Solid phase extraction method for the determination of soil nitrobenzene compounds

- Mar 26, 2021-

1 Introduction

Nitrobenzene is a widely used chemical raw material. Common nitrobenzene compounds include nitrobenzene, dinitrobenzene, dinitrotoluene, trinitrobenzene and dinitrochlorobenzene. These compounds are hardly soluble in water, and easily soluble in other organic reagents such as ethanol and ether. They are used in printing and dyeing, national defense, plastics, medicine and pesticide industries. Nitrobenzene in the environment mainly comes from the waste water and waste gas of chemical plants and dye plants, especially the sewage discharged from aniline dye plants contains a large amount of nitrobenzene. Because nitrobenzene has a stable structure and is difficult to degrade, it will sink into the water as a yellow-green oily substance and penetrate into the soil with groundwater and remain unchanged for a long time. Therefore, the pollution of water and soil will last for a long time. , And produce a series of ecological and environmental effects on the ecosystem. At the same time, the enrichment of plants will also cause harm to the human body. Nitrobenzene in soil is usually analyzed in the mode of extraction, purification, concentration, and sampling. The common purification methods include gel permeation chromatography and solid phase extraction.

2 Instruments and reagents

2.1 Apparatus

SPE400 Fully Automatic Mechanical Arm Solid Phase Extraction Apparatus, Nitrogen Blowing Apparatus

1.2 Reagents and consumables

N-hexane, n-hexane + dichloromethane (1+9), n-hexane + acetone (1+1)

Flori silica solid phase extraction cartridge (1g/6mL)

3 Experimental method

 Pretreatment of soil samples

3.1 Dehydration: Place the collected soil samples in an enamel or glass tray, remove branches, leaves, stones and other foreign objects, and mix them thoroughly. Weigh 10-20g (accurate to 0.01g) of fresh samples for dehydration, add an appropriate amount of anhydrous sodium sulfate, mix well with the sample, and grind into fine particles for later use.

3.2 Extraction: Any one of Soxhlet extraction, pressurized fluid extraction, ultrasonic extraction or microwave extraction can be selected to extract the target. Take Soxhlet extraction as an example:

Carefully transfer the ground soil sample into a paper sleeve, carefully place it in the Soxhlet extractor reflux tube, add 100 ml n-hexane + acetone (1+1) to the round bottom solvent bottle, and extract for 16-18 h , The reflux speed is controlled at 4~6 times/h. Collect the extract.

3.3 Concentration: Nitrogen blowing concentration or rotary evaporator concentration can be selected, the following takes nitrogen blowing concentration as an example:

Transfer the extraction liquid to the concentration tube and place it on the nitrogen blowing instrument. Turn on the nitrogen until the surface of the solvent fluctuates but does not form a vortex. During the nitrogen blowing process, the exposed concentrating tube wall should be repeatedly washed with n-hexane. When about 10 mL of the concentrate remains, add 10 mL of n-hexane to exchange the solvent, and continue to concentrate to about 2 mL.

4. Results and discussion

Nitrobenzene in the soil is a type of pollutant that is difficult to detect. At present, there are standard methods for the detection of nitrobenzene in the atmosphere and groundwater. The determination method in the soil has not yet been unified, but it is aimed at the purification link in the entire experimental process. , Solid-phase extraction automates the purification process and reduces manpower consumption. The organic solvent used in the experiment is sealed, which reduces the harm to the human body. The instrument can accurately control the flow rate of the solvent such as activation, sample loading and elution. Make the sample clean up more fully.