Abstract: In this paper, a splitless analysis method is used to determine naphthalene in gas, a gas sample is directly taken with a syringe, absolute ethanol is used as an absorbent, retention time is used for qualitative determination, and external standard method is used for quantification.
1 Introduction
The determination of naphthalene content in China's coal gas has long adopted picric acid method. Although this method has high accuracy, the lower limit of quantitation is high, and the absorption treatment operation is cumbersome and time-consuming (3-4 hours); and the corresponding national standard gas chromatography also has cumbersome operation (1-2 hours), the lower limit of quantification is high, and the xylene absorption liquid is toxic to the environment and other shortcomings, so its application and promotion are limited. The company's cold rolling production line has high requirements on the technical indicators of gas quality. The naphthalene in the purified gas can reach 10mg / m3 or less, and the requirements on the inspection cycle are further improved. Therefore, it is urgent to improve the sensitivity and accuracy of the analysis method and shorten the analysis cycle. .
2 Experimental part
2.1 Instruments and reagents
Chromatograph: Shandong Jinpu GC-2010
Capillary column: 30m × 0.25mm × 0.5μm SE—54
Detector: FID
Data processing: N2000 workstation
Sampler: 10μl micro syringe
Sampler: 100ml glass syringe, 9-gauge needle absorption bottle: 5ml
Naphthalene: chromatographically pure
Absolute ethanol: analytically pure
2.2 Analysis principle
The so-called splitless analysis method is to set the initial temperature of the chromatographic column to a lower temperature (50-60 ℃), close the shunt before injecting the sample, and after the sample is vaporized, wait until most of the sample is introduced into the column (1- 2min), open the split port, increase the column temperature, the method of eluting, separating and detecting the components condensed at the front end of the column at low temperature is generally suitable for the analysis of low concentration samples with high boiling points. However, this method is easy to thermally decompose the compound, so it is not suitable for the analysis of easily decomposed compounds.
2.3 Chromatographic analysis conditions
Column temperature: 60 ℃ (2min) 200 ℃ (5min)
Vaporization temperature: 2OO ℃ Detector: 200 ℃
Column population pressure: 140kPa Air pressure: 50kPa
Hydrogen pressure: 60kPa Split flow: 40.8ml / min
Septum purge: 12.2ml / min tail blow: 32ml / min
Sampling time: 1.5min Sampler: 1μl
2. 4 Qualitative methods
Under the selected conditions, 1 μl of ethanol and 5% naphthalene ethanol solution were injected in sequence with a l0 syringe, and their retention times were 2.98 min and 7.04 min respectively. It was determined that the peaks at these two retention times corresponded to ethanol and naphthalene in sequence.
2.5 Drawing of the standard curve
Use a microsyringe to extract 1 μl of standard samples (2, 5, 10, 20, 50 mg / m ') into the chromatographic column to measure the peak area of ​​naphthalene. Analyze each standard sample twice to measure the peak area of ​​naphthalene. The standard curve is drawn by the external standard method. The result is shown in Figure 1. The regression coefficient r = 0.999562, and the linear relationship is good.
5 Conclusion
a. Using this method to determine the content of naphthalene in coke oven gas has good reproducibility, and the accuracy and precision of the results are high.
b. This experimental method is easy to operate, and the analysis period is shortened from 3 to 4 hours of the national standard to 20 to 30 rain, which can meet the needs of cold rolling monitoring and analysis.
c. The method has a low quantitative lower limit and high sensitivity, and can accurately measure 2rag / m in gas. The naphthalene can meet the requirements of cold-rolled gas technical indicators.
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