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Five, pre-treatment
(1) Sample preparation
Determination of organochlorine pesticides in soils and sediments by gas chromatography (1)
(2) Sample extraction
Weigh 10g fresh sample, mix a certain amount of substitute (the on-machine mass concentration is recommended to be consistent with the mass concentration of substitute in the standard series), then mix it with a certain proportion of diatomaceous earth, and put it into a 34mL extraction tank
Pressurized fluid extraction conditions: Use an equal volume of mixed solvent of n-hexane and acetone as the extraction liquid, and perform extraction according to the following reference conditions: extraction cell temperature 100℃, extraction pressure 1500psi, static extraction time 10min, elution is 60% of the cell volume, The nitrogen blowing time is 60s, the number of extraction cycles is 2 times, and the extraction liquid is collected
(3) Purification
If the color of the extract is dark, it can be purified with concentrated sulfuric acid first , which can remove most of the organic compounds, including some organochlorine pesticides
1.
Determination of organochlorine pesticides in soils and sediments by gas chromatography (1)
2.
Transfer the above concentrated solution into a 22mL glass tube, add 8mL concentrated sulfuric acid , vortex and shake to mix, centrifuge (speed 3000r/min, time 1min), discard the lower layer of sulfuric acid
3.
Rinse the solid phase extraction column with 10 mL of n-hexane
4.
Wash the silica gel column with about 10 mL of n-hexane
5.
Wash the graphite carbon column with about 10 mL of n-hexane
Concentrate the eluent to less than 1 mL, transfer to a sample bottle, add n-hexane to make the volume to about 1 mL, add a certain amount of internal standard solution, and wait for analysis
(4) Determination of dry matter content
Determination of Organochlorine Pesticides in Soils and Sediments Gas Chromatography (1) ——Determination of Dry Matter Content
Six, analysis and testing
(1) Instrument conditions (for reference only, can be adjusted appropriately according to the actual instrument)
1.
Sampling mode: splitless injection; injection volume: 1.
2.
Mass spectrometry conditions
Ion source temperature: 250℃; ionization energy: 70eV; transmission line temperature 270℃; quadrupole temperature: 150℃; solvent delay time: 7min; scan mode: selective ion scan, scan time range and scan ion are shown in Table 7-7
.
Table 7-7 Scan time period and scan ion
(2) Calibration curve
Prepare a standard series of more than 5 points (such as 20.
0ug/L, 50.
0up/L, 100ug/L, 200ug/L, 500ug/L) that meets the instrument's detection limit, linear range and actual sample mass concentration, and add the same amount as the same product The internal standards and substitutes (such as 200ug/L) of the internal standards, using n-hexane as the dilution solvent, are quantified by the internal standard method
.
The retention time, qualitative and quantitative ions of the compound obtained under the conditions of the reference instrument on the HP-5MS UI chromatographic column are shown in Table 7-8
.
Table 7-8 Retention time and qualitative and quantitative reference ions