Environmental Monitoring Experimental Guide (环境检测英文版实验指导)

《Environmental Monitoring》Experiment Guide

M a j o r：

I n s t r u c t o r：E n v i r o n m e n t a l E n g i n e e r i n g

H u i y a n C h e n g&X i a o m i n g H u a n g

D e p a r t m e n t o f

E n v i r o n m e n t a l S c i e n c e a n d E n v i r o n m e n t a l

E n g i n e e r i n g

M a y10,2016

Experiment 1. Determination of Chroma and Turbidity

1. Principles

Pure water is clear and colorless, but nature water often shows a certain color, which comes mainly from leaves, barks, roots, humus of plants and soluble inorganic minerals and sediment. The color of surface water polluted by industrial waste water will become extremely complex.

Color can be divided into “true color” and “apparent color”. “True color” means the color exist after removing the suspension of the water. If the sample is turbid, it should be placed until clarified to determinate the supernatant. Or be filtered by membrane filters of 0.45μm aperture and then be centrifuged to determinate the color. "Apparent color" refers to the color of water without removing the suspension. To determinate the color of the original water samples without filtration or centrifugation is called measuring its "apparent color". For the water clean or with very low turbidity, the true color is similar to the apparent color. For the industrial water with deep color which is mainly caused by collide and suspended substance, it is allowed to measure either "true color" or "apparent color" according to the actual needs.

Determination of the color of water contains the methods of platinum/cobalt standard colorimetry (cobalt/chromium standard colorimetriy) and dilution multiple method. The former applies to the determination the color of the clean water, natural water with the hue of yellow and drinking water (result expressed as number of degrees). The latter applies to the determination of color of surface water polluted by the industrial wastewater and industrial wastewater (result expressed as diluted multiples).

Platinum/cobalt standard colorimetry use chloroplantinic acid and cobalt chloride to prepare standard color series, and do visual colorimetric analysis against the water samples. Water sample containing 1mg platinum and 0.5mg cobalt per 1000mL is defined as 1 degree, and to be used as the unit of color series.

Dilution multiple method is to dilute industrial waste water by a certain proportion of water to almost colorless, and then record the actual diluted multiple,

which value is called the color of this water sample.

Determination of turbidity of water samples includes visual method and photoelectric turbidimetry. Samples are collected in glass bottles, and determinate the samples after sampling as soon as possible.

Visual method is to prepare different turbidity series depending on the turbidity level of water. Turbidity produced by 1mg a certain size of diatomite (white clay) in 1000mL of the water is known as 1degree. Compare water samples with diatomite (white clay) preparation of the turbidity standard solution, so as to get the result of the turbidity of the water.

2.Equipments and Reagents

(1) 50mL colorimetric tubes with plug, whose scale line should be at the same level.

(2) Platinum and cobalt standard solution: 1.246g potassium chloroplatinate (K2PtCl6) (equivalent to 500mg platinum) and 1.000g cobalt chloride (CoCl2.6H2O) (equivalent to 250mg cobalt) are weighted and dissolved in 100mL water. Then add 100mL hydrochloride and add water to 1000mL. This solution is 500 degree of color and to be preserved in bottles in the dark.

(3) Cobalt-chromium standard solution: 0.0437g K2Cr2O7and Cobalt sulfate (CoSO4.7H2O) is weighted and dissolved into a small amount of water. Then add o.5mL sulfuric acid and dilute it with water to 500mL. This color of this solution is 500 degrees. It is not preserved for a long time.

(1)Turbidity meter.

(2) 100mL colorimetric tube with plug.

(3) 250mL colorless glass bottles, mass and diameter of glass should uniform.

Weight 10g turbidity standard solutions which go through 0.1mm sieve (150 mesh) of diatomite, and add a little distilled water into a mortar to form paste and

grind. Then move to 1000mL graduated cylinder and add water to scale. Fully stirring and standing 24h. Then move carefully 800mL upper suspension to the second 1000mlL graduated cylinder by siphonage. Add water into the second graduated cylinder to 1000mL, fully stirring again and standing 24h.

Move out 800mL upper suspension containing smaller particles by siphonage, and then abandon it. Add water to bottom sediment until 1000mL to dilute. Fully stirred and stored in a glass bottle with plug as the original turbidity solution. Diameter of diatomite particles contained in the solution is about 400μm.

Put 50.0 suspension mentioned above into evaporation dish whose weight id constant, and steam it in the water bath. Baked it in oven at 105℃for 2h, then cool it 30min in the dryer, and weighting it until constant weight. Calculate the mass of diatomite per milliliter of suspension (mg).

Move 250mL of the suspension of diatomite into 1000mL volumetric flask and add water to scale, shaking it up. Turbidity of this solution is 250 degrees.

Move 100mL turbidity standard solution of 250 degrees into volumetric flask, and add water to scale, shaking it up. Turbidity of this solution is 100 degrees. Add 1g/L mercuric chloride into the solution to prevent fungus from growing.

3. Procedures

1）Preparations of standard color series

Add 0, 0.50mL, 1.00mL, 1.50mL, 2.00mL, 2.50mL, 3.00mL, 3.50mL, 4.00mL, 4.50mL, 5.00mL, 6.00mL, 7.00mL cobalt platinum standard solution(or cobalt chromium standard solution) respectively in 50mL-colorimetric tubes. Dilute them to the mark with water and mix it. The color of each tube is of 0, 5degrees, 10degrees, 15degrees, 20degrees, 25degrees, 30degrees, 35degrees, 40degrees, 45degrees, 50degrees, 60degrees,70degrees consequently.

2) Determination of water samples

(1) 50.0mL water samples are placed in the colorimetric tube. If color of water is

deep, take some water sample appropriately and dilute it to 50.0mL.

(2) Make visual comparison between water samples and the standard color. Placed the colorimetric tubes on the white porcelain plate or white paper when observing. Make the light transmission from the bottom to up of liquid column, and the sight downward at the tube vertically. And write down the water color that is the same to the color of platinum-cobalt.

Visual turbidimetry

(1) The turbidity of the water samples is lower than 10 degrees.

①Draw turbidity standard solution of 100 degrees 0, 1.0mL, 2.0mL, 3.0mL,

4.0mL,

5.0mL,

6.0mL,

7.0mL,

8.0mL,

9.0mL, 10.0mL into colorimetric tubes of 10mL, and add water mark line to dilute, mixing. That is standard solutions with turbidity of 0, 1.0 degrees,2.0 degrees, 3.0 degrees, 4.0 degrees, 5.0 degrees, 6.0 degrees, 7.0 degrees, 8.0 degrees, 9.0 degrees, 10.0 degrees respectively.

②Take 100mL mixed water samples to colorimetric tubes of 100mL, and compare with standard solution. It is possible to observe from top to down vertically with black background.

（2）The turbidity of the water samples is above 10 degrees.

①Draw turbidity standard solution of 250 degrees 0, 10mL, 20mL, 30mL, 40mL, 50mL, 60mL, 70mL, 80mL, 90mL, 100mL into colorimetric tubes of 250mL, and add water to mark line to dilute, mixing. That is standard solutions with turbidity of 0, 10 degrees, 20 degrees, 30 degrees, 40 degrees, 50 degrees, 60 degrees, 70 degrees, 80 degrees, 90 degrees, 100 degrees respectively. Move the solutions to 250ml - bottles with plug, adding 1g/L mercuric chloride per bottle to prevent the fungi growing, sealed.

②Take 250mL water samples stirred to a whole set of 250ml bottles with plug. Place a piece of white paper with black lines which are discrimination signs. Observe the bottles from front to back. Elect standard solutions which have similar visual effect to the water samples depending on clarity level object, and write down the turbidity.

③When turbidity of water is lover 100 degrees, dilute and then determinate it.

4. Data Processing

Records measured by the color. The dilution of the water samples, calculation as

follows:

degree of color=AA×50

Where: A —degree of color of di l uted w ater s amples e quivalent t o s tandard platinum/cobalt;

B — volume of water sample (mL).

5.Notes

(1) If water is turbid, stand it to clarify. Otherwise, use centrifugal method or membrane filters with aperture of 0.45μm to remove suspended solids, nit paper

filter. Filter paper can absorb the color dissolved in water.

(2) If soil or other small dispersion of suspended solids in the water, measure

apparent color even so pretreatment and water is not transparent.

6.Throught and Discussion

1. Is there any relationship between the mass concentration and turbidity of the suspended matter? Why?

2. Is it the "true color" or "apparent color" of the water sample determined by

the method of platinum - cobalt standard colorimetry?

Experiment 2 Determination of Chemical Oxygen Demand (COD)

1. Purposes

(1) Know the definition of chemical oxygen demand

(2) Master the principle of determination of chemical oxygen demand

(3) Master the operation of oxidation-reduction titration.

2. Principles

Add known amount of potassium dichromate solution to water samples, and use silver sulfate as the catalyst in strong sulfuric acid solution, after boiling and returning, use Ferroin as the indicator and titrate potassium dichromate not restored in water samples with ferrous ammonium sulfate, then convert the consumption of ferrous ammonium sulfate into mass concentration of oxygen consumption.

Under the condition of acidic potassium dichromate, aromatic hydrocarbon and pyridine are hard to be oxidized, the oxidation rate is low, and the straight-chain aliphatic compounds can be oxidized effectively in silver sulfuric catalysis.

The method is applicable to all types of water samples whose COD values are greater than 30mg/L, and the upper limit of water samples which are not diluted is 7000mg/L. The method is not suited to water samples whose chloride is more than 1000mg/L.

3. Equipments

(1) Reflux condensers (with 250mL or 500mL round-bottomed flasks with ground-glass necks.).

(2) Heating electric furnaces.

(3) 25mL or 50mL burets.

(4)1mL or 5mL pipet.

(5) 250mL conical flasks.

(6) V olumetric flasks.

(7) Small beaker.

(8) 20mL graduated flask.

4. Reagents

(1) Standard potassium dichromate solution [c(1/6K2Cr2O7) = 0.0250mol/L]: dissolved 12.25g K2Cr2O7 dried at 120℃(primary standard grade) in distilled water, transfer to a 1000mL volumetric flask, and dilute to the mark.

(2) Standard ferrous ammonium sulfate reagent {c[(NH4)2Fe(SO4)2.6H2O] =0.1mol/L}: dissolve 39.5g analytical-grade (NH4)2Fe(SO4)2.6H2O in distilled water, add 20mL concentrated H2SO4, cool, transfer to a 1000mL volumetric flask, and dilute to the mark. This solution must be standardized before used.

Standardization:Dilute 10mL standard potassium dichromate to 110mL in a 500mL-besker flask, and add 30mL concentrated H2SO4. Slow and cool it down. Titrate with the ferrous ammonium sulfate titrant using 3 drops of ferroin as the indicator. The normality of the ferrous ammonium sulfate is determined by the following formula:

cc=0.0250×10.00

Where: c— concentration of the standardized ferrous ammonium sulfate reagent (mol/L);

V— volume of the standardized ferrous ammonium sulfate reagent used to the end of titration ( mL).

(3) Silver sulfate-sulfuric acid reagent: dissolved 5g silver sulfate in 500mL

concentrated H2SO4. It will take 1 or 2 days for the silver sulfate to

dissolve.

(4) Mercuric sulfate crystals.

(5) Ferroin indicator solution: dissolve 1.485g 1,10-phenanthroline monohydrate (C12H8N2.H2O) and 0.695g FeSO4.7H2O in distilled water and dilute to 1000mL. This solution should be stored in the dark flask.

5. Procedures

(1) Place 20mL water sample in the reflux flask (250mL round-bottomed flask with ground-glass necks) and add 10mL standard potassium dichromate solution to the flask. Then add several boiling chips. Attached the flask to the reflux condenser, then add 30mL silver sulfate-sulfuric acid reagent slowly to the flask. Swirl to mix it, then reflux it for 2 hours.

(2) After being refluxed the solution is cooled and the reflux condenser is washed down with 90mL distilled water. Detach the flask from the condenser and measure the volume of solution. Bring up to a volume of 140mL with distilled water if necessary.

(3) Add 3 drops of the ferroin indicator and titrate above reflux solution to a reddish-brown end point with the standardized ferrous ammonium sulfate titrant.

(4) A blank consisting of 20mL distilled water in place of the sample is treated. After being refluxed, it can be titrated in the same manner.

(5) Calculations: The CODcr is calculated from the following equation:

CODcr(O2,mg L?)=(VV0?VV1)×cc×8×1000

VV

Where: c—concentration of the standardized ferrous ammonium sulfate reagent (mol/L);

V0—volume of the standardized ferrous ammonium sulfate reagent used for blank (mL);

V1—volume of the standardized ferrous ammonium sulfate reagent used for sample(mL);

V— volume of the water sample (mL);

8 — mass of 1 mol of 1/2O (g/mol).

6. Notes

(1) When the COD of sample is lower than 50mg/L, the concentration of standard potassium dichromate solution should adjust to 0.0250mol/L.

(2) After being refluxed, the leaving of potassium dichromate should be 1/5to 4/5

of the addition.

(3) Use the potassium hydrogen phthalate standard solution check the quality of reagents and technical operations, as per gram of potassium hydrogen phthalate theory COD value of 1.176g, so 0.4251g of potassium hydrogen phthalate (HOOCC6H4COOK) was dissolved in re-distilled water, switched to 1000mL volumetric flasks, to dilute it to become 500mg/L CODcr standard solution. Make solution when using.

(4) COD's results should be retained in the three available digits.

(5) Each experiment, ferrous ammonium sulfate titration should be carried out. The change of its concentration should be noticed at high ambient temperature.

7. Thought and Discussion

1. Why do you need to make a blank correction when determination of water samples?

2. What is the difference between the Chemical Oxygen Demand and Potassium Permanganate Index?

Experiment 3 Determination of Ammonia Nitrogen Content

(Nessler's Reagent Colorimetric Method)

1. Principles

The yellow-brown collodial compound was formed by the reaction between alkaline solution containing potassium iodide & mercury iodide and ammonia. Its chroma is proportional to the concentration of ammonia nitrogen, whose measurement scope of wave length is 410nm to 425nm. The minimum detectable concentration of this method is 0.025mg/L, and the maximum detectable concentration is 2mg/L.

2. Equipments

(1) 500mL glass still;

(2) 50mL colorimetric tube tubes;

(3) Spectrophotometer;

(4) pH meter

3. Reagents

Water for reagent preparation must be free-ammonia water.

(1) Free-ammonia water: Water solution goes through strong acid ion-exchange resin or be added to sulfuric acid and KMNO4, and then be redistilled.

(2) 1mol/L NaOH solution.

(3) Absorption liquid: ①boric acid: Add 20g boric acid to 1L water. ②0.01mol/L sulfuric acid.

(4) Nessler reagent: Dissolve 16g NaOH in 50mL water and be cooled to room temperature.

Then dissolved 7g KI and HgI2to water and inject the solution into NaOH solution slowly. Dilute to 1000mL with water and keep the solution in a polyethylene bottle.

(5) Potassium sodium tartrate: Dissolved 50g potassium sodium tartrate

(KNaC4H4O6.4H2O) in 100mL water, then heat it to boiling to remove ammonia. Cool and keep constant volume to 100mL.

(6) Ammonium reserve standard solution: Dissolved 3.819g NH4Cl dried at 100℃and remove it into 1000mL volumetric flask, then dilute it to mark line with water. In this solution there is 1mg/L ammonia nitrogen.

(7) Ammonium standard solution for use: remove 5mL standard solution to 500mL volumetric flask and then dilute it to the mark line. In this solution there is 0.010mg/L ammonia nitrogen.

4. Procedures

(1) Pretreatment of water samples: Colorless and clarified water can be determined directly, while he water samples with high chroma and turbidity or containing much disturbance must be pretreated, such as distillation or coagulation sedimentation.

(2) Protract specification curve: add 0.50mL, 1.00mL, 3.00mL, 5.00mL, 7.00mL and 10.00mL ammonium standard solution for use to 50mL colorimetric tube and dilute them to the mark line with water. Add 1.0mL potassium sodium tartrate solution, mix them well. Add 1.5mL Nessler's reagent, mix them well too. Place the solution for 10 minutes and then determinate its absorbance by 10mm colorimetric ware at 420nm. The specification curve is prepared by ammonia nitrogen (mg) and correction absorbance that obtained by its absorbance to subtract blank absorbance.

(3) Determination of water samples: Immigrated proper volume of water (in which ammonia nitrogen concentration should be less than 0.1mg) into 50 mL colorimetric tube and dilute it to the mark line by water. Add 1.0mL potassium sodium tartrate and 1.5mL Nessler's reagent in turn and mix them well. The solution shall be placed for 10min and then determinate its absorbance by 10mm colorimetric ware at 420nm.

(4) Blank experiment: Free-ammonia water was used for blank determination instead of water sample.

5. Calculation

Concentration of ammonia nitrogen (mg) is calculated by standard curve at corrective absorbance.

Ammonia nitrogen (N)(mg L?)=mm×1000/VV

Where: m —Ammonium concentration of that calculated by standard curve (mg);

V— volume of the water sample (mL);

6. Notes

(1) Ratio of HgI2 to KI in nessler reagent has great influence on sensitivity of color reaction. The precipitation after standing should be removed.

(2) The filter paper must be washed by non-ammonia water for trace ammonium salt. All glassware must be washed by avoided being contaminated by ammonium in air.

7. Thought and Discussion

1. It is better to use what method to determine the content of ammonia nitrogen when the water sample has the color?

2. What are the factors that affect the accuracy of the measurement?

实验四水中铬（Ⅵ）的测定

一、实验目的和要求

（1）掌握用分光光度法测定六价铬和总铬的原理和方法,熟练使用分光光度计。

（2）复习《环境监测》(第四版）第二章第六节中测定铬的各种方法，比较其优、缺点。

二、原理

水中铬的测定方法有分光光度法、原子吸收光谱法、ICP - AES法和滴定法。本实验采用分光光度法。其原理基于:在酸性溶液中，六价铬与二苯碳酰二肼反应，生成紫红色络合物，其最大吸收波长为540 nm，吸光度与浓度的关系符合比尔定律。如果测定总铬,需先用高锰酸钾将水样中的三价铬氧化为六价铬，再用本法测定。

三、仪器与试剂

（一）仪器

(1)分光光度计。

(2)比色皿：1cm、3cm。

(3)具塞比色管:50mL。

(4)移液管。

(5)容量瓶。

（二）试剂

除另有说明外,所用试剂均为分析纯试剂。

(1)丙酮。

(2)硫酸:1+1。

(3)磷酸:1+1。

(4)氢氧化锌共沉淀剂:称取七水合硫酸锌(ZnS04.7H20)8g,溶于100mL水中；称取氢氧化钠2.4g,溶于新煮沸冷却的120mL水中。将以上两溶液混合。

(5)高锰酸钾溶液:40g/L。

(6)铬标准贮备液:称取于120℃干燥2h的重铬酸钾（优级纯）0.2829g,用水溶解，移入1000mL 容量瓶中，用水稀释至标线，摇匀，每毫升铬标准贮备液含0.100mg六价铬。

(7)铬标准使用液：吸取5.00mL铬标准贮备液于500mL容量瓶中，用水稀释至标线，摇匀。每毫升铬标准使用液含1.00 μg六价铬。使用当天配制。

(8)尿素溶液:200g/L。

(9)亚硝酸钠溶液:20g/L。

(10)显色剂(二苯碳酰二肼)溶液:称取二苯碳酰二肼(简称DPC,C13H14N40)0.2g,溶于50mL丙酮中，加水稀释至100mL,摇匀，贮于棕色瓶内，置于冰箱中保存。颜色变深后不能再用。

(11)浓硝酸、浓硫酸、三氯甲烷。

(12)氨水溶液:1+1。

(13)50g/L铜铁试剂:称取铜铁试剂[C6H5N(NO)ONH4]5g,溶于冰水中并稀释至100mL。临用时现配。

四、测定步骤

(一）水样的预处理

1.测定六价铬水样的预处理方法

（1）对不含悬浮物、低色度的淸洁地表水,可直接进行测定。

（2）如果水样有色但不深，可进行色度校正。即另取一份水样，加入除显色剂以外的各种试剂，以2mL丙酮代替显色剂，用此溶液为测定样品溶液吸光度的参比溶液。

（3）对浑浊、色度较深的水样，应加入氢氧化锌共沉淀剂并进行过滤处理。

（4）水样中存在次氯酸盐等氧化性物质时,干扰测定，可加入尿素和亚硝酸钠消除。

（5）水样中存在低价铁、亚硫酸盐、硫化物等还原性物质时,可将Cr(VI)还原为Cr3+，此时，调节水样pH至8,加入显色剂溶液，放置5 min后再酸化显色，并以同法作标准曲线。

2.测定总铬水样的预处理方法

（1）一般淸洁地表水可直接用高锰酸钾氧化后测定。

（2）对含大量有机物的水样，需进行消解处理。即取50mL或适量（含铬少于50μg)水样,置于150mL烧杯中,加入5mL硝酸和3mL硫酸，加热蒸发至冒白烟。如溶液仍有色,再加人5mL硝酸，重复上述操作,至溶液淸澈，冷却，用水稀释至约10mL,用氨水溶液中和至pH为1～2,移入50mL容量瓶中，用水稀释至标线，摇匀，供测定。

（3）如果水样中钼、钒、铁、铜等含量较大,先用铜铁试剂和三氯甲烷萃取除去,然后再进行消解处理。

（4）高锰酸钾氧化三价铬:取50.0mL或适量（铬含量少于50μg)淸洁水样或经预处理的水样（如不足50.0mL,用水补充至50.0mL)于150mL锥形瓶中,用氨水溶液和硫酸溶液调至中性，加入几粒玻璃珠，加入（1+1)硫酸和(1+1)磷酸各0.5mL,摇匀。加人40g/L高锰酸钾溶液2滴，如紫色消退，则继续滴加髙锰酸钾溶液至保持紫色。加热煮沸至溶液剩约20mL。冷却后，加入1mL200g/L的尿素溶液，摇匀。用滴管加20g/L亚硝酸钠溶液，每加一滴充分摇匀,至紫色刚好消失。稍停片刻，待溶液内气泡逸尽，转移至50mL具塞比色管中，稀释至标线，供测定。

（二）标准曲线的绘制

取9支50mL具塞比色管，依次加入 0mL、l.00mL、2.00mL、4.00mL、6.00mL、8.00mL和10.00mL 铬标准使用液，用水稀释至标线，加入(1+1)硫酸0.5mL和（1+1)磷酸0.5mL，摇匀。加入2mL显色剂溶液，摇匀。5～10min后，于540nm波长处，用1cm或3cm比色皿，以水为参比，测定吸光度并作空白校正。以吸光度为纵坐标，相应六价铬质量为横坐标绘出标准曲线。

(三）水样的测定

取适量（含六价铬少于50μg)无色透明或经预处理的水样于50mL具塞比色管中，用水稀释至标线，以下步骤同标准溶液测定。进行空白校正后根据所测吸光度从标准曲线上查得六价铬质量。

(四）计算

式中:m — 从标准曲线上查得的六价铬的质量，μg;

V — 水样的体积，mL。

（五）注意事项

(1)用于测定铬的玻璃器皿不应用重铬酸钾洗液洗涤。

(2)六价铬与显色剂的显色反应一般控制酸度在0.05～0.3mol/L(l/2H2S04)范围，以0.2mol/L时显色最好。显色前,水样应调至中性。显色温度和时间对显色有影响，在15℃时,5～15min顔色即可稳定。

(3)如测定淸洁地表水样，显色剂可按以下方法配制：溶解0.2g二苯碳酰二肼于100mL体积分数95%的乙醇中,边搅拌边加入（1+9)硫酸400mL。该溶液在冰箱中可存放一个月。显色时直接加入此显色剂2.5mL即可,不必再加酸。但加入显色剂后，要立即摇匀，以免六价铬可能被乙酸还原。

五、思考与讨论

（1）影响测定准确度的因素有哪些？

（2）比较各种测定方法的特点。