Detection of vanadium and chromium in water

The volumetric method is used when the concentration is high, and the photometric method is used when the concentration is low.

I only have the titration method of total vanadium and the spectrophotometry method of Cr6+. Is there a spectrophotometric method for total vanadium? Is there a high concentration detection method for Cr6+?

1. Determination of high-concentration vanadium content http://bbs.hcbbs.com/viewthread.php?tid=311208&highlight=%B7%B0 2. Determination of low-concentration vanadium content (from within the network) Determination of toxic substances in workplace air Vanadium and its compounds 1 Scope This standard specifies the method for monitoring the concentration of vanadium and its compounds in the air of the workplace. This standard is applicable to the determination of the concentration of vanadium and its compounds in the air in workplaces. 2 Normative reference documents The provisions in the following documents become provisions of this standard through reference in this standard. For dated reference documents, all subsequent amendments (excluding corrigenda) or revisions do not apply to this standard. However, parties to an agreement based on this standard are encouraged to study whether the latest versions of these documents can be used. For undated cited documents, the latest version shall apply to this standard GBZ 159 Sampling specifications for monitoring harmful substances in workplace air Method 1 N-cinnamoyl-o-toluylhydroxylamine spectrophotometry 3 Principle Aerosol vanadium and its compounds in the air are collected with a microporous filter membrane. After digestion, in hydrochloric acid solution, vanadium ions react with N-cinnamoyl-o-toluylhydroxylamine to form a red complex, which is extracted with chloroform ； Measure the absorbance and perform quantitation. 4 Instrument 4.1 Microporous filter membrane, pore size 0.8μm. 4.2 Sampling clamp, filter material diameter is 40mm. 4.3 Small plastic sampling clamp, filter material diameter is 25mm. 4.4 Air sampler, flow rate 0~3L/min and 0~10L/min. 4.5 beaker, 50ml. 4.6 Electric hot plate or electric sand bath. 4.7 Graduated separatory funnel, 100ml. 4.8 Colorimetric tube with stopper, 10ml. 4.9 Spectrophotometer. 5. The water used in the reagent experiment is deionized water, and the acid used is of superior grade purity. 5.1 Nitric acid, ρ20=1.42g/ml. 5.2 Hydrochloric acid, ρ20=1.18g/ml. 5.3 Perchloric acid, ρ20=1.67g/ml. 5.4 Sulfuric acid, ρ20=1.84g/ml. 5.5 Phosphoric acid, ρ25=1.68g/ml. 5.6 Potassium permanganate solution, 2.5g/L. 5.7 Sulfamic acid solution, 0.5g/L. 5.8 Saturated sodium fluoride solution. 5.9 Sodium hydroxide solution, 50g/L. 5.10 Sulfuric acid solution, 9mol/L: Slowly add 100ml sulfuric acid to 100ml water. 5.11 N-cinnamoyl-o-toluylhydroxylamine chloroform solution, 2.5g/L. 5.12 Standard solution: Weigh 0.1786g of vanadium pentoxide (dry at 105°C for 1 hour), dissolve it in 10ml of sodium hydroxide solution, and quantitatively transfer it to a 100ml volumetric flask, add 5ml of sulfuric acid solution, and dilute to the mark with water. This solution is a 1.0mg/ml standard stock solution. Before use, dilute with water to 10.0μg/ml vanadium standard solution. Or use * * Preparation of approved standard standard solutions. 6 Sample collection, transportation and storage. On-site sampling shall be carried out in accordance with GBZ 159. 6.1 Short time sampling: At the sampling point, install the sampling clip with the microporous filter membrane and collect air samples for 15 minutes at a flow rate of 5L/min. 6.2 Long-term sampling: At the sampling point, a small plastic sampling clip equipped with a microporous filter membrane is used to collect air samples for 2 to 8 hours at a flow rate of 1L/min. 6.3 Individual sampling: Wear a small plastic sampling clip equipped with a microporous filter membrane on the upper chest of the sampling subject, place the air inlet as close to the breathing zone as possible, and collect air samples for 2 to 8 hours at a flow rate of 1L/min. After sampling, fold the dust-contacting surface of the filter membrane in half twice, put it into a clean plastic bag or paper bag, and place it in a clean container for transportation and storage. Samples can be stored at room temperature for long periods of time. 7 Analysis steps 7.1 Controlled test: Bring the sample with the microporous filter membrane installed to the sampling point. Except for not connecting the air sampler to collect the air sample, operate the same sample as the blank control of the sample. 7.2 Sample processing: Put the sampled filter membrane into a beaker, add 2.5ml sulfuric acid and 5ml nitric acid, and slowly heat on an electric hot plate until the solution is transparent. Remove and cool slightly, carefully add 5 drops of perchloric acid ； Continue to heat until white smoke comes out. Remove and let cool. Add 2ml of phosphoric acid and 5ml of water and heat until bubbles escape and white smoke comes out. Transfer quantitatively with water into a colorimetric tube with a stopper, dilute to 10 ml, shake well, take 5.0 ml of the sample solution into a graduated separatory funnel, and add 7 ml of water for measurement. If the vanadium concentration in the sample solution exceeds the measurement range, it can be measured after dilution with water, and multiplied by the dilution factor when calculating. 7.3 Drawing of standard curve: In 6 graduated separatory funnels, add 0.0, 1.0, 2.0, 3.0, 4.0, 5.0ml vanadium standard solution respectively, add water to each to 10.0ml, then add 1.0ml sulfuric acid and 1.0ml phosphoric acid to form a 0.0, 10.0, 20.0, 30.0, 40.0, 50.0g vanadium standard series. Add potassium permanganate solution dropwise to each standard tube until the solution turns stable light red and leave it for 2 minutes. Add 2 ml of sulfamic acid solution and 2 ml of saturated sodium fluoride solution, then add 8 ml of hydrochloric acid to make the final solution concentration 4 mol/L hydrochloric acid, add water to dilute to 25 ml, and shake well. Add 5 ml of N-cinnamoyl-o-toluylhydroxylamine chloroform solution, shake for 2 minutes, place to separate layers, and use a filter paper strip to wipe away the water in the bottom tube of the separatory funnel. ； Place the chloroform layer into a cuvette and measure the absorbance at a wavelength of 530nm. Repeat the measurement three times for each concentration. Draw a standard curve based on the average absorbance versus vanadium content (μg). 7.4 Sample determination: Determine the sample and blank control solution using the operating conditions of the determination standard series. After subtracting the absorbance value of the blank control from the measured absorbance value of the sample, the vanadium content (μg) was obtained from the standard curve. 8 Calculation 8.1 Convert the sampling volume to the standard sampling volume according to formula (1): 293 P Vo = V × ————— × —————… (1) 273 + t 101.3 where : Vo — standard sampling volume, L ； V — sampling volume, L ； t — temperature at the sampling point,℃ ； P — Atmospheric pressure at the sampling point, kPa. 8.2 Calculate the concentration of vanadium in the air according to formula (2): 2 m C =―――――…… (2) Vo where: C - Concentration of vanadium in the air, mg/m3 ； m - measured vanadium content in the sample solution, μg ； Vo - standard sampling volume, L. 8.3 The time-weighted average allowable concentration is calculated according to the provisions of GBZ 159. 9 Note 9.1 The detection limit of this method is 0.2μg/ml ； The lowest detectable concentration is 0.027mg/m3 (based on collecting 75L air sample). The measurement range is 0.2～5μg/ml ； The relative standard deviation is 0.6% to 5.0%. 9.2 The average sampling efficiency of this method is >95%, and the average digestion recovery rate is 93.9%. During sample processing, after adding phosphoric acid, the heating temperature should not be too high and the digestion should not take too long, otherwise gelatinous substances will easily appear and affect the measurement. 9.3 The concentration of hydrochloric acid has a great influence on the extraction of complexes. The suitable acidity is 4mol/L hydrochloric acid concentration. 9.4 Tetravalent titanium does not interfere with the determination. 20 μg of hexavalent chromium and 200 μg of ferric iron interfere with the determination. Adding 2ml 100g/L sodium hexametaphosphate can eliminate the interference of iron. 9.5 This method can use microwave digestion method. The second method of catalytic polarography 10 Principle: Aerosol vanadium and its compounds in the air are collected with a microporous filter. After digestion, in the range of pH 3.7 to 4.2, vanadium ions generate a sensitive catalytic polarographic wave in the copper-iron reagent-mandelic acid bottom solution, and the vanadium content is determined according to the wave height. 11 Instruments 11.1 Microporous filter membrane, pore size 0.8μm. 11.2 Sampling clamp, filter material diameter is 40mm. 11.3 Small plastic sampling clamp, filter material diameter is 25mm. 11.4 Air sampler, flow rate 0~3L/min and 0~10L/min. 11.5 Beaker, 50ml. 11.6 Electric hot plate or electric sand bath. 11.7 Stoppered colorimetric tube, 25 ml. 11.8 Oscillographic polarograph, using three-electrode system: The dropping mercury electrode is the cathode, the saturated calomel electrode is the reference electrode, and the platinum electrode is the auxiliary electrode. 12. The water used in the reagent experiment is deionized water, and the acid used is superior grade pure. 12.1 Nitric acid, ρ20=1.42g/ml. 12.2 Hydrochloric acid, ρ20=1.18g/ml. 12.3 Perchloric acid, ρ20=1.67g/ml. 12.4 Phosphoric acid, ρ25=1.68g/ml. 12.5 Digestive juices: Take 100ml of perchloric acid and add it to 900ml of nitric acid. 12.6 Phosphoric acid solution, 0.3mol/L: Take 2ml of phosphoric acid and dilute it with water to 100ml. 12.7 Sodium fluoride solution, 40g/L. 12.8 Bromophenol blue ethanol solution: Weigh 0.05g bromophenol blue and dissolve it in 50ml ethanol (95%). 12.9 Saturated sodium hydroxide solution. 12.10 Sodium hydroxide solution, 50g/L. 12.11 Hydrochloric acid solution: Take 5ml of hydrochloric acid and dilute it with water to 100ml. 12.12 Acetic acid–sodium acetate buffer: Weigh 50g of anhydrous sodium acetate, dissolve it in water, add 60ml of glacial acetic acid, dilute to 1000ml with water, and adjust the pH to 4.5 with an acidometer. 12.13 Mandelic acid solution, 100g/L: Weigh 10g of mandelic acid, dissolve it in water with slight heat, and dilute to 100ml. 12.14 Copper and iron reagent solution, 3g/L. Store in a cool and dark place and can be used for 1 month. 12.15 Standard solution: Weigh 0.1786g of vanadium pentoxide (dry at 105°C for 1 hour), dissolve it in 10ml of sodium hydroxide (100g/L) solution, and quantitatively transfer it to a 100ml volumetric flask, and dilute to the mark with water. This solution is a 1.0mg/ml standard stock solution. Take 1.0ml in a 100ml volumetric flask, add about 80ml water and 5ml sulfate and phosphoric acid mixture (1+1), and add water to the mark. Then dilute with water to obtain a 1.0μg/ml vanadium standard solution. Also available * * Preparation of approved standard solutions. 13 The collection, transportation and storage of samples. On-site sampling shall be carried out in accordance with GBZ 159. 13.1 Short time sampling: At the sampling point, install the sampling clip with the microporous filter membrane and collect air samples for 15 minutes at a flow rate of 5L/min. 13.2 Long-term sampling: At the sampling point, a small plastic sampling clip equipped with a microporous filter membrane is used to collect air samples for 2 to 8 hours at a flow rate of 1L/min. 13.3 Individual Sampling: Wear a small plastic sampling clip equipped with a microporous filter membrane on the upper chest of the sampling subject, and collect air samples for 2 to 8 hours at a flow rate of 1L/min. After sampling, fold the dust-contacting surface of the filter membrane in half twice, put it into a clean plastic bag or paper bag, and place it in a clean container for transportation and storage. Samples can be stored at room temperature for long periods of time. 14 Analysis steps 14.1 Controlled test: Bring the sample with the microporous filter membrane installed to the sampling point. Except for not connecting the air sampler to collect the air sample, operate the same sample as the blank control of the sample. 14.2 Sample handling: Put the sampled filter membrane into a beaker, add 5 ml of digestive fluid, heat and digest on an electric hot plate, keep the temperature at about 200°C, and evaporate to dryness. Add 5ml of phosphoric acid solution and heat to dissolve the residue. Take it off, quantitatively transfer it to a colorimetric tube with a stopper using phosphoric acid solution, dilute it to 25ml, shake well, and take 5.0ml into another colorimetric tube with a stopper for measurement. If the concentration of the analyte in the sample solution exceeds the measurement range, it can be diluted with phosphoric acid solution and measured. Multiply the dilution factor when calculating. 14.3 Drawing of standard curve: Take 7 stoppered colorimetric tubes, add 0.0, 0.10, 0.20, 0.40, 0.60, 0.80, 1.0ml vanadium standard solution respectively, and add 5ml phosphoric acid solution each to prepare a 0.0, 0.10, 0.20, 0.40, 0.60, 0.80, 1.0g vanadium standard series. Add 1 ml sodium fluoride solution and 1 drop of bromophenol blue ethanol solution ； Adjust the pH with sodium hydroxide solution and hydrochloric acid solution until the yellow color of the solution just disappears and turns slightly blue. Add 1ml acetic acid-sodium acetate buffer and shake well ； Accurately add 0.5ml mandelic acid solution and 0.4ml copper iron reagent solution, shake well ； Dilute to 10ml with water. Shake well. Use an oscilloscope polarograph, set the origin potential to -0.6V, perform cathode derivative scanning to measure the standard series, and record the wave height. Each concentration was measured in triplicate. Subtract the blank and draw a standard curve using the average wave height versus vanadium content (μg). 14.4 Sample determination: Determine the sample solution and blank control solution using the operating conditions of the determination standard series ； After subtracting the blank control wave height from the measured sample wave height, the vanadium content (μg) was obtained from the standard curve. 15 Calculation 15.1 Convert the sampling volume into the standard sampling volume according to formula (1). 15.2 Calculate the concentration of vanadium in the air according to formula (3): 5 m C = ―――――――…… (3) Vo where: C — Concentration of vanadium in the air, mg/m3 ； m — measured vanadium content in the sample solution, μg ； Vo — standard sampling volume, L. 15.3 The time-weighted average allowable concentration is calculated according to the provisions of GBZ 159. 16 Note 16.1 The detection limit of this method is 0.02μg/ml ； The lowest detectable concentration is 0.007 mg/m3 (based on collecting 75L air samples). The measurement range is 0.02～0.2μg/ml. 16.2 The sample digestion temperature should not be too high, otherwise the result will be low. 16.3 The pH of the solution has a great influence on the wave height and should be strictly controlled. 16.4 The copper-iron reagent solution is easy to oxidize, and the oxidation products are difficult to dissolve in water, so a small amount of precipitation will appear after being placed. The supernatant can be taken when used. 16.5 70 times the amount of iron and aluminum, 30 times the amount of titanium and chromium, and 100 times the amount of selenium in the sample will not interfere with the measurement. 16.6 Microwave digestion method can be used in this method. This post was last edited by lifanwang on 2009-3-14 20:09 ]

High-content chromium determination (determined by the redox method) First, take a sample and dissolve it in an acidic solution. In the acidic solution, +6 chromium exists in the form of Cr2O72-. Add excess potassium iodide solution to it to quantitatively precipitate iodine element Cr2O72- + 6I- +14H+ == 2Cr3+ + 3I2 + 7H2O There is a clear stoichiometric relationship between the amount of precipitated iodine element and the amount of +6 chromium. The precipitated I2 is titrated with sodium thiosulfate. I2 + 2Na2S2O3 == 2NaI + Na2S4O6. There is a clear stoichiometric relationship between the amount of sodium thiosulfate consumed and the amount of iodine element. Therefore, the relationship between the amount of sodium thiosulfate and the amount of +6 chromium can be deduced. This titration analysis method is called displacement titration