Effect of pure water quality on automatic biochemical analyzer and test results

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Water is a very important but easily overlooked reagent in the laboratory. In the process of automatic biochemical analyzer detection, pure water is used as the carrier or medium of biochemical reaction, the dilution solution and solvent of sample or reagent, the cleaning solution of the instrument and the participating reagents of the reaction, and the quality of purification. It is directly related to the credibility of the test results. At present, most of the laboratory laboratories in China use the reverse osmosis central pure water system. Through the analysis of the workflow of the system and the actual situation encountered, Lefeng discovered and summarized several reasons that lead to insufficient water purity and its impact on the detection of automatic biochemical analyzers.

1 Pure water system workflow and influencing factors

1.1 Raw water pretreatment

Raw water refers to tap water entering the laboratory. Pretreatment is to remove most of the impurities in tap water.

1.1.1 Method: Preprocessing generally uses a pre-filter component package, which usually contains the following:

1Deep-filtration filter element filters large particles such as sediment in raw water;

2 activated carbon filter removes most of the organic matter in the water by adsorption, especially the residual chlorine in tap water;

3 softener filter to reduce the concentration of calcium and magnesium ions in water, reducing the hardness of water. If the tap water hardness is low, the softener filter may not be installed.

1.1.2 Influencing factors:

1 Tap water quality: When the content of impurities in tap water is high, the service life of pretreatment parts will be shortened and the water quality will not reach the standard after treatment, and even the pipeline will be blocked. The solid dissolved content (TDS) in tap water is generally required to be less than 1000 ppm.

2 Pretreatment component service life: deep filter filter element, activated carbon filter element, softener filter element, etc. are all materials with service life. They have protective effect on reverse osmosis membrane. If they fail, RO membrane load will be aggravated and life will be shortened. . The specific service life should be reasonably set according to the tap water quality of each place.

1.2 Reverse osmosis membrane (RO) treatment

The reverse osmosis membrane (RO) removes a large amount of ions and other impurities from the water. The removal capacity can usually be greater than 95%.

1.2.1 Influencing factors

1 Inlet water pressure: Generally, the pure water system reverse osmosis membrane needs to maintain a certain inlet pressure with a high pressure pump to maintain normal operation. When the pump pressure is insufficient, the water production will decrease.

2 Maintenance of pure water system: Pure water system generally has automatic backwashing function. When the setting is unreasonable or faulty and manual maintenance is not proper, it will affect the normal operation of the pure water machine, resulting in purification efficiency and water quality.

1.3 Preparation of deionized water

Generally, the water treated by the RO membrane can only reach the standard of three grade pure water (resistivity > 0.2 MΩ·cm). Although the third-stage pure water has removed most of the impurities, the concentration of impurities such as ions is higher, which will affect the micro-detection of the biochemical analyzer. Therefore, the third-stage pure water must be further deionized to reach the first-order pure water (resistance). The standard rate ≥lOMΩ·cm) can be used for biochemical testing.

1.3.1 Method: The ion exchange resin method is a common method for preparing pure water. The components used are ion exchange purification columns (tanks), including anion exchange column, cation exchange column and mixing column, etc., and the reagent is an anion exchange resin. The anion-cation exchange resin is generally a polymer formed by polymerizing styrene and then crosslinking the divinylbenzene to obtain a porous network skeleton structure, and then connecting the active group to the skeleton. The reactive group to which the ion exchange resin is attached can be classified into two major types of an acidic group and a basic group. The ion exchange resin to which the acidic group is attached is referred to as a cation exchange resin, and the resin to which the basic group is attached is referred to as an anion exchange resin.

1.3.2 Principle:

1 cation exchange column principle is the principle of hard water softening: the acidic group in the cation exchange resin has acidic groups such as sulfonic acid group (-S03H), carboxyl group (a COOH) and phenol group (-C6H40H), wherein the hydrogen ion can Metal ions or other cations in the solution are exchanged.

2 Principle of anion exchange column: The basic groups in the anion exchange resin are quaternary amino groups [-N (CH3)30H], amino groups (-NH2) and imino groups (=NH). They produce OH- ions in water and can exchange with various anions.

3 Mixed column: When the two are used in series or in combination, the product is only water.

1.3.3 Influencing factors:

1 The quality of the ion exchange resin: The ion exchange resin has a service life limit. When the ion exchange reaches a certain amount, it saturates and needs to be regenerated. Therefore, the better the quality, the longer the service life is.

2 The connection mode of anion and cation exchange resin: double bed type: several cation exchange columns and several anion exchange columns are connected in series, and the yang is behind the front yin. The advantage is that the regeneration is convenient, and the disadvantage is that the effluent quality is not high (single stage The double bed type effluent resistivity is only 0.5 MΩ·cm, and the two-stage double bed type effluent resistivity is 2 MΩ·cm). Mixed bed type: The cationic resin and the anion resin are uniformly mixed into the same exchange column at a volume ratio of 1:2. The advantage is that the purity of the effluent is high (resistivity ≥1 OMΩ.cm), and the disadvantage is that regeneration is difficult. Combined type: The combination of the double bed type and the mixed bed type is completed, and the effluent quality is high (the resistivity is up to 18.3 MΩ.cm, that is, ultrapure water), and the service life is long.

3 Purity of the third grade pure water: When the quality of the third grade pure water is unqualified, some of the nonionic impurities passing through the ion exchange column will affect the service life of the ion exchange column and cause the effluent water quality to decrease. Some open-ended pure water systems store the third-grade pure water in the water tank for other purposes. The storage time is too long or the secondary pollution caused by other reasons will also reduce the purity of the water.

1.4 Impurity components in unqualified pure water

Unqualified pure water quality means that the purification of pure water system water may occur in any step in the raw water pretreatment process, reverse osmosis process, ion exchange process and pure water storage. No matter which step fails, the source of impurities is nothing more than the pollutants in the water channel of the tap water and the pure water machine. The main ones are:

1 ion, common are H+, Na+, K+, NH4+, Mg2+, Ca2+, Fe3+, Cu2+, Mn2+, Zn2+, Al3+ and other cations and F-, CI-, N03-, HC03-, S042-, P043-, H2P04- , HSi03- and other anions;

2 organic substances, such as pesticides, hydrocarbons, alcohols and esters;

3 particulate matter, such as rust and sediment in the tap water pipe;

4 microorganisms;

5 dissolved gases (Nz, 02, C12, H2S, CO, CO2, CH4, etc.).

1.4.1 Influence of different impurity components on biochemical analyzer and test results

1 high ion content:

The most direct effect is the increase in the determination of the same ion in serum (slurry), such as the determination of Mg2+, Ca2+, Fe3+, Cu2+, Zn2+, etc., and also affect the calibration of these items;

Since many metal ions are coenzymes of enzymes, when the content of metal ions is high, the detection of enzyme activity is often affected (for example, Mg2+ is an activator of various phosphorylation kinases, and when the content in water exceeds the standard, the measured value of these enzyme activities is increased. High; and many heavy metal ions inhibit the enzyme, resulting in decreased enzyme activity);

Many anions also exist as cofactors for enzymes, which have an effect on the determination of enzyme activity (eg CI-activates alpha-amylase);

Water with high ion content is more likely to form crystals and cause organic matter such as proteins to be denatured and attached to the piping system, making the biochemical analyzer piping system more likely to clog, eventually causing distortion or failure of the measurement; at the same time, it is also very useful when cleaning the cuvette Difficult to clean, will accelerate the aging and damage of the reaction cup, so that the cup blank is raised.

2 The influence of organic substances: The influence of organic substances mainly lies in the increase of the results of the determination of similar substances when measuring similar substances. At the same time, an increase in the organic content will also accelerate the cleaning and aging of the piping system and the reaction cup.

3 The influence of particulate matter: It is generally difficult for particulate matter to enter the biochemical analyzer pipeline and reaction system through the pure water system. The source is generally secondary pollution of the storage tank, but once it enters, it will easily lead to blockage of the pipeline. And damage the reaction cup.

4 The influence of microorganisms: The removal of microorganisms mainly depends on the pretreatment of raw water. Some pure water systems also add ultraviolet sterilization or microfiltration and ultrafiltration devices to the ultrapure water to further remove residual bacteria, particles and heat sources in the water. However, once the pretreatment fails or the pure water storage tank is re-contaminated, the microorganisms and their products can enter the biochemical analyzer piping system and the reaction system. There may be two situations: the microorganisms in the pipeline and the reaction system are twinned, causing the pipeline to clog. At the same time, the absorbance and the cup blank are raised; the specific enzyme produced by the microorganism has an influence on the enzyme assay of the biochemical analyzer, and the specific influence depends on the type of the contaminated bacteria.

5 dissolved gas: the effect of increased dissolved gas:

The effect on the determination of the same gas;

It also affects the pH value of water. For example, the increase in the solubility of CO2, Cl2, H2S, etc. leads to the decrease of pH value of water, and also affects the determination of biochemical items with strong pH dependence.

Some gases such as C12 increase, due to their strong oxidative properties, will affect the biochemical measurement items related to redox reactions, such as ALT, AST, BUN, etc. established based on absorption peaks at NADH and NADPH at 340 nm. The method of measurement will result in an increase in the measured value.

6 The influence of other impurities: Some pure water systems also store the ultrapure water or the first-stage pure water finally produced in the water tank. When the water tank is rusted, the iron is not measured normally, and it usually appears in the pressure water tank; There is an increase in the TG measurement result when the oil leakage caused by the mechanical device is not tightly sealed. Although these conditions are rare, they are also the most easily overlooked.

2 Discussion

There are two types of automated pure water systems commonly used in laboratories:

1 Large distiller system, the sunrise water volume is about 100 L, the raw water utilization rate is 10%-15%, the energy consumption is large, the degree of automation is low, the purity of the prepared distilled water is generally low, and the scope of application is narrow, and it has basically been eliminated.

2 The reverse pure osmosis central pure water system consists of mechanical filtration, activated carbon adsorption, reverse osmosis membrane and ion exchange resin. The daily water production is about 500 L, the raw water utilization rate is 30%-40%, the degree of automation is high, and the energy consumption is low. The parts can be used repeatedly, and the effluent has high purity and is widely used at present. In addition, some laboratories directly purchase commercial purified water due to limited conditions, but commercial purified water is mostly drinking water. The standard is different from the laboratory water standard, which is easy to affect the detection.

Common indicators for evaluating water quality:

1 Resistivity is a measure of the conductivity of water in laboratory. It increases with the decrease of inorganic ions in water. However, due to the dissociation of water itself, the resistivity can only reach 18.2MΩ.cm. The main indicator of ion concentration in water;

2 Total organic carbon refers to the concentration of carbon in water, reflecting the content of organic compounds in water;

3 particles, reflecting the concentration of particulate matter in the water;

4 pyrogens, usually cell wall metabolites of Gram-negative bacteria.

3 recommendations

1 Strictly standard quality control of laboratory ultrapure water, regular measurement of pure water resistivity and other indicators, regular printing of water quality reports.

2 Enhance laboratory water quality awareness and actively prevent the impact and loss caused by water use.

3 The water for the open water storage tank should be strictly controlled to prevent secondary pollution caused by this.

4 It is necessary to master the service life and maintenance methods of the components of the pure water machine, and actively prevent various water quality problems caused by the failure of the pure water machine components, and prolong or guarantee the life of the RO membrane and the ion exchange resin.

5 To understand the water quality of the region and evaluate its impact on the water purifier, you can increase the service life by installing a large pretreatment device.

About Shanghai Lefeng Biotechnology Co., Ltd.

Shanghai Lefeng Bio is specialized in the research, development, design and manufacture of high-end water purification and laboratory separation and purification products, and is committed to providing cutting-edge, high value-added innovative products for life sciences and biotechnology. The Lefeng product line includes laboratory pure water systems, Millipore pure water compatible consumables and laboratory separation and purification filtration products. Established ten years ago, Lefeng has established its own brand RephiLe (Ruifeng), with more than 30 patents and multiple software copyrights. Products are sold to nearly 90 countries and regions around the world.

For more information on RephiLe products, please visit: Le Feng official website

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