Resonance fluorescence spectroscopy in laser-induced cavitation bubbles

Trace Selenium Measurement in Water Using Laser-Induced Fluorescence Assisted by Laser Ablation

Selenium detection and removal from industrial and mining effluents have gained attention recently due to the negative effects of this trace element on aquatic life. However, the current methods for the detection of selenium in effluents are off-line by nature. In order to fill this gap, we investigated the use of laser ablation-assisted laser-induced fluorescence (LA-LIF) to measure trace amount of selenium in aqueous solutions. LA-LIF measurements are real time, label-free, standoff, and require no consumables as well as no sample preparation. They can provide a field-amenable, versatile tool for the measurement of selenium in the whole water treatment chain. We describe the system utilized, the temporal and fluence optimization studies, and the resulting calibration curve, which is linear over a wide dynamic range from parts-per-billion to tens of parts-per-million concentration levels. We also show that the achieved limit of detection of selenium can reach 32 µg/L using LA-LIF, without any kind of preconcentration or matrix transfer.

Determination of trace heavy metal elements in aqueous solution using surface-enhanced laser-induced breakdown spectroscopy

Heavy metal pollution is one of the main problems in water pollution, which is harmful to humans. Surface-enhanced laser-induced breakdown spectroscopy (SENLIBS) has been applied to detect trace amounts of heavy metal elements in aqueous solution; however, it is still a big challenge to explore the relationship between the LIBS detection sensitivity and the substrate's physical properties. In this work, four typical substrates, zinc (Zn), magnesium alloy (Mg), nickel (Ni), and silicon (Si), were compared; and the mechanism of spectral enhancement by different substrates in SENLIBS was investigated. The results indicated that the limit of detection (LoD) of heavy metal elements on different substrates is positively proportional to the boiling of the substrate. That is mainly because a higher plasma excitation temperature and electron density are obtained, leading to more intense collision between particles. The signal enhancement is associated with the lower boiling point of the substrate (corresponding to a lower ablation threshold and higher ablation quantity from the substrate). As a result, the best LoD was 0.0011 mg/L for chromium (Cr) and 0.004 mg/L for lead (Pb) on an optimal Zn substrate, respectively. The LoDs were sufficiently low to meet the drinking water sanitation standard. These results showed that the detection sensitivity of heavy metal elements in aqueous solution can be improved by choosing a substrate with a lower boiling point in SENLIBS.

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.

Development and validation of a laser-induced breakdown spectroscopic method for ultra-trace determination of Cu, Mn, Cd and Pb metals in aqueous droplets after drying

The present study reports a fast and accurate methodology for laser-induced breakdown spectroscopic, LIBS, analysis of aqueous samples for environmental monitoring purposes. This methodology has two important attributes: one is the use of a 300nm oxide coated silicon wafer substrate (Si+SiO2) for the first time for manual injection of 0.5 microliter aqueous metal solutions, and two is the use of high energy laser pulses focused outside the minimum focus position of a plano convex lens at which relatively large laser beam spot covers the entire droplet area for plasma formation. Optimization of instrumental LIBS parameters like detector delay time, gate width and laser energy has been performed to maximize atomic emission signal of target analytes; Cu, Mn, Cd and Pb. Under the optimal conditions, calibration curves were constructed and enhancements in the LIBS emission signal were obtained compared to the results of similar studies given in the literature. The analytical capability of the LIBS technique in liquid analysis has been improved. Absolute detection limits of 1.3pg Cu, 3.3pg Mn, 79pg Cd and 48pg Pb in 0.5 microliter volume of droplets were obtained from single shot analysis of five sequential droplets. The applicability of the proposed methodology to real water samples was tested on the Certified Reference Material, Trace Metals in Drinking Water, CRM-TMDW and on ICP multi-element standard samples. The accuracy of the method was found at a level of minimum 92% with relative standard deviations of at most 20%. Results suggest that 300nm oxide coated silicon wafer has an excellent potential to be used as a substrate for direct analysis of contaminants in water supplies by LIBS and further research, development and engineering will increase the performance and applicability of the methodology.

The effect of high viscosity on the collapse-like chaotic and regular periodic oscillations of a harmonically excited gas bubble

In the last decade many industrial applications have emerged based on the rapidly developing ultrasonic technology such as ultrasonic pasteurization, alteration of the viscosity of food systems, and mixing immiscible liquids. The fundamental physical basis of these applications is the prevailing extreme conditions (high temperature, pressure and even shock waves) during the collapse of acoustically excited bubbles. By applying the sophisticated numerical techniques of modern bifurcation theory, the present study intends to reveal the regions in the excitation pressure amplitude-ambient temperature parameter plane where collapse-like motion of an acoustically driven gas bubble in highly viscous glycerine exists. We report evidence that below a threshold temperature the bubble model, the Keller-Miksis equation, becomes an overdamped oscillator suppressing collapse-like behaviour. In addition, we have found periodic windows interspersed with chaotic regions indicating the presence of transient chaos, which is important from application point of view if predictability is required.

Laser-induced breakdown spectroscopy (LIBS), part II: review of instrumental and methodological approaches to material analysis and applications to different fields

The first part of this two-part review focused on the fundamental and diagnostics aspects of laser-induced plasmas, only touching briefly upon concepts such as sensitivity and detection limits and largely omitting any discussion of the vast panorama of the practical applications of the technique. Clearly a true LIBS community has emerged, which promises to quicken the pace of LIBS developments, applications, and implementations. With this second part, a more applied flavor is taken, and its intended goal is summarizing the current state-of-the-art of analytical LIBS, providing a contemporary snapshot of LIBS applications, and highlighting new directions in laser-induced breakdown spectroscopy, such as novel approaches, instrumental developments, and advanced use of chemometric tools. More specifically, we discuss instrumental and analytical approaches (e.g., double- and multi-pulse LIBS to improve the sensitivity), calibration-free approaches, hyphenated approaches in which techniques such as Raman and fluorescence are coupled with LIBS to increase sensitivity and information power, resonantly enhanced LIBS approaches, signal processing and optimization (e.g., signal-to-noise analysis), and finally applications. An attempt is made to provide an updated view of the role played by LIBS in the various fields, with emphasis on applications considered to be unique. We finally try to assess where LIBS is going as an analytical field, where in our opinion it should go, and what should still be done for consolidating the technique as a mature method of chemical analysis.