Organic Matter in Water Prepared by Laboratory Pure Water

Laboratory-grade purified water plays a crucial role in molecular biology research. Key indicators for measuring purified water include resistivity, total organic carbon (TOC), bacteria, and pyrogens. Among these, TOC content directly affects experimental results and reproducibility, and can damage the reverse osmosis membrane and resin function of the purified water system, increasing bacterial growth. To ensure that organic matter levels in the water remain within experimental requirements, researchers need to monitor the TOC in the laboratory purified water system. TOC monitoring must provide reliable and accurate parameters to ensure that researchers' experiments are not affected by organic matter.

Organic Matter in Water

Organic matter in raw water can be generated naturally or anthropogenically. Naturally generated organic matter can be produced by decaying plants or acidic liquids. In addition, bacteria, organisms, and their byproducts can all increase organic matter in water. Anthropogenically added organic matter includes industrial and household fertilizers, such as detergents, solvents, oils, chemical fertilizers, and pesticides. While filters remove impurities from the water, plastic pipes and water tanks can increase organic matter. Other treatments such as chlorination and ozone systems can also increase organic matter in the water.

Impurities in raw water can be treated using methods such as reverse osmosis, microfiltration, ion exchange, adsorption, and ultraviolet light. Most impurities can be removed using one or more of these methods, but what is the relationship between total organic carbon (TOC) and these impurities?

Total Organic Carbon (TOC)

TOC is divided into particulate organic carbon (POC), dissolved organic carbon (DOC), and volatile organic carbon (VOC). Online monitoring of TOC does not differentiate between POC/DOC/VOC. Although TOC does not provide an accurate combination of organic matter, it is the closest indicator of organic matter content, thus ensuring that the TOC in the water remains below the experimental requirements. Once the TOC content in the water reaches the threshold, online monitoring can promptly alert the user.

Ideally, monitoring should provide fast, highly sensitive, and low-cost online monitoring. To achieve this, let's first look at different methods of monitoring organic carbon.

All online monitoring systems operate on the same fundamental principle: pure water passing through a 185 nm wavelength ultraviolet lamp oxidizes organic matter. This oxidation process converts organic carbon into carbon dioxide, which in turn increases the water's conductivity. The total organic carbon (TOC) parameter can then be measured from this conductivity change. Laboratory TOC systems, compared to industrial systems, produce less water; therefore, they need to continuously display the TOC value before water production to ensure that users' experiments are not affected by organic matter.