Gas chromatography determines VOC in water-based coatings

0 With the
increasing attention paid to the quality of indoor environmental protection, the content of volatile organic compounds (VOCs) in water-based coatings, an interior decoration material, has received widespread attention. Although in HJ/T201-2005 "Environmental Marking Product Technical Requirements - Water-based Coatings", the definition of VOC is clarified and the measurement method is standardized. However, the standard for some operational details are not clearly defined, resulting in the actual production, testing personnel in accordance with the above-mentioned standards to detect VOC, such as operational difficulties, long detection cycle and other issues . This paper discusses how to solve the above problems in depth.1 Test Part
1.1 Principle
This method is based on the V O C definition of a boiling point of 250 degrees C, and uses a direct-in gas chromatography with a FID detector to determine the mass fraction of VOC in a water-based coating. Dissolve part of the coating sample in a suitable solvent containing a known quantity of the internal label (hetate, DEA). The resulting solution is injected into a gas chromatography for quantification. This method uses 6% acrylic propylene/94% dimethyl polysilioxane as the coating capillary column (RTX-1301) as the base column, and uses hexate diethylene (DEA) as both an internal target and a 250 degree C boiling point marker to distinguish between VOC and non-VOC substances appearing in the coating sample. Substances that peak before the DEA are distinguished as VOCs, and 2000 substances that are then peaked are distinguished as non-VOCs. The qualitative of VOCs is done through the database of the retention time of known substances on the base column (the database of this laboratory); For those with small peaks and no reference to the substance to establish a known or unknown voC quantification of the relative response factor, the DEA's response factor is used to complete. The total VOC mass score is calculated by adding and calculating all detected VOC mass scores.
1.2 Instruments and Reagents
1.2.1
Agilent-6890;
capillary column RXT-1301 (J-W), 60 m×0.32 mm inner diameter ×1.0 m film thickness;
recorder: Angelen 6890 workstation;
microsyring device: 5.0 μL;
stuffed glass bottles: 10 mL.
1.2.2 Reagents
ethyl acetylene, hexaethyl glycerides, glycol, 1,2-propylene glycol, diglycol monoclothyl ether, ethylene glycol propylene ether, all of which are pure analysis; samples, inner wall latex coatings.
1.3 Measurement Method
1.3.1 Instrument Operating Conditions
Carrier Type: Nitrogen (N2)
Bar Pressure: 9 psi (Normal Pressure Mode)
Column Flow Rate: 0.77 mL/min
Line Speed: 15.3 cm/s
sampler: sifier, 250 degrees C
seine rate: 40
sample size: 2.0 sl
detector: flame ion detector (FID), 250 degrees C
detector airflow rate: H2,45 mL/min; AIR, 500 mL/min;
: 50 mL/min gas chromatography oven temperature program:
Initial temperature: 100 degrees C
Initial time: 1 min
warming rate: 20 degrees C/min
final temperature: 250 degrees C
Final time: 21 min
Full running time: 29.5 min
commercialized sample VOC qualitative analysis
commercialized sample VOC qualitative Analysis
1.3.2 Sample preparation
1.3.2.1 Preparation of the inner marker/marker solution
weighing 1.005 5 g (accurate to 0.1) mg) of the DEA (purity >99%, boiling point 251 degrees C, density 1.009 g/mL) to 100 mL capacity bottle, and add acetylene (ACN) until the tick line. This inner standard solution contains 0.010 06 g/mL of the DEA in the ACN.
1.3.2.2 sample preparation
take an exact 1.0 mL marker/inner label solution, add it to a vial with a screw cap (15 to 20 mL volume capacity), and add 8 mL ACN. Accurate weighing of 1 g (accurate to 0.1 mg) of a fully mixed uniform paint sample, also added to the vial, tightly covered and fully oscillating the vial by hand or oscillator, so that the polymers and pigments in the sample are loose precipitation, while the admission is quenched into the solution. A sample of 1 μL is taken from the sampler and ready for the sample. Each prepared sample solution should contain a DEA of 0.010 055 g (accurate to 0.001 mg).2 Results and Discussion
2.1 Qualitative Analysis
The instrument will be set according to the above conditions, after the instrument is stabilized, the injection of the inner marker/marker solution runs blank solution until the background of the GC does not interfere with the peak. The prepared sample is sampled three times in parallel, while qualitative analysis is carried out, in preparation for quantitative analysis. Qualitative analysis can be found in Table 1. The pilot database is below Table 2.
laboratory database
2.2 quantitative analysis
qualitative analysis from the above data and database results are: 10 samples have been identified substances are: glycol, 1,2-propylene glycol, di glycol monoclode, ethyl glycol propylene ether. Standard correction solution preparation: according to the size of Table 3 to weigh each standard, plus 2 mL ACN dissolved, and accurately added 1 mL of the inner subject matter solution, shake well, ready to sample. The correction factor of the above substances is calculated from the peak area in Table 4. Using the chromatography workstation, the spectral map of qualitative analysis is edified, and the correction curve is used for quantitative analysis, the results are shown in Table 5.
the preparation of the standard correction solution, the correction factors of each substance, quantitative analysis results
The relative average deviation of the measurement results was compared to ≤ 2%. The deviation range required to conform to the gas chromatography ≤ 10%. As you can see, this method has high test accuracy.the establishment of a database for qualitative analysis
(1) for the selection of test conditions, the retention time of the sample/the retention time of the internal object can be used directly. The reason is that even if the setting conditions used each time are the same, there will be some differences and fluctuations, if a fixed time is used in the database, the fixed time must be carefully adjusted before each test, in order to be able to use the database, greatly increasing the detection cycle.
(2) qualitative and quantitative analysis using a pillar, namely: capillary column RXT-1301 (J-W), 60 m×0.32 mm internal diameter ×1.0 m film thickness. Due to the different polarity of the measuring column and the confirmation column, some substances have different peak shapes, which causes some difficulties for the qualitative of the substance. Therefore, in order to make daily detection easier, it is also feasible to establish its own database on the same pillar according to the accumulation of actual detection results.
(3) in quantitative analysis, the use of DEA to do both markers and internal objects, the same simplifies the operation process, and the detection accuracy is high. When the correction factor is obtained, the correction solution should be a concentration gradient because all peaks before the DEA are analyzed.
(4) impurity peak: when the peak area of 5% of the total area can be defined as impurity peak, the correction factor is 1. This does not affect the detection results.4 The diluent of the
(1) dissolved sample, which affects the results of the test, should choose a solvent that is not volatile or volatile very slowly, so that accuracy of 0.000 1 g is guaranteed during the weighing process of the sample. The effect of selecting acetylene in this method is good.
(2) in the preparation phase of the sample, should pay attention to the sample sequence, that is: add diluted solvent →insumer/marker solution→ sample, otherwise, will cause the sample cladding seriously, not conducive to the full release of VOC, so that the test results are small.
(3) When the sample preparation is completed, the sample should be taken in the shortest possible time to prevent the release of VOC from being absorbed again by loose pigment fillers, so that the result is small. If the sample measurement cannot be carried out immediately, the top liquid of the preparation sample can be transferred to another
with sealing plug.
(4) When the selected solvent dilutes the sample, if it is milky, the sample should be in a uniform state, the sample should be sampled. No centrifugation is required, but pay attention to the cleanness of the insular, timely replacement of the tube, otherwise, the peak shape will change, and there will be unnecessary impurity peaks brought in, affecting qualitative results, thus affecting quantitative results.
(5) before the sample test, the first step is to eliminate the background. to eliminate impurities brought in in the air path and affect qualitative results. 5 recovery rate
samples with different contents of VOC are separately made, and the recovery rate is calculated according to the above method, and the results are found in Table 6.
recovery rate was analyzed and
, the recovery rate was 95% to 100%. Thus, the method is reliable.
6 Conclusion
used gas chromatography to determine VOC in water-based coatings, and did a lot of experiments and research. And this method is perfected and supplemented in the operation details. This method is convenient, fast and accurate, and meets the data needed for production monitoring and new product development.