GB/T 37363.2-2019Determination of biocides content of coating materials—Part 2: Determination of diuron content (English PDF)

5.7 One mark pipette: suitable specifications, grade-A of GB/T 12808-2015

Note: Other pipetting equipment, such as piston-type pipettes, that meets the precision requirements, can also be used.

7.1 Parallel test

Perform two tests in parallel.

7.2 Sample preparation

Stir the sample evenly (if the sample is solid, use a smashing device to pulverize the sample at room temperature, and use a stainless steel metal sieve (4.6) whose pore size is 0.5 mm to sieve); weigh about 2.5 g of the sample, accurate to 0.1 mg; place in a 25 mL volumetric flask (5.5); record the sample mass m; use methanol (4.1) to dilute it to the mark; shake it sufficiently to obtain the maximum dispersion of the sample; make a sample solution; record the constant volume V. Use ultrasonic extraction instrument (5.2) for ultrasonic extraction for 20 min; then, transfer about 7 mL of the above solution into a centrifuge tube (the volume of the to-be-centrifuged solution can also be adjusted according to the actual situation); centrifuge under the condition that the temperature of the centrifuge cavity does not exceed 25°C, until the supernatant A appears in the upper layer. If the centrifugation effect is not good and the layering cannot be performed effectively, increase the rotating speed or increase the centrifugation time appropriately. Use a 0.22 µm microporous membrane (4.5) to filter he supernatant A; retain the filtrate B for the determination of the extraction solution (7.7).

When other solvents are selected as the extraction solvent, use a one mark pipette (5.7) to transfer 1 mL of supernatant A into a 10 mL volumetric flask (5.5); use methanol (4.1) to fix-volume to the mark. Take an appropriate amount of the above solution; use a 0.22 µm microporous membrane (4.5) to filter; retain the filtrate C for determination of the extraction solution (7.7).

7.3 Blank test

Perform the blank test in parallel with the test; use the same test procedures; take all reagents in the same amount, but without adding samples.

7.4 LC-MS/MS test conditions

Select appropriate test conditions according to the performance of the used LC- MS/MS and the actual situation of the sample.

Because the test results depend on the used instrument, so, general parameters for chromatographic and mass spectrometric analysis cannot be given. The parameters which are listed in A.1 in Appendix A have been proven to be suitable for testing.

7.5 Preparation of standard working solution

Weigh about 0.02 g of diuron (4.4), accurate to 0.1 mg, in a 100 mL volumetric flask; use methanol (4.1) to fix-volume to the mark. Then, adopt the stepwise dilution method; use a graduated pipette (5.6) or a one mark pipette (5.7) to transfer the above solution into a suitable volumetric flask (5.5); use methanol (4.1) to dilute the above solution to diuron standard working solution of applicable concentration.

Note 1: The concentration range of diuron standard working solution can be adjusted according to the used instrument and sample.

Note 2: It's also available to directly use a diuron standard solution of known concentration.

7.6 Drawing of the standard working curve

Determine the diuron standard working solution (7.5) according to the conditions of LC-MS/MS of 7.4. Inject each standard working solution twice; take the average value of the peak areas; the relative deviation shall not be greater than 5%. Record multiple reaction monitoring (MRM) chromatograms based on quantitatively selected ions and qualitative ions (see Table A.1); take the peak area (minus the area of diuron in the non-standardized working solution) as the ordinate, and the corresponding standard working solution concentration as the abscissa, to draw the standard working curve. The standard working curve shall include at least 5 diuron standard working solutions (7.5). The linear correlation coefficient R2 of the standard working curve shall be greater than 0.995; otherwise, draw a new standard working curve.

7.7 Determination of extraction solution

A.1 LC-MS/MS reference conditions

A.1.1 Chromatographic column: C18 reversed-phase chromatographic column, 2.1 mm × 50 mm, 1.8 µm.

A.1.2 Flow velocity: 0.3 mL/min.

A.1.3 Column temperature: 35°C

A.1.4 Injection volume: 1 µL

A.1.5 Atomizing gas: nitrogen, purity >= 95%

A.1.6 Dry gas temperature: 350°C

A.1.7 Dry air flow: 9 L/min. A.1.8 Atomizing gas pressure: 344 737.85 Pa (50 psi).

A.1.9 Collision gas: high-purity nitrogen, purity >= 99.999%

A.1.10 Mobile phase: water [5 mmol/L ammonium acetate, formic acid volume fraction 0.1%] + methanol (30 + 70). A.1.11 Mass ion source: electrospray ionization source (ESI).

A.1.12 Ionization method: positive-ion scanning

A.1.13 Capillary voltage: +3 000 V

A.1.14 Monitoring mode: multiple reaction monitoring (MRM), see Table A.1 for the monitoring conditions. Table A.1 -- Diuron multiple reaction monitoring conditions

Compound name Parent ion m/z Daughter ion m/z Collision energy (CE)/eV Declustering potential/ Acceleration voltage/ Diuron 232.8 72.1 a 26 105 7 232.8 159.8 18 105 7 a quantitative daughter ion. […]