Blow-sweeping gas chromatography determines benzene products in water-based coatings

The method of determining benzene products in coatings is mainly gas chromatography, and appropriate sample pre-treatment methods are needed for water-based coatings. The traditional liquid extraction method uses more solvents, and commonly used extractors such as ethyl acetate, tethydrofuran, carbon dioxide, etc. are too wide, interfering with the peak of the object to be measured; In addition, due to the interference of other large molecular materials in the coating, it will seriously damage the column and detection instruments, increasing the difficulty of analysis.
In recent years, there have been more reports of benzene products in coatings using static top-air-gas chromatography, and there have also been reports of the use of top-air-solid-phase micro-extraction technology to collect benzene gas chromatography to determine
the chromatography of benzene
gas. These methods are easy to operate and free of solvent contamination, but must have overhead sample equipment.
In recent years, due to the advantages of high abundance efficiency and no need for organic solvents, blow-sweeping capture devices have been widely used in the environment, health, soil monitoring and other industries to determine volatile organic matter, but in the paint industry, the use of blow-sweeping gas chromatography to determine volatility There are few reports of organic matter, and the principle of treating soil samples by blow-sweeping gas chromatography in this study has realized the determination of water-based coatings with low benzene content, the method is fast and sensitive, and the interference of other polymeric materials in the coating to the measurement system is avoided, and the mark-up recovery rate of the sample is greater than 80%.
1 experimental part
1. 1 Instruments and reagents
gas chromatography, model Agilen 7890A GC, Agilent Technology Co., Ltd.; Fully automatic blow-sweep collector (with Solatek 72 Multi - Matrix Vial Autosample autosample), Model Teledyne - Tekmar Stratum Purgeand Trap, Tekmar, USA; Ultra Pure Water System, Model RO - MB - 20, Hangzhou Yongjieda Purification Technology Co., Ltd. Mixing standard samples of 7 benzenes in methanol (lot number 332412) (including benzene, toluene, ethyl benzene, phthalates, xylene, xylene, isopropylene), and standard samples of styrene in methanol (438701): Standard Sample Institute of the Ministry of Environmental Protection.
: high purity nitrogen (99.999%);
1. 2 Experimental methods
1. 2. 1 Blow the preparation of the sample
take 2. 0 g water-based paint samples in 100 mL capacity bottle, distilled water diluted to the scale, the diluted sample 10 mL added to the blow-sweeping set with brown screw glass tube, while adding a clean magnetic mixer, immediately sealed, placed in the sample plate of the blow-sweeping set automatic sampler, according to the method of blow-sweeping collection processing soil samples (soil), preparation of samples and GC analysis. To preserve the time for qualitative, peak area for quantification.
1. 2. 2 Chromatography
- HP - Innowax Column (30 m × 0. 32 mm × 0. 25 μm); inflow temperature 200 degrees C, se through sample, severing ratio 30: 1; column initial temperature of 60 degrees C, 4 degrees C / min to 120 degrees C, maintain 5 min, 8 degrees C / min to 220 degrees C, maintain 10 min; column flow 1.5 mL/min. The detector (FID) is 250 degrees C and the gas carrier is high purity nitrogen; The gas is hydrogen, the flow rate is 40 mL/min; The gas is air and the flow rate is 350 mL/min.
1. 2. 3 Blow-sweeping instrument conditions
sample mode is Soil, blow-broom sample temperature of 50 degrees C, blow-sweeping time 15 min, blow-sweeping gas for high purity nitrogen, blow-sweeping flow rate of 40 mL/min; A constant temperature catch, parsing temperature of 250 degrees C, parsing time of 2 min, parsing flow rate of 300 mL/min, baking temperature of 270 degrees C, baking time of 8 min, baking flow rate of 280 mL/min.
1. 2. The linear relationship of the 4 method and the detection limit
take the appropriate amount of methanol benzene mixture standard sample and methanol standard sample, dilute with methanol to make mixed standard, dilute with distilled water to the following concentration of standard solution 2. 5 μg /L, 5. 0 sg /L, 10. 0 sg /L, 20. 0 sg /L, 30.0 sg /L, 50.0 sg /L, each taking 10 mL into the sample bottle of the blow-sweep set autoseeder, the sample mode is Soil, respectively, to record the retention time and peak area of the peak, to get the linear relationship between each substance. The detection limit of the method is based on the signal-to-noise ratio (S/N) > 3 of the instrument, and the minimum detection limit is 0. 50 to 1. 0 sg /L. The results of the experiment can be found in Table 1. As can be seen from Table 1, the linear correlation of this method is good and the detection limit is low.
standard curves and check-out limits
1. 2. 5 Method recovery rate and relative standard deviation
take 2. 0 g water-based paint as the basic sample, add to the 100 mL capacity bottle, dilute with distilled water to the scale, take the diluted sample 10 mL to add to the blow-sweeping set with brown screw glass tube, add clean magnetic mixer, respectively 5. The benzene labeling recovery experiment at 3 concentration levels of 0 μg/L, 10. 0 0 μg /L, 30.0 μg/L was carried out and the coating sample with a labeled concentration of 5.0 μg/L was measured in parallel 7 times, with the recovery rate and relative standard deviation of each compound seen in Table 2. As can be seen from Table 2, the recovery rate of samples at 3 concentration levels is 88. 3% to 107%, the relative standard deviation (RSD) of 7 parallel determinations of benzene at the same labeled concentration was 1. 8% to 4. 3%。
2 experimental condition selection
2. 1 column selection
The current domestic standard for the content of xylene in the coating is the sum of 3 isomers, the degree of separation of xylene is not required, in the selection of column selection of non-polar columns (e.g. HP - 5 columns), you can meet the measurement requirements. Taking into account the need for further analysis of the content of each isomer, the HP-Innowax column (30 m × 0.32 mm × 0.25 m) in this study was able to separate xylene, xylene, phthalates well. The chromatography is shown in Figure 1.
of the diabenzene family to look for a
2. 2 The choice of the severity ratio
the preparation of a standard solution of benzene with a concentration of 25.0 μg /L, select the "diversion" sample mode for detection and analysis, and select 10:1, 30:1, respectively. The results show that when the seism ratio is 30:1, a sharp, symmetrical and completely separated chromatography can be obtained, and there is a high response value, and benzene is separated from the solvent peak. If the diversion ratio of 10:1 is used, due to the high rich efficiency of the blow-sweeping trap, there are some target peak deformation, tailing, and benzene and solvent peak overlap more, can not achieve a good separation effect. Therefore, this study uses a 30:1 severity ratio.
2. 3 Selection of blow-sweeping capture method
For water-based coatings, because of the low concentration of benzene, this study selected blow-sweeping method to collect samples. If the water sample is prepared according to the conventional blow-sweeping method, the system will automatically transfer a certain volume of paint samples to the blow-sweeping tube, this process will seriously pollute the entire blow-sweeping system. Therefore, according to the method principle of handling soil samples by blow-sweeping collection equipment, the diluted paint sample is loaded directly into the glass tube of the special brown screw of the 40 mL blow-sweeping collection, and magnetic stirrer is added to deliver the sample to the sample position of the blow-sweeping collection device through the automatic sample in the sample. In accordance with the method of processing soil samples, do not transfer samples, but automatically add distilled water for treatment, through heating, blowing, concentration, analysis and other steps, will be collected to capture the trap of volatile benzene products automatically into the gas chromatography, complete the separation and analysis of the sample. This method is highly efficient and easy to operate, and only brings the volatile organic object with low boiling point into the column, avoids pollution, and can achieve a good separation effect.
2. 4 Optimization of the blow-sweeping set parameters
2. 4. 1 Selection of traps
There are many filling materials for traps, commonly used in activated carbon, silicone, Tenax, carbon molecular sieve, wood carbon, OV-1, Carbopack B, Carbopack C, etc. The trap used in this study consists of the equivalent Tenax, silicone and activated carbon, which is suitable for the capture and thermal analysis of trace multi-component volatile organic matter in water, soil and coatings.
2. 4. 2 Selection of blow-sweeping time
One of the most important aspects of the blow-sweeping capture device in the sample pre-processing process is the continuous blow-sweeping of the sample, in principle, the longer the blow-sweep time, the more the extraction of the target compound in the sample, the higher the representativeness and reproducibility of the analysis. In this experiment, four representative benzene (benzene, toluene, ethyl benzene, styrene) standards were selected to be added to the paint sample to determine the best blowing time by comparing the relationship between blow-sweeping time and blow-sweeping efficiency. The results showed that the blow-off efficiency of the other three benzenes increased with the extension of the blow-sweeping time, and the blow-off efficiency of the benzene was basically more than 95% at 20 min, but considering the longer the blow-off time, the blowing efficiency of the benzene was basically more than 95% at 25 min. The more moisture that is swept out, the more time-consuming and time-consuming the collection system, reducing the experimental efficiency, and at 15 min benzene blow-off efficiency has reached more than 90% at 20 min, after 20 min benzene blow-off efficiency has decreased, so the system chose 15 min as the blow-out time. The results are shown in Figure 2.
four benzenes were measured at different blow-off times
2. 4. 3 The selection of blow-sweeping temperature
the blow-sweeping temperature is also an important blow-sweeping set parameters, according to the principle of top air liquid balance, in the top-air analysis, the response value of the part to be measured is directly related to the gas sub-pressure of the liquid space in the gas-liquid balance bottle, the increase of the blow-sweeping temperature is conducive to the increase of the sub-pressure of the gas on the liquid, Figure 3 lists the value of the different blowing temperature at 15 min blow-off time, 4 kinds of benzene system.
4 benzene products at different blow-sweeping temperature measurement values
as shown in Figure 3, with the increase of blow-sweeping temperature, the blow-sweeping efficiency of benzene products has been improved to varying degrees, in the blow-off temperature reached more than 60 degrees C, benzene blow-off There is a downward trend in efficiency, which has a certain relationship with the low boiling point of benzene, volatile and slightly soluble in water and other properties, and with the increase of blow-sweeping temperature, the moisture brought out by the blow-sweeping system will also increase accordingly, so the selection of blow-off temperature of 50 degrees C.
2. 4. 4 Parsing temperature and time
the preparation of a standard solution of benzene with a concentration of 50.0 μg/L, under the above blow-sweeping set and GC conditions, the resolution temperature of 250 degrees C, analysis of 2 min, benzene recovery rate of more than 80%, to meet the analysis requirements.
2. 4. 5 Baking temperature and time
Baking is the step of re-activating the trap, the main purpose of baking is to remove the residue of the previous analysis, and can improve the adsorption activity of adsorbents in the trap, play the role of activating the trap. The baking temperature requirement is slightly higher than the temperature at the time of chromatography analysis, with the aim of removing volatile organic compounds with higher boiling points other than the ingredients to be measured in the analytical sample. The maximum column temperature of this method chromatography is 220 degrees C, considering that the higher boiling point of volatile organic matter in water-based coatings other than benzene is more interference, so it is more appropriate to choose 270 degrees C baking temperature. Avoiding the effects of residues, this study selected a baking time of 8 min, which, while increasing the cycle time of the entire blow-sweeping set system, ensures the largest amount of removal of interference.
3 Actual sample
based on the above method, 6 batches of water-based paint samples were taken 2. 0 g measurement, the results show that benzene, toluene, xylene, ethylbenzene, isopropylbenzene have been detected, but the content is lower, far lower than the State Environmental Protection Administration issued the "environmental marking products technical requirements of water-based coatings" (HJ /T 201-2005) on the limits of harmful substances in water-based coatings (benzene, toluene, xylene, ethylbenzene total ≤500 mg / kg). The results are shown in Table 3, and the chromatography is shown in Figure 4.
The determination of benzene products in water-based coatings, sample 1 determination chromatography
4 conclusion
The method established in this study applies the principle of preparing soil samples by blow-sweeping trap, and achieves the rich treatment of benzene products in water-based coating samples, the method is simple, fast and accurate, the sensitivity is high, the interference is low, and the system pollution is avoided, and the results are satisfactory.