Infrared absorption spectrometer for detecting oil pollutants (such as petroleum hydrocarbons)

Infrared absorption spectrometer for detecting oil pollutants (such as petroleum hydrocarbons)

1. Target detection

• oil and greaseIncluding petroleum hydrocarbons (such as diesel, gasoline, lubricants), animal and vegetable fats, etc.
• key metricsThrough specific infrared absorption peaks (such asC-H bond stretching vibration absorption peak）Quantitative analysis of oil concentration.

2. Basic principles

• Infrared absorption characteristics: In oil moleculesC-H bondIn the mid infrared band（3.4–3.5 μm， Namely 2940-2850 cm ⁻¹）Generate strong absorption peaks (stretching vibrations of methyl and methylene groups).
• Quantitative basisAccording to Lambert Beer's law（Lambert-Beer Law）The absorbance is directly proportional to the concentration of oil:
  $$A=\epsilon \cdot c\cdot l$$
  • $A$: absorbance
  • $\epsilon$Molar absorption coefficient
  • $c$Oil concentration
  • $l$: Optical path length (sample cell thickness)

3. Testing process

1. sample pretreatment：

   • extractionUse carbon tetrachloride (CCl ₄) to remove oil from water or solid samplesorTetrachloroethylene (C ₂ Cl ₄) * * extraction (both without absorption interference in the infrared region).
   • purify(Optional): Remove animal and vegetable oils (interferents) and retain petroleum hydrocarbons through a silicone column.

2. instrument calibration：

   • Standard Curve MethodPrepare a series of concentrations using standard oils (such as n-hexadecane, isooctane, benzene, etc.), measure absorbance, and draw a standard curve.
   • Reference methodUsing the extraction solvent as a blank reference, eliminate solvent background interference.

3. Sample measurement：

   • Inject the extraction solution into the sample pool and scan it3.4–3.5 μmBand absorbance.
   • Calculate the oil concentration based on the standard curve (unit: mg/L or mg/kg).

4. Key parameters and interference factors

• detection limitUsually:0.1–1 mg/L(depending on extraction efficiency and instrument sensitivity).
• Main interference：
  • Animal and vegetable oils and fatsOrganic compounds containing C-H bonds (to be separated by silica gel column).
  • suspended particulate matterFilter (<0.45 μ m filter membrane) to avoid scattering interference.
  • Solvent purityCarbon tetrachloride needs to be dealromatized to avoid residual benzene interference.

5. Instrument type

• Non dispersive infrared (NDIR) spectrometer：
  • Specially designed for oil detection, with a fixed wavelength (3.4 μ m), simple structure, and low cost (commonly used for online monitoring).
• Fourier Transform Infrared (FTIR) Spectrometer：
  • Full band scanning can distinguish oil components (such as petroleum hydrocarbons and vegetable oils), but the operation is complex and the cost is high (laboratory analysis).

6. Application scenarios

• environmental monitoring：
  • Oil pollution detection in surface water, groundwater, and soil (such as emergency response to oil spills).
• industrial wastewater：
  • Monitoring of oil content in wastewater from industries such as petrochemicals and mechanical processing.
• Regulatory compliance：
  • comply withEPA 418.1(United States)ISO 9377-2(International) and other standards.

7. Comparison of advantages and disadvantages

8. Comparison with other oil detection methods

9. Precautions

• Solvent selectionProhibit solvents containing C-H bonds (such as hexane) and prioritize the use of carbon tetrachloride (requires fume hood operation).
• Sample preservationAfter extraction, the sample needs to be refrigerated in the dark (analyzed within 24 hours).
• instrument maintenanceRegularly clean the sample pool