Complete knowledge of laboratory water usage

The product knowledge I am sharing with you today is about laboratory water. I hope the following content will be helpful to you.

1Basic properties of water

1A water molecule(H2O)is caused by1An oxygen atom and2A hydrogen atom is bent and bonded together. Due to the inconsistency of the centers of positive and negative charges, it belongs to polar molecules. when2When a water molecule exists simultaneously, the two will be attracted to each other and maintain a certain distance through electrostatic interaction and hydrogen bonding. But1A water molecule can simultaneously interact with4A water molecule combines to form a crystal like neat structure.

In water molecule aggregates, due to the partial breakage of the network structure of hydrogen bonding, a state of gradual movement and change is formed. Therefore, water appears liquid as a whole, and this structural change can reach up to per second1012Next time.

Generally speaking, if water contains an appropriate amount of sodium, potassium ions, and minerals such as silicates, it will feel good to drink. If it contains a large amount of residual salts, such as magnesium, calcium, and other non acidic and neutral salts, it will feel unpleasant to drink. That is to say, the so-called water, besidesH2OIn addition, it also contains many other ingredients, and the type and content of these ingredients determine the taste of water.

Water is highly soluble in salts, and even if cations and anions are strongly bound together through electrostatic interactions, they are easily electrolyzed in water. This is because water molecules can combine with ions to produce "hydrated ions". The radius of ions is very small, and ions with high charges will strongly interact with water molecules, which are tightly arranged around the ions. At this point, cations will interact with oxygen atoms with negative moments, while anions will form the opposite structure.

2Impurities present in water

Impurities in source water (total)5Class)

A.electrolyte

B.organic matter

C.particulate matter

D.microorganism

E.dissolved gas

A.Electrolytes: Electrolytes in water include soluble inorganic substances, organic compounds, and charged colloidal particles. Affects the conductivity of water. The more impurities in water, the higher the conductivity of water. We know that water with high impurities can have a very negative impact on our chemical analysis. Electrolytes are mainly composed of cations and anions. Generally, its content can be determined by ion chromatography or atomic absorption spectroscopy. It can also be analyzed by mass spectrometry to preliminarily identify the unknown components.

B.Organic matter: The organic matter contained in water usually refers to organic acids and organic metal compounds, and the determination method is usually to measure their chemical oxygen consumption.

C.Particulate matter: sediment, dust, organic matter, microorganisms, etc. It can be measured using a specialized particle analyzer

D.Microorganisms: bacteria, plankton, algae, etc

E.Dissolved gases:N2TheO2TheCL2TheCOTheCO2Wait, its content can be determined by gas chromatography

3Purity required for experimental water

The so-called experiment refers to the action of verifying hypotheses inferred from phenomena. Whether a hypothesis can be proven to be true and whether the hypothesis can have reproducible results are crucial. The reproducibility of experiments is not only influenced by good techniques, but also by the purity of the chemical reagents used and the precision of the analytical instruments. The chemical reagents used to prepare the solution in the experiment and the purity of the water used are also very important. If pollutants in water have an impact on experimental testing, they must be removed. In addition, in order to achieve good reproducibility results, it is necessary to use pure water that can maintain stable water quality.

With the increase in sensitivity of analytical systems used in experiments, higher requirements have been placed on the purity of water.

1ppm = 1mg/L

1ppb = 1μg/L

1 ppt = 1 / L = 1 μ g / ml

4Method for expressing the purity of water

In the water, measure the distance1cmThe surface area of the two pieces is1cm2By applying electricity to electrodes of different sizes, the conductivity between the two poles can be monitored. The resistance value between the two poles can be determined by the applied voltage and measured current. This value is commonly referred to as resistivity or specific resistance in water quality analysis, and is measured in units ofMΩ.cm(mega ohm-centimeter)To express.

The reciprocal of resistivity is called conductivity or electric conductivity, expressed in μ ms/cm(micro Siemens per centimeter)To express.

These two parameters are the most commonly used parameters to indicate the purity of water.

Removing ions from tap water will increase the electrical resistivity (decrease the conductivity), but not an unlimited increase. This is because some water molecules will ionize into hydrogen ions and hydroxide ions, with their maximum electrical resistivity value18.248MΩ.cm(25℃)In addition, the resistivity value varies with the ionization constant of water and is therefore affected by water temperature. For example,25The resistance value of ultrapure water at ℃ is18.2MΩ.cm,but in0℃ is84.2MΩ.cm, 100℃ is1.3MΩ.cmIn25 Around ℃, when the temperature rises1 At ℃, its resistance value will decrease0.84MΩ.cmTherefore, use compensation more often25 The resistivity value of ℃ is used as a measurement standard.

In addition, factors such as total organic carbon content（TOC）Heat source endotoxin content, bacterial content, particle content, microbial content, total dissolved solids content（TDS）Waiting is often used as an important parameter to supplement the explanation of water quality. Therefore, the purity standard of water is usually comprehensively described and graded by one or several of the above parameters.

5Classification standards for pure water

according toGB/T 6682-2008The water used in the analysis laboratory can be divided into three levels: first level water, second level water, and third level water.

First grade water is used for analytical experiments with strict requirements, including tests with particle requirements. Such as using water for liquid chromatography analysis.

Secondary water is used for inorganic trace analysis experiments, such as atomic absorption spectroscopy analysis.

Third grade water is used for general chemical analysis experiments.

Now let's take a look at some water concepts that we often encounter in the laboratory.

1.Distilled water: Water prepared by condensing water vapor through distillation, called distilled water. Generally, large-scale water production is obtained by condensing steam generated by boilers. Used for formulations, pharmaceuticals, and experimental water with low requirements.

2.Purified water: Water that is deodorized through sand filtration and activated carbon adsorption, and then filtered through a reverse osmosis membrane to remove ions. It is also known as purified water or space water (the recycling technology of water in aerospace technology). The purified water available on the market is prepared in this way.

3.Mineral water: Mineral water and water extracted from deep wells contain various mineral elements, including trace elements such as calcium, selenium, strontium, and silicon, depending on the place of origin. This water has been disinfected and filled to become mineral water on the market.

4.Deionized water: Water is passed through a cation anion exchange resin bed to remove anions and cations from the water through exchange, resulting in deionized water. It is generally used for chemical laboratory water needs.

Deionized water refers to pure water after removing impurities in the form of ions. Standardization OrganizationISO/TC 147The prescribed definition of "deionization" is: "Deionized water * or not * removes ionic substances, mainly referring to the use of ion exchange resin treatment methods." The current process mainly adoptsROThe method of reverse osmosis is used for production. Ion exchange resin is used to remove anions and cations from water, but soluble organic matter still exists in the water, which can contaminate the ion exchange column and reduce its effectiveness. Deionized water can also easily cause bacterial growth after storage.

5.Ultra pure water: It not only removes almost all conductive media from water, but also removes colloidal substances, gases, and organic substances that do not dissociate from water to a very low level. The resistivity is greater than18MΩ*cm, or approaching18.3MΩ*cmLimit value.

6. UPWater refers to High-purity water,ultral pure water（UPW）.

High purity water is water with a chemical purity of *, in which the content of impurities is less than0.1mg/LAt present, the purity of high-purity water produced by people has reached99.999999%Among them, the impurity content is lower than0.01mg/LHigh purity water mainly refers to water with a temperature of25At ℃, the conductivity is less than0.1us/cm,pHvalue6.8-7.0And remove other impurities and bacteria from the water.

7.RoPure water is generally referred to as purified water and does not retain any minerals in the water,PHValue in6-7Between them, it is weakly acidic and is generally used for medical purposes such as dialysis, or for special purposes such as laboratories and electronics. Due to severe water pollution, it is also used for daily drinking water to ensure its safety. It is a hygienic and safe drinking water

At present, there are several commonly used pure water standards in the world, including:

Standardization Organization（ISO）The American Society of Clinical Pathology（CAP）Trial grade water standard, organized by the American Society for Testing and Materials Testing（ASTM）The Clinical Trial Standards Committee（NCCLS）The American Pharmaceutical Association（USP）Wait. At the same time, China also has corresponding pure water standards: China National Electronic Grade Ultra Pure Water SpecificationGB/T11446-1997Specifications for Water Use in Chinese National LaboratoriesGB6682-92Wait. Therefore, the vast majority of pure water systems on the market, whether imported or domestically produced, are designed according to these standards.

6Application of pure water

At present, pure water is mainly used in two major fields:

1、 Application field of life sciences

2、 Analysis and Conventional Application Fields

In terms of life science applications, there are mainly:

Bacterial cell culture, clinical biochemistry, electrophoresis, electrophysiology, enzyme-linked immunosorbent assay, endotoxin analysis, histology, hydroponics, cellular immunohistochemistry, mammalian cell culture, medium preparation, microbiological analysis, molecular biology, monoclonal antibody research, plant tissue culture, radioimmunoassay, and more.

In terms of analysis and routine applications, there are mainly:

Distiller water supply, steam generator, glassware cleaning, sample dilution and reagent preparation, ultrapure water system water supply, solid-phase extraction, general chemistry, electrochemistry, spectrophotometer,TOCAnalysis, water quality analysis, ion chromatography, flame atomic absorption spectroscopy（Flame-AAS）Graphite Furnace Atomic Absorption Spectroscopy（GF-AAS）, liquid chromatography（HPLC）Liquid chromatography-mass spectrometry (LC-MS)（HPLC-MS）Electric Coupled Plasma Spectrometer（ICP-AES）Plasma Mass Spectrometry（ICP-MS）Trace metal detection, gas chromatography-mass spectrometry（GC-MS）Wait a minute.

Several main applications of water purity requirements:

Electrophoresis: The most important requirement for electrophoresis water is biologically active substances such as endotoxins (usually less than)0.05EU/ml）Removal of ribonucleases and proteases (undetectable). Using electrical resistivity18.2 MΩ-cm，TOC<10ppb，0.1MmOr smaller pore size microfiltration and bacterial content below1CFU/mlUltra pure water is used as water supply.

cfu/cmIt refers to the total number of bacterial colonies contained in each square centimeter of the sample

Endotoxin analysis: From isolation to cell culture, various application fields require the specification of endotoxin indicators for water. The maximum range of endotoxin indicators is from0.25IU/mlto0.03IU/mlFor endotoxin analysis, ultrapure water with low endotoxin content is usually used0.05IU/mlOr smaller. Ultrafiltration is a necessary method for producing ultrapure water with low endotoxin content (usually used in the above)MWCOfor5000Dalton's ultrafiltration membrane), and it can bind withUVWait for photo oxidation.

IUIt should mean unit,IU/MLIf it is the concentration of a substance in a liquid, it is the number of units of that substance per megaliter. Generally, a type of substance without a clearly defined fixed structural component, such as antibiotics, is compared based on the antibacterial activity of its components, just like penicillin30Ten thousand units(IU)wait

Stone mill furnace atomic absorption spectroscopy:GF-AASThe difference from other atomic absorption spectroscopy measurements is that its flame furnace is replaced by electron heating graphite tubes or rods, which can achieve high sensitivity in elemental analysis.GF-AASRequest * Pure water system, providepptThe level of impurities,18.2 MΩ-cmThe resistivity and lowTOCLevel. The built-in monitoring device provides purity assurance, and the ultimate water quality indicators are achieved through a good pretreatment system, continuous circulation flow path, and ultra purification of pure water.

Inductively Coupled Plasma Spectrometer: inICP-AESIn applications, the sensitivity to different elements varies significantly, but the detection limits for metals, transition metals, phosphorus, and sulfur are all within the range ofppbWithin the scope.ICP-AESThe purity requirements for water are quite strict, with a resistivity greater than18 MΩ-cmUltra pure water is necessary,TOCThe requirements are generally not very important, and pre-treatment requires reverse osmosis or ion exchange.

Plasma Mass Spectrometry:ICP-MSCan be used to determine inpptHorizontal elements. For this sensitiveICP-MSAnalysis work requires very strict purity requirements for water, requiring impurities in the water to be presentpptHorizontal, electrical resistivity18.2 MΩ-cmAnd lower onesTOCThe ultimate water quality indicator is achieved through a good pretreatment system, continuous circulation flow path, and ultra purification of pure water.

Mass spectrometry analysis: Mass spectrometry can perform trace analysis on mixtures, and due to its high sensitivity, high-purity water is required. All sample preparation and pre-processing, such as solid-phase extraction, require ultrapure water. Require impurities in the water to be presentpptHorizontal, electrical resistivity is required for organic matter analysis18.2 MΩ-cmVery lowTOCGenerally, the indicators are less than3ppb.

Trace metal detection: Advanced modern analytical instruments continuously improve the sensitivity of analysis. Trace elements are now being used through methods such asICP-MSTechnology, measurable inpptAnd YapptHorizontal material. Trace analysis requires pure water without detectable components, and the water quality requirements are suitable for the most rigorous and sensitiveICP-MSWork. Therefore, blank reagents, standard sample dilution, and sample preparation all require ultra pure water with the highest purity, and even require operation in a clean room.

With the development of technology, more and more applications require the use of high-purity ultrapure water.

7Methods for maintaining water quality in ultrapure water

Ultra pure water is prone to environmental pollution after being taken, so it is most appropriate to take water before use (i.e. use it immediately). Only by shortening the time of contact between ultrapure water and the environment to a very short extent can we obtain ultrapure water with * purity.

When configuring high-purity chemical reagents, try not to use ultrapure water stored in storage tanks for a long time, because after long-term use, the water quality will deteriorate due to impurities and microbial contamination. Water like this is no longer ultrapure water when used.

Install air filters in pure water storage tanks to prevent pollution caused by environmental factors.

Do not place the water storage tank in direct sunlight as the water temperature may rise and cause microbial growth. Especially semi transparent water storage tanks can also cause algae growth due to the transparency of sunlight.

When taking ultrapure water, it is necessary to discharge the initial effluent to obtain stable water quality.

When taking water, let ultrapure water flow in along the side wall of the container, avoiding the formation of bubbles as much as possible, which can reduce air pollution.

Please do not connect the hose after the terminal filter, and use direct water intake to obtain high-purity ultrapure water.

When pure water is not used for a long time, the pressure storage tank should be filled withRODrain all the water to prevent pollution.

If the ultrapure water machine is not used for a long time, the initial pure water should be fully drained when it is reused to ensure water quality.

In principle, a pure water machine should be used at least once7—10Tiantongshui once to prevent microbial contamination.

Key points for using ultrapure water:

1.Ready to use

2.Drain the initial water at the front end

3.Avoid generating bubbles when taking water