Introduction: For some chemical plants and coking plants, most of them are sewage. In the discharge of sewage, benzene, toluene, xylene and nitrobenzene are used to cause pollution water bodies to report more incidents. According to these benzene substances in water For the dissolution, benzene and nitrobenzene can be separated and qualitatively and quantitatively analyzed by gas chromatograph using FID detector and 6201 sorbitol chromatography packed column.
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Part
1. 1 Instrument and reagent instrument is gas chromatograph, equipped with FID detector, manual injection, configuration workstation, syringe: 0.5uL, 1 uL, 5 uL, 10 uL.
Standard: Benzene (chromatographically pure)
Toluene (chromatographically pure)
Xylene (chromatographically pure)
Nitrobenzene (chromatographically pure)
Water: distilled water
1. 2 Principle: The mixture of benzene, toluene, xylene and nitrobenzene is separated by gas chromatography column, detected by hydrogen flame ionization detector (FID), using external standard method or internal standard method, using curve correction or single point Calibration is performed for quantitative analysis.
1. 3 internal standard isopropanol (ethanol or methanol) chromatographically pure, carrier: acid washed 6201 carrier (60-80 mesh).
1. 4 instruments: gas chromatograph with hydrogen flame ionization (FID) detector, sensitivity ml × 10-10g / s, column: column length 5-6m, inner diameter 3-4mm stainless steel tube, fully cleaned before use Clean, dry and ready for use.
1. 5 Preparation of stationary phase: Weigh 25-30g sorbitol in 600ml beaker, add 300ml methanol to dissolve, put the beaker in the water bath and heat it slightly and stir it gently. After sorbitol is dissolved, add 70-75g carrier to continue. While heating, stir gently, wait until the methanol solvent evaporates to dryness, then transfer it to a vacuum oven at 50-60 ° C for 4-6 hours or 70-80 ° C oven for 6 hours to dry, remove the packed column, and the column is plugged in. Aging at 130 ° C for 8-12 hours under gas conditions.
1. 6 chromatograph operating conditions:
Column temperature: 100 ° C
Vaporization chamber temperature: 150 ° C
Detector temperature: 150 ° C
Nitrogen, air and hydrogen are adjusted according to the actual conditions, so that the peak separation is sufficient, and the detector reaches the high sensitivity requirement of Zui.
2 test results and discussion
2. 1 qualitative analysis:
Add a small amount of benzene, toluene and xylene to the water and stir well. Benzene, toluene and xylene can be well characterized and quantified on the activated column. The retention time of benzene is 0.84min and the toluene is 1.00min. The retention time of m-xylene was 1.14 min. When 0.25 uL of nitrobenzene was injected into 25 ml of water and shaken well, it was found that there was a peak at 5.66 min, which was converted to 0.02 uL× 1.2g/cm3×25/1000=0.9mg/L, after the sample was diluted 10 times, the peak of the peak was very good at 5.66min, and then 0.02uL of nitrobenzene was injected into the new syringe to inject 0.09 mg. After the sample of /L, shake well, and then use a new syringe to inject 4uL, and find that the peak of the chromatogram is obviously increased, so that the acidified 6201 carrier is coated with sorbitol pure, at a column temperature of 100 ° C, the vaporization chamber, detection When the temperature is 150 °C, benzene, toluene, xylene and nitrobenzene can achieve good separation, and the next step is to prepare for quantitative calibration.
2.2 Quantitative analysis For benzene, toluene, xylene chromatography, the response signal is good, the reaction speed is fast, and the quantitative linearity is good. The standard sample concentration is 0.01mg/L, the peak height is 105uV, and the peak height of nitrobenzene is 35uV. The standard sample is prepared as follows: 0.1000 g of benzene or nitrobenzene is weighed in a balance, dissolved in 10 mL of methanol. (or ethanol), S0 = 10g / l, then take S01ml diluted with distilled water to 100ml, S1 = 103.5mg / l, then take S11.0ml diluted with distilled water to 100ml, get S2 = 1.013mg / l, and then separately Different volumes of S2 are diluted with distilled water to 50ml, 100ml, 1000ml or other volumes. Different standard benzene and nitrobenzene samples can be prepared, and then different concentrations of standard samples can be identified and injected according to peak area (peak). High) can calculate the curve correction factor, and can also be directly labeled with water as a solvent. A small amount of benzene is dissolved in water more uniformly. I have done this by dissolving benzene in organic solvent methanol, ethanol and directly dissolved in water. In the comparative test, the two methods did not differ much. The speed of dissolving benzene and nitrobenzene in water is slow, and it must be shaken well. This can ensure the consistency with the environment of the sewage. It can be quantified by external standard method. It can be used for calibration curve calibration or single point calibration. It is also convenient and easy to use. Methanol, ethanol or isopropanol was used as an internal standard for internal standard method quantification. The internal standard method was quantitative and accurate, and was less affected by the injection volume and the injection level of the laboratory personnel.
2. 3 sample processing:
The sewage sample can be used as a 250ml brown fine-mouth bottle. After the sample is full, the coat wrap is sealed immediately, and the sample is directly injected. In some sewage samples, there is an oil mixture. After the injection, there are many chromatographic peaks, which can be directly added to the sample. A small amount of standard material was re-qualified according to the increase of peak height. The author once had a nitrobenzene content of 0.2184 mg/L on the sewage sample, and it was placed in the indoor 20 °C for three days. After re-injection analysis, it was not detected. When entering the standard sample, the instrument calibration factor does not change, so the sewage is affected by the adsorption of the sample bottle and the decomposition of some substances such as bacteria, microorganisms, chemical elements or ions in the ambient temperature, light, etc., and the specific changes and reactions. The mechanism has not seen the media so far. The author also tested the standard sample stored in the refrigerator at 4 ° C. The peak height and the peak height of the sample injected at 20 ° C were repeated and found that the peak height did not change. Since the sample of the sorbitol column needs to be finished after 15 minutes, the sample is kept at about 20 minutes. I have injected a total of 7 minutes in the calibration curve. A total of more than 300 times, the peak height of the sample with high concentration was found to be the same as that of the low concentration sample. The poisoning phenomenon of the column appeared because the boiling point of nitrobenzene was 210.8 ° C, although the mass transfer rate of water vapor with the gasification chamber Soon, high-concentration samples and multiple injections in a short period of time add difficulty to the reduction or aging of the column, causing poisoning of the injection separation system. Therefore, large molecular weight and high-boiling substances are analyzed by gas chromatography. When the packed column is analyzed, there are still many constraints on the conditions, and there are many difficulties that need to be overcome.
The quantitative formula of the external standard method is:
Cx=Ax(Hx)/A (H standard)×C standard×100%
Ax----the peak area of ​​the sample
A standard----the peak area of ​​the standard
C mark ------ is the concentration of the standard
3 Conclusion:
Using FID detector, 6201 sorbitol chromatography packed column, can quantitatively analyze samples containing benzene and nitrobenzene in wastewater. If the detector of the instrument is changed to ECD (electron capture), the detection limit will be lower and the concentration will be lower. The extraction and enrichment method can also be used to detect lower limit analysis. When the sample concentration is high, the TCD detector is used, so that the sample can be easily processed by a single column, and the benzene, toluene, xylene or nitrate can be analyzed and determined. The base benzene is mixed with each component of the sample.
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