Surface water sampling types can be divided into single water sample (instantaneous water sample), mixed water sample and comprehensive water sample.
3. 1.4. 1. 1 single water sample
It is suitable for monitoring non-uniform water body, unstable parameters and pollution degree. A single water sample, whether on the water surface, at a specific depth or at the bottom, can usually be collected immediately by hand or automatically.
3. 1.4. 1.2 mixed water sample
Mixed water sample is to mix several kinds of water samples in a sampling bottle by equal volume or volume weighing method, and then analyze the water body according to the specified items. Mixed water samples are suitable for water bodies with uniform water quality distribution in horizontal or vertical direction. Mixed water samples can be mixed by time or flow ratio.
3. 1.4. 1.3 comprehensive water sample
Comprehensive water samples are suitable for evaluating the total or average water quality of a certain section of a river and the water quality when several wastewater channels enter the comprehensive treatment plant respectively. The sampling time of mixing a single water sample into a sample should be as close as possible to obtain the required comprehensive water sample data.
3. 1.4.2 groundwater sampling type
3. 1.4.2. 1 Determination of iron and ferrous water samples
When determining ferrous and ferric iron, it is necessary to take 250mL water samples from polyethylene plastic bottles or hard glass bottles, add 2.5ml 1+ 1 sulfuric acid solution and 0.5 ~ 1.0g ammonium sulfate, seal the bottle mouth with paraffin and send it to the laboratory for testing.
3. 1.4.2.2 adopt corrosive carbon dioxide water sample.
When measuring corrosive carbon dioxide in water, a bottle of 250mL water sample should be taken and 2g marble powder should be added. There should be a space of 10 ~ 20 ml in the bottle for sealing inspection.
3. 1.4.2.3 Determination of sulfide water samples
In a 500mL glass bottle, first add 10mL of 200g/L zinc acetate solution and 1mL of 1mol/L sodium hydroxide solution, then fill the bottle with water samples, cap the bottle, shake it repeatedly, seal the bottle with paraffin wax, label it, indicate the volume of zinc acetate solution, and send it for inspection.
3. 1.4.2.4 Determination of dissolved oxygen in water samples
It is best to conduct in-situ testing. For those who do not have the conditions, the following methods can be taken:
(1) Determine the dissolved oxygen in water by iodometry, and the water sample should be directly collected into the sample bottle. When collecting water samples, care should be taken not to make water samples explode or bubbles remain in the sampling bottle. If the sample is not directly collected by dissolved oxygen bottle, but needs to be subpackaged from sampler (or sampling bottle), the dissolved oxygen sample must be collected first, and it should be carried out immediately after the sampler is lifted off the water surface. That is, one end of the latex tube is connected to the drain nozzle of the water sampler or connected to the sampling bottle by siphon method, and the other end of the latex tube is inserted into the bottom of the dissolved oxygen bottle. When injecting water sample, slowly inject it into a small half bottle first, and then fill it up quickly. In case of overflow, slowly pull out the pipe and quickly plug the cork.
(2) Before sampling, prepare a frosted glass bottle with a volume of 200~300mL, rinse it with the water sample to be taken for 2 ~ 3 times, and then connect the siphon directly to the bottom of the bottle for sampling. When the water sample overflows from the bottle mouth for a moment, slowly pull out the siphon from the bottle, add 1mL alkaline potassium iodide solution with a pipette (2mL can be added when the hardness of water is more than 7mol/L), and then add 3mL manganese chloride solution. It should be noted that when adding alkaline potassium iodide and manganese chloride solution, the pipette should be inserted into the bottom of the bottle before releasing the solution; Then quickly plug the cork (leaving no gap), shake it evenly and seal it, and record the total volume and water temperature of the added reagent.
3. 1.4.2.5 Water sample for determination of organic pesticide residues
Take 3 ~ 5l water samples in hard glass bottles (plastic bottles are not allowed), add acid for acidification, make the pH of water samples ≤ 2 ≤ 2, shake well, seal and store at low temperature.
Collect gas samples
(1) Analysis and sampling of dissolved gas (absolute) content in groundwater;
① The sampling amount can range from several milliliters to dozens of milliliters, which is determined by the sensitivity of the analysis system (especially the mass spectrometer). The sampler shall be obtained from the laboratory and subject to the technical guidance of the experimenter.
② The sampler is a copper tube with a special fixture at one end and a glass window at the other. Stainless steel tube sampler equipped with two metal vacuum valves can also be used to collect samples to analyze the content of constant gas components, such as O2, N2 and CO2.
(3) After starting the pump to pump out three times the volume of the well tube, measure the water temperature and conductivity, and take samples only after the two indicators are stable.
(4) When collecting samples with a copper tube sampler, connect one end of the copper tube with a plastic tube about 2m long, insert it into the water flow of the water pump, and connect a plastic tube with a length of more than 2m at the other end of the glass tube window. Observe the glass tube w3mindow. After the bubbles in the window disappear completely, continue to pass water for 3 minutes, and then use a special card to intercept the required volume of water sample on the copper tube.
⑤ The sampling process of stainless steel tube sampler equipped with metal vacuum valve is the same as that of copper tube sampler, except that the water sample is intercepted by rotating vacuum valve.
⑥ The sampler should be packed in a special wooden box and sent to the laboratory within 1 week after sampling.
(2) Collection of samples for analysis of dissolved gas (relative) content in groundwater:
① Escape gas sampling: Generally, the principle of drainage and gas collection is adopted for the escape gas sampling in water, as shown in Figure 3. 1. 1. Sink the glass funnel connected with the gas collecting pipe 2 into the water, and close the spring clip 5 when the water level rises above the spring clip 5; Then, the lower bottle 3 filled with water is lifted and water is injected into the gas collecting pipe 2. After the gas collector 2 is filled with water (bubbles are not allowed), close the spring clips 4 and 6; Then, the lower bottle 3 is filled with water and placed under the gas collecting pipe 2. Move the funnel 1 to the place where the underwater gas escapes, open the spring clips 4 and 5, and the gas will enter the gas collector 2 along the funnel L; When the water in the gas collector 2 is discharged, the spring clips 4 and 5 are closed. In this way, the gas to be measured is collected in the gas collector and can be sent to the laboratory for analysis.
Another method can be used to collect gas samples. Choose a 250mL glass bottle 4 with a rubber stopper 5 and a glass funnel1; Drill two round holes in the rubber plug 5, and insert two glass tubes 6 and 7 with rubber tubes and spring clips at both ends respectively. A glass tube is connected to the glass funnel 1 (see figure 3. 1.2). When sampling, first fill the glass bottle 4 with water (air is not allowed) and clamp the spring clips 2 and 3; Then, the glass bottle 4 is inverted in the water, the glass funnel 1 is aimed at the underwater gas escape place, and the spring clips 2 and 3 are opened; When the glass bottle is almost filled with gas (there should be about 10mL water sample in the bottle), close the spring clips 2 and 3, pull out the funnel 1, tighten the rubber tube, and immediately seal the bottle mouth with wax; Put the glass bottle upside down in a wooden box and send it to the laboratory for analysis.
Figure 3. 1. 1
Figure 3. 1.2
② Sampling and separation of dissolved gas samples: Generally, vacuum method is used to separate and collect dissolved gas samples on site. The sampling and separation device is shown in Figure 3. 1.3. Take a 5L large glass bottle 2 with a rubber stopper 3 with two holes and two copper tubes 8 and 9 inserted in it; The lower end of the copper tube is connected with a rubber bladder 1. Make a mark at 2 places in the 3000ml glass bottle. Before sampling and separating dissolved gas, check whether the glass bottle is sealed. The method is as follows: inject 40mL water sample into the bottle, plug the bottle stopper 3, clamp the spring clip 5, open the spring clip 6, and exhaust the air in the bladder with a vacuum pump; Then close the spring clip 6 and open the spring clip 5 to vacuum the glass bottle (the water pumped into the bottle boils and bubbles until it no longer bubbles); Close the spring clip 5 and turn the bottle upside down. If the bottle is completely sealed, no bubbles will escape from the water. On the other hand, it shows that there is air leakage, so it is necessary to find out the reason and vacuumize again. After the seal inspection, the dissolved gas can be separated. Insert the rubber tube 10 (the tube should be filled with the water sample to be taken in advance to prevent air from entering the vacuum bottle) into the water source to be taken, open the spring clip 5, and introduce the water sample into the vacuum bottle 2; When the water sample volume reaches the mark of 3000mL, close the spring clip 5, unplug the rubber hose 10, and connect the drainage and gas gathering devices such as the gas collector 1 1 which has been filled with water sample in advance (Figure 3.1.3); Open the spring clip 6 and let the air enter the bladder; At this point, the dissolved gas is concentrated at the bottleneck. Open the spring clip 5 and the upper and lower cocks of the gas collector 1 1, 16 (the cocks should be coated with high vacuum grease), and introduce the dissolved gas at the bottleneck into the gas collector 1 1 by lowering the position of the lower bottle1(set to close after the dissolved gas is completely extracted. Therefore, the airbag must be evacuated again with a vacuum pump. At this time, the water sample in the bottle is restored to the 3000mL mark, and the low pressure is formed again in the bottle; The air bag is refilled with air, and the separated dissolved gas is still collected in the gas collector by drainage gas collection method. Repeat the separation for 3 ~ 5 times, and the separation can be basically completed. Then seal the gas collector with paraffin, label it with water temperature, atmospheric temperature, air pressure during sampling, dissolved gas volume, sampling volume (mL), and send it to the laboratory for analysis. The laboratory only accepts separated gas samples, not water samples.
Figure 3. 1.3
3. 1.4.2.7 radon measurement sampling
If conditions permit, the glass diffuser (Figure 3. 1.4) evacuated in advance should be used as far as possible to sample directly from the water source. When sampling, sink the horizontal water inlet of the vacuum diffuser into the water, then open the spring clip 3, and the water will be sucked into the diffuser. When the scale of 100mL is reached, close the spring clip 3 and record the sampling time (year, month, day, hour and minute). When sampling, do not expose the water inlet of the diffuser to avoid inhaling air. Take a good sample and try to avoid vibration. Because of the short half-life of radon, in order to ensure the accuracy of analysis, it is best to measure radon within 24 hours after sampling, and no more than 3 days if conditions do not permit.
If there is no diffuser, you can also use a 500mL glass bottle, fill it with water samples (without gaps), seal it, record the sampling time and send it to the laboratory as soon as possible.
Figure 3. 1.4
3. 1.4.2.8 General bacterial detection is carried out with water samples.
For general bacterial analysis of water samples, the required volume is 100 ~ 200ml. Before sampling, the glass
Glass containers should be strictly disinfected. When sampling, directly take representative samples; There is no need to wash bottles with water samples to prevent pollution. After sampling, a certain space should be left in the bottle, sealed and stored in the dark at 0 ~ 10℃, or the sample should be transported in a container with ice. Under the condition of cold storage, it can be sent to the laboratory for no more than 24 hours; If there is no refrigeration condition, it should be sent to the laboratory within 6 ~ 9 hours.
Attention should be paid to sampling: when collecting surface water samples, you should hold the bottom of the bottle with the bottleneck extending to about 25 ~ 40 cm below the water surface. When filling water, tilt the bottle neck slightly upward, and the bottle mouth is facing the water flow. When sampling on the surface of stagnant water, hold the bottle horizontally and push it forward until it is full of water, and quickly cover the bottle cap and wrap the wrapping paper.
To collect water samples with a certain depth, a single-layer sampler or a deep sampler should be used. When sampling, fix the sample bottle in the sampler, put it into the water body to reach the specified water level, and open the bottle cap with a lanyard; When the water is full, quickly lift the water surface to cover the cork, wrap it with wrapping paper, and keep it according to the sample preservation conditions.
3. 1.4.2.9 Determination of pH value of water sample
Because the pH value of water sample is unstable, it is not suitable for storage, so it is best to carry out in-situ testing. If the conditions are not met, the following methods can be adopted, and the sample should be injected immediately after collection. Before filling samples, each sample bottle and bottle stopper (bottle cap) must be thoroughly cleaned with water samples. When filling the sample, the sample container should be slowly and completely filled from the bottom of the sampling bottle and tightly sealed to isolate the air.
3. Determination of conductivity of1.4.2.10 water sample
It is best to conduct in-situ testing. Do not have the conditions, can be collected according to the requirements of measuring pH samples (see 3. 1.4.2.9). Some samples can also be taken from the samples whose pH value has been determined for the determination of conductivity (but the samples whose pH value has been determined cannot be used for the determination of conductivity).
3. 1.4.2. 1 BOD
Water samples for determination of biochemical oxygen demand shall be collected according to the requirements for determination of dissolved oxygen samples (see 3. 1.4.2.4).
3. 1.4.2. 12 turbidity and suspended solids
For water samples used to determine turbidity and suspended solids, the samples should be released from the sampler as soon as possible after collection, and the sampler should be shaken when bottling to prevent suspended solids from settling in the sampler.
3. 1.4.2. 13 heavy metals and chemical oxygen consumption
Collect and determine heavy metals and some organic substances in water samples. After the sample collection, release the sample from the sampler as soon as possible, and fill the sample container while shaking the sampler (or sampling bottle) to prevent the substance to be measured from settling with the suspended matter in the sampler.
3. 1.4.2. 14 oil
When determining the content of dissolved oil or emulsified oil in water, a single-layer water sampler should be used to fix the sample bottle and put it directly into the water (it is forbidden to wash it with water samples in advance). After sampling, it should be lifted off the water surface quickly, keeping a certain headspace volume, and extracted with petroleum ether at the scene.
When measuring the oil content of oil-bearing film in water, the oil film samples on the water surface should be collected together, and the oil film thickness and coverage area should be measured at the same time.
Sampling of CFCs
In the field, a 50 ml glass bottle with a metal foil plug was used to collect water samples. The plug of the metal-lined foil has good sealing performance, and CFC and air adsorbed on the surface of the metal-lined foil are easily washed away by water. Put the empty glass bottle and bottle stopper into a metal bucket, which must be higher than the glass bottle. Groundwater samples used for CFC analysis go directly to the bottom of glass bottles through suitable pipes (metal, PTFE or nylon), and other plastic pipes are not suitable for sampling (very important! )。 When the metal cylinder 5 is filled with water, the overflow should last for at least 5 minutes until all the air in the sample bottle is driven away (CFC pollution). In this case, before the sampling begins, the gas and CFC absorbed by the inner surface of the glass bottle and the stopper should be cleaned with plenty of water. After overflowing (at least 5 minutes), take out the test tube from the glass bottle and plug the glass bottle with a stopper. It should be confirmed that the glass bottle is tightly covered with water (still in the metal barrel), and the metal barrel is still washed with water to avoid air pollution of the sample.
Figure 3. 1.5
Sealed glass bottles are transported to the laboratory for analysis. If possible, fix the stopper and glass bottle with adhesive tape to prevent the stopper from loosening and sample leakage during transportation.
Attention should be paid to when sampling:
Multiple glass bottles can be placed in a metal barrel at a time for parallel sampling, but the bottles should be thoroughly cleaned in turn to ensure that the air and CFC adsorbed on the inner surface of each bottle are washed away.
3. 1.4.2. 16 Water sample for determination of hydrogen and oxygen isotopes
Take 100mL water sample in a hard glass bottle (fill it as full as possible without leaving any gap), seal it, and send it to the laboratory for stable isotope determination of hydrogen and oxygen.
Take 1L water sample in a glass bottle, seal it, and record the sampling date (year, month and day) for tritium determination.