Monitoring cobalt ions siting in BEA and FER zeolites by in-situ UV–Vis spectroscopy: A DRS study

Facile Detection of Vitamin B12 with Copper Oxide Nanocrystal Graphenic Composite Electrode

Vitamin B12 (VB12) is applied as the cofactors in various important enzymatic reactions and is involved in gene expression regulation mediated by B12-riboswitch and the VB12-dependent photoreceptor. Rapid detection VB12 concertation in a given environment may provide insights in the evaluation of micronutrient levels and the physiological and ecological performances of organisms under the relevant condition. This study demonstrating an amperometric approach to quantify the VB12 in biological samples without complicated sample pretreatment. The electrochemical oxidation step was conducted with a plain graphenic electrode to convert all nitrogen groups within the VB12 molecules to NO3− at 1.3 V vs. Ag/AgCl for 15 min. VB12 was quantified stoichiometrically according to the oxidized nitrate anions, which were reduced with copper oxide nanocrystal decorated graphenic electrode. Cathodic polarization was conducted with a graphite rod electrode before nitrate reduction to eliminate the potential interferences. Under optimized experimental conditions, the presented approach gave a wide detection linear range of 0.15–7378 nmol L−1 and the detection limit was 0.59 nmol L−1. The results for biological samples were comparable to those of the HPLC method. These results indicated that successively combined anodic and cathodic polarization enhanced the detection sensitivity and efficiency of the electrode towards VB12. The proposed electrode shows potential in terms of efficiency, reliability and accuracy for rapid determination of VB12 in biological samples.

Using diffuse reflectance spectroscopy (DRS) technique for studying biofilm formation on LDPE and PET surfaces: laboratory and field experiments

Biofilm formation on plastic debris needs to be further investigated, because microorganisms attached to plastics are transferred in all three dimensions to new regions by ocean currents. The current study aims to investigate biofilm formation on plastic strips in aquatic ecosystems using a simple physicochemical method commonly used to characterize solid surfaces, namely, the diffuse reflectance UV-Vis spectroscopy (DRS) method. Using virgin polymers that have not being exposed to the environment as a reference, DRS peaks can be attributed to the microorganisms attached to the polymer surface with time. The polymers tested were low-density polyethylene (LDPE) and polyethylene terephthalate (PET). For LDPE strips for all sampling times in the field, the development of the peaks among 10 similar samples was rather uniform in terms of peak wavelength with time. For PET strips during the early sampling time, the development of the peaks among 10 similar samples was rather uniform in terms of peak wavelength but varied in terms of intensity. This last observation phased out with longer exposure times that the peaks had similar distribution in terms of peak wavelength and intensity. Similar experiments were run for longer exposure times both in an oligotrophic laboratory bioreactor and in the marine environment. In both cases, the biofilm on PET samples seems to reach a steady state faster than LDPE with similar peaks found on both samples DRS proved to be a robust and useful tool to study the formation of biofilm on plastic samples without any pretreatment and without sample destruction. Graphical abstract.

Determination of Vitamin B12 and cobalt in egg yolk using vortex assisted switchable solvent based liquid phase microextraction prior to slotted quartz tube flame atomic absorption spectrometry

A switchable solvent based liquid phase microextraction (SS-LPME) has been proposed for the determination of cobalt in egg yolk and Vitamin B12 at trace levels. N,N-Dimethylbenzylamide (DMBA) was used as a switchable solvent and converted to protonated DMBA form by the addition of dry ice. Cobalt was complexed with 1,5-diphenylcarbazone (DPC) and extracted into the DMBA phase. After the extraction, HNO₃ was added to increase nebulization efficiency of the DMBA phase. Slotted quartz tube (SQT) was combined with FAAS to enhance the detection power of the system when compared to the conventional FAAS. Under the optimum conditions, limit of detection values were recorded as 75 µg L^-1 for FAAS, 33 µg L^-1 for SQT-FAAS, 7.6 µg L^-1 for SS-LPME-FAAS, and 2.3 µg L^-1 for SS-LPME-SQT-FAAS. The developed method was applied for the determination of cobalt in egg yolk and Vitamin B12 and the recovery results were found in the range of 105-114% with 0.30-7.6 standard deviation values (n = 3).