How To Measure Hydrogen Peroxide Concentration In Water
Hydrogen peroxide is a vital oxidant, bleach, disinfectant and dechlorination agent, which can also be used for bleaching cotton fabrics and other fabrics, bleaching and deinking of pulp, treatment of toxic wastewater, etc. However, too much hydrogen peroxide in water is harmful to the body, so how to measure hydrogen peroxide in water?
Determination method of hydrogen peroxide
There is high-performance liquid chromatography, spectrophotometry and chemical titration to determine hydrogen peroxide. Among them, chemical titration is the primary method, including potassium permanganate titration and iodometry.
Pros:
Low cost
High accuracy
Cons:
Need reagents, complex operation
chemical pollution, low speed.
In order to solve the above issues, now the refractive method is a fast and straightforward method to determine the concentration of hydrogen peroxide solution, which is easy to operate and does not need chemical reagents, including a concentration meter, digital concentration meter, handheld concentration meter, hydrogen peroxide concentration meter and other measuring tools.
Laboratory chemical titration measurement
In dilute sulfuric acid solution, H2O2 reacts with potassium permanganate. Therefore, we can measure its content by the potassium permanganate method.
The formula is:
2 MnO4-＋5 H2O2＋6H+＝2Mn2+＋5O2↑＋8H2O
There is a small amount of MnO2 and other impurities for KMnO4 available on the market, such as sulfate, chloride and nitrate. Distilled water also contains a small amount of reducing substances, which can react with MnO to precipitate MnO (OH) 2 (MnO2 hydrate), and the MnO2 and MnO (OH) 2 can further increase the decomposition of KMnO4. Therefore, we can not prepare the KMnO4 standard solution by the direct method.
The materials for calibrating KMnO4 solution include Na2C2O4, H2C2O4 · 2H2O, (NH4) 2Fe (SO4) 2 · 6H2O, As2O3 and pure iron wire. Since there is no crystal water in Na2C2O4, it is easy to purify and does not absorb moisture, so it is most commonly used.
The reaction of C2O42 – with MnO4 – in acidic solution:
2MnO4-＋5 C2O42-＋16H+＝2Mn2+＋10CO2↑＋8H2O
It must be heated to 75 ~ 85 ℃ to speed up the reaction. However, not too high the temperature, otherwise it is easy to cause partial decomposition of oxalic acid:
H2C2O4＝H2O＋CO2↑＋CO↑
In the titration, the reaction between the first few drops of KMnO4 and C2O42 – is still prolonged, even when heated. When Mn2 + is produced in the solution, the reaction speed is gradually accelerated because Mn2 + has a catalytic effect on the reaction.
In the titration process, it must keep a certain acidity of the solution; otherwise, it is easy to produce MnO2 precipitation and cause errors. Adjust the acidity with sulfuric acid because Cl – in hydrochloric acid is reductive, NO3 – in nitric acid is oxidizing, and the acidity of acetic acid is too weak to reach the required acidity. The suitable acidity for titration is about C (H +) = 1mol · L-1. Because the KMnO4 solution itself has a special purplish-red colour, when the KMnO4 solution is slightly excessive during titration, we can see that the solution is light pink, indicating that the endpoint has been reached.
3. Instruments and reagents
Instruments: analytical balance, 10ml acid burette, 5ml pipette, 100ml volumetric flask, 250ml conical flask, beaker, dropper, ear ball, glass rod, bottle washing, etc.
Reagent: KMnO4 solid, C (H2SO4) = 3 mol · l-1h2so4 solution, Na2C2O4 (a · R): dry at 105 ~ 110 ℃ for 2h. H2O2 solution (30g / L): dilute 10 times with 30% H2O2 commercially available.
Steps
1. Preparation of C (KMnO4) = 0.01 mol · L-1 KMnO4 standard solution: weigh about 0.4 g of KMnO4 solid with a bench scale, dissolve it in 250 ml distilled water, cover the surface dish, heat it to boiling and keep it slightly boiling for 1H. After cooling, filter with a microporous glass funnel (No. 3 or No. 4). The filtrate is stored in a brown reagent bottle.
2. Preparation of Na2C2O4 standard solution: Accurately weigh 0.4g Na2C2O4 by subtraction method, put it into a 50ml beaker, add about 20ml hot distilled water to dissolve it, after cooling, transfer it into a 100ml volumetric flask, wash the inner wall of the beaker and the glass rod with distilled water for three times, transfer all the washing liquid into the volumetric flask, and then fix the volume with distilled water to the scale, shake it well and set it aside.
3. Calibration of 0.01 mol ·L-1 KMnO4 solution: accurately put 20.00 ml Na2C2O4 solution into a 100 ml conical flask, add 4 ml 3 mol · L-1 H2SO4 solution, mix well, heat to 75 ~ 85 ℃, and titrate with KMnO4 standard solution while hot. In the beginning, the reaction is slow; drop a drop of KMnO4 standard solution, shake it, and then add a second drop after the solution fades (at this time, Mn2 + is generated in the reaction to act as a catalyst).
With the acceleration of the reaction, we can also gradually accelerate the titration speed, but not too fast, especially when it is close to the stoichiometric point. Be careful to add drops, and shake or stir constantly. Titrate until the solution is light pink and the colour does not fade within 30 s, which is the endpoint. Repeat the operation 3 times to calculate the results and relative deviation.
4. Determination of H2O2 Content: pipette 10.00 ML 30 g / L H2O2 sample into a 250 ml volumetric flask, add water to dilute the scale, and shake well. Put 25.00 ml of the dilute solution into a 250 ml conical flask, add 30 ml of deionized water and 30 ml 3 mol / L sulfuric acid solution respectively, and then titrate with the calibrated KMnO4 standard solution until the solution is slightly red and does not disappear within 30 s, which is the endpoint. Titrate 3 parts in parallel to calculate the concentration of the H2O2 sample.
Determination of anions in hydrogen peroxide by Ion Chromatography
The traditional determination of inorganic anions in hydrogen peroxide common are turbidimetry and colourimetry, but they can only determine a single ion and cannot determine trace anions. How to improve it? We can accurately determine the anion in hydrogen peroxide by ion chromatography. However, hydrogen peroxide will cause irreversible damage to the ion chromatography column, so we must remove hydrogen peroxide in sample pretreatment.
There are many pretreatment methods for hydrogen peroxide samples. It is to decompose hydrogen peroxide into water and oxygen. The traditional distillation method is long and lows the decomposition efficiency, which will also cause ion loss. Moreover, there are certain potential safety problems under high temperatures due to the large amount of oxygen produced in the decomposition process. So, we will introduce a platinum catalytic decomposition method for the pretreatment of hydrogen peroxide samples, which is simple and fast, does not cause ion loss, and is safe and convenient.
Sample pretreatment
Sample: hydrogen peroxide
Catalyst: platinum mesh or platinum sheet
Stabilizer: sodium hydroxide
Container: colourimetric tube
Step:
1. Take a 5ml hydrogen peroxide sample into a 50ml colorimetric tube
2. Add 1ml evaporation stabilizer,
3. Add platinum wire mesh for self disproportionation reaction
4. When there are no obvious bubbles, the hydrogen peroxide is completely decomposed and tested on the instrument after purification.
Instrument configuration and chromatographic
Ion chromatograph: conductivity detector ic6200;
Automatic sampler: as3100;
Chromatographic column: anion analysis column 4 × 250mm；
Eluent: 3.6mmol/l;
Flow rate: 0.8ml/min;
Column temperature: 45 ℃;
Tank temperature: 45 ℃;
Suppression current: 30mA
Chromatogram – Standard
Sample determination
Blank sample spectrum:
sample
The overlapping spectrum of sample and standard
Note:
- Addition amount of platinum mesh: the amount of platinum mesh or platinum sheet directly affects the decomposition efficiency of hydrogen peroxide. Less addition, slow decomposition, long time, excessive addition, violent reaction and risk of ion loss. Therefore, we should add an appropriate platinum mesh according to the hydrogen peroxide concentration and sampling amount. The amount of platinum mesh added to the left colourimetric tube is less than that of the right colourimetric tube.
- Hydrogen peroxide sample cannot be passed directly under this chromatographic condition, and the matrix interferes with the analysis and damages the packing of the chromatographic column.
- There are organic and heavy metal residues in the sample, which can be tested only after purification
- To accelerate the platinum-catalyzed reaction rate, we can combine platinum-catalyzed self disproportionation reaction and electrolysis.
