溶解性有机碳对微库仑法测定水中可吸附有机卤素的影响

微库仑法测水样中可吸附有机卤素(AOX)受多种因素影响,其中溶解性有机碳(DOC)的影响非常显著。DOC对微库仑法2种前处理方法(双柱法和振荡法)的影响差异很大。双柱法受DOC影响较小,当DOC浓度小于1 000 mg/L时,AOX加标回收率范围为94.0%~104%。振荡法受DOC影响较明显,随着DOC浓度的升高,AOX回收率持续下降,当DOC浓度达到1 000 mg/L时,AOX加标回收率下降至72.1%,但DOC浓度小于100 mg/L时,AOX加标回收满足方法要求。进一步研究发现,DOC对振荡法的影响主要由于竞争吸附降低了活性炭对AOX的吸附容量,而非吸附速率,虽然增大活性炭用量可在一定程度上减小DOC对AOX测定的影响,但对样品进行稀释是减少DOC影响的最简单高效的办法。同时,DOC对不同类型的有机卤代物影响不同,有机溴受DOC影响程度小于有机氯。

Influence of Dissolved Organic Carbon on the Determination of Adsorbable Organic Halogen in Water by Microcoulometry

The determination of absorbable organic halogen (AOX) in water by microcoulometry is influenced by many factors,among which the influence of dissolved organic carbon (DOC) is very significant.The influence of DOC on two pretreatment methods (column method and batch method) has great differences.The column method is less affected by DOC.When DOC concentration is less than 1000 mg/L,the recovery of AOX ranges from 94.0% to 104%.The batch method is more obviously affected by DOC.With the increase of DOC concentration,the recovery of AOX decreases continuously.When DOC concentration reaches 1000 mg/L,the recovery of AOX drops to 72.1%,but when DOC concentration is less than 100 mg/L,the recovery of AOX can meet the requirements of the method.Further study finds that the impact of DOC on the batch method is mainly due to the competitive adsorption that reduces the adsorption capacity of activated carbon for AOX,rather than the adsorption rate.Although increasing the amount of activated carbon can reduce the influence of DOC on the AOX determination to a certain extent,diluting the sample is the simplest and most efficient way to reduce the influence of DOC.At the same time,DOC has different effects on different types of organic halides,and organic bromine is less affected by DOC than organic chlorine.