Solid-phase extraction case study

Case Study A.4 Scaled-up Oxidative Degradation and Isolation Using Solid-Phase Extraction and Preparative HPLC... 

Automation of solid-phase extraction (SPE) is an important contribution to sample processing. If many samples are to be analyzed in the laboratory, automation provides precise and accurate methods when compared to manual methods. This chapter will discuss three major ideas on automation. First is why automate SPE. Second are the types of automation hardware, and third, how to automate an SPE method is discussed. Finally several case studies will be examined that show the automation process taken from a manual method. 

Capella-Peiro et al. (28) used a 3 full factorial design to optimize the capillary zone electrophoresis (CZE) separation of a group of seven antihistamines (brompheniramine, chlorpheniramine, cyproheptadine, diphenhydramine, doxylamine, hydroxyzine, and loratadine). In this case, critical parameters such as pH (a concentration of 20 mM phosphate was kept constant in all the experiments) and the applied voltage were studied to evaluate their effect on the resolution and efficiency. Maximum response was achieved at pH 2.0 and an applied voltage of 5 kV. After a repeatability study to check the precision of the electrophoretic method, as well as a suitable calibration, the usefulness of this optimized method was demonstrated through the determination of the listed histamines in pharmaceuticals, urine, and serum samples (recoveries were in agreement with the stated contents). Urine samples were diluted and directly injected in the CE system, while serum samples were previously extracted by means of a solid-phase extraction (SPE) procedure. 

Colegate SM, Edgar JA, Knill AM, Lee ST (2005) Solid-phase extraction and HPLC-MS profiling of pyrrolizidine alkaloids and their V-oxides a case study of Echium plantagineum. Phytochem Anal 16 108-119... 

Systems have been developed that allow the recycling of catalysts. The first case study involved simple adsorption of proline onto silica gel [6], but the system suffered from a loss in enantioselectivity. More recently, promising results have been obtained with fluorous proline derivatives [64] used for aldol reactions the recycling of fluorous catalysts has been demonstrated using fluorous solid-liquid extraction. Solid phase-supported catalysts through covalent bonds [65] and through noncovalent interactions [66] were also used for aldol reactions. Proline and other catalysts can be recycled when ionic liquids or polyethylene glycol (PEG) were used as reaction solvents [67]. 

Different procedures have been used to study the extractant retention on the polymeric support as a result of these weak extractant-support interactions. In all cases the retention process has been studied using the analysis of the distribution isotherm of the impregnated reagent between water and a solid phase. Because of the complex nature of the resins no precise assumptions were made about the kind of adsorption sites, and the adsorption model used in the approach was the classical Branauer, Emmet, and Teller... 

The solid phase epitaxy of amorphous on crystalline silicon systems has been studied by molecular dynamics simulations. First a simulation scheme is consolidated in the case of an amorphous layer recrystallization where the a/c velocity is well known from experiments. An atomic model of the a/c interface is constmcted and annealed by MD using one suitable interatomic potential for Si-Si interactions. The motion of the amorphous/crystalline interface is extracted and compared to the experimental law by Olson and Roth. Although none of the potentials is in agreement with the experiments, two stand out Tersoff for SPE but accounting for a shift to higher temperatures compared to the real ones, and StiUinger-Weber, for LPE. 

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