HJ 924-2017Technical requirement and test procedures for rapid COD photometric analyzer (English PDF)

4.1 Methodology

Add a certain amount of potassium dichromate solution in the sample, in a strong acid medium, silver sulfate as a catalyst, closed by high temperature After solution, the absorbance of hexavalent chromium (Cr6) or trivalent chromium (Cr3) was measured by spectrophotometry to determine the COD value.

4.2 Measuring range

Instrument measurement range of 15 ~ 1000 mg/L, the sample Cl - concentration <= 1000 mg/L.

5.1 Appearance

5.1.1 Analyzer surface should not have obvious files, scratches, cracks, deformation and stains, coating the surface of the instrument should be uniform, no foaming, cracking, peeling off and abrasion, no damage and cracks on the display panel, clear characters and figures.

5.1.2 The identification of the measuring instrument shall comply with the requirements of GB/T 12519, and the nameplate shall be fixed in an appropriate and obvious place, on which should have the following logo.

a) manufacturer's name and address;

b) instrument name, model specifications;

c) factory number;

d) date of manufacture;

e) measurement range, lower limit of quantification;

f) Production license number.

5.2 Equipment Construction

The analyzer consists of thermostatic digestion device, digestion tube, photometer and other functional components.

5.3 Basic functions

5.3.1 Thermostat digestion device

5.3.1.1 should have regular reminders, temperature calibration and other functions.

5.3.1.2 should have a transparent and ventilated protective cover.

5.3.1.3 The preheating time should not exceed 20 min.

5.3.1.4 digestion time should not exceed 30 min.

5.3.1.5 heating hole depth should be higher than the digestion tube liquid height.

5.3.2 Digestion tube

5.3.2.1 Digestion tubes shall comply with the relevant requirements of HJ/T 399.

5.3.2.2 digestion tube should be made of acid-resistant glass, at 165 °C can withstand 600 kPa pressure, tube cover should be heat-resistant acid, Digestion tube and tube cover should not be any wear or tear.

5.3.2.3 If the digestion tube is used as a colorimetric tube, the part used for photometric determination should be smooth and transparent without scratches and roughness.

5.3.3 Photometer

5.3.3.1 The absorbance and concentration values should be clearly displayed.

5.3.3.2 should have data storage, access functions.

5.3.3.3 should have the curve storage, inspection, calibration function.

7.1 Test conditions

7.1.1 Ambient temperature. 0 ~ 40 °C, within ± 5 °C.

7.1.2 Relative humidity. 90% or less.

7.1.3 Atmospheric pressure. 86 ~ 106 kPa, the variation range is within ± 5%.

7.1.4 Voltage. AC (220 ± 22) V.

7.1.5 Power frequency. (50 ± 0.5) Hz.

7.1.6 tester warm-up time. according to the instructions for implementation.

7.2 Reagents

Unless otherwise indicated, the reagents used in this standard are analytical reagents in line with national standards, experimental water for the newly prepared Deionized or distilled water or water of equal purity.

7.2.1 Potassium hydrogen phthalate standard solution. rho (KHC8H4O4) = 850.2 mg/L.

Weigh 0.8502 g of potassium hydrogen phthalate (KHC8H4O4) dried at 105 ° C for 2 h, dissolved in water and diluted to 1000 ml, Mix well. With potassium dichromate as oxidant, the CODCr value for complete oxidation of potassium hydrogen phthalate was 1.176 g oxygen/g (ie 1 g Potassium hydrogen phthalate consumption 1.176 g), so the standard solution theory CODCr value of 1000 mg/L.

7.2.2 COD standard test solution.

By potassium hydrogen phthalate standard solution (7.2.1) stepwise dilution with water to obtain the theoretical CODCr values were 30 mg/L, 50 mg/L,.200 mg/L, 500 mg/L, 800 mg/L standard test solution.

7.2.3 Chloride solution. rho (Cl -) = 5000 mg/L.

Sodium chloride (NaCl) is placed in a porcelain crucible and fired at 500-600 ° C for 40-50 min. Cool in the dryer After weighing 8.240 g dissolved in water and diluted to 1000 ml, mix.

7.2.4 Chloride interference test solution. rho (CODCr) = 300 mg/L, rho (Cl -) = 1000 mg/L.

Pipette 300 ml of potassium hydrogen phthalate standard solution (7.2.1),.200 ml of chloride ion solution (7.2.3) in 1000 ml the volumetric flask, diluted with water to the mark, mix well.

7.2.5 Other Reagents. Prepare required reagents in advance according to the instruction manual.

7.3 Equipment

7.3.1 Electronic Thermometer. Measuring range 0 ~.200 °C, sub-value 0.5 °C.

7.3.2 Electronic stopwatch. Division value 1/100 s.

7.3.3 Megger. The terminal voltage is 500 V.

7.4 Test preparation

After the power is turned on, preheat the analyzer according to the preheating time specified in the instruction manual so as to make each part function and display Recording unit is stable.

7.5 Performance test methods

7.5.1 Digestion time indication error

The digestion time is set to work digestion time, when the digestion timer function starts, while starting the electronic seconds

Table (7.3.2), when the end of timing, stop timing, repeated measurements 3 times, calculate the average xt, according to equation (1) Solution time indication error deltat.

7.5.2 Digestion temperature uniformity

Set the digester control temperature to the digestion temperature, start the digestion device, until the displayed temperature is stable, according to digestion the number of holes, uniformly selected 6 to 9 digestion holes (to ensure that the middle hole and around the hole can be detected), with an electronic thermometer Respectively, measured digestion hole temperature, each digestion hole interval 1 min read 1 number, read a total of 3 times, calculate 3 measurements Arithmetic mean Ti, select the maximum value of Tmax and minimum value Tmin, according to equation (2) calculate the uniformity of digestion temperature W.

max min W = T - T (2) where. W - digestion temperature uniformity error, °C;

Tmax - the average temperature of the highest digestion hole, °C;

Tmin - average temperature of the lowest digestion hole, °C.

7.5.3 Digestion temperature indication error

Set the digester control temperature to the digestion temperature, start the digestion device, until the displayed temperature is stable, according to digestion the number of holes, uniform selection of 6 to 9 digestion holes (to ensure that the middle hole and around the hole can be measured), with electronic thermometer the volume of digestion hole temperature, each digestion hole 1 minute interval to read a number read a total of 3 times, calculate the arithmetic value of 3 measurements Average Ti, calculate the indication error deltaTi of each Ti and the set temperature T according to the formula (3), and take the maximum indication error deltaTmax to digest the temperature indication error deltaT.

Where. deltaTi - digestion temperature indication error, °C;

T - digester set temperature, °C;

Ti - The arithmetic mean of the third temperature reading of the ith digestion hole, ° C.

7.5.4 Absorbance indication stability

Take the air as the reference, measure and record the initial absorbance of the instrument at the working wavelength, and then display the absorbance at 5 min, After 10 min, 15 min, 20 min, 25 min and 30 min, the absorbance of the instrument was recorded once, and six absorbers Degree Ai, according to equation (4) Calculate absorbance indication stability deltaA.

max min A = A - A (4) where. deltaA - absorbance indication stability;

Amax - absorbance maximum;

Amin - minimum absorbance.

7.5.5 Measurement repeatability

The test solution with COD concentration of 30 mg/L, 50 mg/L,.200 mg/L, 500 mg/L and 800 mg /Repeated determination of each concentration test solution 6 times, according to formula (5), (6) calculate the standard deviation of the six measured values S and relative standards Deviation RDS, take the maximum value of RDS as the measurement repeatability of the analyzer.

7.5.6 Measurement error

The test solution with COD concentration of 30 mg/L, 50 mg/L,.200 mg/L, 500 mg/L and 800 mg /the test solution was repeated 3 times for each concentration and the arithmetic mean was calculated. When the test solution COD concentration greater than or equal to 50 mg/L, According to formula (7) calculation; When the test solution concentration is less than 50 mg/L, according to formula (8) calculation.

7.5.7 Chloride interference

Select the COD concentration of 300 mg/L, chloride ion concentration of 1000 mg/L test solution was tested repeatedly measured 6 Times, calculated according to formula (9).

7.5.8 Actual water sample comparison test

At least five different types of wastewaters were collected and tested using the Rapid Tester and the HJ 828 method, each of which Sample with a rapid determination of the number of times should not be less than 6 times, with the HJ 828 method should not be less than 3 times the number of tests. Use quick test Tester and HJ 828 method analysis results for comparison, when the measured water sample COD concentration greater than or equal to 50 mg/L, according to the public (10) Calculate the average value of the relative error of the water sample comparison test, when the COD concentration of the water sample is less than 50 mg/L, according to formula (11) to calculate the kind of water samples than the absolute value of the absolute value of the test error.

7.5.9 Voltage stability

COD concentration of.200 mg/L of the standard solution, rapid tester at 220 V voltage test 3 times, calculate 3 the arithmetic mean of the second measurement value Vs, adjust the voltage to 242 V and 198 V, were measured three times the same standard solution, total Calculate 198 V, 242 V conditions 3 times the arithmetic mean value of Vi, calculated according to formula (12). Due to voltage changes Caused by the relative error deltaV, of which the greater the absolute value of the voltage stability as a judge.

7.5.10 Insulation resistance

Under normal environmental conditions, turn off the digestion instrument, photometer circuit, the use of megger measurement of the power phase and the chassis (ground) the insulation resistance between.