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浅谈影响卡尔费休测定精度的几个原因

内容摘要:影响测定精度的因素很多,有样品的性质,测定的方法,标定物质的选用,取样方法和进样量的大小等,本文将介绍除上述因素外,还必须注意的其他几个问题。

综述:

YINGXIANGCEDINGJINGDUDEYINSUHENDUO,YOUYANGPINDEXINGZHI,CEDINGDEFANGFA,BIAODINGWUZHIDEXUANYONG,QUYANGFANGFAHEJINYANGLIANGDEDAXIAODENG,BENWENJIANGJIESHAOCHUSHANGSHUYINSUWAI,HAIBIXUZHUYIDEQITAJIGEWENTI。


原因分析:

1、YOUYUKAERFEIXIUDIDINGSHIJIHENRONGYIXISHOUSHUIFEN,YINCIYAOQIUDIDINGJIDIDINGXITONGDEDIDINGGUANHEDIDINGCHIDENGCAIQUJIAOHAODEMIFENGXITONG。FOUZEYOUYUXISHIXIANXIANGZAOCHENGZHONGDIANZHANGSHIJIANDEBUWENDINGHEYANZHONGDEWUCHA。

2、KAERFEIXIUSHIJIDEDIDINGDUDEDAXIAO, GENJUSHIYEHANSHUILIANGDEDUOSHAOLAIJUEDING。ZAICEDINGHANSHUILIANGJIAODADESHIYESHI,KAERFEIXIUSHIJIDEDIDINGDUYINGGAIXUANDEDAYIXIE,ZHEIYANGZAIBAOZHENGCEDINGJINGDU(<5%)DEQIANTIXIA,KEYIJIAKUAICEDINGSUDU。DANZAICEDINGSHIYEHANSHUILIANGJIAOXIAOSHI,KAERFEIXIUSHIJIDEDIDINGDUJIUYINGGAIXUANDEXIAOYIXIEHEDIDINGGUANDEZUIXIAODUSHUXIAOYIXIE, FOUZEJIANGCHANSHENGJIAODADECEDINGWUCHA。RUGUODIDINGGUANDEZUIXIAODUSHUWEI0.01mL,KAERFEIXIUSHIJIDEDIDINGDUWEI2.5mg/mL,ZESHIJIYIDIWUCHAJIANGCHANSHENG0.025mg(25ppm)DECELIANGWUCHA。RUGUOSHIJIDEDIDINGDU1.00mg/mL,ZESHIJIYIDIANWUCHAJIANGCHANSHENG0.015mg(15ppm)DECELIANGWUCHA。

3、KAERFEIXIUDIDINGFACEDINGSHUIDEZHONGDIANPANBIEFANGYOU:

(1).YIKAORENDESHIJUEGUANCHARONGYEYANSETUBIANDEMUSHIFA;

(2).YIKAOGUANCHADIANLIUBIAOPIANZHUANTUBIANZHIYIDINGZHIBINGWENDINGYIDUANSHIJIANRU60MIAOZUOWEIDIDINGZHONGDIANDEYONGTINGZHONGDIANFA(YINGJIANDIDING);

(3).YIYONGTINGZHONGDIANFAYOUCHENGWEISITINGZHONGDIANFAWEIJICHU,WEIJIZIDONGKONGZHIDERUANJIANDIDINGSANZHONGFANGFA。

MUSHIZHONGDIANFASHIZHISHIZHONGDIANZUIJIANDANYIZHONGFANGFA,KEYISHENGQUDIDINGYIZHONGDEZHISHIXITONGZHUANGZHI,ZAICHANGLIANGDIDINGZHONGKEYIHUODEBIJIAOMANYIDECEDINGJIEGUO,DANZAIHAOKEDANGLIANGYIXIAWUZHIDECEDINGZHONG,ZHEIZHONGFANGFADELINGMINDUHEZHUNQUEDUBIJIAOCHA, YIBANDOUCAIYONGBIJIAOLINGMINDEDIANHUAXUEFANGFA。DIERZHONGYUDISANZHONGFANGFADOUSHIDIANHUAXUEFANGFA,TAYOUKUAISU、LINGMINERQIEZHUNQUEDUYOUBIJIAOGAO,YISHIXIANZIDONGHUADENGYOUDIAN,TONGCHANGKECEDINGGELEIYANGPINZHONGJIGEppmDAOBAIFENZHIJISHIDESHUIFEN。

4、DIDINGSHIJIDEDIDINGTOUDEJIEGOUYUWEIZHIYESHIDIDINGWUCHADEYIGEFEICHANGZHONGYAODEYINSU。TONGCHANGYAOQIUDIDINGTOUNEIJINGHEDIDINGTOUYAOZUODEHENXI,MUDEFANGZHIDIDINGJIDEGUADIXIANXIANG,BAOZHENGCELIANGJINGDU。ZAIDIDINGTOUCHARUYANGPINRONGYEZHONGSHI, DIDINGTOUDEYEJIECHUYOUKENENGFASHENGHUAXUEFANYINGERYINGXIANGCEDINGJINGDU。

5、ZAIDIDINGSHIJIAOBANYAOJUNCHONGFENQIEJUNYUN。ZAIDIDINGZHANDUJIAODADEYANGPINRONGYESHIGENGYAOZHUYIJIAOBANDECHONGFENHEYIZHI, BAOKUOCILIJIAOBANQIDESUDUYAOYIZHIHEDIDINGCHIZHONGDEYEMIANGAODUDATIXIANGTONG,ZHEIYANGCAINENGDEDAOJIAOHAODECEDINGJINGDU。

6、ZAIJINYANGSHI,YAOFANGZHIZHUSHEQITOUSHOUWAIJIEDEWURANERYINGXIANGCEDINGJIEGUO,RUCAOZUOZHEHUQIHECAZHUSHEQITOUSHIDEWURANDENG。TONGSHIYAOFANGZHIJINYANGSHIYANGPINDESUNSHI, RUZHUSHEQITOUSHANGDEGUADIHEJIANDAOCELIANGCHIBIHUODIANJIGANSHANG。

7、卡尔费休试剂瓶进气口要安装干燥器, 以防止试剂吸收空气中的水分而使试剂的滴定度下降造成严重的测定误差。(干燥

8、ZAIJINXINGKAERFEIXIUDIDINGGUOCHENGZHONG,YOUSHIHUICHUXIANTIQIANDAODAZHONGDIANXIANXIANG,ZAOCHENGCEDINGJIEGUOPIANDI。TEBIEZAICEDINGDINONGDUHANSHUILIANGDEYANGPINSHIYINGXIANGGENGDA,SHENZHIWUFAJINXINGCEDING。ZHEIZHUYAOSHIKONGQIZHONGDEYANGJIANGDIDINGCHIZHONGDEDIANLIZIYANGHUAWEIDIAN, CONGERJIANSHAOLESHIJIDEHAOYONGLIANG。TAIYANGGUANGYEHUIMINGXIANDICUJINYANGYUDIANLIZIDEYANGHUAFANYING,DUISHIJIYAOCAIQUBIGUANGCUOSHI。LINGWAISHIJIDEZUCHENGHECAOZUOHUANJINGDUIZHEIGEFANYINGDESUDUYOUYIDINGDEYINGXIANG。RUKAERFEIXIUSHIJIZHONGERYANGHUALIUGUOLIANG,SHIJIBUCHUN,PEIZHISHIJIDEHANSHUILIANGGUOGAODENGDOURONGYIFASHENGZHONGDIANTIQIANXIANXIANG。

9、卡尔费休法测水反应中会生成硫酸,当它的浓度高于0.05%时可能发生逆反应,影响测定结果。而吡啶能与这个反应所产生的酸化合,保证化学反应向一个方进行。在滴定测水中,如果没有甲醇共存时,则水或其它任何含活泼氢的化合物都能代替甲醇中间化合物发生反应,这样就会扰乱化学反应的化学计量,使这个反应对水没有特殊的选择性。因此在测定过程中要注意到试剂和滴定底液中是否有足够的吡啶和甲醇量。(甲醇含量

10、在用卡尔费休法测定试样含水量时, 要注意被测定的试样中是否有能与卡尔费休试剂生成水的物质, 如有这类物质应分别采取相应的措施才能得到满意的结果。如活泼的醛和酮与卡尔费休试剂中的甲醇反应生成缩醛和缩酮与水消耗碘,使滴定反应达不到终点。有时在分析含酮样品中水分时,减少试剂中的甲醇量,增加吡啶含量,可以得到满意的结果。但这种方法不适用于含醛类化合物,曾有人用吡啶作为溶剂减少缩醛形成的比例, 得到了较为可靠的分析结果。金属氧化物和氢氧化物,也能与HI发生反应生成水,可用二甲苯共沸蒸馏或汽化携带法来分离提取样品中的水,然后进行测定。 (醛和酮类试剂

11、能被碘还原者, 如硫醇和硫化氢等能被碘还原使水分析结果偏高。可以用烯烃进行加成反应除去。

12、NENGJIANGDIANHUAWUYANGHUAWEIDIANZHE,BENSHENBEIHAIYUANWEIQINGKUN。RUWUJIHUAHEWUDEGUOYANGHUAWU,GESUANYAN,ERJIATONGHESANJIATIEYANDENGNENGCHANSHENGZHEIYANGDEFANYING,SHICEDINGCHANSHENGWUCHA。

13、一些弱的含氧酸盐,如碳酸盐,硼酸盐主要与HI反应生成水干扰测定。而无机酸和酸性氧化物不干扰测定。氨利用卡尔费休试剂直接滴定时会形成碘化氮,可以在滴定前加过量的醋酸以消除这种干扰。

14、LVHUATIEHESHIJIZHONGBAOHANDEHUOXINGLV,RUERLVYIQINGSUANYANKEYIBEIKAERFEIXIUSHIJIZHONGDEHISUOHAIYUAN,ZHEIZHONGGANRAOKEYONGBIDINGHEERYANGHUALIUJIJIACHUNRONGYEYUCHULISHIYANGJIAYUXIAOCHU。ZAISILVHUATANZHONGBAOHANDAYUE1%DEYOULILVYIQINGSUANJIAYAN,DANGHANLIANGZAI0.001%DAO0.1%FANWEINEI,KETONGGUOYIYONGGUODEJIACHUNJIBIDING,ERYANGHUALIURONGYECHULIHOUJINXINGCEDING。

15、硅烷醇和卡尔费休试剂也有定量反应, 这种干扰可通过使用高分子醇和吡啶稀释来防止。


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