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[吃货报道] 不同溶液PH值测试与PH计电极的选择,阔思提供PH计电极

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发表于 2018-7-29 16:40:21 | 只看该作者 回帖奖励 |阅读模式
绿野福利|想申请绿豆的朋友 来这里跟帖哈
<p style="font-family:微软雅黑;font-size:16px;vertical-align:baseline;background-color:#FFFFFF;text-align:justify;">
        <span style="font-family:Arial;vertical-align:baseline;color:#404040;"><span style="font-family:宋体;vertical-align:baseline;">本文将着重揭示</span>PH<span style="font-family:宋体;vertical-align:baseline;">测定中遇到的问题,并介绍电极经过发展后能解决这些问题的特性。大多数情况下,普通电极不能测定的样品</span><span style="vertical-align:baseline;">PH</span><span style="font-family:宋体;vertical-align:baseline;">值现在都可由某些专用的</span><span style="vertical-align:baseline;">PH</span><span style="font-family:宋体;vertical-align:baseline;">电极来完成。</span></span>
</p>
<p style="font-family:微软雅黑;font-size:16px;vertical-align:baseline;background-color:#FFFFFF;text-align:justify;">
        <span style="font-family:Arial;vertical-align:baseline;color:#404040;"><br />
</span><span style="vertical-align:baseline;font-weight:700;"><span style="font-family:Arial;vertical-align:baseline;color:#404040;"><span style="font-family:宋体;vertical-align:baseline;">标准</span>PH<span style="font-family:宋体;vertical-align:baseline;">值的测定</span></span></span><span style="font-family:Arial;vertical-align:baseline;color:#404040;"><br />
</span><span style="font-family:Arial;vertical-align:baseline;color:#404040;"><span style="font-family:宋体;vertical-align:baseline;">实验室测定一般由常规复合</span>PH<span style="font-family:宋体;vertical-align:baseline;">电极来完成。</span><span style="vertical-align:baseline;">&nbsp;</span></span><span style="font-family:Arial;vertical-align:baseline;color:#404040;"><br />
</span><span style="font-family:Arial;vertical-align:baseline;color:#404040;"><span style="font-family:宋体;vertical-align:baseline;">通常需具备下列条件:</span>&nbsp;</span><span style="font-family:Arial;vertical-align:baseline;color:#404040;"><br />
</span><span style="font-family:Arial;vertical-align:baseline;color:#404040;"><span style="font-family:宋体;vertical-align:baseline;">测定范围在</span>PH2<span style="font-family:宋体;vertical-align:baseline;">和</span><span style="vertical-align:baseline;">PH12</span><span style="font-family:宋体;vertical-align:baseline;">间,温度在</span><span style="vertical-align:baseline;">10℃</span><span style="font-family:宋体;vertical-align:baseline;">及</span><span style="vertical-align:baseline;">50℃</span><span style="font-family:宋体;vertical-align:baseline;">间、离子浓度</span><span style="vertical-align:baseline;">0.5</span><span style="font-family:宋体;vertical-align:baseline;">和</span><span style="vertical-align:baseline;">4mol/L</span><span style="font-family:宋体;vertical-align:baseline;">间。而且,被测物是经过缓冲的均匀水溶液。</span></span>
</p>
<p style="font-family:微软雅黑;font-size:16px;vertical-align:baseline;background-color:#FFFFFF;text-align:justify;">
        <span style="font-family:Arial;vertical-align:baseline;color:#404040;"><br />
</span><span style="vertical-align:baseline;font-weight:700;"><span style="font-family:Arial;vertical-align:baseline;color:#404040;"><span style="font-family:宋体;vertical-align:baseline;">低离子浓度样品</span></span></span><span style="font-family:Arial;vertical-align:baseline;color:#404040;"><br />
</span><span style="font-family:Arial;vertical-align:baseline;color:#404040;"><span style="font-family:宋体;vertical-align:baseline;">离子浓度只有或低于几个</span>mmol<span style="font-family:宋体;vertical-align:baseline;">的样品 属于低离子型。这样样品将产生很差的导电性。在低离子样品中液接部会产生增高电阻。该传递电阻会导致参比电解液与被测溶液间的接触问题,进而引发扩散电位。而且,信号会受搅拌的影响。</span><span style="vertical-align:baseline;">&nbsp;</span></span><span style="font-family:Arial;vertical-align:baseline;color:#404040;"><br />
</span><span style="font-family:Arial;vertical-align:baseline;color:#404040;"><span style="font-family:宋体;vertical-align:baseline;">上诉问题可通过使用含环形接地液接部(见图</span>1<span style="font-family:宋体;vertical-align:baseline;">)的电极来解决,该液接部能达到参比电解液和被测溶液间的最佳接触。</span><span style="vertical-align:baseline;">&nbsp;</span></span><span style="font-family:Arial;vertical-align:baseline;color:#404040;"><br />
</span><span style="font-family:Arial;vertical-align:baseline;color:#404040;"><span style="font-family:宋体;vertical-align:baseline;">图</span>1<span style="font-family:宋���;vertical-align:baseline;">:含环形接地液接部的复合电极。</span></span>
</p>
<p style="font-family:微软雅黑;font-size:16px;vertical-align:baseline;background-color:#FFFFFF;text-align:justify;">
        <span style="font-family:Arial;vertical-align:baseline;color:#404040;"><br />
</span><span style="vertical-align:baseline;font-weight:700;"><span style="font-family:Arial;vertical-align:baseline;color:#404040;"><span style="font-family:宋体;vertical-align:baseline;">半含水或者无水溶液</span></span></span><span style="font-family:Arial;vertical-align:baseline;color:#404040;"><br />
</span><span style="font-family:Arial;vertical-align:baseline;color:#404040;"><span style="font-family:宋体;vertical-align:baseline;">在无水溶液(低于</span>5%<span style="font-family:宋体;vertical-align:baseline;">的水)中只可能测得相对</span><span style="vertical-align:baseline;">PH</span><span style="font-family:宋体;vertical-align:baseline;">值。半含水溶液基本上也属于低���子型。如果样品含水量高于</span><span style="vertical-align:baseline;">5%</span><span style="font-family:宋体;vertical-align:baseline;">,则应用</span><span style="vertical-align:baseline;">PH</span><span style="font-family:宋体;vertical-align:baseline;">测定的传统定义,即:所得的数值是绝对值而非相对值。</span><span style="vertical-align:baseline;">&nbsp;</span></span><span style="font-family:Arial;vertical-align:baseline;color:#404040;"><br />
</span><span style="font-family:Arial;vertical-align:baseline;color:#404040;"><span style="font-family:宋体;vertical-align:baseline;">电解液与被测溶液的接触区域(液接部)通常会有相分隔,从而引起信号不稳定。而且,液接部还有沉淀的可能性。当将饱和</span>KCL<span style="font-family:宋体;vertical-align:baseline;">溶液用作参比溶液时很容易发生这类情况。</span><span style="vertical-align:baseline;">&nbsp;</span></span><span style="font-family:Arial;vertical-align:baseline;color:#404040;"><br />
</span><span style="font-family:Arial;vertical-align:baseline;color:#404040;"><span style="font-family:宋体;vertical-align:baseline;">要最大限度的防止这种现象,必须确保电解液和被测样品间具备流动性和相容性。</span>&nbsp;</span><span style="font-family:Arial;vertical-align:baseline;color:#404040;"><br />
</span><span style="font-family:Arial;vertical-align:baseline;color:#404040;"><span style="font-family:宋体;vertical-align:baseline;">将含</span>LiCL<span style="font-family:宋体;vertical-align:baseline;">的乙醇或含</span><span style="vertical-align:baseline;">LiCL</span><span style="font-family:宋体;vertical-align:baseline;">的乙酸用作无水样品的参比电解液能解决上诉问题。</span></span>
</p>
<p style="font-family:微软雅黑;font-size:16px;vertical-align:baseline;background-color:#FFFFFF;text-align:justify;">
        <span style="font-family:Arial;vertical-align:baseline;color:#404040;"><br />
</span><span style="vertical-align:baseline;font-weight:700;"><span style="font-family:Arial;vertical-align:baseline;color:#404040;"><span style="font-family:宋体;vertical-align:baseline;">富含蛋白质的溶液</span></span></span><span style="font-family:Arial;vertical-align:baseline;color:#404040;"><br />
</span><span style="font-family:Arial;vertical-align:baseline;color:#404040;"><span style="font-family:宋体;vertical-align:baseline;">当高浓度的蛋白质与</span>KCL<span style="font-family:宋体;vertical-align:baseline;">参比电解液接触时,它可能会在液接部处沉淀。使用专用电解液能解决这个矛盾。被蛋白质污染的液接部一般可通过几个小时浸泡电极于胃蛋白酶和</span><span style="vertical-align:baseline;">HCL</span><span style="font-family:宋体;vertical-align:baseline;">混合液中而得到的清洁。</span></span>
</p>
<p style="font-family:微软雅黑;font-size:16px;vertical-align:baseline;background-color:#FFFFFF;text-align:justify;">
        <span style="font-family:Arial;vertical-align:baseline;color:#404040;"><br />
</span><span style="vertical-align:baseline;font-weight:700;"><span style="font-family:Arial;vertical-align:baseline;color:#404040;"><span style="font-family:宋体;vertical-align:baseline;">含硫化物的溶液</span></span></span><span style="font-family:Arial;vertical-align:baseline;color:#404040;"><br />
</span><span style="font-family:Arial;vertical-align:baseline;color:#404040;"><span style="font-family:宋体;vertical-align:baseline;">在使用</span>Ag/AgCL<span style="font-family:宋体;vertical-align:baseline;">参比系统时,参比电解液总是含有溶解银。当液接部的溶液银与测定溶液中的硫化物一接触,即有难溶的硫化银产生。硫化银阻塞液接部并使之变成黑色,这便导致缓慢及不稳定的测量信号。</span><span style="vertical-align:baseline;">&nbsp;</span></span><span style="font-family:Arial;vertical-align:baseline;color:#404040;"><br />
</span><span style="font-family:Arial;vertical-align:baseline;color:#404040;"><span style="font-family:宋体;vertical-align:baseline;">在使用含银离子扑捉阱的参比系统的情况下,可选用不含</span>AgCL<span style="font-family:宋体;vertical-align:baseline;">的电解液。受硫化物污染的连接部有时可通过电极侵泡于硫基尿素</span><span style="vertical-align:baseline;">/HCL</span><span style="font-family:宋体;vertical-align:baseline;">溶液中清除物硫化银。</span></span>
</p>
<p style="font-family:微软雅黑;font-size:16px;vertical-align:baseline;background-color:#FFFFFF;text-align:justify;">
        <span style="font-family:Arial;vertical-align:baseline;color:#404040;"><br />
</span><span style="vertical-align:baseline;font-weight:700;"><span style="font-family:Arial;vertical-align:baseline;color:#404040;"><span style="font-family:宋体;vertical-align:baseline;">含氢氟酸的溶液</span></span></span><span style="font-family:Arial;vertical-align:baseline;color:#404040;"><br />
</span><span style="font-family:Arial;vertical-align:baseline;color:#404040;"><span style="font-family:宋体;vertical-align:baseline;">氢氟酸会损坏玻璃膜并且在低浓度时亦可阻碍凝胶层的形成。这会导致测量值的不稳定并缩短电极的使用寿命。氢氟酸只有在</span>PH<span style="font-family:宋体;vertical-align:baseline;">值低于</span><span style="vertical-align:baseline;">5</span><span style="font-family:宋体;vertical-align:baseline;">时才有损伤作用。</span><span style="vertical-align:baseline;">&nbsp;</span></span><span style="font-family:Arial;vertical-align:baseline;color:#404040;"><br />
</span><span style="font-family:Arial;vertical-align:baseline;color:#404040;"><span style="font-family:宋体;vertical-align:baseline;">当总氟离子浓度在</span>0.2g/L<span style="font-family:宋体;vertical-align:baseline;">(</span><span style="vertical-align:baseline;">PH3</span><span style="font-family:宋体;vertical-align:baseline;">;</span><span style="vertical-align:baseline;">20℃</span><span style="font-family:宋体;vertical-align:baseline;">)与</span><span style="vertical-align:baseline;">1g/L</span><span style="font-family:宋体;vertical-align:baseline;">(</span><span style="vertical-align:baseline;">PH1</span><span style="font-family:宋体;vertical-align:baseline;">;</span><span style="vertical-align:baseline;">20℃</span><span style="font-family:宋体;vertical-align:baseline;">)间。有专用电极适合这类应用。当氟离子浓度较高时必须使用锑(</span><span style="vertical-align:baseline;">Sb</span><span style="font-family:宋体;vertical-align:baseline;">)电极及专用参比电极。</span></span>
</p>
<p style="font-family:微软雅黑;font-size:16px;vertical-align:baseline;text-indent:2em;background-color:#FFFFFF;">
        <span style="font-family:宋体;vertical-align:baseline;line-height:32px;">&nbsp; &nbsp; &nbsp; &nbsp;&nbsp;</span>
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        <span style="font-family:宋体;vertical-align:baseline;line-height:32px;"><span style="font-family:&quot;vertical-align:baseline;color:#548DD4;">&nbsp; &nbsp; &nbsp; &nbsp; 上海阔思是您水处理领域小伙伴!</span>&nbsp;</span>
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