Handheld FTIR Spectrometer Soil TPH Prediction
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Solution Overview
Problem
Current methods for estimating total petroleum hydrocarbons (TPH) in soils are time-consuming and impractical for real-time field decisions, requiring lengthy laboratory processes or complex field test kits, and lack a quick and simple alternative for contaminated soil analysis.
Innovation Solution
A method using site-specific predictive models generated by correlating gas chromatography data with attenuated total reflectance (ATR) Fourier transform infrared (FTIR) spectroscopy data, allowing for rapid TPH concentration estimation in soils with a handheld FTIR spectrometer, eliminating the need for solvent extraction and sample drying, and validating the model with GC-FID measurements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If gas chromatography (GC-FID) is used to measure TPH concentration in soils, then measurement precision is improved, but loss of time increases significantly
Solution Approach 1:
The patent introduces FTIR-ATR spectroscopy as an intermediary method that provides rapid screening results, while GC-FID serves as the reference method for validation. The FTIR-ATR acts as a mediator that delivers quick preliminary data without requiring lengthy laboratory analysis, thus resolving the time-precision tradeoff by providing a fast screening pathway while maintaining confidence through selective GC-FID validation.
Solution Approach 2:
The patent segments the measurement process into two distinct stages: rapid FTIR-ATR screening for initial TPH concentration estimation, followed by selective GC-FID analysis only for samples that require confirmation or are near decision thresholds. This segmentation allows most samples to be processed quickly while maintaining measurement precision for critical cases.
2Measurement precision
If field test kits with solvent extraction are used for TPH analysis, then measurement capability is improved, but device complexity and ease of operation worsen due to time-consuming preparation
Solution Approach 1:
The patent extracts and eliminates the time-consuming solvent extraction step from the field test methodology. By using FTIR-ATR spectroscopy directly on intact soil samples, the method removes the complex preparation workflow while maintaining TPH detection capability, thus improving ease of operation without sacrificing measurement precision.
Solution Approach 2:
The patent replaces the mechanical/chemical extraction process (solvent extraction requiring filtration and preparation) with an optical detection method (FTIR-ATR spectroscopy) that requires minimal sample preparation. This substitution eliminates complex manual operations while preserving the ability to measure TPH concentrations accurately.
3Productivity
If near- and mid-DRIFT methods are used for TPH estimation, then productivity is improved through rapid analysis, but device complexity increases due to portable spectrometer requirements
Solution Approach 1:
The patent employs a handheld FTIR-ATR spectrometer that serves multiple functions: it can analyze various soil types, different TPH concentrations, and provides both qualitative and quantitative information. This multi-functionality justifies the device complexity by enabling rapid productivity improvements across diverse field conditions without requiring multiple specialized instruments.
Solution Approach 2:
The patent utilizes the high sensitivity of alkyl-CH3 vibrational groups in the mid-infrared region to achieve rapid TPH detection. By focusing on specific spectral parameters (C-H stretching vibrations), the method transforms the complex spectral data into straightforward TPH concentration estimates, thereby improving productivity while managing device complexity through targeted parameter analysis.
4Measurement precision
If sampling density is increased to reduce uncertainty, then measurement precision is improved, but loss of time and project cost increase
Solution Approach 1:
The patent applies partial action by using FTIR-ATR for rapid screening of all samples and reserving GC-FID analysis only for samples that fall near regulatory thresholds or require confirmation. This partial application of the more precise but time-consuming method reduces the overall number of expensive, time-intensive analyses needed, thereby maintaining measurement precision where critical while reducing overall time and cost.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
Enables quick and accurate prediction of TPH concentrations in soils, reducing turnaround time and project costs by providing a reliable field screening tool with a detection threshold of approximately 2000 ppm, suitable for identifying high TPH concentrations, while maintaining accuracy and minimizing false positives and negatives.
Implementation Method 1
In attenuated total reflectance (ATR) Fourier transform infrared spectroscopy, also referred to interchangeably as FTIR-ATR and ATR-FTIR, infrared light is introduced into a prism at an angle exceeding a critical angle for internal reflection. An evanescent wave is produced at the surface on which the sample is supported, extending into the sample.
Implementation Method 2
The spectrum is measured and subjected to a Fourier transform. Partial least squares regression analysis is used to correlate the GC-FID TPH concentration data with the FTIR-ATR absorbance data
Implementation Method 3
Measurements of total petroleum hydrocarbons (TPH) in soils are often required to assess environmental remedial endpoints and satisfy regulatory requirements. Soil TPH concentrations can be obtained in analytical laboratories, typically using gas chromatography (GC) such as GC with a flame ionization detector (GC-FID).
Implementation Method 4
Gas chromatography (GC) such as GC with a flame ionization detector (GC-FID)
Data Source
AI summary
Disclosed is a method for generating a site specific model for predicting TPH concentration in soil. The method includes dividing a plurality of soil samples taken from a field site into two sets of samples. One set is analyzed using GC-FID, and the other set is analyzed using a handheld FTIR spectrometer with an ATR window to obtain FTIR-ATR absorbance data. Partial least squares regression analysis is used to correlate the GC-FID TPH concentration data with the absorbance data to generate a calibration model. The model is validated with soil samples having unknown TPH concentration. The model is used to predict the TPH concentration of soil samples taken from the field site analyzed using the handheld Fourier transform-infrared spectrometer to obtain FTIR-ATR absorbance data for the soil samples. During all absorbance measurements, each of the soil samples has a moisture content of 1 to 30 wt % and each sample is pressed against the ATR window with sufficient pressure to ensure intimate contact between the sample and the window.