Investigation of common Indian edible salts suitable for kidney disease by laser induced breakdown spectroscopy

Highly Precise Laser-Induced Breakdown Spectroscopy Analysis of Major Mineral Nutrients in Edible Salts Using Miniaturized Salt Ponds and Alternating Laser-Ablation Data Sampling

In this work, we applied a hydrophilicity-enhanced solid substrate and an alternating laser-ablation data sampling (ALADS) scheme to improve laser-induced breakdown spectroscopy (LIBS) measurement precision and demonstrated the performance in analyzing K, Mg, Ca, and S contained in commercially available edible salt products. Five edible salt products from Australia, Bolivia, France, and South Korea were dissolved in water and a tiny volume of each solution was dropped on the solid substrate, that is, a miniaturized salt pond. After being dried, the residual salt crystals distributed still inhomogeneously, but the homogeneity could be significantly improved in comparison with that from typical drop-and-dry methods. The ALADS scheme was applied to extract three precise measurements from 9798 single-shot LIBS spectra covering the entire salt pond. The measurements obtained by ALADS were found to agree well with one another regardless of the inhomogeneous distribution of salt crystals. As a result, the measurement precision was proved remarkably. Limits of detection for K, Mg, Ca, and S were estimated to be 0.64, 1.7, 14, and 530 mg/kg, respectively, which are enough to analyze those elements contained in salts typically at the level of 100 parts per million (ppm) to ∼3 wt% for the purpose of salt quality assessment.

A Simple Laser-Induced Breakdown Spectroscopy Method for Quantification and Classification of Edible Sea Salts Assisted by Surface-Hydrophilicity-Enhanced Silicon Wafer Substrates

Salt, one of the most commonly consumed food additives worldwide, is produced in many countries. The chemical composition of edible salts is essential information for quality assessment and origin distinction. In this work, a simple laser-induced breakdown spectroscopy instrument was assembled with a diode-pumped solid-state laser and a miniature spectrometer. Its performances in analyzing Mg and Ca in six popular edible sea salts consumed in South Korea and classification of the products were investigated. Each salt was dissolved in water and a tiny amount of the solution was dropped and dried on the hydrophilicity-enhanced silicon wafer substrate, providing homogeneous distribution of salt crystals. Strong Mg II and Ca II emissions were chosen for both quantification and classification. Calibration curves could be constructed with limits-of-detection of 87 mg/kg for Mg and 45 mg/kg for Ca. Also, the Mg II and Ca II emission peak intensities were used in a k-nearest neighbors model providing 98.6% classification accuracy. In both quantification and classification, intensity normalization using a Na I emission line as a reference signal was effective. A concept of interclass distance was introduced, and the increase in the classification accuracy due to the intensity normalization was rationalized based on it. Our methodology will be useful for analyzing major mineral nutrients in various food materials in liquid phase or soluble in water, including salts.

Chemical Characterization for the Detection of Impurities in Tainted and Natural Curcuma longa from India Using LIBS Coupled with PCA

The present manuscript explores a spectroscopic technique to select turmeric powder, free from impurities, and has compounds of medicinal importance among the tainted and natural turmeric. Six Curcuma longa (turmeric powder) samples, named S1, S2, S3, S4, S5, and S6, were analyzed to discriminate between tainted and natural turmeric using the LIBS and multivariate technique. Other techniques such as UV–Vis, FTIR, and EDX are also used to ascertain the elements/compounds showing the medicinal properties of C. longa. Spectral lines of carbon, sodium, potassium, magnesium, calcium, iron, strontium, barium, and electronic bands of CN molecules were observed in the LIBS spectra of turmeric samples. Spectral signatures of toxic elements such as lead and chromium are also observed in the LIBS spectra of all samples except S6. Adulteration of metanil yellow, a toxic azo dye, is used to increase the appearance of curcumin when the actual curcumin content is low. The presence of spectral lines of lead and chromium in the LIBS spectra of S1 to S5 suggested that it may be adulterated with lead chromate which is used for coloring turmeric. Further, the presence of sulfur in EDX analysis of sample S5 indicates that it may also have been adulterated with metanil (C18H14N3NaO3S). The concentration of samples’ constituents was evaluated using CF-LIBS, and EDX was used to verify the results obtained by CF-LIBS. The principal component analysis applied to the LIBS data of the turmeric samples has been used for instant discrimination between the sample based on their constituents. We also analyzed antioxidant activity and total phenolic and flavonoid content of different turmeric samples and found a negative Pearson correlation with heavy metals. The presence of curcumin in turmeric is confirmed using LIBS and UV–Vis, which have medicinal properties.

Two-Step Partial Least Squares-Discriminant Analysis Modeling for Accurate Classification of Edible Sea Salt Products Using Laser-Induced Breakdown Spectroscopy

Laser-induced breakdown spectroscopy (LIBS) has been widely applied to material classification in various fields, and partial least squares-discriminant analysis (PLS-DA) is one of the frequently used classical multivariate statistics to construct classification models based on the LIBS spectra. However, classification accuracy of the PLS-DA model is sensitive to the number of classes and their similarities. Considering this characteristic of PLS-DA, we suggest a two-step PLS-DA modeling approach to improve the classification accuracy. This strategy was demonstrated for a six-class problem in which six commercial edible sea salts produced in Japan, South Korea, and France are classified using their LIBS spectra. At the first step, test spectra were sorted into four classes and one extended class, composed of the two other most confusing classes, and then the test spectra in the extended class were further classified into each of the two constituent classes which were modeled separately from the other four classes. This two-step classification has been found to remarkably improve the PLS-DA classification accuracy by maximizing the difference between the confusing classes in the second-step modeling.

Structural characterization of Himalayan black rock salt by SEM, XRD and in-vitro antioxidant activity

Salt is an essential component of daily life that balances the physiological functions of the human body as well as other living systems. Different varieties of salts are available in the global market. Out of many salt varieties, Himalayan rock salts have gained tremendous importance among consumers due to its diverse nutritional and medicinal properties. There are two types of Himalayan rock salts. One is the Himalayan pink salt and the other one is Himalayan black salt. Out of the two, the Himalayan pink salt is studied extensively but the black salt is underexplored. In the present study, the Himalayan black rock salt was explored to generate more scientific evidence in terms of its geochemical characterization using FE-SEM, X-ray diffractometry (XRD), elemental content using atomic absorption spectrophotometry (AAS) and in vitro antioxidant activity by different methods for the first time. The study revealed that Himalayan black salt was irregular in shape with a quadrilateral, cubic, irregular crystalline structure. The Himalayan black salt exhibited antioxidant effect and interestingly showed low Na levels than common sea salt and Himalayan pink salt. The Himalayan black salt also contained important minerals like iron, calcium and magnesium which are beneficial to human health thus exhibiting superior characteristics over other conventional table salts.

Feasibility of Quantitative Analysis of Magnesium and Calcium in Edible Salts Using a Simple Laser-Induced Breakdown Spectroscopy Device

Feasibility of a simple laser-induced breakdown spectroscopy (LIBS) device has been investigated for the analysis of Mg and Ca in edible salts. The LIBS spectrometer was assembled with a compact low-power diode-pumped solid-state laser (DPSSL) and a non-gated low-resolution handheld spectrometer. A simple sampling process was employed for on-site application. A piece of filter paper was dipped in the aqueous solution of a sample salt and dried for analysis using LIBS. Maintaining the sample surface height at the optimum position was critical to generate plasmas persistently due to the low pulse energy of the DPSSL. The varying height of the filter paper surface was monitored and compensated, while the sample stage was translated to collect spectra from different positions. The variation of line intensities of Mg and Ca could be attributed to the inhomogeneous distribution of dry residues. To correct this, the peak that consists of the Na(I) and C(II) lines at 568 nm was employed as a reference signal for intensity normalization of the analyte Mg(II) and Ca(II) lines. For edible salt products, the normalized Mg(II) and Ca(II) line intensities could be well correlated with the concentrations of Mg and Ca determined using inductively coupled plasma optical emission spectroscopy. Our results indicate that a simple LIBS device in combination with the simple sampling method is promising as an on-site salt quality assessment methodology.

Laser-induced breakdown spectroscopy (LIBS): a novel technology for identifying microbes causing infectious diseases

With the advent of improved experimental techniques and enhanced precision, laser-induced breakdown spectroscopy (LIBS) offers a robust tool for probing the chemical constituents of samples of interest in biological sciences. As the interest continues to grow rapidly, the domain of study encompasses a variety of applications vis-à-vis biological species and microbes. LIBS is basically an atomic emission spectroscopy of plasma produced by the high-power pulsed laser which is tightly focused on the surface of any kinds of target materials in any phase. Due to its experimental simplicity, and versatility, LIBS has achieved its high degree of interest particularly in the fields of agricultural science, environmental science, medical science, forensic sciences, and biology. It has become a strong and sensitive elemental analysis tool as compared to the traditional gold standard techniques. As such, it offers a handy, rapid, and flexible elemental measurement of the sample compositions, together with the added benefits of less cumbersome sample preparation requirements. This technique has extensively been used to detect various microorganisms, extending the horizon from bacteria, molds, to yeasts, and spores on surfaces, while also being successful in sensing disease-causing viruses. LIBS-based probe has also enabled successful detection of bacteria in agriculture as well. In order for good quality processing of food, LIBS is also being used to detect and identify bacteria such as Salmonella enteric serovar typhimurium that causes food contamination. Differences in soil bacteria isolated from different mining sites are a very good indicator of relative environmental soil quality. In this connection, LIBS has effectively been employed to discriminate both the inter- and intra-site differences of the soil quality across varying mining sites. Therefore, this article summarizes the basic theory and use of LIBS for identifying microbes causing serious agricultural and environmental infectious diseases.

Laser-Ablation Sampling for Accurate Analysis of Sulfur in Edible Salts

We evaluated the performance of laser ablation analysis techniques such as laser-induced breakdown spectroscopy (LIBS), laser ablation inductively coupled optical emission spectrometry (LA-ICP-OES), and laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS), in comparison with that of ICP-OES using aqueous solutions for the quantification of sulfur (S) in edible salts from different geographical origins. We found that the laser ablation based sampling techniques were not influenced by loss of S, which was observed in ICP-OES with aqueous solutions for a certain salt upon their dissolution in aqueous solutions, originating from the formation of volatile species and precipitates upon their dilution in water. Although detection of S using direct laser sampling with LA-ICP-MS has well-known isobaric and polyatomic interferences, LIBS and LA-ICP-OES showed good accuracy in the detection of S for all salts. LIBS also provided the ability to identify the dominant chemical form in which S is present in salts. Correlation between S and oxygen, observed in LIBS spectra, provided chemical information about the presence of S^2- or [Formula: see text], which are associated with the origin and quality of edible salts.

Importance of laser-induced breakdown spectroscopy for hard tissues (bone, teeth) and other calcified tissue materials

Laser-induced breakdown spectroscopy (LIBS) as a sensitive optical technique capable of fast multielemental analysis proved to be a versatile tool in different applications. It became visible in the analytical atomic spectroscopy scene in the late 1980s and since then, its applications having been developed continuously in different field of science and technology including biomedical science. Here, we review the use and importance of LIBS for trace element determination in different calcified tissue materials. In this article, we have also reported a comprehensive review of the recent progress of biomedical applications of LIBS.

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.