Effect of liquid-sheet thickness on detection sensitivity for laser-induced breakdown spectroscopy of aqueous solution

Detection of Low Lithium Concentrations Using Laser-Induced Breakdown Spectroscopy (LIBS) in High-Pressure and High-Flow Conditions

This paper describes the effects of laser pulse rate and solution flow rate on the determination of lithium at high pressure for water and 2.5% sodium chloride solutions using laser-induced breakdown spectroscopy (LIBS). Preliminary studies were performed with 0-40 mg L^-1 Li solutions, at ambient pressure and at 210 bar, and in static and flowing (6 mL · min^-1) regimes, for a combination of four different measurement conditions. The sensitivity of calibration curves depended on the pressure and the flow rate, as well as the laser pulse rate. The sensitivity of the calibration curve increased about 10% and 18% when the pressure was changed from 1 to 210 bar for static and flowing conditions, respectively. However, an effect of flow rate at high pressure for both 2 and 10 Hz laser pulse rates was observed. At ambient pressure, the effect of flow rate was negligible, as the sensitivity of the calibration curve decreased around 2%, while at high pressure the sensitivity increased around 4% when measurements were performed in a flow regime. Therefore, it seems there is a synergistic effect between pressure and flow rate, as the sensitivity increases significantly when both changes are considered. When the pulse rate is changed from 2 to 10 Hz, the sensitivity increases 26-31%, depending on the pressure and flow conditions. For lithium detection limit studies, performed with a laser pulse energy of 2.5 mJ, repetition rate of 10 Hz, gate delay of 500 ns, gate width of 1000 ns, and 1000 accumulations, a value around 40 µg L^-1 was achieved for Li solutions in pure water for all four measurement conditions, while a detection limit of about 92 µg L^-1 was determined for Li in 2.5% sodium chloride solutions, when high pressure and flowing conditions were employed. The results obtained in the present work demonstrate that LIBS is a powerful tool for the determination of Li in deep ocean conditions such as those found around hydrothermal vent systems.

Highly sensitive detection of sodium in aqueous solutions using laser-induced breakdown spectroscopy with liquid sheet jets

Laser-induced breakdown spectroscopy (LIBS) combined with liquid jets was applied to the detection of trace sodium (Na) in aqueous solutions. The sensitivities of two types of liquid jets were compared: a liquid cylindrical jet with a diameter of 500 µm and a liquid sheet jet with a thickness of 20 µm. Compared with the cylindrical jet, the liquid sheet jet effectively reduced the splash from the laser-irradiated surface and produced long-lived luminous plasma. The limit of detection (LOD) of Na was determined to be 0.57 µg/L for the sheet jet and 10.5 µg/L for the cylindrical jet. The LOD obtained for the sheet jet was comparable to those obtained for commercially available inductively coupled plasma emission spectrometers.

Simple method for liquid analysis by laser-induced breakdown spectroscopy (LIBS)

As a fast-developing technique for in situ multi-element analysis method, laser induced breakdown spectroscopy - LIBS is, however, developing slowly on liquid analysis due to some technical difficulties. We propose a new method, namely capillary mode, to quantify the concentrations of the elements in solution using LIBS. A Nd:YAG laser with repetition of 10 Hz were used to analyze the solution of Na₂CrO₄ and no any sample preparation in measurements. The experimental results show that the splashing of liquid induced by laser pulses is decreased significantly and the pollution of mirrors is avoided effectively using liquid capillary mode. The results of quantitative analysis for liquid are also improved than other method. The calibration curves of Cr and Na are well characterized by straight lines and the regression coefficient values of the linear fit are better than 0.998. The limits of detection (LODs) of Cr and Na are determined to be 28.9 mg/L and 1.0 mg/L in this work, respectively. The experimental results show that the liquid capillary mode provides a more practical and very simple approach to improve accuracy of quantitative element analysis in liquids by LIBS technique.

Differentiation of fibrotic liver tissue using laser-induced breakdown spectroscopy

Hepatic cirrhosis is a major cause of morbidity and mortality worldwide due to hepatitis C, alcoholism and fatty liver disease associated with obesity. Assessment of hepatic fibrosis relies in qualitative histological evaluation of biopsy samples. This method is time-consuming and depends on the histopathologists' interpretation. In the last decades, non-invasive techniques were developed to detect and monitor hepatic fibrosis. Laser-induced breakdown spectroscopy (LIBS) is a good candidate for a real-time, independent and fast technique to diagnose hepatic fibrosis. In this work LIBS was employed to characterize rat liver tissues with different stages of fibrosis. Depth profiling measurements were carried out by using a nanosecond Nd:YAG laser operated at the fundamental wavelength and an echelle spectrometer coupled with an ICCD camera. Due to the soft nature of the samples, plasma conditions largely change between consecutives shots. Thus, a theoretically supported procedure to correct the spectral line intensities was implemented. This procedure allows the reduction of the intensities' dispersion from 67% to 12%. After the correction, the LIBS signal shows an enhancement in calcium intensity by a factor of three as the fibrosis progressed. Calcium is known to increase crosslinking of extracellular matrix proteins in the fibrous septa. Therefore, our result singles it out as a key participant in the hepatic fibrosis.

Application of picosecond laser-induced breakdown spectroscopy to quantitative analysis of boron in meatballs and other biological samples

This report presents the results of laser-induced breakdown spectroscopy (LIBS) study on biological and food samples of high water content using a picosecond (ps) laser at low output energy of 10 mJ and low-pressure helium ambient gas at 2 kPa. Evidence of excellent emission spectra of various analyte elements with very low background is demonstrated for a variety of samples without the need of sample pretreatment. Specifically, limits of detection in the range of sub-ppm are obtained for hazardous Pb and B impurities in carrots and meatballs. This study also shows the inferior performance of LIBS using a nanosecond laser and atmospheric ambient air for a soft sample of high water content and thereby explains its less successful applications in previous attempts. The present result has instead demonstrated the feasibility and favorable results of employing LIBS with a ps laser and low-pressure helium ambient gas as a less costly and more practical alternative to inductively coupled plasma for regular high sensitive inspection of harmful food preservatives and environmental pollutants.

Laser-induced breakdown spectroscopy of liquid solutions: a comparative study on the forms of liquid surface and liquid aerosol

Liquid surface and liquid aerosol as the traditional liquid forms for laser-induced breakdown spectroscopy (LIBS) and inductively coupled plasma (ICP), respectively, have been used to analyze chromium (Cr) and cadmium (Cd) elements using LIBS in a liquid solution. The spectral differences, the effects of laser energy and laser frequency, the accumulated number of laser pulses, gate delay time, and the quantitative analyses for a liquid surface and a liquid aerosol were compared. The results showed that the liquid surface demonstrated a lower plasma threshold, higher optical emission intensity, and higher single-to-noise ratio. Moreover, the relative standard deviations (RSDs) of the intensities of the liquid aerosol are better than those of the liquid surface. Furthermore, the results of the quantitative analyses of Cr I 357.86 nm and Cd I 361.05 nm of the liquid surface are close to those of the liquid aerosol. The limit of detections of Cr and Cd of the liquid surface were 2.764 and 86.869  μg/mL, which were close to those of liquid aerosol, 2.847  μg/mL of Cr and 97.635  μg/mL of Cd. For both the liquid surface and liquid aerosol, the coefficient of determination R² of the calibration curve for Cr and Cd were above 0.99, and the average RSDs of Cr and Cd of the liquid surface were 0.027 and 0.054, which were similar to the 0.020 of Cr and 0.042 of Cd of the liquid aerosol. These results suggest that both the liquid surface and aerosol have similar detection abilities for water quality monitoring.

Quantitative detection of metallic traces in water-based liquids by microwave-assisted laser-induced breakdown spectroscopy

The enhancement of laser-induced breakdown spectroscopy (LIBS) assisted with microwave radiation is demonstrated for an aqueous solution of indium using the 451.13 nm emission line. Microwave power was delivered via a near-field applicator to the LIBS measurement volume where the indium aqueous solution was presented as a liquid jet. The microwave enhancement effect was observed to decrease with increasing laser pulse fluence at 532 nm resulting in a maximum emission intensity occurring at a laser pulse fluence of 85.2 J∙cm(-2), independent of the microwave power used. The detection limits of indium in an aqueous solution were determined to be 10.8 ± 0.7 and 124 ± 5 ppm for the cases of microwave enhanced and standard LIBS, respectively. The 11.5-fold detection limit enhancement obtained in the liquid phase is of the same order of magnitude as that reported for other elements in solid samples, but lower than that obtained in solid phase utilizing a similar experimental setup. This establishes microwave enhancement as an effective technique for the detection of metals in aqueous solutions. In addition, the temporal evolution of plasma emission intensity was investigated and was found to be qualitatively similar to that of plasma produced from solid phase samples, which reveals the same coupling mechanism between laser generated plasma and microwave radiation.