Rajesh Nayak

Bio: Rajesh Nayak is an academic researcher from Manipal University. The author has contributed to research in topics: Laser-induced breakdown spectroscopy & Elemental analysis. The author has an hindex of 9, co-authored 21 publications receiving 335 citations.

Analytical predictive capabilities of Laser Induced Breakdown Spectroscopy (LIBS) with Principal Component Analysis (PCA) for plastic classification

Abstract: A Laser Induced Breakdown Spectroscopy (LIBS) technique has been applied for the identification of four widely used plastics, polyethylene terephthalate (PET), high-density polyethylene (PE), polypropylene (PP) and polystyrene (PS), whose recycling is required from commercial and biosafety points of view. The 3rd harmonic (355 nm) nanosecond pulse from an Nd:YAG laser is used to create plasma on the sample surface and identification of the type of the plastic is derived from the plasma emission. Principal Component Analysis (PCA) of the LIBS spectra is employed for the classification of plastics. Distinct methods have been used, apart from principal components of PCA, to further confirm our results. Statistical parameters, viz., Mahalanobis distance (M-distance) and spectral residuals were used for decisive match/no match test which provided successful classification of plastics. Receiver Operating Characteristic (ROC) and Youden's index analyses were carried out to obtain the diagnostic threshold for classification of all four classes of plastics. Sensitivity, specificity, predictive values and discriminative accuracy of the classification tests based on the optimum threshold were calculated. This proves the analytical predictive capabilities of the LIBS technique for plastic identification and classification. The technique of LIBS, in future, can be routinely used in field applications such as plastic waste sorting and recycling.

Calibration-free laser-induced breakdown spectroscopy for quantitative elemental analysis of materials

Abstract: The application of calibration-free laser-induced breakdown spectroscopy (CF-LIBS) for quantitative analysis of materials, illustrated by CF-LIBS applied to a brass sample of known composition, is presented in this paper The LIBS plasma is produced by a 355 nm pulsed Nd:YAG laser with a pulse duration of 6 ns focussed onto a brass sample in air at atmospheric pressure The time-resolved atomic and ionic emission lines of Cu and Zn from the LIBS spectra recorded by an Echelle spectrograph coupled with a gated intensified charge coupled detector are used for the plasma characterization and the quantitative analysis of the sample The time delay where the plasma is optically thin and is also in local thermodynamic equilibrium (LTE), necessary for the elemental analysis of samples from the LIBS spectra, is deduced An algorithm relating the experimentally measured spectral intensity values with the basic physics of the plasma is developed Using the algorithm, the Zn and Cu concentrations in the brass sample are determined The analytical results obtained from the CF-LIBS technique agree well with the certified values of the elements in the sample, with an accuracy error <1%

Analysis of trace elements in complex matrices (soil) by Laser Induced Breakdown Spectroscopy (LIBS)

Abstract: Direct spectro-chemical analysis of trace elements in complex matrices like minerals and soil is usually difficult because of possible interference from the intense background spectrum of the major components generated in the plasma. Optimization of the Laser Induced Breakdown Spectroscopy (LIBS) technique is essential for routine analysis of such samples. In the present work, we have shown that low detection limits can be achieved for trace elements like copper, zinc, and calcium in soil samples by using high resolution echelle spectrographs coupled to the LIBS system, and eliminating the background by subtraction of a suitable matrix “blank” spectrum. It is also shown that the LOD (limits of detection) can be further reduced by suitable data processing techniques like signal addition from multiple lines provided by the wide-range echelle system and use of correlation function calculation with a pure element spectrum. The validity of our LIBS technique was confirmed by conventional Atomic Absorption Spectroscopy (AAS) analysis for the same analyte after pre-concentration.

Optimized LIBS setup with echelle spectrograph-ICCD system for multi-elemental analysis

Abstract: Laser-Induced Breakdown Spectroscopy (LIBS) is well recognized as a promising tool for in situ/remote elemental analysis of environmental, archeological, clinical, and hazardous samples. With the aim of quantifying trace elements in such samples, using LIBS technique, an echelle spectrograph-ICCD system with high sensitivity and good resolution has been assembled. Various important parameters of this system were studied and optimized. Conditions for getting good quality LIBS spectra and signal for multielemental analysis have been achieved, and these are discussed and illustrated in this paper.

Processing, characterisation and biocompatibility of iron phosphate glass fibres for tissue engineering

Abstract: Iron-phosphate glass fibres based on the CaO-Na2O-Fe2O3-P2O5 system have been processed and characterised via thermal, XRPD, dissolution rates, diameter and biocompatibility studies. The compositions investigated were fixed at 50mol% P2O5, and the CaO content was varied between 30, 35 and 40mol%. The Fe2O3 was added in low amounts from 1-5mol%, substituting it for the Na2O mol%. The number of Tc (crystallisation temperature) peaks detected from the thermal analysis traces only showed correlation with XRPD analysis, for five out of the 15 compositions investigated. It has been suggested that either the crystalline phases had very similar Tc temperatures or that the other phase(s) were present in very small quantities. There was a good match seen with number of Tm (melting temperature) peaks picked up from the DTA traces, with the number of phases identified from XRPD analysis. The main phases identified from XRPD were NaCa(PO3)3, CaP2O6 and NaFeP2O7. Using network connectivity (NC), predictions on Qn species present within the compositions investigated were made. The predicted species (metaphosphates) matched with phases identified from XRPD analysis. A decrease in dissolution rates for the bulk glass and glass fibres was seen with an increase in CaO mol%, along with an increase in Fe2O3 mol%. An increase in fibre dissolution rates was seen with a decrease in diameter size. The biocompatibility studies were conducted using a conditionally immortal muscle precursor cell line derived from the H-2Kb-tsA58 immortomouse. It was found that iron-phosphate glass fibres containing 4-5mol% Fe2O3 was sufficient for cell attachment and differentiation. It was seen that myotubes formed along the axis of the fibres (which was indicative of differentiation). The biocompatibility of these compositions was attributed to the enhanced chemical durability of the glass fibres.

LIBS analyses for industrial applications – an overview of developments from 2014 to 2018

Abstract: Measuring distances in the range between a few centimetres and a few metres are of special interest for automated industrial LIBS applications. They allow for a reliable optical access to measuring objects in a process line under harsh industrial environments. In that range a compromise can be found between the conflicting requirements with respect to the protection of the optics facing the measuring object on one side, and sufficiently high laser irradiance and high receiving solid angle of the measuring radiation on the other side. A concise overview about LIBS studies published in the last four years focusing on industrial applications or perspectives therefore is given. Recent RD (b) sorting of refractories; (c) identification of steel blooms in a rolling mill; (d) inverse production scenario for the recovery of valuable materials from end-of-life electronic equipment. For measuring distances of only a few centimetres the size of a LIBS instrument can be downscaled significantly allowing to set up handheld LIBS analysers. Whereas the precursors of such concepts were studied already more than fifteen years ago, quite recently a competitive market arose where various models of handheld LIBS systems are offered. Industrial application fields are mainly positive material identification of metals and sorting of light metal scraps for recycling purposes. A comparative synopsis of features of these LIBS systems will be presented and arising research themes in this context are outlined.