GBZ/T 300.162-2018Determination of toxic substances in workplace air -- Part 162: Benzoquinone (English PDF)

4.1 Principle

The vapor phase of phenylhydrazine in the air is collected by a silicone tube, desorbed with 2,4-dinitrophenylhydrazine acetonitrile solution, and benzoquinone and 2,4-dinitrophenylhydrazine at room temperature.

It can react quickly to form pale yellow 2,4-dinitrophenylhydrazine, which is separated by high performance liquid chromatography C18 column and detected by UV detector.

Qualitative, peak height or peak area quantified.

4.2 Instrument

4.2.1 Silicone tube. solvent desorption type, containing.200mg/100mg silica gel.

4.2.2 Air sampler. flow rate 0mL/min ~ 1000mL/min.

4.2.3 Solvent desorption bottle. 5mL.

4.2.4 Microinjector. 10 µL, 50 µL.

4.2.5 Electronic balance. one in 100,000.

4.2.6 High performance liquid chromatography, UV detector.

Instrument operation reference conditions.

a) Column. C18 column, 4.6 mm × 250 mm × 5 µm;

b) mobile phase. acetonitrile/water = 65/35 (volume ratio);

c) detection wavelength. 390 nm;

d) Flow rate. 1.0 mL/min;

e) Injection volume. 20 µL.

4.3 Reagent materials

4.3.1 The test water is double distilled water.

4.3.2 Acetonitrile (chromatographically pure), chromatographic identification of interference-free peaks.

4.3.3 2,4-Dinitrophenylhydrazine (liquid chromatography pure).

4.3.4 Phosphoric acid, 85% (volume fraction), analytically pure.

4.3.5 p-benzoquinone (chromatographically pure), >99.5%.

4.3.6 Desorbed solution. Take 0.10g of 2,4-dinitrophenylhydrazine, 85% (by volume) of phosphoric acid 0.5mL into a 100mL volumetric flask, add acetonitrile Mix to the scale.

4.3.7 Benzoquinone standard solution. Accurately weigh 0.1000g of phenylhydrazine into a 10mL volumetric flask, add acetonitrile to the scale, this liquid is the standard stock solution, the concentration was 10.0 mg/mL, and it was allowed to stand for 3 months in a refrigerator (4 ° C). Dilute to 100.0 µg/mL standard solution with acetonitrile before use. or Formulated with a nationally recognized standard solution.

4.4 Sample collection, transportation and storage

4.4.1 On-site sampling shall be performed in accordance with GBZ 159.

4.4.2 Short-time sampling. At the sampling point, open both ends of the silicone tube and collect the air sample for 15 minutes at a flow rate of.200 mL/min.

4.4.3 Long-time sampling. At the sampling point, open both ends of the silicone tube and collect the air sample for 1h~4h at a flow rate of 50mL/min.

4.4.4 Individual sampling. Open both ends of the silicone tube at the sampling point, and wear it on the upper part of the chest of the monitoring object, as close as possible to the breathing zone.

The air sample was collected for 1 h to 4 h at a flow rate of 50 mL/min.

4.4.5 Sample blank. Bring the silicone tube to the sampling point. Except for not collecting air, the other operations are the same as the blank control of the sample.

4.4.6 Immediately after sampling, the ends of the silicone tube are closed, transported and stored in a clean container, and stored at room temperature for 14 days.

4.5 Analysis steps

4.5.1 Sample processing. Pour the front and back sections of the sampled silicone tube into the sample desorption bottle, add 2.0 mL of desorbing solution, and after blocking, vibrate After shaking for 1 min, the reaction was allowed to stand at room temperature for 2 h.

4.5.2 Standard curve drawing. Dilute the benzoquinone standard solution with a desorption solution to a concentration range of 0.0-25.0 µg/mL. After blocking, shake for 1 min.

The reaction was allowed to stand at room temperature for 2 hours. Adjust the HPLC to the best measurement state according to the operating conditions of the instrument, and inject 20 µL.

Each standard series was determined, and each concentration was repeatedly measured 3 times to measure the peak height or the mean value of the peak area to the corresponding phenylhydrazine concentration (µg/mL).

Draw a standard curve.

4.5.3 Sample determination. Determine the peak height or peak area value by measuring the sample and sample blank desorption solution using the operating conditions of the standard series.

The standard curve gives the concentration of phenylhydrazine (µg/mL). If the concentration of phenylhydrazine in the desorbed solution exceeds the measurement range, it can be diluted with a desorbent solution and then measured.

Multiply by the dilution factor.

4.6 Calculation

4.6.1 Convert the sample volume to the standard sample volume according to equation (1).

3.101273

VV x

In the formula.

0V - standard sampling volume in liters (L);

V - sampling volume in liters (L);

t - the temperature of the sampling point in degrees Celsius (°C);

P - the atmospheric pressure of the sampling point in kilopascals (kPa).

4.6.2 Calculate the concentration of phenylhydrazine in the air according to formula (2).

Vcc

21)( x= .(2)

In the formula.

C - concentration of phenylhydrazine in air, in milligrams per cubic meter (mg/m3);

C1, c2- measured the concentration of phenylhydrazine (minus sample blank) in the silicone tube desorption solution before and after, in micrograms per milliliter (µg/mL);

v - volume of desorbent in milliliters (mL);

0V - standard sampling volume in liters (L);

D - desorption efficiency, %.

4.6.3 The time-weighted average contact concentration (CTWA) of phenylhydrazine in the workplace air is calculated in accordance with GBZ 159.

4.7 Description

4.7.1 The detection limit is calculated by the standard deviation method. The detection limit of this method is 0.02µg/mL; the lower limit of quantification is 0.06µg/mL; the minimum detection concentration (based on the collection of 3.0 L air sample) was 0.013 mg/m3; the lower limit concentration (based on the collection of 3.0 L air sample) was 0.04 mg/m3.

The measurement range is from 0.0 µg/mL to 25.0 µg/mL, and the relative standard deviation is from 1.81% to 6.81%. The average sampling efficiency of this method is 100%, average the desorption efficiency was 95.0%, the sample recovery rate was 93.3% to 95.1%, and the breakthrough capacity was 7.9 mg.

4.7.2 Sample desorption method. firstly pour the front part of the silicone tube into the desorption bottle and desorb it, and if the measurement result shows that it has not exceeded the suction when the penetration capacity of the attached agent is used, the latter stage may not be desorbed and measured; when the measurement result indicates that the penetration capacity of the adsorbent is exceeded, the latter stage is sucked again.

The attached agent is desorbed into the desorption bottle and desorbed, and the results of the front and back stages are added after the calculation and the corresponding treatment is performed.

4.7.3 Under the conditions of this method, phenylhydrazine reacts with 2,4-dinitrophenylhydrazine to form stable 2,4-dinitrophenylhydrazine.

2,4-Dinitrophenylhydrazine can be stable for at least 24 hours under acidic conditions; on-site coexistence of aniline, hydroquinone and 2,4-dinitro the phenylhydrazine reaction did not produce a peak under the measurement conditions (see Figure 1 for chromatographic separation).

Description.

1--2,4-dinitrophenylhydrazine;

2--2,4-dinitrophenylhydrazine.

Figure 1 chromatogram