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The present work aims to examine the effect of silicon substitution on thermal and in-vitro dissolution properties of carbonated hydroxyapatite. Hydroxyapatite [Ca10(PO4)6(OH)2, HA], carbonate substituted hydroxyapatite [Ca10(PO4)6-x(CO3)x(OH)2, x=1, 1CHA] and carbonate, silicate co-substituted hydroxyapatite [Ca10(PO4)6-x-y(CO3)x(SiO4)y(OH)2, x=1,y=1, 1C1SiHA] nanoparticles were prepared by microwave synthesis method under identical processing conditions. The XRD results of HA, 1CHA and 1C1SiHA correspond to the standard hexagonal HA (JCPDS 9-432). The crystallite size and lattice strain of the synthesized powder particles were estimated by Williamson-Hall isotropic strain model (W-H ISM) from powder X-ray diffraction data. The dislocation density was calculated by Williamson-Smallman formula. The functional groups present in the as-synthesized powder particles were analyzed by Fourier transform infrared (FT-IR) spectroscopy method. The size and the morphology were examined using a transmission electron microscope (TEM). The in-vitro dissolution behaviour of the synthesized powder particles was studied by ethylenediamine tetra-acetic acid (EDTA) titrimetric method. The W-H ISM results confirm that the prepared powder particles of HA, 1CHA and 1C1SiHA are nanocrystalline with an average crystallite size of 40 nm, 36 nm and 32 nm, respectively. Thus the crystallite size of hydroxyapatite was observed to be decreased gradually with increase in substitutions as indicated by the least size for the 1C1SiHA. In addition, the XRD results of powders annealed at 900 °C for 2 h show the improved thermal stability of 1C1SiHA compared to 1CHA. The TEM results show rod-like shaped morphology for HA, near rod-like with modified edge morphology and increased agglomeration for 1CHA and needle-like shaped morphology for 1C1SiHA powder particles. The in-vitro dissolution study results show a gradual increase in the solubility of HA with carbonate and carbonate-silicate co-substitutions. The calculated microstructural parameters, namely, crystallite size, root mean squared strain and dislocation density were correlated with in-vitro dissolution behaviour of hydroxyapatites.

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A multi‐residue analytical method for analysis of 34 pesticides was standardized and validated using gas chromatography‐tandem mass spectrometry. The calibration curve constructed for each pesticide was linear over the concentration of 10 to 100 μg/L and the correlation coefficient ranged between 0.998 and 0.999. The limit of quantification and detection were in the range of 1.6 to 3.5 and 4.9 to 10.5 μg/kg, respectively. The sample preparation technique involving solid‐phase extraction using primary secondary amine and magnesium sulfate with acetonitrile provided acceptable recoveries in the range of 70.60 to 119.56% for 10 μg/kg, 70.12 to 115.58% for 50 μg/kg, and 71.51 to 118.11 for 100 μg/kg spiking levels with acceptable relative standard deviation. The field‐collected red chili samples were screened and the pesticide residues were quantified by using gas chromatography with tandem mass spectrometry. The mean residues of red chili samples assessed for the potential risk to consumers showed no risk.

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