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Analysis Of Biodiesel (Fame) By Icp-Oes
Huyền Diệu - 16/07/2024
INTRODUCTION
The need for energy has been greatly intensified because of the exponential progress in population and industrialization. However, the global focus on energy security and the mitigation of greenhouse gas emissions has spurred extensive research and technology advancements in the field of renewable energy. For example, petroleum fuels can also be blended with biofuels to reduce the carbon footprint of a vehicle. One of the most common biofuels is biodiesel (Fatty Acid Methyl Ester). The quality and purity of biodiesel are critical for its performance and compliance with regulatory standards. One key aspect of biodiesel quality is the presence of Na, K, Ca, Mg, and P building elements, which can affect its stability and combustion properties. Inductively Coupled Plasma Optical Emission Spectroscopy (ICP-OES) is a powerful analytical technique used to determine the concentration of trace elements in biodiesel.
METHOD
Inductively Coupled Plasma Optical Emission Spectroscopy (ICP-OES) is a highly sensitive analytical technique. It is used to detect chemical elements in various samples by utilizing a high-temperature plasma to ionize the sample and analyze the emitted light from excited atoms and ions. Based on the principle that when an atom or ion is excited, the electrons of an atom or ion will release energy from lower to higher and then return to their original state. Each atom emits at a characteristic wavelength. These characteristic lines are used for quantitative and qualitative analysis. While ICP-OES offers robustness and high sensitivity, it requires significant initial investment, skilled operation, and thorough sample preparation. Despite these limitations, its versatility and efficiency made it a critical tool in many scientific and industrial fields.
Figure 1 Schematic of a typical ICP-OES system
Table 1 European and U.S. Specifications Limit (mg/kg) for Biodiesel
| Element | EN14214 | ASTM D6751 |
| S | 10.0 | 15.0 |
| P | 10.0 | 10.0 |
| Na | sum 5.0 | sum 5.0 |
| K | ||
| Ca | sum 5.0 | sum 5.0 |
| Mg |
The biodiesel samples were either diluted in absolute 1-propanol. The reference biodiesel samples recently introduced by the National Institute of Standards and Technology (NIST SRM 2772 biodiesel produced from soybean and NIST SRM 2773 biodiesel produced from animal fat) were used to check the accuracy of the method. The method was applied to the analysis samples: biodiesel samples produced from different raw materials: animal fat, castor bean, fodder turnip, rapeseed, soybean and residual cook oil. In this procedure, a reference spectrum of the solvent was recorded first and then it was automatically subtracted.
Figure 2 Emission spectrum of biodiesel, a. Certified biodiesel sample, b. Measured emission spectrum and corrected spectrum obtained upon using smart BG correction system
Table 2 Experimental results (μg g-1) obtained by ICP-OES following sample dilution with 1-propanol
| Biodiesel | S | P | Na | K | Ca | Mg |
| Animal fat | 8.7±0.9 | 3.6±0.6 | < 0.3 | < 0.6 | < 0.2 | < 0.3 |
| Castor bean | 99.4±1.1 | 0.6±0.2 | 29 ± 1 | < 0.6 | 0.4± 0.1 | 0.33±0.03 |
| Fodder Turnip | 14.2±0.4 | 0.7±0.1 | 0.9±0.2 | < 0.6 | 0.8± 0.1 | 0.16±0.05 |
| Rapeseed | 2.6±0.3 | < 0.3 | < 0.3 | < 0.6 | < 0.2 | < 0.3 |
| Residual cook oil | 2.3±0.2 | 0.7±0.1 | < 0.3 | 17.5±0.4 | < 0.2 | < 0.3 |
| Soybean | 1.4±0.2 | < 0.3 | < 0.3 | < 0.6 | 0.4± 0.1 | < 0.3 |
The determination of Ca, K, Mg, Na, P, and S concentrations in biodiesel samples from different raw materials were carried out under the optimized conditions. The elemental analysis of biodiesel samples is performed using system software, revealing varying concentrations of trace elements. Take a closer look in table 2 for the results, almost all biodiesel samples meet standards, especially soybean oil samples that had significantly lower concentrations of elements such as Ca, K, Mg, Na, P, and S. This finding aligns with the expectation that biodiesel, typically derived from purified oils, would exhibit lower elemental concentrations. The results underscore the variability in elemental composition across different biodiesel and vegetable oil samples, reflecting the impact of purification and raw material sources on trace element concentrations.
SYSTEM
Integrating the HR4000 spectrometer from Ocean Insight into an ICP-OES system can be beneficial due to the spectrometer's high-speed data acquisition and good spectral resolution.
The HR4000 spectrometer from Ocean Insight enhances the system's performance due to its high-speed data acquisition (up to 3.8 ms) and good spectral resolution (0.03 - 1.0 nm). This rapid data capture and precise resolution are crucial for real-time monitoring and detailed elemental analysis, enabling the accurate detection and quantification of multiple elements simultaneously. The compact design of the HR4000 allows for seamless integration into existing ICP-OES setups, offering flexibility in experimental configurations. Moreover, ensuring software compatibility is vital to fully utilize the HR4000's capabilities and achieve reliable, reproducible results. This integration can benefit various fields, including environmental monitoring, pharmaceutical quality control, and geochemical analysis, where speed, precision, and flexibility are paramount.