Jihyun Kwak

Detection of Nutrient Elements and Contamination by Pesticides in Spinach and Rice Samples Using Laser-Induced Breakdown Spectroscopy (LIBS)

The laser-induced breakdown spectroscopy (LIBS) technique was applied to quantify nutrients (Mg, Ca, Na, and K) in spinach and rice and to discriminate pesticide-contaminated products in a rapid manner. Standard reference materials (spinach leaves and unpolished rice flour) were used to establish a relationship between LIBS intensity and the concentration of each element (Mg, Ca, Na, and K) (i.e., calibration line). The limits of detection (LODs) for Mg, Ca, Na, and K were found to be 29.63, 102.65, 36.36, and 44.46 mg/kg in spinach and 7.54, 1.76, 4.19, and 6.70 mg/kg in unpolished rice, respectively. Concentrations of those nutrient elements present in spinach and unpolished rice from a local market were determined by using the calibration lines and compared with those measured with ICP-OES, showing good agreement. The data also suggested that the LIBS technique with the chemometric method (PLS-DA) could be a great tool to distinguish pesticide-contaminated samples from pesticide-free samples in a rapid manner even though they have similar elemental compositions. Misclassification rates were found to be 0 and 2% for clean spinach and pesticide-contaminated spinach, respectively, by applying the PLS-DA model established from the training set of data to predict the classes of test samples.

Development of an Aerosol Focusing-Laser Induced Breakdown Spectroscopy (Aerosol Focusing-LIBS) for Determination of Fine and Ultrafine Metal Aerosols

An Aerosol Focusing-Laser Induced Breakdown Spectroscopy (Aerosol Focusing-LIBS) with a sheath air focusing and an aerodynamic lens focusing was developed to determine elemental composition of fine and ultrafine metal aerosols. Data showed that with a sheath air focusing, the LIBS qualitatively detected various metals (Al, Ca, Cd, Cr, Cu, K, Mg, Na, Ni, Zn) in submicrometer to micrometer aerosols, but that detection of ultrafine particles smaller than 100 nm was not successful due to weak intensity of emitted light. Also, the hitting rate was so low for particles at low number concentration and the single particle detection approach was only valid when aerosol loading is low. Thus, we concentrated aerosols on to a collection substrate by using the aerodynamic lens focusing system, resulting in the strong emission light from the generated plasma even for nanoparticles and the better quantification performance by the LIBS. We found the linear relationship between LIBS signal response and metal mass concentration. For example, as Cu metal concentration increased, peak area of LIBS emission line for Cu increased. The resulting correlation coefficient was 0.94 and the LOD for Cu mass concentration was found to be ∼80 ng/m3, which can be further lowered by extending current collection time (∼5 min). A similar linear relationship was found for Cd and Ni ultrafine metal aerosols. We also successfully detected internally mixed metal aerosols. When particles were collected on a substrate with the aerodynamic lens for 5 min prior to analysis of the deposit it was possible to analyze particles as small as 60 nm.

Rapid detection of soils contaminated with heavy metals and oils by laser induced breakdown spectroscopy (LIBS)

A laser induced breakdown spectroscopy (LIBS) coupled with the chemometric method was applied to rapidly discriminate between soils contaminated with heavy metals or oils and clean soils. The effects of the water contents and grain sizes of soil samples on LIBS emissions were also investigated. The LIBS emission lines decreased by 59-75% when the water content increased from 1.2% to 7.8%, and soil samples with a grain size of 75 μm displayed higher LIBS emission lines with lower relative standard deviations than those with a 2mm grain size. The water content was found to have a more pronounced effect on the LIBS emission lines than the grain size. Pelletizing and sieving were conducted for all samples collected from abandoned mining areas and military camp to have similar water contents and grain sizes before being analyzed by the LIBS with the chemometric analysis. The data show that three types of soil samples were clearly discerned by using the first three principal components from the spectral data of soil samples. A blind test was conducted with a 100% correction rate for soil samples contaminated with heavy metals and oil residues.

Determination of Heavy Metal Distribution in PM10 During Asian Dust and Local Pollution Events Using Laser Induced Breakdown Spectroscopy (LIBS)

Hourly concentrations of heavy metals in PM10 samples were continuously measured using Laser Induced Breakdown Spectroscopy (LIBS) to determine the metal distribution among Asian Dust (AD) events, local pollution events, and nonevents. Quantification of metals was performed by establishing a calibration line between 24 h average data determined by the ICP-MS after filter sampling and LIBS intensity data. It was found that in AD and local pollution events, significant anthropogenic heavy metals, such as Pb, Cr, Ni, and Zn, were detected compared to a nonevent, and that crustal elements (e.g., Al, Ca, Mg) were more abundant in the AD events than those in a local pollution event or nonevent. The AD events were further classified into “nonpolluted AD” and “polluted AD” events, depending on the air mass transport pathways. During “polluted AD” events where the air mass passed over industrialized zones, both crustal (Al, Ca, Mg) and anthropogenic (Cr, Ni, Zn) metal elements simultaneously increased with time, suggesting that the AD particles could not only include crustal elements but also have a significant quantity of anthropogenic heavy metals. The concentration of anthropogenic heavy metals (Cr + Pb + Zn) was the highest in the AD3 event in order of AD3 (polluted) > AD1 (polluted) > local pollution > AD2 (nonpolluted). However, the PM10-weighted value (Cr + Pb + Zn/PM10) was the highest in the local pollution event where concentrations of only anthropogenic heavy metals increased. Also, the hourly LIBS data was successfully used to discriminate metal contributions between AD events and local pollution events or among AD events by employing a chemometric method. Copyright 2012 American Association for Aerosol Research

Determination of lead in soil at a historical mining and smelting site using laser-induced breakdown spectroscopy

Laser-induced breakdown spectroscopy (LIBS) was used to determine lead (Pb) concentration in soil and tailing samples collected from a historical mining and smelting area. The Pb emission line at 405.781 nm was found to have the strongest intensity and highest linearity with concentration. It was further normalized by the Al emission line (394.401 nm), and a relationship between the peak area ratio (Pb/Al) and Pb concentration was established to determine Pb concentration of unknown samples. The Pb concentration was the highest at the former smelter site and unremediated mine-tailing areas, indicating that severe Pb contamination is still occurring. The Pb concentration decreased with increasing distance from the two major source areas (smelting and mine-tailing sites), although all samples exceeded the 400 mg/kg standard set by the United States Environmental Protection Agency. The limit of detection (LOD) for Pb was found to be 48 mg/kg, and the Pb concentrations determined by LIBS were in reasonable agreement with concentrations obtained by inductively coupled plasma mass spectroscopy (ICP-MS; within 26%). When Pb concentrations were determined by calibration-free (CF)-LIBS, which does not require standard soil samples and dilution, both LIBS and ICP-MS were also in good agreement, suggesting that the CF-LIBS method can be used to determine Pb concentrations in highly contaminated soil samples. In addition to Pb, other metal emission lines from LIBS spectra were used to classify soil samples among the sites using a principal component analysis (PCA) method, showing a distinct difference in metal distribution between sites that are heavily contaminated by two major sources.

Application of Laser Based Spectroscopic Monitoring into Soil Remediation Process of PAH-Contaminated Soil

ABSTRACT The application of Laser-Induced Fluorescence (LIF) into soil remediation process is not popular due to the difficulties of the interpretation of remediation process. The monitoring for the lab-scale surfactant enhanced electrokinetic remediation process using the LIF was performed. The variation of the fluorescence intensity and the change of the fluorescence spectral signature reflecting the nature of the surrounding environment were investigated. The diffuse reflectance correction method for the soil matrix properties on fluorescence, and the time resolution for isolation of surfactant which can be overlapped with PAHs spectra of interest were considered to provide the information of contaminants taking place during the remediation process. Eletrokinetic (EK) remediation process as control experiment was also performed and this result was compared with the surfactant-enhanced EK process especially in terms of the spectral signature of PAHs. The LIF monitoring for soil remediation process showed that the relative quantities and the state of contaminant in soil media which can be an important key to assess the feasibility of remediation process.

Development of laser-induced breakdown spectroscopy (LIBS) with timed ablation to improve detection efficiency

ABSTRACT A laser-induced breakdown spectrometer (LIBS) was developed for determining the elemental composition of individual airborne particles. The system employs two lasers focused on a narrow beam of particles. A continuous wave laser placed upstream scatters light from particles, while a pulse laser downstream ablates the particles. The scattered light from the upstream laser is used to trigger the downstream pulse laser, resulting in more accurate hitting of the particles than a free-firing laser system without the triggering signal (i.e., constant pulse laser firing). Various laboratory-generated aerosols (NaCl, MgCl2, KCl, and CaCl2) were used to evaluate the newly developed LIBS system. Particles were tightly focused into a center line with a sheath air focusing system using an optimum aerosol-to-sheath air velocity ratio. The locations of both the scattering laser and pulse laser beams were precisely controlled by a motorized X-Y stage controller. Data showed that for the LIBS with the triggering system, the hitting efficiency (%) of particles (200–600 nm) significantly increased (e.g., 350 nm particles had more than 26 times higher hitting efficiency at 1,000 particles/cm3), and much lower limits of particle size (∼200 nm) and number concentration (<100 particles/cm3) were achieved compared to the free-firing laser condition. Additionally, the hitting rate (hits/min) significantly increased with the triggering system. Our results suggest that the LIBS with the triggering system can be useful for real-time detection of elements of particles existing at low number concentrations (e.g., atmospheric particles) and for the determination of the variation of elemental composition among particles.