Application Areas of Pure Water/Ultrapure Water

Currently, pure water is mainly used in two major areas:

1. Life Science Applications

2. Analytical and Routine Applications

Life Science Applications

These mainly include: bacterial cell culture, clinical biochemistry, electrophoresis, electrophysiology, enzyme-linked immunosorbent assay (ELISA), endotoxin analysis, histology, hydroponics, cellular immunochemistry, mammalian cell culture, media preparation, microbial analysis, molecular biology, monoclonal antibody research, plant tissue culture, radioimmunoassay, etc.

Analytical and Routine Applications

These mainly include: water supply for distillation systems, steam generators, glassware cleaning, sample dilution and reagent preparation, ultrapure water system supply, solid-phase extraction, general chemistry, electrochemistry, spectrophotometers, TOC analysis, water quality analysis, ion chromatography, flame atomic absorption spectrometry (Flame-AAS), graphite furnace atomic absorption spectrometry (GF-AAS), high-performance liquid chromatography (HPLC), liquid chromatography-mass spectrometry (HPLC-MS), intra-inductively coupled plasma atomic emission spectrometry (ICP-AES), inductively coupled plasma mass spectrometry (ICP-MS), trace metal detection, gas chromatography-mass spectrometry (GC-MS), etc. Several key applications requiring extremely high water purity:

Electrophoresis:

The most important requirement for water used in electrophoresis is the removal of bioactive substances such as endotoxins (typically less than 0.05 Eu/ml), ribonucleases, and proteases (not measurable). Ideally, ultrapure water with a resistivity of 18.2 MΩ·cm, TOC <10 ppb, a pore size of 0.1 μm or smaller, and a bacterial content below 1 CFU/ml should be used as the supply water.

Endotoxin Analysis:

Water used in various applications, from separation to cell culture, requires specified endotoxin levels, with maximum endotoxin levels ranging from 0.25 IU/ml to 0.03 IU/ml. For endotoxin analysis, ultrapure water with low endotoxin levels is suitable, typically 0.05 IU/ml or less. Ultrafiltration is essential for producing ultrapure water with low endotoxin levels (internationally, ultrafiltration membranes with an MWCO of 5000 Daltons are commonly used), and it can be combined with photo-oxidation methods such as UV.

Stone Furnace Atomic Absorption Spectrometry (GF-AAS):

GF-AAS differs from other atomic absorption spectrometry methods in that its flame furnace is replaced by an electronically heated graphite tube or rod, achieving very high sensitivity in elemental analysis. GF-AAS requires a top-purity water system providing ppt-level impurities, a resistivity of 18.2 MΩ·cm, and low TOC levels. Built-in monitoring ensures purity; the final water quality indicators are achieved through a good pretreatment system, continuous circulation, and ultrapure water purification.

Inductively Coupled Plasma Spectrometry (ICP-AES):

In ICP-AES applications, sensitivity varies significantly for different elements, but the detection limits for metals, transition metals, phosphorus, and sulfur are all within the ppb range. ICP-AES has very strict requirements for water purity; ultrapure water with a resistivity greater than 18 MΩ·cm is essential. TOC requirements are generally less important; pretreatment requires reverse osmosis or ion exchange.

Inductively Coupled Plasma Mass Spectrometry (ICP-MS):

ICP-MS can be used to determine elements at the ppt level. For this sensitive ICP-MS analysis, water purity requirements are extremely stringent, demanding impurities at the ppt level, a resistivity of 18.2 MΩ·cm, and a low TOC. The final water quality specifications are achieved through a robust pretreatment system, continuous circulation, and ultrapurification of the water.

Mass Spectrometry:

Mass spectrometry enables trace analysis of mixtures. Due to its high sensitivity, it requires water of the highest purity. All sample preparation and pretreatment, such as solid-phase extraction, requires ultrapure water. Impurities in the water must be at the ppt level. For organic matter analysis, a resistivity of 18.2 MΩ·cm and a very low TOC are required, typically less than 3 ppb.

Trace Metal Detection:

Advanced modern analytical instruments continuously improve analytical sensitivity. Trace elements can now be determined at ppt and sub-ppt levels using techniques such as ICP-MS. Trace analysis requires pure water free of measurable components, and the water quality requirements are suitable for the most stringent and sensitive ICP-MS operations. Therefore, blank reagents, standard dilutions, and sample preparation all require ultrapure water of the highest purity, and may even necessitate operations in a cleanroom.

With technological advancements, an increasing number of applications are demanding even higher purity ultrapure water.