Coal Discrimination Analysis Using Tandem Laser-Induced Breakdown Spectroscopy and Laser Ablation Inductively Coupled Plasma Time-of-Flight Mass Spectrometry

Abstract

The contribution and impact of combined laser ablation inductively coupled plasma time-of-flight mass spectrometry (LA-ICP-TOF-MS) and laser-induced breakdown spectroscopy (LIBS) were evaluated for the discrimination analysis of different coal samples. This tandem approach allows simultaneous determination of major and minor elements (C, H, Si, Ca, Al, Mg, etc.) and trace elements (V, Ba, Pb, U, etc.) in the coal. The research focused on coal-classification strategies based on principle component analysis (PCA) combined with K-means clustering, partial least-squares discrimination analysis (PLS-DA), and support vector machine (SVM) for analytical performance. Correlation analyses performed from TOF mass and LIBS emission spectra from the coal samples showed that most major, minor, and trace element emissions had negative correlation with the volatile content. Suitable variables for the classification models were determined from these data. The individual TOF data, LIBS data, and combined data of TOF and LIBS as the inputs for different models were analyzed and compared. In all cases, the results obtained with the combined TOF and LIBS data were found to be superior to those obtained with the individual TOF or LIBS data. The nonlinear SVM model combined with TOF and LIBS data provided the best coal-classification performance, with a classification accuracy of up to 98%.

Elemental Analysis of Solid Food Materials Using a Reliable Laser Ablation Inductively Coupled Plasma Mass Spectrometry Method

“…Monitoring trace and minor nutrient elements in food products (such as, vegetables, grains, and meat) is important for maintaining human health. Laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) is a promising technique for the multielemental analysis of food and other samples because it allows for direct solid sampling, which avoids contamination or loss of analytes during the sample decomposition steps and eliminates solvent-related polyatomic interferences. − However, accurate quantification is the primary challenge with this technique, mainly because of the lack of commercially available matrix-matched food calibration standards in combination with an internal standard (IS) required to overcome the matrix-related effects on material ablation, aerosol transport, and analyte ionization, as well as the effects of instrument instability or signal drift. − …”

“…Generally, LA-ICP-MS quantification calibration relies on in-house-prepared calibration standards that use pelletization techniques and involve doping similar matrix materials with known amounts of analytes for the analysis of food or biological materials. − However, this has two main drawbacks, namely, the pellet standards lack sufficient homogeneity owing to their large grain size (approximately 150 μm) and poor particle cohesion, and practicability is limited because the preparation of standards involves the handling of materials, implying that they must be prepared individually for each matrix. ,, Reducing the grain size is an important step to achieve more homogeneous and cohesive undiluted pressed pellets. − Researchers recently reported a method for producing undiluted pressed powder pellets without binder additions by applying wet-milling protocols in an aqueous suspension using a high-power planetary ball mill and agate tools . This method is used for the preparation of refractory geological materials or materials containing refractory mineral phases for subsequent analysis by LA-ICP-MS. , Although grinding a sample to reduce the grain size (<10 μm) is time-consuming (approximately 60 min), this method opens up new prospects for the production of pressed powder pellets with excellent cohesion and homogeneity suitable for LA analysis.…”

“…An alternative strategy is the use of doped media that mimic the composition of biological samples. ,− Hydrocolloid gel-based materials are becoming a promising material for use as the matrix-matched calibration standard for biological samples in which gelatin gel is chosen to mimic animal or proteinaceous materials, and agarose gel is employed for botanical samples. ,− However, element-dependent heterogeneities are evident in both gelatin and agarose-gel films, which are due to the so-called “coffee stain” effect (visible in the elemental image as higher concentrations are found at the edges) and the “Marangoni” effect (visible as higher elemental concentrations in the center). , Recently, we reported a mold-prepared procedure for synthesizing spiked agarose and gelatin gels, which greatly improved the homogeneity of the elemental three-dimensional (3D)­(surface- and depth-mapping) distributions in gels. Although satisfactory results were obtained for food materials using the mold-prepared agarose or gelatin gels as matrix-matched external standards in LA-ICP-MS analysis, , there are two limitations, namely, hydrocolloid gel-based materials are easily deteriorated by moisture absorption and cannot be preserved for long durations, and practicability is still limited . Surprisingly, an extremely interesting phenomenon was observed in these studies, that is, the ratio of the C contents in the food samples to that in the gel standard was almost the same, 1.08–1.22 for plant-derived materials (normalized to agarose gel) and 1.57–1.74 for the animal-based materials (normalized to gelatin gel) .…”

Improved plasma stoichiometry recorded by laser ablation ionization mass spectrometry using a double‐pulse femtosecond laser ablation ion source

“…Today, various hybrid systems commercially exist that integrate both LA-ICP-MS and LIBS instrumentation to extend the measurement capabilities for the chemical analysis of solids. [17][18][19][20] The application of a pulsed laser system to probe the analyte of interest has many advantages, as structures down to tens of nanometers can be targeted, layered materials can be chemically profiled by consecutive laser pulses, and sample contamination via handling can be minimized as no mechanical or chemical contact is required during preparation, among others. 9,21,22 With the replacement of, e.g., nanosecond or picosecond laser systems with powerful and stable ultra-fast pulsed femtosecond laser systems, the analytical capabilities and figures of merit of all laser-based measurement techniques have improved significantly, including, e.g., minimized matrix effects and element fractionation effects due to the absence of laser plasma plume interaction, improvement of spatial resolution due to reduced heat dissipation, increased reproducibility of measurements, enhanced ionization and stoichiometry, among others.…”

“…LA‐ICP‐MS is among the most widespread laser‐based analytical technique due to its accurate quantification, high reproducibility, and low limits of detection. Today, various hybrid systems commercially exist that integrate both LA‐ICP‐MS and LIBS instrumentation to extend the measurement capabilities for the chemical analysis of solids 17–20 …”