Gas chromatographic determination of residual monomer content in synthetic resin emulsions - Master's thesis - Dissertation

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Abstract: The method for the determination of unreacted residual monomer content in synthetic resin emulsion by gas chromatography internal standard method was discussed. The precision and accuracy of the method were investigated/experienced. The method is simple and accurate. Reliable, suitable for a variety of synthetic resin emulsion samples.

0 Preface

Since the promulgation of the ten national mandatory standards, the hazardous substances in various coatings on the market must meet the relevant national standards. Since unreacted residual monomers in synthetic resin emulsions have different effects on human health and the environment, it is necessary to control the concentration of residual monomers in the emulsion. The technical analysis of the residual monomer content in the emulsion, due to the large investment in the instrument, and the sample recovery rate is not ideal, the sample pretreatment is more troublesome, and the investment for SMEs is less, and it is easy to be promoted in SMEs. It is more difficult to promote, and we introduce the common analysis method. A small-diameter capillary column was used for detection by a hydrogen flame ionization detector (FID) and quantified by an internal standard method. The column temperature is programmed and the separation effect is ideal. The recoveries of the spiked samples are between 94% and 103%, respectively. The precision and accuracy of the analytical results fully meet the testing requirements.

1

.1

Experimental part: 1.1 Instrument and reagent electronic analytical balance (one ten thousandth); GC7800 gas chromatograph (with shunt device); 1.0ul micro-injector; 20ml small plastic bottle with rubber stopper; medical syringe 1ml, 2ml each Two; small diameter capillary column DB-17HT (0.25mm x 30mx0.15um; maximum operating temperature is 360 ° C); integrator or chromatography workstation. Vinyl acetate VAM (chromatographically pure), methyl methacrylate MMA (chromatographically pure), styrene ST (chromatographically pure), butyl acrylate BA (chromatographically pure) propylene isooctyl ester 2-EHA (chromatographically pure), acetone ( Analytically pure) formulated into a 4 1 mixed aqueous solution (as a diluent), water (pure water or distilled water).

Internal standard: cyclohexanone (chromatographically pure)

1.2 Determination principle

Add appropriate amount of internal standard in the sample and dilute with a little acetone (4 1), then dilute the diluted solution into the gas chromatograph with a micro-syringe. The sample is carried into the column by the carrier gas and separated into corresponding columns. For the components, the chromatogram was detected and recorded by a hydrogen flame ionization detector, and the content of each residual monomer to be tested in the sample solution was calculated by an internal standard method.

1.3 Determination conditions Determine the determination conditions based on whether the components in the sample are completely separated.

Gasification temperature: 280 ° C Detection temperature: 320 ° C carrier gas: nitrogen: purity ≥ 99.99%, color changing silica gel 5A molecular sieve water removal, degreasing, pre-column pressure is 60Kpa (30 ° C); hydrogen: purity ≥ 99.99%, color changing silica gel 5A molecular sieve water removal, degreasing, pre-column pressure is 65Kpa (30 ° C); air: color changing silica gel 5A molecular sieve water removal, degreasing, pre-column pressure is 55Kpa (30 ° C); column temperature is programmed temperature: initial temperature 30 ° C , constant temperature 3min, increase to 140 ° C at 10 ° C / mm heating rate, and then increase to 260 ° C at 50 ° C / min heating rate for 4 min. Split ratio: 45:1 injection volume: 0.2ul1.4 relative correction factor determination 1.4.1 Preparation of standard sample In a 20ml sample vial, weigh 0.03g (accurate to 0.0001g) of vinegar shuttle vinyl ester VAM, butyl acrylate Bt, wait for the chromatographic purity of the monomer and the internal standard cyclohexanone. Add 2 mL of acetone (4 1) and dilute and shake vigorously for 3 min. (Note: Immediately after each measurement, the vial should be tightly closed to prevent loss of sample evaporation.)

1.4 Determination of relative correction factor After the instrument is stable, draw 0.2uL standard sample into the chromatograph and record the chromatogram and chromatographic data. Chromatogram of typical synthetic resin emulsion The relative retention times of each monomer and internal standard are: VAM1.771'; MMA3.078'; BA5.498'; St5.683'; 2-EHA8.495'; Calculation of the relative correction factor of cyclohexanone 6.218'1.4.3 Calculation The relative correction factor Fi of the remaining monomers to be tested, such as vinyl acetate, butyl acrylate and styrene, is calculated by the following formula: where: mi - the respective masses of the residual monomers to be tested; gAs - the peak area of ​​the internal standard cyclohexanone; ms - the mass of the internal standard cyclohexanone; gAi - the peak area of ​​each residual monomer.

1.5

The parallel deviation of the relative correction factor Fi of the residual monomer to be tested for cyclohexanone (internal standard) should be less than 0.05.1.5 plus the recovery test. In order to prove the reliability of the determination result, weigh a certain amount. Prepare a known try solution for each pure monomer to be tested, determine the concentration of each solution according to the above analytical method, and calculate the respective recovery rates. The results are shown in Table (1).

1.6

Determination of the sample After the sample is evenly stirred, accurately weigh about 2g and a small drop (with 1mL syringe) of the internal standard (about 0.001g) of cyclohexanone in the sample vial in a 20mL sample vial, add appropriate amount (2~3mL) Acetone (4 1) thinner, immediately capped with a stopper and shake well for 2 min. Under the same analytical conditions as the calibration factor, 0.2 μl of the test solution was injected into the chromatograph with a 1 μl microinjector and recorded. The chromatogram and data are characterized according to the retention time of the internal standard by the residual monomers to be tested.

1.7 Calculation of results The respective mass fractions of the residual monomers to be tested are calculated by the following formula: where: Fi - the relative correction factor of each monomer to the internal standard; Ms - the quality of the internal standard, gAi - The peak value of each residual monomer to be tested in the sample; Mi——the mass of the sample to be tested, gAs——the peak area of ​​the internal standard is taken as the arithmetic mean of the two results in parallel. The measurement result of the monomer.

1.8 Reproducibility The relative deviation of the results of the two measurements by the author is less than 0.5%. 2. Results and discussion (1) The analytical method uses a medium-sized small-diameter high-temperature capillary column, the injection volume can not be greater than 0.2ul, and the shunt It is bigger than it is. Since the boiling point of each residual monomer is relatively high, we choose a capillary column with high temperature resistance, and the column has a better separation effect on the ester.

(2) The vaporization chamber shall be provided with a quartz glass liner, and an appropriate amount of treated glass wool shall be filled to prevent the residue from entering the capillary column, and the liner shall be replaced frequently.

(3) Because the relative response values ​​of the monomers to the internal standard are different, the mass of each monomer weighed in the preparation of the standard solution is not necessarily 0.03 g. The principle is to make the peak area of ​​each monomer as much as possible. The ratio of the peak areas of the internal standard is close to one.

(4) Some samples will be emulsified after being diluted by acetone for a period of time. When preparing samples, the supernatant should be taken into the chromatograph for analysis.

(5) The phenomenon of water in the presence of vinegar shuttle vinyl ester VAM. Therefore, when the recovery rate is used, the solvent can be effectively analyzed for the hydrolysis of VAM by dehydration analysis of hydrazine acetone. However, in the test sample, the solvent was an aqueous acetone solution (4 1), which was caused by some samples dissolved in acetone (dehydration).

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