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

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 labs use reverse osmosis central water system. According to the analysis of the workflow of the system and the actual situation encountered, several reasons leading to insufficient water purity and its influence on the detection of the automatic biochemical analyzer can be found and summarized .

 

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 :

â‘  depth filtration filter filters the raw water sediment and other large particles;

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. Generally, the solid dissolved content (TDS) in tap water is less than 10 00 ppm .

â‘¡ preprocessing component life: depth filtration filter, activated carbon filters, softeners, etc. are all life of the filter material, which have a protective effect on the reverse osmosis membrane, if they fail, the RO membrane will increase the load, 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 M Ω · 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. Method 3.1: an ion exchange resin is a commonly used method for the preparation of pure water, is used in the ion exchange purification column member (tank), comprising an anion exchange column, a mixed bed of a cation exchange column and the like, as reagent anion and cation exchange resins . 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.

1.2.2 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 (-S0 3 H), carboxyl group (a COOH) and phenol group (-C 6 H 4 0H). The hydrogen ions therein can be exchanged with metal ions or other cations in the solution.

â‘¡ anion exchange column principle: basic anion exchange resin in quaternary amino group [-N (CH 3) 3 0H ], amino (-NH 2) and the imino group (= NH) and the like. 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 .

1.2.3 Influencing factors:

â‘  mass ion exchange resin: the ion exchange resin is limited service life, when the ion-exchange saturation reached a certain amount, the regeneration process is required, so the larger the total mass, the better the longer the life.

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 M Ω · 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 water 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 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 water purity.

2.1 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+, NH 4 +, Mg 2 +, Ca 2 +, Fe 3 +, Cu 2 +, Mn 2 +, Zn 2 +, Al 3 + and other cations and F-, CI -, N0 3 -, HC0 3 -, S0 4 2 -, P0 4 3 -, H 2 P0 4 -, HSi0 3 - anion;

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, C1 2 , H 2 S, CO, CO 2 , CH4, etc.) .

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

2.2.1 The effect of high ion content:

1 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 ;

â‘¡ Since many metal ions are enzyme co-factor enzyme, so when a high metal ion content often affect the activity detection (e.g., Mg2 + is more phosphorylated kinase activators, which lead to activity determination value when the water content exceeded Elevation; and many heavy metal ions inhibit the enzyme, resulting in decreased enzyme activity) ;

3 Many anions also exist as cofactors of enzymes, which have an effect on the determination of enzyme activity (such as CI -activated α -amylase) ;

4 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, which makes the biochemical analyzer piping system more clogging, eventually causing distortion or failure of the measurement; at the same time, when using the cleaning cup for cleaning It is difficult to clean, which will accelerate the aging and damage of the reaction cup and increase the blank of the cup.

2.2.2 Effects 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.

2.2.3 Effects 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 it is easy to increase the absorbance once it enters. Block the pipe and damage the reaction cup.

2.2.4 Effects 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. Wait. 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: 1 The microorganisms in the pipeline and the reaction system are twinned, resulting in the pipeline. Blockage, while increasing the absorbance and cup blank; 2 microbial production of specific enzymes affect the biochemical analyzer enzyme assay, the specific impact depends on the type of contaminating bacteria.

2.2.5 Dissolved gases: The effects of increased dissolved gases are:

1 the effect on the determination of the same gas;

2 also affects the pH value of water, such as increased solubility of water such as C0 2 , Cl 2 , H 2 S, etc., which also affects the determination of biochemical items with strong pH dependence;

3 Some gases such as C1 2 increase, due to their strong oxidative properties, will affect the biochemical measurement items related to redox reactions, such as ALT, AST established based on absorption peaks at NADH and NADPH at 340 nm. The measurement method of BUN or the like causes an increase in the measured value.

2.2.6 Effects 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 properly , and it usually appears in the pressure water tank. There is also 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.

3 Discussion

3.1 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 now it has been basically eliminated .

2 The reverse 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 50,000 L, the raw water utilization rate is 30%-40%, the automation degree is high, and the energy consumption is low. The main part can be used repeatedly, and the effluent has high purity and is widely used at present. In addition, some laboratories use commercial purified water directly because of the limited conditions, but the commercial purified water is mostly drinking water. The standard is different from the laboratory water standard, which is easy to affect the detection.

3.2 Common indicators for evaluating water quality

① resistivity, electrical conductivity is a measure of laboratory water, which reduces the water with inorganic ions increases, but due to its water dissociation, the maximum resistivity of only about 18. 2 MΩ.cm, Is the main indicator for detecting the 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 .

3.3 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.