CN102854264A - Method for determining methanol content and methyl acetate content in polyvinyl alcohol - Google Patents

Abstract

The present invention discloses a method for determining methanol content and methyl acetate content in polyvinyl alcohol. The method comprises unit processes of dissolving, salting out, filtering, and determining. In the dissolving process, polyvinyl alcohol is added to distilled water, and is completely dissolved under a heating reflux condition to obtain a polyvinyl alcohol solution, wherein a mass ratio of the polyvinyl alcohol to the distilled water is 1:20-30. In the salting out process, the polyvinyl alcohol solution is added with an inorganic salt, and normal temperature stirring is performed to precipitate the polyvinyl alcohol, wherein an addition amount of the inorganic salt is 6-8 times the mass of the polyvinyl alcohol. Filtration separation is performed to collect the filtrate. A gas chromatography method is adopted to determine methanol content and methyl acetate content in the filtrate. Compared with the general purpose static headspace gas chromatography method, the method of the present invention has advantages of high accuracy, high precision, good repeatability, and convenient operation.

Description

A kind of method of measuring methyl alcohol and methyl acetate content in the polyvinyl alcohol (PVA)

One, technical field

The present invention relates to a kind of assay method, specifically a kind of method of measuring methyl alcohol and methyl acetate content in the polyvinyl alcohol (PVA).

Two, technical background

Polyvinyl alcohol (PVA) is a kind of high molecular weight water soluble polymer, it is as monomer take vinyl acetate, be polyvinyl acetate through the initiating agent initiated polymerization, cotton-shaped, the sheet or the granular solids that process through operations such as alkali (preparing with methyl alcohol) alcoholysis, pulverizing, squeezing, dryings again.The a large amount of methyl acetate of association in the alkali alcoholysis process, though process through squeezing, the operation such as dry, still residual in the polyvinyl alcohol (PVA) product have a small amount of methyl alcohol and a methyl acetate.Methyl alcohol and methyl acetate are inflammable, explosive, volatile organic matter, have certain toxicity, and their existence can cause certain environment to pollute and potential safety hazard to storage, the use working environment of polyvinyl alcohol (PVA) product, affects the healthy of employee.Particularly be used as pharmaceutic adjuvant at polyvinyl alcohol (PVA), make the filmogen of capsule material, film and the plastics of microencapsulation, and the aspects such as making of eye drops, Determination of Residual Organic Solvents in the polyvinyl alcohol (PVA) there is strict demand.Therefore methyl alcohol and methyl acetate content just seem particularly important in Accurate Determining and the strict control polyvinyl alcohol (PVA).

The aqueous solution of polyvinyl alcohol (PVA) is commonly used for tackifier, and increases and the viscosity enhancing with the degree of polymerization and the concentration of aqueous solution of polyvinyl alcohol (PVA), therefore the polyvinyl alcohol water solution direct injected can not be carried out stratographic analysis (gluey aqueous solution is stopped up microsyringe and chromatographic column).By literature search, the universal method of methyl alcohol and methyl acetate content is the Static Headspace vapor-phase chromatography in the mensuration polyvinyl alcohol (PVA) at present, its principle is: sample is put into an airtight glass sample bottle and keep the sample top of sample bottle to leave the gas space over half, after making two-phase (the space gas of sample and sample top) reach balance under the stationary temperature, with head space gas in the impermeability syringe equal portions draw samples bottle, be directly injected in the chromatographic column entrance, carry out chromatographic resolution and mensuration.Then according to tested the component distribution coefficient in the gas phase and gaseous phase volume after biphase equilibrium, the content of tested component in the calculation sample.But, in actual sample is measured, these data are unknown and are difficult to Accurate Determining, can only estimate by analogy method, namely prepare certain density methyl alcohol (methyl acetate) aqueous solution, replace polyvinyl alcohol (PVA) sample (solid), under the same operation condition, carry out Static Headspace gas phase chromatographic determination, according to measurement result Computation distribution coefficient.Because the volatilization degree varies sample of methyl alcohol (methyl acetate) in the polyvinyl alcohol (PVA) solid sample and in water, the distribution coefficient that analogy method calculates is inaccurate, simultaneously owing between the particle of polyvinyl alcohol (PVA) solid sample (graininess or powdery) space being arranged, when therefore measuring the polyvinyl alcohol (PVA) sample with the method, gaseous phase volume can't Accurate Determining, can only estimate.Therefore accuracy and repeatability with methyl alcohol and methyl acetate content in the Static Headspace vapor-phase chromatography mensuration polyvinyl alcohol (PVA) sample are not high.

Three, summary of the invention

The present invention aims to provide a kind of method of measuring methyl alcohol and methyl acetate content in the polyvinyl alcohol (PVA), and technical matters to be solved provides a kind of accuracy and precision is high, the method for methyl alcohol and methyl acetate content in the good reproducibility, mensuration polyvinyl alcohol (PVA) easy and simple to handle.

The present invention measures the method for methyl alcohol and methyl acetate content in the polyvinyl alcohol (PVA), comprises dissolving, saltouts, filters and measure each unit process:

Described dissolving is that polyvinyl alcohol (PVA) is added in the distilled water, and the mass ratio of polyvinyl alcohol (PVA) and distilled water is 1:20-30, adds under the condition of hot reflux polyvinyl alcohol (PVA) to be dissolved fully to obtain poly-vinyl alcohol solution;

Described saltouing is to add inorganic salts in described poly-vinyl alcohol solution, and the addition of inorganic salts is 6-8 times of polyvinyl alcohol (PVA) quality, and stirring at normal temperature is separated out polyvinyl alcohol (PVA), and isolated by filtration is collected filtrate; Content by methyl alcohol and methyl acetate in the described filtrate of gas chromatography determination.

Described inorganic salts are selected from sodium chloride or lime chloride.

Compare with existing Static Headspace vapor-phase chromatography, the invention has the advantages that:

1, the present invention does not need the simulated determination of distribution coefficient and the analogue measurement of gaseous phase volume, and is easy and simple to handle.

2, the present invention adopts the firing equipment heating for dissolving of heating up in a steamer condensing unit with returning in polyvinyl alcohol (PVA) sample dissolution process, and tested component (methyl alcohol and methyl acetate) is loss not.

3, high, the good reproducibility, easy and simple to handle of the inventive method quantitative measurement accuracy and precision.

Four, description of drawings

Fig. 1 is the chromatogram of standard specimen chromatogram and test determination of the present invention.Wherein Fig. 1 (a) is the chromatogram of standard specimen; Fig. 1 (b) is the chromatogram of Specimen Determination of the present invention.Peak 1 is the absorption peak of methyl acetate among the figure, and peak 2 is the absorption peak of methyl alcohol, and peak 3 is the absorption peak of propyl alcohol.

Five, embodiment

(1) mensuration of sample

1, takes by weighing 2.500g polyvinyl alcohol (PVA) sample (claiming accurate to 0.001g), pour in the 250mL ground conical flask, add 50.0ml distilled water and 20.0uL propyl alcohol (AR, internal standard compound), puts into magnetic stir bar, load onto back and heat up in a steamer condensing unit, be put on the magnetic force heating stirrer, the magnetic agitation heating after polyvinyl alcohol (PVA) dissolves fully, is cooled to room temperature with solution and obtains poly-vinyl alcohol solution.

2, take by weighing 15g sodium chloride (AR), join in the poly-vinyl alcohol solution under stirring, after sodium chloride adds, cover the taper bottle cap, continued magnetic agitation 1 hour under the room temperature, polyvinyl alcohol (PVA) is separated out.

3, with the solution Filter paper filtering, collect filtered fluid.

4, with the content of methyl alcohol and methyl acetate in the filtrate of gas chromatography determination step 3 collection, the chromatogram that obtains is seen Fig. 1.

The gas chromatography operating conditions:

Chromatographic column: immobile liquid is the quartz capillary column of BP20, long 15m, internal diameter 0.53mm;

Carrier gas (nitrogen): 50mL/min;

Hydrogen: 30mL/min; ML/min;

Air: 400mL/min;

Injector temperature: 200 ℃;

Detector temperature: 250 ℃;

Temperature programme: 50 ℃ of initial temperatures, keep 5min, be warming up to 170 ℃ with 10 ℃/min speed, keep 3min.

Sample size: 0.5uL.

5, according to the content of methyl alcohol and methyl acetate in the calculated by peak area sample of methyl alcohol, methyl acetate, propyl alcohol (internal standard compound), computing formula is as follows:

$\mathrm{Wi}=\frac{\mathrm{Ai}}{\mathrm{As}}\×G_{\mathrm{Wi}/s}\×\frac{\mathrm{Ms}}{M}\×100\%$

In the formula: Wi---the mass percent of component to be measured in the sample (methyl alcohol or methyl acetate), %;

The peak area of Ai---component to be measured;

The peak area of As---internal standard compound (propyl alcohol);

The quality of Ms---internal standard compound (propyl alcohol), g;

M---sample quality, g;

G _Wi/s---component to be measured is for the relative mass correction factor of internal standard compound (but its Determination of The Proper Motions, or by i component in the document and internal standard compound s the relative mass correction factor of benzene is converted and to obtain).

(2) method accuracy and precision test

1, the preparation of inner mark solution

Accurately pipette 0.400mL propyl alcohol (AR), place the 1000mL volumetric flask, add water and make its dissolving and be diluted to scale, shake up.Measure simultaneously the density of propyl alcohol.

2, the preparation of standard specimen solution

Accurately take by weighing methyl alcohol (AR) and each 500.0mg of methyl acetate (AR), place the 50mL volumetric flask, with inner mark solution dissolving and be diluted to scale, shake up, the concentration of this solution be 10.00mg/mL(in methyl alcohol or with methyl acetate, lower with).Get respectively this solution 0.50mL, 1.00mL, 2.00mL, 3.00mL, 4.00mL, 5.00mL, place 250mL ground conical flask also to be designated as successively 1-6 number, in the 1-6 conical flask, add inner mark solution 49.50mL, 49.00mL, 48.00mL, 47.00mL, 46.00mL, 45.00mL respectively in order, making the total amount of solution in the 1-6 conical flask is 50.0mL all, is mixed with the 1-6 standard specimen solution that concentration is followed successively by 0.100mg/mL, 0.200mg/mL, 0.400mg/mL, 0.600mg/mL, 0.800mg/mL and 1.000mg/mL after mixing.By the identical operation steps of mensuration of (one) sample, in standard specimen solution, add 15g sodium chloride (AR), after stirring and dissolving is complete, filter, collect filtered fluid.

3, the system suitability of method

Select the standard specimen filtered fluid (No. 4 conical flasks) of 0.600mg/mL, measure by above-mentioned chromatographic condition, chromatogram is seen Fig. 1 (a).Chromatographic peak degree of separation between methyl alcohol, methyl acetate, the propyl alcohol is all greater than 1.5.Show that chromatographic column is good to the system suitability of the selectivity of each component and method.

4, linear relationship test

By above-mentioned chromatographic condition, measure respectively each standard specimen filtered fluid, record each component peaks area.Take determinand and interior mark peak area ratio as ordinate, the concentration range of linearity (mg/mL) of component to be measured is horizontal ordinate in the standard specimen solution, carries out linear regression.The results are shown in Table 1.In each range of linearity shown in the table 1, determinand and interior mark peak area ratio and detectable concentration are good linear relationship.Correlation coefficient r is respectively 0.9970 and 0.9997.

Table 1 regression equation and range of linearity test findings (n=6)

5, minimum detectability test

Select the standard specimen filtered fluid (No. 4 conical flasks) of 0.600mg/mL, measure by same chromatographic condition, with 3 times of calculating of baseline noise, the limit of identification of methyl alcohol and methyl acetate is respectively 0.40ug/mL and 0.15ug/mL.

6, recovery of standard addition test

Three parts of weighing polyvinyl alcohol sample 2.50g, place three 250mL ground conical flasks, the standard specimen solution 1.25mL, 2.50mL, the 3.75mL that add respectively 10.00mg/mL, be sequentially added into again inner mark solution 48.75mL, 47.50mL, 46.25mL, press the Specimen Determination step with the molten sample of condition, separate, mensuration, result of calculation.With the standard addition method calculate recovery rate, the results are shown in Table 2.Recovery scope is 98.6-101.8% as can be seen from Table 2, shows that the accuracy of this method is very high.

Table 2 method recovery result (n=3)

7, precision test

Select the standard specimen filtered fluid (No. 4 conical flasks) of 0.600mg/mL, measure by same chromatographic condition, repeat sample introduction 5 times, calculate the relative standard deviation RSD of component methyl alcohol to be measured, methyl acetate peak area and the ratio of internal standard compound propyl alcohol peak area, be respectively 1.25%, 1.48%, illustrate that precision is good.

Claims (2)

1. a method of measuring methyl alcohol and methyl acetate content in the polyvinyl alcohol (PVA) comprises dissolving, saltouts, filters and measures each unit process, it is characterized in that:

Described dissolving is that polyvinyl alcohol (PVA) is added in the distilled water, and the mass ratio of polyvinyl alcohol (PVA) and distilled water is 1:20-30, adds under the condition of hot reflux polyvinyl alcohol (PVA) to be dissolved fully to obtain poly-vinyl alcohol solution;

Described saltouing is to add inorganic salts in described poly-vinyl alcohol solution, and the addition of inorganic salts is 6-8 times of polyvinyl alcohol (PVA) quality, and stirring at normal temperature is separated out polyvinyl alcohol (PVA), and isolated by filtration is collected filtrate; Content by methyl alcohol and methyl acetate in the described filtrate of gas chromatography determination.

2. assay method according to claim 1 is characterized in that:

Described inorganic salts are selected from sodium chloride or lime chloride.