SpME-GC/MS/O method analyzes odor problems in water-based coatings

SPME-GC/MS/O method analyzes the odor problem of water-based coatings
Dong Wei, Julie, Fang Fang, Chen Yanhui (Solvay China Investment Co., Ltd., Shanghai 201108)
VoC detection of water-based coatings is the existing national standard method for gas chromatography, and some researchers use the top-air-gas chromatography method to detect the residual monolith concentration of coating emulsions of 20 μg/mL. Accordingly, major water-based coating manufacturers have launched a series of low VOC (low/odorless) water-based coating products
china
. Paint manufacturers in the development of low VOC water-based coating formulations, sometimes encounter some unpredictable odor problems, with existing analytical methods can not be accurately determinized analysis, so it is necessary to develop a method to determine the molecular structure of these unpleasant odors, so as to better promote low VOC (low/odorless) water-based paint products.
solid-phase micro-extraction (SPME, solid-phase micro-⁃) technology was introduced in the 1990s. The principle of top-to-air-solid-phase micro-extraction (HS-SPME) is to insert quartz glass or metal fibers coated with a polymer fixed phase into the gas phase layer of the sample to extract volatile and semi-volatile target organic molecules and concentration, and then in the gas chromatography sample in the inset directly pyrolyze into the column for separation and detection, so SPME is a collection of extraction, concentration, de-absorption, sample in one of the efficient solvent-free treatment method. In the 20 years since its infested, SPME has developed and perfected rapidly with the advantages of convenient operation, high selectivity, small sample size required, unlimited sample status (gas/liquid/solid state), high sensitivity, and widely used in various fields, such as food, health care products, tobacco, Chinese medicine, water quality, agricultural residues, forensics, fire analysis, etc.
GC/O is a odor detection technique that adds a sifier at the end of the gas chromatography column to allow a portion of the compound that flows well into the GC detector, while the other part is sniffed into the odor detector, where the researchers can analyze and evaluate the odor of the compound by sniffing it. In view of the characteristics and purpose of the samples tested, this study analyzed and studied the same formula products with odorless and odor by using this comprehensive measurement method of solid-phase micro-extraction-temperament olfactory joint.1 Experimental part
1. 1 Source of odor problems
This laboratory prepared 2 water-based paint samples using the same formula and materials when helping customers develop new formulations, the raw materials of these 2 paint samples were odor-free before mixing, were applied to cement fiberboards after mixing, and one of the samples had unpleasant odors (similar to cat urine odor) after 24 h.
1. 2 Instruments and materials
gas chromatography-mass spectrometrometromety-olfactory measurement instrument (Agilent 6890-5973 MSD-O), solid-phase micro-extraction device (Combi-PAL, CTCSPME), extraction Fibers (Supelco, 50/30 sm DVB/CAR/PDMS StableFlex/SS 1 cm), 20 mL overhead sample bottle (VWR), 15 cm fast quantitative filter paper (double-circle plate), etc. Water-based paint A (homemade, odorless/low odor), water-based paint B (homemade, with a strong odor).
1. 3 Sample preparation
Add 1 g sample A and 1 g sample B to 2 sheets of filter paper, place 24 h at room temperature, and then cut the filter paper into a small strip of 0.3 cm×5 cm, sealed in a 20 mL top empty sample bottle for testing.
1. 4 Solid-phase micro-extraction-gas chromatography-mass spectrometrometrometrometromety operating conditions
Solid-phase micro-extraction (SPME) operating conditions: equilibrium time 10 min; equilibrium temperature 40 degrees C; extraction time 15 min; de-attachment time 5 min. Gas chromatography-mass spectrometry (GC-MS) conditions: Agilent DB-1 MS capillary column, 30 m×250 mm×0. 25 m; 5 kPa, no flow in, carrying helium, MS interface transmission line temperature of 250 degrees C, mass spectrometry EI ionologic source temperature of 230 degrees C, ion ionizer energy 70 eV, single four-stage rod mass analyzer, full spectrum scanning range of 45 to 500 amu, NIST02 mass spectrometry data retrieval library.
1. 5 Sample Analysis
the two samples prepared according to the method described in 1.3 will be analyzed and tested with the working conditions described in 1.4, and when peaks appear in the total ion flow map of MS are observed, the artificial olfactory measurement evaluation is carried out by olfactory meter, and a background test is applied to eliminate background influence.2 results are different from the choice of
2. 1 extraction fiber
solid phase micro-extraction fibers are different in their adsorption ability to compounds due to the polymer fixation phase of the coating. Commonly used polymer fixation phases are polydymethane (PDMS), carbon molecular sieve (Carboxen), polyethylene glycol (PEG), polypropylene (PP), dvinyl benzene (DVB) and so on. The selective adsorption of compounds by extracting fibers is based on the volatility (molecular weight) and polarity of the compounds, similar to similar suction. Depending on the nature of the sample to be tested and the purpose for which it was tested, two extract fibers were selected⁃: (1)
85 sm Carboxen/PDMS Stableflex/SS for gas and low molecular weight compounds; Test 2 comparative samples under the same conditions to determine the extraction effect of these 2 extracted fibers based on peak time, peak number and peak area. Figure 1 is a temperament-total ion flow map of the
made of 2 extracted fibers.
the whole graph in Figure 1, the peak time of the extraction fiber using No. 1 is after 5 min, and the apparent peak appears after 10 min, at which point the bar temperature exceeds 90 degrees C. And with the 2nd extraction fiber 2. There is a noticeable peak at 5 min, at which point it is still a column temperature of 40 degrees C, and a large amount of material is detected before 10 min. Comparing the total number of peaks, a total of 41 peaks using No. 1 extraction fiber and 44 peaks using No. 2 extraction fiber, the difference is not very large. The peak area is compared, with a maximum peak area of 211 (A×Sec using Extraction Fiber No. 1 and a maximum peak area of 113 (A×Sec) using Extract fiber No. 2. Combining the above analysis results, taking into account that the ultimate goal of this experiment is to check the cause of the sample's odor at room temperature, select the No. 2 extraction fiber, i.e. 50/30 m DVB/CAR/PDMS StableFlex/SS as the solid-phase micro-extraction fiber used in this study.
2. GCMS spectral analysis of 2 samples
Figure 2 is a total ion flow map obtained after testing with the method of 1.4 after placing 24 h of blank filter paper at room temperature and cutting and placing it in a top empty bottle.
As can be seen from Figure 2, the filter paper used to prepare the sample is a very clean material, and almost no compounds are detected throughout the testing process, with only a few very small peaks appearing at about 8, 12, 15, 28 min.
Figure 3 is a total gas mass spectrometum ion flow map of water-based coating sample A (odorless) and sample B (odorous), after the concentration of SPME, you can see that its signal value is much larger than the signal of several small peaks of the blank sample in Figure 2, so the background signal of the blank sample can be completely ignored.
can be clearly seen from Figure 3 in the area of 6 to 7 min, sample B appears in the sample A does not have the composition peak. When these peaks appeared, artificial olfactory measurements were performed with olfactory meters, and 6. 22 min and 7. The smell at 13 min is very similar to the odor found.
retrieved from NIST02's MS database, a mass spectromet graph of the two components at 6.22 min and 7.13 min is obtained, as shown in Figures 4 and 5.
composition at 6. 22 min in sample B was searched by the spectral library and confirmed to be positive propylene, and the upper half of Figure 4 is a mass spectrometry at 6.22 min, and the lower half is the standard mass spectrometry of positive propylene. Sample B 7. The ingredients at 13 min were searched by the spectral library and confirmed to be benzene formaldehyde, and the upper half of Figure 5 was 7. Mass spectrometography at 13 min, the lower half of which is the standard mass spectrometromet line of benzene formaldehyde.
2. 3 Comparative experiment
Although similar odor evaluation results were obtained during artificial olfactory determination using olfactory meters, in order to further confirm that the source of the odor in sample B was caused by the two components of propylene benzene and phenylale formaldehyde, an added experiment of odorless sample A was carried out to confirm the results of the previous analysis. In odorless water-based paint sample A, a certain amount of positive propylene, benzene formaldehyde pure substances and a mixture of the two (see table 1 for specific additions), and recorded as sample C1, sample C2, sample C3, and then these samples and odorous sample B are painted on the cement fiber board, room temperature after placing 24 h to compare its odor. The addition of positive propylene and phenyl formaldehyde
to Sample
Table 1 by odor ratio, the odor of sample C3 is closest to that of water-based coating sample B, further confirming that the cause of odor in sample B is positive propylene and benzene formaldehyde 2 substances. 3 Conclusion
The analysis method of SPME-GC/MS/O established in this study makes full use of the rich function of solid-phase micro-extraction, breaks the detection limit bottleneck of the top-air method, combines the powerful separation and structural identification function of GCMS, and uses the olfactory measurement evaluation, which solves the problem of identifying trace components that cause odor in water-based coatings. This method of analysis is also of great reference for VOC testing of finished coatings or other additives.