We report an approach for selecting an internal standard to improve the precision of laser-induced breakdown spectroscopy (LIBS) analysis for determining calcium (Ca) concentration in water. The dissolved Ca²⁺ ions were pre-concentrated on filter paper by evaporating water. The filter paper was dried and analyzed using LIBS. By adding strontium chloride to sample solutions and using a Sr II line at 407.771 nm for the intensity normalization of Ca II lines at 393.366 or 396.847 nm, the analysis precision could be significantly improved. The Ca II and Sr II line intensities were mapped across the filter paper, and they showed a strong positive shot-to-shot correlation with the same spatial distribution on the filter paper surface. We applied this analysis approach for the measurement of Ca²⁺ in tap, bottled, and ground water samples. The Ca²⁺ concentrations determined using LIBS are in good agreement with those obtained from flame atomic absorption spectrometry. Finally, we suggest a homologous relation of the strongest emission lines of period 4 and 5 elements in groups IA and IIA based on their similar electronic structures. Our results indicate that the LIBS can be effectively applied for liquid analysis at the sub-parts per million level with high precision using a simple drying of liquid solutions on filter paper and the use of the correct internal standard elements with the similar valence electronic structure with respect to the analytes of interest.

Laser-induced breakdown spectroscopy (LIBS) was explored for the first time for discrimination of gallbladder (GB) polyp and GB cancer (GBC) by direct measurement of raw bile juice without pretreatment. Initially, for reproducible LIBS measurement, a laser-patterned silicon wafer (LPSW) incorporating 40 × 40 crossed trenches in an area of 1 × 1 cm² was used to spread bile juice as homogeneous as possible over the surface without substantial localization, and LiCl was employed as an internal standard. Mg, Ca, Na, and K peaks were dominant in the spectra of raw bile samples, with lower peak areas in cases of GBC. The lower elemental concentrations in GBC samples probably result from dilution of bile by a degraded water absorption ability of the thickened GB wall due to cancer and carcinogenesis. In particular, the Mg and K peak intensities were further lower and improved discrimination of GBC against normal/GB polyp. Moreover, discrimination was distinct when using the ratio of Na and K peak areas. Misbalancing of Na and K in cell metabolism induced by cancer progression was presumed to be the origin of enhanced discrimination. Overall, the LIBS-based direct bile analysis scheme is a simple and potential tool for screening of GBC.

The chemical properties including toxicity of selenium depend on the concentration and chemical structure present in the natural environment. Inorganic selenium is more toxic than organic selenium; thus, the accurate determination of inorganic selenium in various sample has been needed. HG-AAS, HPLC-ICP-MS, and GC-MS are the current methods for the determination of inorganic selenium. However, these methods have the disadvantage of expensive equipment, complicated sample preparation, and long analysis time. LIBS coupled with ion exchange membrane was used for the determination of inorganic selenium. The detection limit of inorganic selenium by the analytical method was 11.21 mg/kg, and the recoveries of 50 and 100 mg/kg Se(VI) were 98.5 % and 101.80 %, respectively. The speciation method is cost-effective, simple, and not labor intensive for the quantitation of inorganic selenium.

Analytical methods for the determination of inorganic arsenic species have attracted much attention due to the high toxicity of these compounds and related legislative regulations for food. A new method for the separation and quantitation of As(III) and As(V) was developed using ion-exchange membranes and laser-induced breakdown spectroscopy (LIBS). Using the anion-exchange polymer membrane, As(V) was selectively collected on the membrane, and As(III) was filtered through the membrane. The separated As(V) on the membrane was directly determined by LIBS. The As(III) in the filtrate was subsequently oxidized to As(V) and collected by the membrane for LIBS analysis. The detection limit for As(V) was estimated to be 10 mg/kg. The recovery efficiencies for the arsenic species as standards were in the range of 97–99%. This method was applied for the analysis As-spiked water certified reference materials, and the results showed that the recovery for As(V) was 98.9%. This new speciation method is cost-effective, simple, and low labor-intensive for the quantitation of inorganic arsenic.