CN102854264B - 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 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 polyvinyl alcohol (PVA).

Two, technical background

Polyvinyl alcohol (PVA) is a kind of high molecular weight water soluble polymer, it is taking vinyl acetate as monomer, be polyvinyl acetate through initiating agent initiated polymerization, more cotton-shaped, the sheet processing through alkali (preparing with methyl alcohol) alcoholysis, pulverizing, squeezing, the operation such as dry or granular solids.The a large amount of methyl acetate of association in alkali alcoholysis process, though through squeezing, the operation processing such as dry, still remain a small amount of methyl alcohol and methyl acetate in polyvinyl alcohol (PVA) product.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 the storage of polyvinyl alcohol (PVA) product, use working environment, affects the healthy of employee.Particularly at polyvinyl alcohol (PVA) as pharmaceutic adjuvant, make the filmogen of capsule material, film and the plastics of microencapsulation, and the aspect such as the making of eye drops, Determination of Residual Organic Solvents in polyvinyl alcohol (PVA) is had to strict demand.Therefore in Accurate Determining strict control polyvinyl alcohol (PVA), methyl alcohol and methyl acetate content just seem particularly important.

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

Three, summary of the invention

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

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

Described dissolving is that polyvinyl alcohol (PVA) is added in 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 completely 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; By the content of methyl alcohol and methyl acetate in filtrate described in gas chromatography determination.

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

Compared 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, 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, the inventive method quantitative measurement accuracy and precision are high, reproducible, easy and simple to handle.

Four, brief description of the 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.The absorption peak that in figure, peak 1 is methyl acetate, the absorption peak that peak 2 is methyl alcohol, the absorption peak that peak 3 is propyl alcohol.

Five, embodiment

(1) mensuration of sample

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

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

3,, by solution Filter paper filtering, collect filtered fluid.

The content of methyl alcohol and methyl acetate in the filtrate of 4, collecting by gas chromatography determination step 3, the chromatogram obtaining is shown in Fig. 1.

Gas chromatography operating conditions:

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

Carrier gas (nitrogen): 50mL/min;

Hydrogen: 30mL/min; ML/min;

Air: 400mL/min;

Injector temperature: 200 DEG C;

Detector temperature: 250 DEG C;

Temperature programme: 50 DEG C of initial temperatures, keep 5min, be warming up to 170 DEG C with 10 DEG C/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 formula: Wi---the mass percent of component to be measured in 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 (it can Determination of The Proper Motions, or by i component in document and internal standard compound s, the relative mass correction factor of benzene is converted and obtained).

(2) method accuracy and precision test

1, the preparation of inner mark solution

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

2, the preparation of standard specimen solution

Accurately take methyl alcohol (AR) and the each 500.0mg of methyl acetate (AR), be placed in 50mL volumetric flask, dissolve and be diluted to scale with inner mark solution, 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, be placed in 250mL ground conical flask and be designated as successively No. 1-6, in 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 1-6 conical flask is all 50.0mL, is mixed with concentration and is followed successively by the 1-6 standard specimen solution of 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 shown in Fig. 1 (a).Chromatographic peak degree of separation between methyl alcohol, methyl acetate, propyl alcohol is all greater than 1.5.The system suitability that shows the selectivity of chromatographic column to each component and method is good.

4, linear relationship test

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

Tri-parts of weighing polyvinyl alcohol sample 2.50g, be placed in three 250mL ground conical flasks, add respectively standard specimen solution 1.25mL, 2.50mL, the 3.75mL of 10.00mg/mL, be sequentially added into again inner mark solution 48.75mL, 47.50mL, 46.25mL, by the molten sample of Specimen Determination step and condition, separate, mensuration, result of calculation.With 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 polyvinyl alcohol (PVA), comprises dissolving, saltouts, filters and measures four steps, it is characterized in that:

Described dissolving is that polyvinyl alcohol (PVA) is added in 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 completely to obtain poly-vinyl alcohol solution; In polyvinyl alcohol (PVA) course of dissolution, adopt the firing equipment heating for dissolving of heating up in a steamer condensing unit with returning;

Described step of saltouing and filter 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; By the content of methyl alcohol and methyl acetate in filtrate described in gas chromatography determination.

2. the method for methyl alcohol and methyl acetate content in mensuration polyvinyl alcohol (PVA) according to claim 1, is characterized in that:

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