油脂中不皂化物即油脂皂化时,与碱不起作用,不溶于水的物质,包括在甾醇,脂溶性维生素和色素等。
(一) 仪器和用具
锥形瓶:250ml;冷凝管; 恒温水浴锅;电炉;分液漏斗:250ml;量筒:50ml;索氏提油器;电热恒温箱;烧杯、试剂瓶等;天平:感量0.0001g。
(二) 试剂
1.0 N氢氧化甲乙醇溶液;0.5N氢氧化钾水溶液;乙醇、乙醚;中性乙醚乙醇混合液(2:1)。
(三) 操作方法
称取混匀试样5g(W)注入锥形瓶中,加1.0NKOH乙醇溶液50ml,连接冷凝管,在水浴锅上煮沸约30min,煮到溶液清澈透 明为止。用50ml蒸馏水将皂化液转移入分液漏斗中,加入50ml乙醚,趁温热时猛烈摇动1min后,静止分层。将下层皂化液放
第二只分液漏斗中,每次用50ml乙醚提取两次。合并乙醚提去液,加水20ml轻轻旋摇,待分层后,放出水层,每次再加水20ml猛烈摇动洗涤两次。
先后用0.5NKOH水溶液和水各20ml,充分振摇洗涤一次,如此再洗涤两次。最后用水洗至加酚酞指示剂时不显红色为止 。
用索氏抽提器回收乙醚,将抽提瓶中的残物在105℃温度下烘1h,冷却称重,再烘30min,直至恒重为止。将称重后的残留物溶于30ml中性乙醚乙醇中,用0.02N氢氧化钾滴定至粉红色。
(四) 结果计算
油脂中不皂化物含量按公式3-32计算:
不皂化物(%)=W1-0.28VN / W×100
式中:W1—残留物重量,g; W—试样重量,g; V—滴定所消耗的氢氧化钾溶液体积,ml; N—氢氧化钾溶液的当量浓度;0.28—每毫克当量的油酸重量,g。双试验结果允许差不超过0.2%,求其平均数,即为测定结果。测定结果取小数点后第一位。
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