Direct Determination of Ca, K, and Mg in Soy Leaf Samples Using Laser-Induced Breakdown Spectroscopy

Area of Science:

• Agricultural Science
• Analytical Chemistry
• Spectroscopy

Background:

• Accurate macronutrient analysis in soy is crucial for crop management and yield optimization.
• Traditional methods like ICP-OES require sample digestion, increasing time and cost.
• Laser-induced breakdown spectroscopy (LIBS) presents a potential for direct, rapid elemental analysis.

Purpose of the Study:

• To develop and validate analytical methods for determining Ca, K, and Mg in soy leaves using LIBS.
• To evaluate LIBS as a direct, rapid alternative to conventional elemental analysis techniques.
• To apply chemometric tools for effective data interpretation and signal correction in LIBS analysis.

Main Methods:

• Utilized Laser-induced breakdown spectroscopy (LIBS) with optimized instrumental conditions (70 mJ pulse energy, 1.0 µs delay, 100 µm spot size).
• Analyzed 896 soy leaf samples (with and without petioles), comparing LIBS data against ICP-OES reference values.
• Tested 12 normalization modes and 2 calibration strategies, including partial least squares (PLS) multivariate calibration and univariate calibration.

Main Results:

• Multivariate calibration models using partial least squares (PLS) demonstrated good accuracy for Ca, K, and Mg determination.
• Univariate calibration methods and models for micronutrients (P, S) did not yield satisfactory results.
• The Euclidean norm was identified as the most effective normalization mode for most developed models.

Conclusions:

• LIBS, coupled with chemometric analysis (specifically PLS and Euclidean normalization), is a promising technique for direct macronutrient quantification in soy leaves.
• The developed LIBS method provides accurate and reliable results for Ca, K, and Mg, offering a faster alternative to ICP-OES.
• Further optimization is needed for micronutrient analysis and to address sample matrix microheterogeneity in complex plant tissues.