Liquid chromatography mass spectrometry (LC-MS) combined with high performance liquid chromatography (HPLC) or ultra high performance liquid chromatography (UHPLC) for rapid separation And the extremely sensitive analytical capabilities of mass spectrometry are indispensable tools in research. In practical use, the purity requirements for standards, organic solutions or other mobile phases are of the highest level. However, what is often overlooked by researchers is that if the water quality of ultrapure water is not good or the pure water system is not working properly, it will also have an adverse effect on LC-MS.
Effect of pollutants in water on LC-MS
Organic contaminants can have a series of serious consequences when the mobile phase is contaminated with organic matter. First, contaminants may compete with the analyte for binding sites, which may cause the analyte to be unbundled and washed out, reducing signal intensity or extending retention time. Ultimately, the sensitivity and accuracy of the analytical method are reduced.
Organic pollutants will also accumulate on the surface of the column. As the number of experiments increases, the contact between the analyte and the column will become more and more difficult. In addition to causing the background value to rise, affecting the resolution, too much Organic contaminants can make the sample difficult to pass, resulting in excessive pressure, causing damage to the column or instrument.
When there are too many organic contaminants, it will mix with the solvent to form a new mobile phase, causing unpredictable changes in the way the analyte or column is combined or moved, resulting in a shift in residence time or a tailing peak ( Peaking tailing).
Bacteria Bacteria secrete enzymes, endotoxins or other organic substances that have the same effects on LC-MS as organic pollutants.
Ion (salt) ion contamination can cause changes in the ionic strength of the solvent. If it is contaminated with sodium and potassium ions, it is more likely to form adducts with the analyte and interfere with the mass spectrometry at the back end.
If there are many colloids or particulate matter in the colloids and partsiculates , the pipeline will become blocked, so that the pump needs to operate under a large pressure, which will cause damage to the pump in the long run. Colloidal and particulate matter can also clog the column, and a small amount of blockage can have a serious impact on LC-MS operating at very high pressures.
How to remove organic pollutants from water
Among the four major pollutants mentioned above, we can find that organic pollutants account for two of them. In the application of LC-MS, we also pay special attention to the removal of organic pollutants. Let’s take a look at how to remove organic Removal of contaminants.
Activated carbon can utilize its broad surface area and active functional groups to adsorb organic pollutants. It is recommended to use fully synthetic refined activated carbon. The particles are fine and uniform, and the removal effect of organic pollutants is better.
The dual-wavelength UV lamp emits light at both 185 and 254 nm wavelengths, wherein 185 nm of light oxidizes oxygen molecules in the water to form hydroxyl radicals and further oxidizes the organics to form carbon dioxide. Light at 254 nm can also destroy bacterial DNA and inhibit its metabolism.
The organic pollutants in the active circulation environment tend to accumulate in the stationary water, so the water is allowed to flow in the pipeline at regular intervals, and the UV irradiation can effectively reduce the organic pollutant content in the water.
TOC - Indicator of organic pollutants in water
Scientifically choose to use "total organic carbon" to express the concentration of total organic matter in water. The total organic carbon is Total Organic Carbon, which is prefixed with three words TOC to represent the carbon concentration of organic matter in water. The TOC measurement method usually uses photooxidation or chemical oxidation to oxidize the carbon in the organic matter in the water, immediately turns it into carbon dioxide, and then measures the amount of carbon dioxide added, which makes it easy to calculate the TOC in the water.
How many TOC waters do you need to experiment to qualify? In general, we recommend using <5ppb of ultrapure water for LC-MS sample preparation, tubing and column cleaning to reduce background in water. Value (Figure 1).
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Figure 1 HPLC experiments using TOC < 5 ppb of ultrapure water, to a lower background value.
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