The cetane index (ASTM D613), flash point (ASTM D56), cold filter plug point (CFPP) (ASTM D6371), D95 (ISO 3405), and viscosity at 40 °C (ISO 3104) are key parameters to determine for diesel quality. The primary test methods are labor intensive and challenging due to the need to use different analytical methods.
This application note demonstrates that the XDS RapidLiquid Analyzer, operating in the visible and near-infrared spectral region (Vis-NIR) provides a cost-efficient and fast solution for the simultaneous determination of these key parameters in diesel. Vis-NIR spectroscopy allows for the analysis of diesel in less than one minute without sample preparation or using any chemical reagents.
Diesel samples were measured in transmission mode with a XDS RapidLiquid Analyzer (RLA) over the full wavelength range (400–2500 nm). The built-in temperature controlled sample chamber was set to 30 °C to provide a stable sample environment. For convenience reasons, disposable vials with a path length of 8 mm were used, which made a cleaning procedure obsolete. The Metrohm software package Vision Air Complete was used for data acquisition and prediction model development.
Equipment | Metrohm number |
---|---|
XDS RapidLiquid Analyzer | 2.921.1410 |
Disposable vials, 8 mm diameter, transmission | 6.7402.000 |
Vision Air 2.0 Complete | 6.6072.208 |
The obtained Vis-NIR spectra (Figure 2) were used to create prediction models for the determination of key diesel parameters. The quality of the prediction models was evaluated using correlation diagrams, which display the correlation between Vis-NIR prediction and primary method values. The respective figures of merit (FOM) display the expected precision of a prediction during routine analysis.
Result cetane index
Figures of merit | Value |
---|---|
R2 | 0.991 |
Standard error of calibration | 0.093 |
Standard error of cross-validation | 0.143 |
Result flash point
Figures of merit | Value |
---|---|
R2 | 0.977 |
Standard error of calibration | 2.22 °C |
Standard error of cross-validation | 2.50 °C |
Result CFPP
Figures of merit | Value |
---|---|
R2 | 0.973 |
Standard error of calibration | 1.99 °C |
Standard error of cross-validation | 2.24 °C |
Result D95
Figures of merit | Value |
---|---|
R2 | 0.861 |
Standard error of calibration | 3.07 °C |
Standard error of cross-validation |
3.47 °C |
Result viscosity
Figures of merit | Value |
---|---|
R2 | 0.983 |
Standard error of calibration | 0.038 cSt |
Standard error of cross-validation | 0.047 cSt |
This study demonstrates the feasibility of NIR spectroscopy for the analysis of the key parameters of diesel samples. In comparison to the standard methods, no sample preparation is needed. Samples are analyzed as they are, which allows for simple operation when using NIR spectroscopy.
To view the information for all key parameters and to get the latest information, please check out our precalibrations: