Comprehension of soil composition is essential in its applications in agriculture, environmental science, and land management. Conventional methods, such as ICP-OES or XRF, may require a significant amount of time and involve cumbersome sample preparation. LIBS, however, applies high-energy laser pulses to shoot a small part of the sample surface and produce plasma. The elemental composition is analyzed by the light emitted from the plasma. In situ, multi-element detection can be carried out with minimal preparation, allowing for rapid on-site decision-making. Such peculiarities of speed, portability, and versatility enable this technique, LIBS in particular, to be a valuable tool in soil diagnostics, both in research and for on-site decision-making.
Methodology
A pulsed laser is applied to the soil sample, which evaporates the surface and shapes high-temperature plasma. During the process of cooling the plasma, it radiates a light that has a definite wavelength, which is characteristic of the elements in that matter. This emission is recorded by a spectrometer and scaled up into electronic spectral data that is used to identify and quantify the elements. One can test both loose and pelletized soil. The standards used allow the instrument to be calibrated, thereby increasing the accuracy of the signal. Lasers are fired repeatedly on non-identical points on the sample to average the variance of the sample.
Instrumentation
Essential components include a high-power pulsed laser, an optical system to focus the laser, a spectrometer, and a detector (e.g., a CCD or ICCD) to record and analyze the reflected light. Increasingly, portable LIBS devices are available, which can be used in the field and are fully integrated with GPS. Pelletizing samples in laboratory-based systems can use soil processing equipment (grinders, presses).
Strengths
LIBS has the capability of real-time, fast, multi-elemental analysis with little to no sample preparation. It is applicable in both fields and laboratories, and it applies to both primary and trace elements. The method is non-contact and less destructive. Thus, the contamination risk is low. LIBS is a handy tool in mapping soil nutrients, tracking heavy metals, and precision agriculture.
Limitations
This point could lead to inaccuracy because LIBS is susceptible to matrix effects and moisture content. Complex calibration models are frequently needed in quantitative analysis. The test can only measure surface composition, as its depth of penetration is limited. Also, the emission lines may overlap in spectral regions, thus making it challenging to identify the elements involved. It requires standardization to be widely accepted in regulation.
