HJ 493-2009Water quality. Technical regulation of the preservation and handling of samples (English PDF)

2.1 Reasons for changes in water samples

2.1.1 Physical effects. Light, temperature, standing or vibration, storage conditions such as exposure or sealing and the material of the container will affect the nature of the water sample.

If the temperature rises or strong vibration will cause some substances such as oxygen, cyanide and mercury to volatilize, long-term standing will make Al(OH)3, CaCO3, Precipitation such as Mg3(PO4)2. The inner wall of some containers irreversibly adsorbs or absorbs some organic matter or metal compounds.

2.1.2 Chemical action. The chemical reaction of each component of the water sample and the water sample may change the content and properties of certain components. Such as air the oxygen in the oxygen can oxidize divalent iron, sulfide or the like, depolymerize the polymer, and polymerize the monomer compound.

2.1.3 Biological effects. The metabolism of bacteria, algae, and other organisms consumes certain components of the water sample, producing some new groups.

Points, changing the properties of some components, biological effects will be some items in the sample to be tested such as dissolved oxygen, carbon dioxide, nitrogen compounds, phosphorus and the content and concentration of silicon and the like have an influence.

2.2 Precautions for sample preservation

The extent to which a water sample changes during storage depends mainly on the type of water and the chemical and biological properties of the water sample, and also on preservation.

Conditions, container materials, transportation and climate change.

These changes are often very fast. Samples often change significantly in a short period of time, so the necessary must be taken in all circumstances Save the measure and analyze it as quickly as possible. Preservation measures are useful in reducing the degree of change or the speed of slow change, but to the point all previous preservation measures have not completely suppressed these changes. And for different types of water, the resulting preservation effect is different, drink Water is easy to store, because it is not sensitive to biological or chemical effects, and general preservation measures can be effectively stored on surface water and groundwater.

But it is different for wastewater. The nature of the wastewater or the sampling location of the wastewater is different, and the preservation effect is different, such as from the urban drainage pipe network and sewage.

The wastewater of the water treatment plant has different preservation effects, and the wastewater from the biochemical treatment plant and the untreated wastewater have different preservation effects.

The analysis project determines the storage time of the wastewater sample. Some analysis projects require separate sampling, and some analysis projects require on-site analysis.

Samples of some items can be stored for a longer period of time. Due to the difference in sampling location and sample composition, no suitable field has been found so far.

The absolute criterion for the situation of integration. In all cases, the storage method should match the analytical technique used. This standard specifies the most versatile Use technology.

2.2.1 Selection of containers

Containers for collecting and preserving samples should take into account the following aspects (especially when the components being analyzed are present in trace amounts).

2.2.1.1 Minimize contamination of samples by containers and stoppers. Generally, glass can dissolve sodium, calcium, magnesium, silicon when storing water samples.

For elements such as boron, glass containers should be avoided when measuring these items to prevent new contamination. Some colored corks contain a lot of heavy gold Genus.

2.2.1.2 The wall of the container should be easy to clean and handle to reduce the surface contamination of the container by trace elements such as heavy metals or radionuclides.

2.2.1.3 The chemical and biological properties of the container or container stopper should be inert to prevent the container from reacting with the sample components. When measuring fluorine, Water samples cannot be stored in glass bottles because the glass reacts with fluoride.

2.2.1.4 Prevent the container from absorbing or adsorbing the component to be tested, causing a change in the concentration of the component to be tested. Trace metals are susceptible to these factors.

Others such as detergents, pesticides, and phosphates are also affected.

2.2.1.5 Dark glass can reduce photosensitivity.

2.2.2 Preparation of the container

2.2.2.1 General rules

All preparations should ensure that no positive or negative interference occurs.

Use a dedicated container whenever possible. If a special container cannot be used, it is best to prepare a container for the determination of specific contaminants to reduce Less cross contamination. At the same time, care should be taken to prevent the previously collected high-concentration analytes from contaminating the subsequently collected low-concentration contaminants due to incomplete washing.

sample.

For new containers, it should be washed first with detergent and then thoroughly with pure water. However, detergents and solvents used for cleaning may be cited Interference, such as when the nutrient is analyzed, the residue of the phosphate-containing detergent is contaminated. If used, ensure detergent and solvent quality. If silicon, boron and surfactant are determined, detergents cannot be used. The type of detergent used and the material of the selected container should be treated Determine the components to determine. Phosphate-containing detergents should not be used for the determination of phosphates; chromic acid-sulphuric acid washes cannot be used for the determination of sulfates or chromium. Measuring the weight of metal Glass containers and polyethylene containers are usually washed with hydrochloric acid or nitric acid (c = 1 mol/L) and soaked for 1 to 2 days, then rinsed with distilled or deionized water.

2.2.2.2 Cleaning agent cleaning plastic or glass containers

This procedure is as follows.

a) washing the container and the container cap with a mixed dilution solution of water and a cleaning agent;

b) Wash twice with laboratory water;

c) Control the dry water and cover the container cap.

2.2.2.3 Solvent washing glass container

This procedure is as follows.

a) washing the container and the container cap with a mixed dilution solution of water and a cleaning agent;

b) thoroughly cleaned with tap water;

c) Wash twice with laboratory water;

d) washed with acetone and dried;

e) Wash with a solvent matching the analytical method and immediately cover the container cap.

2.2.2.4 Pickled glass or plastic containers

This procedure is as follows.

a) washing the container and the container cap with a mixed dilution solution of tap water and a cleaning agent;

b) thoroughly cleaned with tap water;

c) washing with 10% nitric acid solution;

d) after being dried, filled with 10% nitric acid solution;

e) sealed and stored for at least 24 h;

f) Wash with laboratory water and immediately cap the container.

2.2.2.5 Preparation of containers for the determination of samples such as pesticides and herbicides Plastic containers other than Teflon will cause significant interference in the analysis, so brown glass bottles are generally used. Cleaned according to general rules (ie After water and detergent-chromic acid-sulfuric acid-distilled water (see 2.2.2.4), it is dried in an oven at 180 ° C for 4 h. After cooling, use pure Rinse the hexane or petroleum ether several times.

2.2.2.6 Samples for microbiological analysis

Containers and plugs and lids for microbiological analysis should be autoclaved at a temperature that ensures that they are not released or produced at this temperature.

How to inhibit biological activity, inactivate or promote the growth of biological substances.

Glass containers, washed according to general cleaning principles (see 2.2.2.3), soaked in nitric acid and rinsed with distilled water to remove heavy metals or chromates the remains. Sodium thiosulfate (Na2S2O3) can be added to the vessel before sterilization to remove the residual inhibition of bacteria by the residual chlorine (per 125 the ml container is metered with 0.1 ml of 10 mg/L Na2S2O3).

2.2.3 Storage of containers

For samples that need to be assayed for physico-chemical analytes, the water sample should be filled to the container to overflow and sealed for storage to reduce oxygen in the air.

Gas, carbon dioxide reaction interference and oscillation interference during sample transportation. However, when the sample needs to be stored frozen, it should not overflow.

2.2.4 Processing and preservation of biological detection

The samples used for chemical analysis are different from the samples used for biological analysis. The chemicals added to the bioassay sample can be fixed or to preserve the sample, "fixed" is used to describe the preservation of the morphological structure, while "storage" is used to prevent biochemical or chemical degradation of the organic matter.

Preservatives, by definition, are toxic, and the addition of preservatives can lead to the death of living things. Vibration can cause those before death Fragile creatures without strong nuclear walls collapse before "fixed" is completed. In order to minimize this effect, the preservative quickly enters the nucleus it is very important that there are some preservatives, such as Lug's solution, which can lead to the loss of taxa, within a specific season of a specific range.

Can become a problem. For example, in the summer, when the silicon-flagellate is frequently detected, it can be solved by adding a preservative such as Luger's alkaline solution.

Decide.

Bioassay samples should be stored in accordance with the following criteria.

a) Know in advance the effect of preservatives on the prevention of loss of biological organisms;

b) preservatives can effectively prevent the biological degradation of organic matter at least during storage;

c) Preservatives should ensure that the taxonomic group is adequately studied during the shelf life.

2.2.5 Treatment and preservation of radiochemical analysis samples

The samples used for chemical analysis are different from the samples used for radiochemical analysis. Safety measures depend on the nature of the radioactivity of the sample.

The preservation techniques for such samples depend on the type of radiation and the half-life of the radionuclide.

2.2.6 Refrigeration and freezing of samples

In most cases, from sample collection to transport to the laboratory, refrigerate at 1 to 5 ° C and store in the dark, save the sample enough. Refrigeration is not suitable for long-term storage and has a shorter storage time for wastewater.

The freezing temperature of -20 °C generally extends the storage period. Analysis of volatile materials is not applicable to freezing procedures. If the sample contains cells, bacteria or microalgae, which will rupture and lose cellular components during freezing, and is also not suitable for freezing. Freezing requires mastery of freezing and melting techniques.

In order to allow the sample to quickly and uniformly recover its original state upon melting, rapid freezing with dry ice is a satisfactory method. General choice of plastic Plastic containers such as polyvinyl chloride or polyethylene are highly recommended.

2.2.7 Filtration and centrifugation

When sampling or after sampling, filter the sample with a filter (filter paper, Teflon filter, glass filter) or centrifuge the sample.

To remove suspended solids, sediment, algae and other microorganisms. The selection of the filter should be matched with the analytical method, before cleaning and avoiding Free of adsorption and absorption loss. Because various heavy metal compounds and organic substances are easily adsorbed on the surface of the filter, the soluble compounds in the filter are as follows.

The surfactant will be filtered into the sample. Sand core funnels and fiberglass funnels are generally used in the measurement of organic projects, and are commonly used in the determination of inorganic projects.

Filter through a 0.45 µm filter.

The purpose of filtering the sample is to distinguish between the soluble and insoluble proportions of the analyte (such as soluble and insoluble metal fractions).

2.2.8 Adding a preservative

(1) Control solution pH. The water sample for measuring metal ions is usually acidified to pH 1-2 with nitric acid, which can prevent the hydrolysis of heavy metals.

The lake can prevent the adsorption of metal on the surface of the wall, and can also inhibit the activity of the organism in the acidic medium of pH 1-2. Use this method Save, most metals can be stable for weeks or months. The water sample for the determination of cyanide needs to be adjusted to pH 12 with sodium hydroxide. Determination of water samples of hexavalent chromium Sodium hydroxide should be added to pH 8, because in the acidic medium, hexavalent chromium has a high oxidation potential and is easily reduced. To preserve the total chromium water sample, it should Add nitric acid or sulfuric acid to pH 1-2.

(2) Addition of inhibitor. In order to inhibit biological action, an inhibitor may be added to the sample. Such as measuring ammonia nitrogen, nitrate nitrogen and COD in the water sample, add mercury chloride or add chloroform or toluene as a protective agent to inhibit the redox of the nitrite, nitrate and ammonium salts.

use. In the phenol water sample, the pH of the solution was adjusted with phosphoric acid, and copper sulfate was added to control the activity of the phenol-decomposing bacteria.

(3) Adding oxidant. Trace mercury in water sample is easily reduced, causing volatility loss of mercury. Adding nitric acid-potassium dichromate solution can make mercury Maintaining in a high oxidation state, the stability of mercury is greatly improved.

(4) Adding a reducing agent. measuring the water sample of the sulfide, and adding ascorbic acid is advantageous for preservation. Containing residual chlorine water, can oxidize cyanide ions, the phenols, hydrocarbons and benzenes are chlorinated to form corresponding derivatives. For this purpose, the appropriate sodium thiosulfate is added during the sampling to reduce the residue.

Chlorine interference. Sample preservatives such as acids, bases, or other reagents should be subjected to a blank test prior to sampling. The purity and grade must meet the analytical requirements.

Add some chemical reagents to fix some of the components in the water sample. The preservative can be added to the empty bottle in advance, or added immediately after sampling.

Into the water sample. The added preservative does not interfere with the determination of the component to be tested. If there is any doubt, the necessary test should be done first. When adding a preservative After dilution, the product should be fully considered when analyzing the calculation results. But if you add a thick enough preservative, because of the small volume, you can Ignore the dilution effect. Solid preservatives, due to local overheating, adversely affect the sample and should be avoided.

The added preservative may change the chemical or physical properties of the components in the water, so the selection of the preservative must be considered Purpose impact. If the item to be tested is a dissolved substance, acidification will cause dissolution of the colloidal component and solid, and it must be acidified and stored after filtration.

A preservative blank test must be performed, especially for the detection of trace el...