Online petroleum analyzergravimetric method
The weight method is a commonly used method that is not limited by the type of oil, but it is cumbersome to operate and has low sensitivity. It is only suitable for determining oil containing water samples above 10mg/L.
The principle of method determination is to acidify the water sample with sulfuric acid, extract mineral oil with petroleum ether, evaporate the petroleum ether, weigh the residue, and calculate the mineral oil content. This law refers to the total amount of substances in water that can be extracted by petroleum ether, which may contain heavier petroleum components that cannot be extracted. When the solvent is evaporated, it can also cause loss of light oil.

Online petroleum analyzerinfrared spectrophotometry
Extract oil substances from water using carbon tetrachloride, and then determine the total extract. The extract is adsorbed with magnesium silicate, and after removing polar substances such as animal and vegetable oils, the petroleum substances in the filtrate can be determined.
The total extract and petroleum content are determined by wavelengths of 2930cm, respectively^-1（CH₂The stretching vibration of C-H bond in the functional group, 2960 cm^-1（CH₃The stretching vibration of C-H bond in the functional group and 3 030cm^-1The absorbance A at the spectral band of C-H bond stretching vibration in aromatic rings₂₉₃₀、 A₂₉₆₀And A₃₀₃₀Perform calculations. The content of animal and vegetable oils is calculated based on the difference between the total extract and the petroleum content.
The key points of method determination are as follows: first, extract the total extract from the water sample directly or by flocculation enrichment with carbon tetrachloride (for water samples with low petroleum content), and divide the extract into two parts: one part is used to determine the total extract; Another one is adsorbed by magnesium silicate and used for the determination of petroleum substances. Then, using carbon tetrachloride as the solvent, prepare solutions of n-hexadecane, 2,6,10,14-tetramethylpentadecane, and toluene at certain concentrations, and measure their A values separately_2　930、 A_2　960And A_3　030List the simultaneous equations using the following formula and calculate the corresponding correction coefficients X, Y, Z, and F:
In the formula: ρ - the content of a certain substance in the prepared solution, mg/L；
A_2　930、 A_2　960And A_3　030——The absorbance of three substance solutions at corresponding wavelengths;
　　X. Y, Z - absorbance correction coefficient;
F - Correction coefficient for the effect of aliphatic hydrocarbons on aromatic hydrocarbons, i.e. n-hexadecane at 2930cm^-1And 3030cm^-1The ratio of absorbance.
Measure the absorbance A of the total extract of the water sample after measurement_1,2930、 A_1,2960And A_1,3030And the absorbance A of the extract after removing animal and vegetable oils_2,2930、 A_2,2960And A_2,3030Calculate the total extract content in the water sample using the following three equations₁（mg/L）、 Petroleum substances ρ₂(mg/L) and animal and plant content ρ₃（mg/L）：　
In the formula: V₀——Extract the solvent from the water sample to a constant volume, ml；
V_W——Water sample volume, ml；
D - dilution ratio of extraction solution;
L - the optical path length of the colorimetric dish used to determine the correction coefficient, cm；
L - the optical path length of the colorimetric dish used for measuring water samples, cm。
This method is applicable for the determination of petroleum, animal and vegetable oils in various types of water. The detection limit of the method is 0.1mg/L when using a colorimetric dish with an optical path length of 4cm and a sample volume of 500ml; When the sample volume is 5L, 0.01mg/L can be detected through enrichment.
（3） Non dispersive infrared absorption method
This legal system utilizes the methyl group (- CH) of petroleum substances₃）Methylene (- CH)₂There is characteristic absorption in the near-infrared region (3.4 μ m), which serves as the basis for determining the oil content in water samples. Standard oil can be extracted from contaminated water using petroleum ether extract. According to the characteristics of crude oil components in China, mixed petroleum hydrocarbons can also be used as standard oil, with a composition of hexadecane: isooctane: benzene=65:25:10 (V/V).
When measuring, first acidify the water sample with sulfuric acid, add sodium chloride to break the emulsion, and then extract with trichlorotrifluoroethane. The extract is filtered through an anhydrous sodium sulfate layer, diluted, and injected into an infrared analyzer to measure its content.
All organic substances containing methyl and methylene groups will cause interference. If there are animal and plant oils and fatty acid substances in the water sample, they should be separated in advance. In addition, some heavier components in petroleum are insoluble in trichlorotrifluoroethane, resulting in lower measurement results.