RESUMEN
In some cases, trace component analysis only requires a sensitive and high-resolution mass spectrometer. However, enantiomers must be completely separated to be differentiated with a mass spectrometer, which is highly dependent on the stationary-mobile phase composition. In case of a challenging chiral separation, instead of trying new columns for screening purpose, resolution enhancement techniques could be used to resolve partially overlapping peaks. A well-known enhancement method is the power law, which increases the linear dynamic range of each analyte and reduces excessive noise. In many cases, the peak noise can decrease significantly by applying the power law. However, the main drawback is that this approach changes relative peak areas and heights of each peak in a non-linear fashion which limits its use for quantitative purposes. In this study, a normalized power law was utilized for extracting correct area information. It is a simple (5 step) protocol that only requires Microsoft Excel, and results in enhanced visualization of trace components, especially in low signal/noise environments, and makes integration convenient and reproducible. Several difficult chiral trace component analyses were investigated, including applications pertaining to ultrafast high-throughput chromatography, enantiopurity, and peak purity analysis. For complicated cases with multiple overlapped peaks of different resolutions, a segmented normalized power law was utilized. A trace component coeluting near a dead volume peak and a trace enantiomeric component in the tail of the corresponding enantiomeric peak were virtually enhanced. As an additional tool, first and second derivatives were utilized to identify if an enantiomeric impurity is coeluting with the dominant enantiomer under overload conditions. Idiosyncrasies of the derivative test are discussed. This study shows how these simple approaches can be used for accurate quantitation, specifically for trace enantiomeric components.
Asunto(s)
Técnicas de Química Analítica/métodos , Cromatografía , Técnicas de Química Analítica/instrumentación , EstereoisomerismoRESUMEN
The objective of this work was to convert corncobs to activated carbon by low temperature chemical treatment for removing copper from wastewater. The parameters for developing a new adsorbent i.e. sorption capacity, selectivity, regenerability, suspension test, and kinetics were investigated. All studies were performed in batch experiments. Removal of copper from aqueous solutions varied with the amount of adsorbent, metal ion concentration, agitation time, solution pH and the species of copper present. It was found that the effect of temperature was very small. The Langmuir model was found to best fit the equilibrium isotherm data. Kinetics of copper removal at two different temperatures obeyed Lagergren pseudo-first-order equation. Effect of water hardness, other cations (Pb(2+) and Zn(2+)) on copper removal was also studied. Experiments with anionic and cationic complexes of copper showed that anionic copper species are not removed at all by the prepared material. To observe the nature of surface and pore structure scanning electron microscope (SEM) images of modified corncobs were used. To study the interaction forces between the adsorbent and the metal ion functional group analysis with infrared spectroscopy and proximate analysis were carried out. In addition, recovery of the metals ion and regeneration of spent adsorbent was possible by acidified hydrogen peroxide. Since the uptake capacity of the prepared adsorbent is 26mg Cu/g for copper, it can be a potential adsorbent for removing and recovering other heavy metal ions from contaminated wastewaters. The sorption capacity of the treated corncobs for copper was better than the reported capacity of other activated carbons prepared from agricultural sources.