【讨论】TOC的测量技术TOC(TC-TIC)和NPOC这两种模式对比，哪种更准确？

根据样品性质，水中含挥发性物质的话用ＴＣ－ＴＩＣ，但如果是测地表水呀，地下水之类的，ＴＩＣ含量很高的话就最好用ＮＰＯＣ＋ＰＯＣ，但如果你只测ＮＰＯＣ的话你的结果肯定是偏小的，因为你把ＰＯＣ给忽略了

If samples with TOC concentrations of 100ug/L or less (such as purified water or ultra-pure water) are measured, NPOC analysis is recommended. Measuring TOC in ULtra-pure water samples by using the difference between TC and IC is prone to large analysis errors for the following reason:

1) The TOC value is significantly affected since a large portion of TC often comprises IC. Errors in TC analysis and IC analysis are additive.

2)CO2 is absorded from the atmosphere during sample collection and analysis.As a result, causing the IC result to be higher than the IC content in the TC result, subtracting the elevated IC result from the TC result yields a biased TOC value.

3) The TOC value can also be greatly influenced if standard solutions are not prepared and measured carefully. Errors are compounded since two calibration curves must be generated for TC and IC.

4) The calibation curves are used in sample analysis by extending a two-point calibration curve through the origin.

5) In NPOC analysis, POC may be volatilized from the sample during sparging for IC removal. This is not problem since the ultra-pure water contains practically no POC.

TC-TIC同NPOC的测试过程有本质不同：TC-TIC过程是测得这两个结果后，自动减除得结果； 而NPOC测试是直接酸化后测出的有机碳结果。
减除法会引入所有测试过程的多种误差（楼上已有总结），理论上这些误差是叠加关系，所以，误差值会比较大，而NPOC测试路径不同，步骤要少很多，所以，同条件下，引入的误差机会会小，但可能会有手工过程，对于POC（吹出性碳）比较高的样品，实际上更适合单测POC的方式，同时要考虑空气中二氧化碳背景问题。
我们采用更好的光度库仑技术，绝值测定法，消除了标准曲线误差问题，并大大提高了检测器的精度。

TOC 的测定
（1）差减法
    TOC = TC – IC （当TOC远高于IC，如废水。）
(2）NPOC法
TOC = POC + NPOC= NPOC（如果 POC 可忽略）
（高灵敏度催化剂，TOC＜500ppb，如纯水；普通灵敏度催化剂，
当IC ＞＞TOC或TC≈ IC时。）
（3）加和法
TOC=POC+NPOC
（当样品中POC不可忽略。）