which reduces the intracellular calcium concentration transient following calcium influx during membrane depolarization. The calcium influx is unaffected, so the cell's ability to buffer calcium transients is reduced. Purified tetraethylammonium does not have these effects.