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5种常见水分测定仪器的原理

内容摘要:1.卡尔费休水分测定仪:  卡尔费休法简称费休法,是1935年卡尔费休(KarlFischer)提出的测定水分的容量分拆方法。卡费休法是测定物质水分的各类化学方法中,对水最为专一、最为准确的方法。虽属经典方法但经过近年改进,提高了准确度,扩大了测量范围,已被列为许多物质中水分测定的标准方法。  卡费休法属碘量法,其基本原理是利用碘氧化二氧化硫时,需要—定量的水参加反应:  12十S02十2H2O=2HI十H2SO4  上述反应是可逆的。为了使反应向正方向移动并定量进行,须加入碱性物质。实验证明,

1.卡尔费休水分测定仪:

  KAERFEIXIUFAJIANCHENGFEIXIUFA,SHI1935NIANKAERFEIXIU(KarlFischer)TICHUDECEDINGSHUIFENDERONGLIANGFENCHAIFANGFA。KAFEIXIUFASHICEDINGWUZHISHUIFENDEGELEIHUAXUEFANGFAZHONG,DUISHUIZUIWEIZHUANYI、ZUIWEIZHUNQUEDEFANGFA。SUISHUJINGDIANFANGFADANJINGGUOJINNIANGAIJIN,TIGAOLEZHUNQUEDU,KUODALECELIANGFANWEI,YIBEILIEWEIXUDUOWUZHIZHONGSHUIFENCEDINGDEBIAOZHUNFANGFA。

卡尔?费休水分测定法是一种非水溶液中的氧化还原滴定法, 其滴定的基本原理是碘氧化二氧化硫时需要一定量的水参与反应,化学反应方程式如下:

I2+SO2+2H2O 2HI+H2SO4 2-1

I2+SO2+H2O+3RN+R1OH 2RNHI+RNSO4R1 2-2

上述反应是可逆的。为了使反应向正方向移动并定量进行,须加入碱性物质。实验证明,吡啶是最适宜的试剂,同时吡啶还具有可与碘和二氧化硫结合以降低二者蒸气压的作用。因此,试剂必须加进甲醇或另一种含活泼OH基的溶剂,使硫酸酐吡啶转变成稳定的甲基硫酸氢吡啶。

卡尔费修试剂中含有分子碘而呈深褐色,当含有水的试剂或样品加入后,由于化学反应,生成甲基硫酸化合物(RNSO4R1)而使溶液变成黄色,由此可用目测法判断终点,即由浅黄色变成橙色.但是目测法误差教大而且在测定有颜色的物质时会遇到麻烦。 国家标准大都规定用“永停法”来判定卡氏反应的终点,其原理为:在反应溶液中插入双铂电极,在两电极之间加上一固定的电压,若溶剂中有水存在时,则溶液中不会有电对存在,溶液不导电,当反应到达终点时,溶液中存在 I2 I-电对,即:

2I- = I2+2e 2-3

因此, 溶液的导电性会突然增大, 在设有外加电压的双铂电极之间的电流值突然增大,并且稳定在我们事先设定一个信息值上面,即可判断到了滴定终点,机器便会自动停止滴定,从而通过消耗卡尔费休试剂的体积计算出样品的含水量。

卡尔费试剂的组成

I2

二氧化硫 SO2

溶剂 甲醇

有机碱 吡啶(咪唑)

 

影响卡尔费休的几个因素

无水甲醇作为样品的溶解剂,适用范围很广。一般的有机化合物、饱和或不饱和的碳氢化合物以及一般的无机化合物、酸性氧化物、部分有机和无机的盐都能适用。

但是部分酮和醛类样品不能用甲醇反应。如发现反应不能中断,无终点,反应连续进行时,应该考虑到是否有副反应这个问题。当产生副反应时,其实只需要几分钟的反应,却一直进行。此时可用乙二醇甲醚代替甲醇。
PH值过高、样品碱性过高等,也会引起副反应,即连续反应,而无终点出现。此时,PH值过高可用缓冲溶液调节PH值,碱性过高加入甲苯酸、水杨酶,可缓和碱性溶液,但不能用醋酸。

与碘发生反应的化合物不能用卡尔费来测试。

 

影响卡尔费休试剂浓度变化的主要有以下几个原因 :

? DIDINGJIDEHUAXUEWENDINGXINGHENDI,QIZHONGDEDIANHEERYANGHUALIUDOUSHIHENHUOPODEWUZHI,RONGYIHEQITAWUZHIFASHENGFAYING。

? DIDINGJIYIYOUJIHUIJIUHUIXISHOUKONGQIZHONGDESHUIFENERSHIZIJIDENONGDUJIANGDI,YINWEIQIZHONGDEJIACHUNXISHUIXINGJIQIANG。

? YINWEIRONGJIZHONG90%DEWUZHIWEIJIACHUNHUOYICHUN,SUOYIKFSHIJIZHONGCHUNDEMIDUDUIWENDUDEBIANHUAHENMINGAN,WENDUDEYIDIANSHENGGAOJIANGYINQISHIJINONGDUDEJIJUXIAJIANG,WENDUSHENGGAO1SHESHIDU,KEYISHINONGDUXIAJIANG0.1%。

? JISHIZHUANGSHIJIDERONGQIMIFENGCHENGDUFEICHANGHAO,SHIJIZHONGGEZUFENJIANRENGKENENGFASHENGFANYING。



  2.红外水分仪:


  HONGWAIXIANJIAREJILI:DANGYUANHONGWAIXIANFUSHEDAOYIGEWUTISHANGSHI,KEFASHENGXISHOU、FANSHEHETOUGUO。DANSHI,BUSHISUOYOUDEFENZIDOUNENGXISHOUYUANHONGWAIXIANDE,ZHIYOUDUINEIXIEXIANSHICHUDIANDEJIXINGFENZICAINENGQIZUOYONG。SHUI,YOUJIWUZHIHEGAOFENZIWUZHIJUYOUQIANGLIEDEXISHOUYUANHONGWAIXIANDEXINGNENG。DANGZHEIXIEWUZHIXISHOUYUANHONGWAIXIANFUSHENENGLIANGBINGSHIQIFENZI,YUANZIGUYOUDEZHENDONGHEZHUANDONGDEPINLVYUYUANHONGWAIXIANFUSHEDEPINLVXIANGYIZHISHI,JIRONGYIFASHENGFENZI、YUANZIDEGONGZHENHUOZHUANDONG,DAOZHIYUNDONGDADAJIAJU,SUOZHUANHUANCHENGDERENENGSHINEIBUSHENGGAOWENDU,CONGERSHIDEWUZHIXUNSUDEDAORUANHUAHUOGANZAO。


  YIBANDEJIAREFANGFASHILIYONGREDECHUANDAOHEDUILIU,XUYAOTONGGUOMEIZHICHUANBO,SUDUMAN,NENGHAODA,ERYUANHONGWAIXIANJIARESHIYONGREDEFUSHE,ZHONGJIANWUXUMEIZHICHUANBO。TONGSHI,YOUYUFUSHENENGYUFARETIWENDUDE4CIFANGCHENGZHENGBI,YINCI,BUJINJIEYUENENGYUANERQIESUDUKUAI、XIAOLVGAO。CIWAI,YUANHONGWAIXIANJUYOUYIDINGDECHUANTOUNENGLI,YOUYUBEIJIAREGANZAODEWUZHIZAIYIDINGSHENDUDENEIBUHEBIAOCENGFENZITONGSHIXISHOUYUANHONGWAIFUSHENENG,CHANSHENGZIFAREXIAOYING,SHIRONGJIHUOSHUIFENZIZHENGFA,FAREJUNYUN,CONGERBIMIANLEYOUYUREZHANGCHENGDUBUTONGERCHANSHENGDEXINGBIANHEZHIBIAN,SHIWUZHIWAIGUAN、WULIJIXIEXINGNENG、LAODUHESEZEDENGBAOCHIWANHAO。


  HONGWAIXIANSHUIFENCEDINGYIZHUYAOYOUHONGWAIFUSHEJIAREQIHEDIANZITIANPINGQUEDINGQIJINGDUHEWENDINGXING.


  (HONGWAIFUSHEJIAREQI:WUSIZHENKONGGUANKEFUSHEJINHONGWAIXIAN,TANHUAGUISHUZHANGBOZHANGDEYUANHONGWAIFUSHEJIAREQI,SHIYINGBOLIHETAOCIHONGWAIJIAREQINENGFUSHEZHONGHONGWAIXIAN)


  HONGWAIXIANSHUIFENCEDINGYISHUIFENCEDINGJIZHUNDEGONGRENBIAOZHUNCEDINGFADE「GANZAOJIANLIANGFA」JIQILEISIDEJIAREGANZAO、ZHILIANGCEDINGDEHONGWAIXIANSHUIFENYI。GONGRENBIAOZHUNCEDINGFADE「GANZAOJIANLIANGFA」YEBEICHENGZHIWEI(105°C?5XIAOSHIFA)、(135°C3XIAOSHIFA)DENG,TONGGUOZAIGANZAOJIZHONGFANGRUYANGPINJINXINGZHANGSHIJIANDEJIAREGANZAO,LAIJINGQUEDECEDINGGANZAOQIANYUGANZAOZHIHOUDEZHILIANGBIANHUA,YICIJISUANCHUSHUIFENLIANG。WEICI,XUYAOCEDINGRENYUANDUISHEBEIHEJISHUFEICHANGJINGTONG。YOUYUCEDINGXUYAOJIAOZHANGDESHIJIAN,YINCIKUAISUCEDINGDALIANGDEYANGPINBIJIAOKUNNAN。SUOYI,DUIYUGAOZHUNQUEDUDEZHENDUIDUOZHONGDUOYANGDEYANGPINJINXINGCEDINGERYAN,CHUHONGWAIXIANSHUIFENJIZHIWAIBUZUOTAXIANG。SUIRANYEYOUYIXIEQITADEDIANQIYIJIGUANGXUEDECEDINGFANGFA,DANSHI,DOUSHUYUXIANDINGCEDINGDUIXIANGDEZHUANYONGYIQI。CONGTONGYONGXINGDEJIAODUERYAN,DOUYUANBUJIHONGWAISHUIFENJI。


  适用范围:可以测定谷物、淀粉、面粉、干面、酿造品、海产品、鱼类加工品、食用肉类加工品、调料、点、心、乳制品、干燥食品、植物油等食品相关物品,药品、矿石砂、焦碳、玻璃原料、水泥、化学肥料、纸、纸浆、棉、各种纤维等的工业制品等。

  3.露点水分仪:


  LUDIANSHUIFENCEDINGYICAOZUOJIANBIAN,YIQIBUFUZA,SUOCEJIEGUOYIBANLINGRENMANYI,CHANGYONGYUYONGJIUXINGQITIZHONGWEILIANGSHUIFENDECEDING。DANCIFAGANRAOJIAODUO,YIXIEYILENGHUANQITITEBIEZAINONGDUJIAOGAOSHIHUIBISHUIZHENGQIXIANJIELUCHANSHENGGANRAO。


  4.微波水分仪:


  WEIBOSHUIFENCEDINGYILIYONGWEIBOCHANGGANZAOYANGPIN,JIASULEGANZAOGUOCHENG,JUYOUCELIANGSHIJIANDUAN,CAOZUOFANGBIAN,ZHUNQUEDUGAO、SHIYONGFANWEIGUANGDENGTEDIAN,SHIYONGYULIANGSHI、ZAOZHI、MUCAI、FANGZHIPINHEHUAGONGCHANPINDENGDEKELIZHUANG、FENMOZHUANGJIZHANCHOUXINGGUTISHIYANGZHONGDESHUIFENCEDING,HAIKEYINGYONGYUSHIYOU、MEIYOUJIQITAYETISHIYANGZHONGDESHUIFENCEDING。


  5.库仑水分仪:


  KULUNSHUIFENCEDINGYICHANGYONGLAICEDINGQITIZHONGSUOHANSHUIFEN。CIFACAOZUOJIANBIAN,YINGDAXUNSU,TEBIESHIYONGYUCEDINGQITIZHONGDEHENLIANGSHUIFEN。RUGUOYONGYIBANDEHUAXUEFANGFACEDING,ZESHIFEICHANGYINNANDESHIQING。DANDIANJIEFABUYIYONGYUJIANXINGWUZHIHUOGONGESHUANGXITINGDECEDING。


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