Determination of carbon in soil by laser spectral analysis

Abstract

We have used a combination laser/electrospark method for fast determination of carbon content in soil. Excitation of the spectra is carried out both directly in a laser ablation plume and when a pulsed electric discharge is applied to it. We have plotted a calibration curve that is linear for the major concentration range of practical importance for the analyte element, all the way up to 8.6%. The carbon detection limit for the combination discharge approach is 0.07%. We have analyzed the ratio of the nitrogen and carbon contents, and also the hydrogen and carbon contents as a function of the carbon concentration in the studied soils samples.Description of the Method. The laser spectral analysis method (LIBS, laser-induced breakdown spectrometry) essentially involves exposure of the analyte sample to a focused high-power laser radiation flux, ablation of the sample material and formation of a plasma plume, the luminescence spectrum of which is recorded by a detector and processed by a measurement system [1][2][3]. Generally the amount of the material entering the plasma plume is fractions of a microgram, so LIBS is actually considered a nondestructive method.Broad development and application of LIBS began as a result of technical upgrade and expansion of production of high-power laser radiation sources based on yttrium aluminum garnet operating in the frequency regime. An important role was played by development of semiconductor 2-D array optical signal detectors, systems for data accumulation and processing, and optical instruments with high spectral resolution. Expansion of the area of application of LIBS is also due to more thorough study of the laser plasma itself: methods have been refined for determining the electron concentration and temperature of the plasma plume, self-absorption of emission spectral lines, the presence of local thermodynamic equilibrium (LTE). Thus the foundations have been laid for determination of the elemental composition of analyte objects without using certified samples [4,5], although the latter have maintained their role in validation of LIBS methods and also in cases involving analysis of samples of rather complex composition. The correctness of the results obtained by LIBS in the standard-free variant can be ensured, in the absence of matrix effects, when stoichiometry is satisfied in the composition of the plasma and the test object, which is possible when the power density of the laser radiation is at a level higher than 1 GW/cm 2 .In order to improve the sensitivity of LIBS, "dual" laser pulses are used [6,7], i.e., a second laser pulse is applied to the ablation plume with a certain time delay, which excites the material vaporized by the precursor in the relatively rarefied state of the vapor/gas atmosphere; in this case, robustness of the discharge is increased, re-absorption of the spectral lines is reduced.LIBS is a very promising method for solving practical problems in many areas of science and technology: quality control for industrial production, the composition of c...

Cropland Field Monitoring: MMV Page 1 Montana Cropland Enrolled Farm Fields Carbon Sequestration Field Sampling, Measurement, Monitoring, and Verification: Application of Visible-Near Infrared Diffuse Reflectance Spectroscopy (VNIR) and Laser-induced Breakdown Spectroscopy (LIBS)

“…For example, Cremers et al (2001) and Ebinger et al (2003) calibrated LIBS to samples from three farm fields in Colorado, and Martin et al (2010) calibrated LIBS using soil samples from Illinois, Michigan, and North Dakota farm fields. Furthermore, the range in measured TC and IC content (55 and 45 gC kg -1 , respectively) was similar to soil carbon content ranges reported by others [32 to 57 gC kg -1 , (Bel'kov et al, 2008;Belkov et al, 2009;Cremers et al, 2001;Ebinger et al, 2003;Martin et al, 2003;Martin et al, 2010;Martin et al, 2007)]. Researchers therefore suspect that difficulties associated with interrogation of intact cores contributed to relatively low calibration and validation statistics.…”

Laser-Induced Breakdown Spectroscopy (LIBS), Part II: Review of Instrumental and Methodological Approaches to Material Analysis and Applications to Different Fields

“…In fact, as reported by Cremers and Chinni in their recent review: 33 “It is not an exaggeration to state that LIBS is probably the most versatile method of elemental analysis that is currently practiced.” In this review, several examples are given. Our selection includes topics relevant to the environment (soils and vegetation 627,,–649 and minerals 650,,–655 ), aerosols and bioaerosols, 656,,–670 combustion, 671,,–682 forensics, 683,,–691 pharmaceutical, 692,,–697 medical, 698,…”

Improved Intact Soil-Core Carbon Determination Applying Regression Shrinkage and Variable Selection Techniques to Complete Spectrum Laser-Induced Breakdown Spectroscopy (LIBS)

“…The current one-sample-out calibrations also approach accuracies reported for determining C in processed soil samples. 4,6,45,46 Although LIBS has been proposed as an in situ soil C measurement tool, 2 it remains to be demonstrated that the in situ results will quantitatively and statistically match those obtained with prepared samples. It is common practice for soil samples to be processed using some combination of air drying, sieving (2 mm mesh), packing in quartz tubes, pelletizing under pressure, or treating with acid to remove carbonates prior to LIBS analysis for TC or SOC.…”