Colorimetric and visual determination of ultratrace uranium concentrations based on the aggregation of amidoxime functionalized gold nanoparticles.

The authors describe the synthesis and characterization of 3-mercaptopropionylamidoxime functionalized gold nanoparticles (AuNPs) for visual detection of uranium (U) by cloud point extraction. The method is capable of quantifying U at the concentration limits set by the World Health Organization in drinking water i.e., 30.0 ng mL-1. The method is based on the gradual color change from red to blue that occurs as a result of the interaction between uranyl ion and the modified AuNPs leading to particle aggregation. Such analyte-triggered aggregation results in AuNP's peak absorbance quenching as well as red shift in the wavelength range of 520 to 543 nm. The colorimetric response at 520 nm is linear in the 2-100 ng mL-1 U concentration range, and the limit of detection is 0.3 ng mL-1. No interferences by other ions are found, and the relative standard deviation is ≤4% (for n = 5). The method is validated by analyzing a certified reference material (NIST SRM 1640a; natural water), and also applied to the quantification of U in four (spiked) water samples. Graphical abstract Schematic presentation of cloud point extraction (CPE) assisted coloirmetric and visual detection of uranium (U). In CPE of gold nanoparticles (AuNPs) the color of surfactant rich phase (SRP) turns red in absence of U(VI) and blue in presence of U(VI).

Simultaneous determination of borate, chloride and molybdate in pyrohydrolysis distillates of plant and soil samples by ion chromatography.

Determination of concentrations of micronutrients in plant samples is important in order to assess the growth and quality of plants. An ion chromatography (IC) method was developed for the simultaneous determination of B, Cl and Mo (micronutrients present in their anionic form in aqueous samples) using a gradient elution with d-mannitol and NaOH. Despite their different chemical nature, these elements could be separated from the matrix by employing pyrohydrolysis. IC was employed for their sequential determination from single aliquot injection into the IC column. It was observed that the optimised procedures developed earlier in our laboratory for the separation of B and halogens using d-Mannitol-NaOH or bicarbonate eluents could not be extended to B-Mo-Cl separation. The concentration levels of d-mannitol in the eluent required for separation of boron impeded the conductivity detection of Mo and the peak sensitivity was seen to be critically dependent on d-mannitol concentration in the eluent. In addition, d-mannitol in NaOH eluent altered the retention times of analytes (B, F-, Cl-, NO3-, SO42-and MoO42-) which were not observed in the case of bicarbonate eluent. The current study deals with the investigation on the influence of d-mannitol on the molybdate as well as its role on the retention time. Formation of Mo-mannitol complex at different pH conditions and de-protonation of mannitol were correlated to the observed effects. Based on the observations, a gradient elution method was proposed for the simultaneous separation and determination of B, Cl and Mo in the pyrohydrolysis distillates of plant samples. The method was calibrated for B (0.05-1 mg/L), Cl (0.1-10 mg/L) and Mo (0.5-10 mg/L) and the linear regression coefficients obtained were 0.9992, 0.9998 and 0.997 respectively. The limit of detection (LOD) for B, Cl and Mo was calculated to be 19, 23 and 96 µg/L, respectively. The developed IC method after pyrohydrolytic separation of B, Cl and Mo was successfully applied for the analysis of real samples.

Selective Micellar Extraction of Ultratrace Levels of Uranium in Aqueous Samples by Task Specific Ionic Liquid Followed by Its Detection Employing Total Reflection X-ray Fluorescence Spectrometry.

A task specific ionic liquid (TSIL) bearing phosphoramidate group, viz., N-propyl(diphenylphosphoramidate)trimethylammonium bis(trifluoromethanesulfonyl)imide, was synthesized and characterized by 1H NMR, 13C NMR, 31P NMR, and IR spectroscopies, elemental (C H N S) analysis, and electrospray ionization mass spectrometry (ESI-MS). Using this TSIL a cloud point extraction (CPE) or micelle mediated extraction procedure was developed for preconcentration of uranium (U) in environmental aqueous samples. Total reflection X-ray fluorescence spectrometry was utilized to determine the concentration of U in the preconcentrated samples. In order to understand the mechanism of the CPE procedure, complexation study of the TSIL with U was carried out by isothermal calorimetric titration, liquid-liquid extraction, 31P NMR and IR spectroscopies, and ESI-MS. The developed analytical technique resulted in quantitative extraction efficiency of 99.0 ± 0.5% and a preconcentration factor of 99 for U. The linear dynamic range and method detection limit of the procedure were found to be 0.1-1000 ng mL-1 and 0.02 ng mL-1, respectively. The CPE procedure was found to tolerate a higher concentration of commonly available interfering cations and anions, especially the lanthanides. The developed analytical method was validated by determining the concentration of U in a certified reference material, viz., NIST SRM 1640a natural water, which was found to be in good agreement at a 95% confidence limit with the certified value. The method was successfully applied to the U determination in three natural water samples with ≤4% relative standard deviation (1σ).

Separation of boron from borated paraffin wax by pyrohydrolysis and alkali extraction methods and its determination using ion chromatography.

A method based on the pyrohydrolysis extraction of boron and its quantification with ion chromatography was proposed for paraffin waxes borated with H3BO3 and B4C. The optimum pyrohydrolysis conditions were identified. Wax samples were mixed with U3O8, which prevents the sample from flare up, and also accelerates the extraction of boron. Pyrohydrolysis was carried out with moist O2 at 950°C for 60 and 90 min for wax with H3BO3 and wax with B4C, respectively. Two simple methods of separation based on alkali extraction and melting wax in alkali were also developed exclusively for wax with H3BO3. In all the separations, the recovery of B was above 98%. During IC separation, B was separated as boron-mannitol anion complex. Linear calibration was obtained it between 0.1 and 50 ppm of B, and LOD was calculated as 5 ppb (S/N = 3). The reproducibility was better than 5% (RSD).