A new microextraction method for trace nickel determination in green tea samples: Solventless dispersion based dispersive liquid-liquid microextraction combined with slotted quartz tube- flame atomic absorption spectrophotometry

In this study, a simple and novel analytical approach was developed in order to determine nickel at trace levels. For this purpose, a dispersive liquid-liquid microextraction (DLLME) method based on solventless dispersion of extraction solvent was developed to separate/preconcentrate nickel from aqueous solution. Combination of the DLLME method with slotted quartz tube-flame atomic absorption spectrophotometry (SQT-FAAS) lowered the analyte’s detection limit. In the DLLME method, the extraction solvent was dispersed into aqueous solution by generating fine droplets through air assisted spraying in order to reduce organic solvent consumption and avoid relative error by reducing multiple operation steps. Complexation of nickel(II) was done by using a Schiff Base synthesized from the reaction between 3,5- dibromosalicylaldehyde and 2-aminophenol. All experimental parameters were optimized comprehensively by the step-by-step approach in order to determine optimum conditions to get maximum absorbance values. Under the optimum conditions, analytical performance values were examined, and limit of detection values were obtained as 286 ng mL-1 for FAAS, 137 ng mL-1 for SQT-FAAS, 7.9 ng mL-1 for DLLME-FAAS and 3.9 ng mL-1 for DLLME-SQT-FAAS. The enhancement in detection power was obtained as 82-folds over the detection limit of the conventional FAAS system. Chinese green tea sample was used in recovery studies to check applicability and accuracy of the developed method. Recovery results were close to 100 % with low standard deviation values (n = 4) and this showed that the method appropriate for the selected matrix.     

Determination of trace nickel in chamomile tea and coffee samples by slotted quartz tube-flame atomic absorption spectrometry after preconcentration with dispersive liquid-liquid microextraction method using a Schiff base ligand

In the present study, an accurate and selective preconcentration/extraction method was developed for the determination of nickel at trace levels. Slotted quartz tube flame atomic absorption spectrometry (SQT-FAAS) combined with dispersive liquid-liquid microextraction (DLLME) was used to obtain a very low detection limit for nickel. A Schiff base ligand derived from the reaction of 5-bromosalicylaldehyde and o-phenylenediamine was used for the formation of a coordinate nickel complex. Under the determined experimental conditions, the detection and quantification limits of the DLLME-SQT-FAAS system were calculated as 4.9 and 16.4 ng/mL, respectively. Satisfactory analytical performance values of the SQT-FAAS, DLMME-FAAS and DLLME-SQT-FAAS methods were obtained and 1.8, 32.0, 66.4-fold enhancements in detection power were respectively obtained over the conventional FAAS system. The percent recovery ranges obtained for two different spike concentrations were 88.1–113.2% and 102.1–120.2% for coffee and chamomile tea samples, respectively.     

Simple and sensitive determination of vitamin A and E in the milk and egg yolk samples by using dispersive solid phase extraction with newly synthesized polymeric material

A simple and sensitive determination method for trace amounts of vitamins A and E has been developed based on dispersive solid phase extraction (DSPE) and HPLC-DAD analysis in this study. In the proposed method, the vitamin molecules were retained on a newly synthesized solid phase material consisting of tetracycline-grafted polyacrylamide polymer (PAA-T). The method was applied by the conventional batch method and desorption of retained vitamins from PAA-T surface were carried out with acetonitrile. Then, the samples were filtered through a 0.45 μm filter, transferred to HPLC vials. The analysis of the samples was carried out using a C18 column at a flow rate of 1 mL min⁻¹ with isocratic elution consisting of methanol (30 %) and acetonitrile (70 %). For vitamin A (retinol) and vitamin E(α-tocopherol) respectively; determination wavelengths: 324 and 292 nm, linear ranges: 20−700 ng mL^-1 and 50−1800 ng mL⁻¹, limit of detections (LOD): 5.71 ng mL⁻¹ and 14.28 ng mL⁻¹, relative standard deviations(RSD) for 5 repetitive measurements: 3.25 % and 2.85 %. For application of the developed method, recovery experiments were carried out and quantitative values were obtained in milk and egg yolks.     

Synthesis and characterization of functionalized silica with 3,6-ditia-1,8-octanediol for the preconcentration and determination of lead in milk employing multicommuted flow system coupled to FAAS

Novel functionalized silica, containing 3,6-dithia-1,8-octanediol (Si-DIO), was synthesized and characterized by infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), scanning electron microscope (SEM) and nuclear magnetic resonance (NMR) of ¹³C and ²⁹Si. The Si-DIO was used to pre-concentrate and determine the amount of Pb(II) in milk samples employing a multicommuted flow system coupled to flame atomic absorption spectrometry (FAAS). For the adsorption process, a pre-concentration minicolumn with 100 mg of Si-DIO, a solution of 0.005 mg L⁻¹ Pb(II) at pH 9.0 and HNO₃ as the eluent was used, obtaining an enrichment factor of 28 times with retention efficiency higher than 99%. The Pb(II) ion, using the multicommuted flow system coupled to FAAS, showed a linear response between 0.005 and 20.0 mg L⁻¹; a linear coefficient where r = 0.9939 and n = 7; a detection limit estimated at 0.001 mg L⁻¹ and a relative standard deviation of 3.8% (n = 50). Fifty pre-concentrations runs were tested in the minicolumn without significant variation in the analytical signal. The proposal system showed analytical applicability to determine Pb(II) ion in milk samples, presenting recovery of 90.7–102.5%.     

Development of a new method for determination of aluminum (Al) in Jordanian foods and drinks: Solid phase extraction and adsorption of Al3+-d-mannitol on carbon nanotubes

In this work, a new method was developed for determination of aluminum (Al) in traditional Jordanian foods (Mansaf, Kofta, Tabboola, Hummous, bread), tea, Arabian coffee and water samples. The method involved solid phase extraction (SPE) of Al³⁺ from the digested samples after complexation with d-mannitol using carbon nanotubes (CNT) as the extractive sorbent. Formation of the Al³⁺-d-mannitol complex was confirmed by infrared spectroscopy. Optimization of the SPE method involved sample pH, d-mannitol-to-Al mole ratio, sample loading and elution flow rates, adsorbent mass, eluent concentration and volume. Based on spiked water samples, the characteristics of the method were as follows: the limit of quantification: 23 μg l⁻¹; sensitivity: 0.0036 (mg l⁻¹)⁻¹; %RSD range: 0.4–1.9%; recovery range: 76.0–93.0%. The equilibrium, thermodynamic and kinetic adsorption studies of Al³⁺-d-mannitol on CNT revealed that adsorption was spontaneous, exothermic, preferred, of physical nature; followed second-order rate kinetics; pore diffusion was not the only rate-controlling step; both Langmuir and Freundlich isotherms represented the data satisfactorily.