Improvement and discussion of VOC testing methods in GB18582-2008 standard

0 Foreword
GB18582-2008 "Indoor decoration materials in the interior wall paint limit of harmful substances" has been announced, requiring the implementation of October 2008 to replace the G B18582-2001 version of the standard. The biggest difference between the new standard and the original standard is that volatile organic compounds (V O C) are measured differently, the original standard V O C measurement method is to use drying method to measure the total volatile value of the coating, and then subtract the moisture in the coating, that is, the V O C content.
new standard is to use capillary chromatography to determine the amount of all organic compounds in the coating with an initial boiling point of less than or equal to 250 degrees C, and then add the VOC content of . Moisture is still measured using gas chromatography or Carl-Fisher.
G B18582-2001 standard is the first time issued by the state on the inner wall paint in the limit of harmful substances standards, is a mandatory standard, its implementation has greatly improved the paint industry's environmental awareness. In the implementation, the determination method of V O C of the inner wall coating has aroused wide concern, questioned the accuracy of the measurement method, and discussed it, and agreed that the detection method of V O C is not accurate for latex paint, and the detection results are high and low compared with the calculated value. The results of the same sample in different testing units (Guangdong, Beijing, Changzhou) vary greatly, and the reproducible and reproducible are very poor.the authors of
literature argue that the most important error in water-based coating V O C assays is due to the determination of moisture, as the standard is proposed to measure about 40% of the moisture in coatings using gas chromatography and Carl-Fishu method, because gas chromatography will bring about 5 The relative average deviation of % to 10% (but some people think that it can be done less than 0.3%), therefore, the current determination of VOC in coatings is an urgent problem to solve the problem of the accuracy of high-content moisture measurement, should be developed as soon as possible an accurate measurement method of high-content moisture.
in the implementation of the new standard, the focus is on improving the reproducibleness of gas chromatography in measuring moisture, reducing measurement errors, and obtaining more satisfactory results.
1 Test Part
1.1 Volatile Organic Compound Determination - Gas Chromatography
1.1.1 Materials and Reagents
Carrier Gas: High Purity Nitrogen;
Gas: High Purity Hydrogen;
Gas: Air, Supplied by Gas Generator;
Thinner: Methanol;
Internal Label: Ethylene Glycol Monoclode;
Markers: Alcohol Esters-12 in Paint (boiling point 255 degrees C);
propanol: content ≥99%.
1.1.2 Instruments and equipment
G C-7890F gas chromatography, Shanghai Tianmei Instrument Co., Ltd.;
N2000 chromatography workstation, Zhejiang University Zhida Information Engineering Co., Ltd.;
syringes: 10 sl, 1 mL, 10 mL glass syringe;
sample bottle: 10 mL (penicillin vial), 100 mL glass bottle with sealable plug;
electronic analysis balance: accuracy 0.1 mg;
table centrifuge (Shanghai Anting Scientific Instrument): maximum speed 5 000 r/min.
1.1.3 chromatography conditions
seeding temperature (gasification): 250 degrees C;
detector: FID, temperature 200 degrees C;
chromatography column: PEG20000, 30 cm×0.32 mm×0.25 m;
column temperature: qualitative analysis using program heating
(see 1.1.4), quantitative analysis using fixed column temperature
of 160 degrees
C;
1.1.4 Qualitative Analysis
Add 10 glass beads to the sample bottle, take about 0 . 8 g sample, add 4 m L methanol, shake well and put into the centrifuge, with 4,500 r/min centrifugal 10 min, take the upper liquid according to the conditions described below for qualitative analysis.
is programmed to heat up: the initial temperature is 100 degrees C, the initial retention time is 1 min, the warming rate is 20 degrees C/min, the termination temperature is 200 degrees C, and the final temperature retention time is 5 min.
with retention time qualitative, the sample only propylene glycol and alcohol esters-12, other substances are very trace, chromatography as shown in Figure 1.
in the coating
1.1.5 Quantitative analysis
1.1.5.1 preparation of the internal standard thinner
added to the 100 mL sample bottle 60 mL methanol and accurately called its quality, sealed, with 1 m L syringe accurately named 0.1 g g g g g g glycol monodylene into the sample bottle, shake well, calculate the quality score of ethylene glycol monoclode wis, to be used.
1.1.5.2 Determination of correction factor Ri
1.1.5.2.1 Standard preparation
accurately named propylene glycol 0.02 g (m c i) in the sample bottle, and 5 m L with a 10m L syringe Standard thinner injection sample bottle, accurate weighing, shake, spare, quality of the inner label according to type (1) calculation:
mis s m inner ×wis (1)
type: mis - inner label quality, g;
m - inner label thinner quality, g;
wis - mass fraction of glycol monoclode in the inner label thinner, g/g.
1.1.5.2.2 R i of the determination
after the chromatography conditions are stable, take 1 μ L of the above specimen, inject the chromatography, typical chromatography as shown in Figure 2.
R i assay spectrometry
the relative mass correction factor of propylene glycol R i:
: R i - the relative mass correction factor of propylene glycol;
mis - mass of the inner object, g;
mci - the mass of propylene glycol,
g;
A is - the peak area of the internal target;
1.1.5.2.3 Measurement of propylene glycol mass score wi in coatings
10 glass beads are added to the sample bottle and then accurately weighed (0.8±0 .1) g Fully shake the coating, add 5 m L inner label thinner with a 10 m L syringe, seal it with a seal, accurately weigh its mass and shake well, calculate the mass of the inner label m i s by type (1). Two samples are provided at the same time, and then centrifuged at a speed of 4,500 r/min on the centrifuge at 10 min, spare.
take the above-mentioned centrifugal upper liquid 1 sl into the chromatography, wait for propylene glycol to flow out to the column temperature to 200 degrees C, alcohol esters-12 flow out and then adjust the column temperature to 160 degrees C, ready to do the next sample. Typical chromatography as shown in Figure 3.
of propylene glycol in the coating
by (3) to calculate the quality score of propylene glycol in the coating wi:
type: wi - the quality score of propylene glycol in the coating under test, g/g;
R i - relative quality correction factor of propylene glycol;
mis - mass of the inner object, g;
ms - quality of the coating under test, g;
A is - peak area of the inner marker;
A i - peak area of propylene glycol.
1.1.5.2.4 The results of propylene glycol (i.e., organic volatiles) in coatings
the six paint samples of two models and different batches were analyzed, and the results were as shown in Table 1.
1.2 Moisture Content Determination - Gas Chromatography
1.2.1 Materials and Reagents
Carriers: High Purity Hydrogen;
Distilled Water: In accordance with the requirements of triple water in GB/T6682;
Thinners: DMF, AR;
the contents: isopropyl alcohol, AR;
internal label thinner: made from dimethyl methylamine (D M F) and isopropyl alcohol;
1.2.2 instrument equipment
G C-7890T gas chromatography (Shanghai Tianmei Instrument Co., Ltd.);
1.2.3 chromatography conditions
-sample (gasification) temperature: 200 degrees C;
detector: T C D, temperature 200 degrees C, range (bridge current) 150mA;
column: column length 1 m, outer diameter 3 m, fill 177 to
250 m (60 to 80 eyes) G D X-102
(polymer porous micro-ball) stainless steel column;
1.2.4 Test step
1.2.4.1 Inner standard thinner preparation
in a 100 mL sample bottle, said to take 60 mLDMF (about 58 g) seal, accurate weighing. Then add 5.5 m L isopropyl alcohol (about 5 g) with a syringe, weigh accurately, shake the spare, and calculate the mass fraction of isopropyl alcohol wis.
1.2.4.2 standard preparation
accurately named 0.2 g distilled water in a 10 m L sample bottle, and 4 m L internal standard diluent with a 10 m L syringe is injected into the sample bottle, weighing up to 0. 1 mg, the quality of isopropyl alcohol in the specimen m i according to the formula (4) calculation:
mi s m inner ×mis (4)
type: mi - isopropyl alcohol quality, g;
m inside - the quality of the internal label thinner, g;
mis - isopropyl alcohol mass score, g/g.
1.2.4.3 Moisture determination in the internal label diluent, i.e. A 0 determination
because both D M F and isopropyl alcohol contain a certain amount of water, must accurately measure the peak area of A 0 equivalent to it, deducted from the later calculations, otherwise the measurement results are high.
measurement operation: start collecting data, then take 1 μ L internal label thinner injection chromatography, wait for isopropyl alcohol to fully flow out (about 2m i n), click "stop collection" to save the data. The bar temperature is then raised to 200 degrees C, and after the D M F has fully flowed out, the bar temperature is then adjusted to 130 degrees C, ready for the next measurement. Record the peak area of the water A 0, measure it at least 3 times, and then average it.
of the relative mass correction factor R w for water 1.2.4.4
1 μ L sample (1.2.4.2) is injected into the chromatography according to the operation of assay A 0. Calculating the relative mass correction factor R w:
of water by formula (5): R w - water relative mass correction factor;
mw - water mass, g;
mi - isopropyl alcohol mass, g;
Ai - peak area of isopropyl alcohol;
A w - peak area of water;
A0 - peak area of water in the internal standard diluent.
1.2.4.5 Sample Analysis
shakes the sample well, adds 10 glass beads to the sample bottle, accurately weighs 0.6 to 0.8 g samples, and adds 4 m L internal standard diluent with a syringe to accurately weigh its mass. The quality of isopropyl alcohol mi in the inner label thinner is calculated by formula (4). Make two samples at the same time, then shake the sample bottle with force until the sample is fully dispersed and centrifuge 30 min to full precipitation on a centrifuge of 4,500 r/min.
the operation of A0 by (1.2.4.3) and the upper liquid after the centrifugation is injected into the chromatography, the typical chromatography is shown in Figure 4.
water content in the coating www to determine the spectral map
by type (6) to calculate the moisture content in the sample:
type: ww - the quality score of water in the coating, g/g;
R w - relative quality correction factor of water;
mi - quality of isopropyl alcohol, g;
ms - quality of paint, g;
a i - peak area of isopropyl alcohol;
A w - peak area of water in samples;
A 0 - peak area of water in the internal label thinner.
of 1.2.4.6 moisture content
the moisture content of two different models of coatings as shown in Table 2.
the determination results and relative deviation of moisture content in
coatings
1.2.4.7 Content of V O C in two different models of coatings and measurement relative deviation
ρ

ww - Water Mass Score in Paint, g/g;
wi - Quality Score of propylene Glycol in Paint, g/g;
ρ s - Paint Density, g/mL;
ρ w - Water Density, g/mL;
1 000 - Conversion Factor.
content and measurement relative deviation of VOC in two different models of coatings such as Table 3.
voC content and relative deviation
2 Conclusion and discussion
2.1 Conclusion
(1) G B18582-2008 Determination of volatile organic matter using capillary chromatography, improving ρ (V O C) The precision of the measurement, the drying method to determine volatile organic matter, the boiling point of more than 250 degrees C of organic matter is also included, such as alcohol ester-12, in the oven 105 degrees C 1 h is all volatile, so that the ρ (VOC) determination value is high.
(2) In this test, the use of fixed column temperature can improve the detection speed, in the case of each part can be separated as far as possible to use constant temperature, especially the determination of moisture content using a constant column temperature (130 degrees C) to determine a sample of the most