RESUMO
A new analytical procedure was developed for the determination of lead in human placental tissue by direct ultrasonic slurry sampling combined with electrothermal atomic absorption spectrometry (SS-ET AAS). Samples of dried and crushed placental tissue were mixed with 10 mL of 0.20% (v/v) HNO3 and homogenised. The slurries were then transferred to autosampler cups where they were sonicated using an ultrasonic probe prior to injection into a graphite tube with an L'vov platform. The effects of several chemical modifiers, including Mg(NO3)2, Pd(NO3)2, and NH4H2PO4, were investigated for the stabilisation of lead during thermal pre-treatment. Lead in the slurries was effectively stabilised up to 1200 °C with the Pd(NO3)2 modifier providing the best results with complete atomisation at 1900 °C. H2O2 was used as a chemical modifier; dilute HNO3 and HCl were examined as slurry media. The limit of detection and the limit of quantification for lead obtained under optimised conditions were 0.17 µg g-1 and 0.56 µg g-1, respectively. The relative standard deviation estimated from twenty replicate measurements of spike solution at a concentration of 50.00 µg L-1 for lead was 1.51%. The accuracy of the method was confirmed by analysis of the standard reference material BCR 185R "Bovine Liver". The proposed technique is simple, sensitive and environmentally friendly, and the risk of contamination is low. The method was applied to lead determination in real samples of human placental tissue. The 14 samples were taken just after delivery at the Gynaecology and Obstetrics Department of the Faculty Hospital with Outpatients Clinic in Bratislava over the course of 2019.
Assuntos
Grafite , Peróxido de Hidrogênio , Animais , Bovinos , Feminino , Humanos , Placenta , Gravidez , Espectrofotometria Atômica , UltrassomRESUMO
An electrochemical study was performed on the behavior of Ti3C2Tx MXenes prepared by using either HF (MXene1) or LiF/HCl as etchants (MXene2). The use of two redox probes indicates the presence of a higher negative charge density on MXene2 in comparison to MXene1. The characterization of two nanomaterials shows that titanium and fluoride are present higher by one order of magnitude at the interface of MXene2, compared to MXene1. The high Ti and F content is accompanied by a 82-fold larger (249 µA·cm-2 vs. 5.64 µA·cm-2) anodic peak at the peak potential near 0.4 V (vs. Ag/AgCl). Similarly, the peak current on MXene2 is 317-fold higher for the oxygen reduction at pH 7.0 (at a voltage of -0.84 V) and 215-fold higher for the reduction of H2O2 at -0.89 V, when compared to MXene1. Graphical abstractDifference in electrochemical behavior of MXene prepared by HF (MXene1) and LiF/HCl (MXene2) as etchants.
RESUMO
This work is focused on separation and determination of amygdalin and its unnatural form neoamygdalin in natural food supplements. Reversed-phase high-performance liquid chromatography with a high-stability silica-based column with C18 functional group has been used for solving this problem. The effect of the mobile phase composition as well as the column temperature on the separation of the amygdalin epimers has been investigated. Isocratic elution using a mobile phase composed of 0.05% aqueous formic acid and acetonitrile achieved the required separation within 17 min. Under optimum chromatographic conditions, the developed method was validated and was applied for the determination of amygdalin epimers in natural food supplements containing apricot or peach kernels. A simple extraction method using methanol as an extractant supported by an ultrasonic bath was used with recovery in the range of 94.8% to 104.3%. The limit of detection and limit of quantification values for R-amygdalin were 0.13 mg/L and 0.40 mg/L, respectively. The developed method proved to be precise with the intra-day and inter-day relative standard deviation values less than 2.23%.
