Ultrapure Water Purification Methods Suitable for Organic Analysis (HPLC, LC/MS)

HPLC is frequently used for the analysis of various organic substances. When combined with mass spectrometry (MS), it forms LC/MS, enabling the analysis of extremely small quantities.

Ultrapure water is used for mobile phase preparation, standard solution preparation, and as a blank experiment. Organic matter in the ultrapure water used in experiments can cause background noise and interfere with the analytical results. When the organic matter content of different ultrapure waters was detected by HPLC (with UV detection), the results showed a positive correlation between the organic matter content and the absorption background value (Figure 1).

At this point, ultraviolet light (wavelength 185 nm) can be used to reduce the organic matter content. The oxidized and decomposed organic matter exists in the water in ionic form and can be removed using ion exchange resins in subsequent purification processes (Figure 2). Therefore, ultraviolet light can be used in the purification process to significantly reduce the concentration of total organic matter (TOC) (Table 1).

Table 1. Effect of UV lamps on reducing TOC

LC/MS is a highly sensitive system that uses liquid chromatography to separate analytes and then uses ionization analysis to determine their mass. Therefore, the organic content of the purified water used is subject to very strict requirements. A comparative analysis of the spectra of four synthetic bactericides was performed using ultrapure water irradiated with ultraviolet light.

 
The results showed that the standard solution prepared using ultrapure water irradiated with ultraviolet light yielded stable and low background values and symmetrical, non-overlapping peaks. In contrast, the analysis results using ultrapure water without ultraviolet irradiation showed excessively high background values, causing overlap with the target components and resulting in incorrect analysis. Therefore, these results confirm that ultrapure water purified using an ultrapure water system equipped with a UV lamp is suitable for trace organic matter analysis using LC/MS.