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用氟硼酸根离子选择电极作指示电极,以 AgNO_3回滴过量的四苯硼化钠(NaBPh_4)测定钾或用四苯硼化钠直接滴定钾。由于卤族元素及铵离子的存在,限制了其使用范围。为了快速测定 KNO_3-NH_4Cl 样品中的钾,我们研究了在样品中加入甲醛,消除铵的干扰;在 pH10的磷酸盐缓冲溶液中,同样用氟硼酸离子选择电极作指示电极,以溴化十六烷基三甲铵(CTMAB)滴定过量四苯硼化钠测定钾。操作步骤:吸取 KNO_3-NH_4Cl 溶液10ml(钾含量为6～9mg)于50ml 容量瓶中,加入3ml 甲醛,1滴酚酞指示剂,用20%NaOH 调至红色,并过量两滴,再加入10mlpH10磷酸钠缓冲液和25ml 0.01M NaBPh4,标准液,稀释至刻度、摇匀。经10分钟后,进行于过滤,移取25ml 滤液置于100ml 烧杯中,稀释至约50ml。
Using fluoroborate ion selective electrode as the indicator electrode, titration of potassium with sodium tetraphenylborate (NaBPh_4) by titration with AgNO_3 excess or direct titration with sodium tetraphenylborate. Due to the presence of halogen elements and ammonium ions, their use is limited. In order to quickly determine potassium in KNO_3-NH_4Cl samples, we studied the addition of formaldehyde to the samples to eliminate the interference of ammonium. In pH10 phosphate buffer solution, the fluoroborate ion-selective electrode was also used as the indicator electrode. Alkyl trimethylammonium (CTMAB) titration excess potassium tetraphenylborate determination of potassium. Operation steps: Pipette 10ml of KNO3-NH4Cl solution (potassium content is 6 ~ 9mg) in a 50ml volumetric flask, add 3ml of formaldehyde, 1 drop of phenolphthalein indicator, adjusted to red with 20% NaOH, and excess two drops, then add 10mlpH10 phosphoric acid Sodium buffer and 25ml 0.01M NaBPh4, standard solution, diluted to the mark, shake well. After 10 minutes, filtration was carried out. Pipette 25 ml of the filtrate into a 100 ml beaker and dilute to about 50 ml.