Separation in size exclusion HPLC has a specific type of equilibrium, as presented in Section 4.4 and is not based on partition or adsorption. This type of chromatography separates the compounds according to their molecular size (hydrodynamic volume). When only size exclusion is taking place and no energetic interaction of the analyte and stationary phase is present, the separation is based on the difference in the conformational entropy outside of the pores of the stationary phase where they are in an "expanded" shape and inside the pore where their conformational entropy decreases. For organic mobile phase, the method is indicated as gel permeation chromatography (GPC) and for aqueous mobile phase the technique is indicated as gel filtration chromatography (GFC).
This chapter includes a discussion on different types of forces at the molecular level that are involved in an HPLC separation. These forces occur between the molecules of the analyte, mobile phase, and stationary phase. The forces include those involving electrically charged molecules, polar molecules, polarizable molecules, etc. A discussion about hydrogen bond formations, and about solvophobic interactions, is also included. A separate section presents the interactions between molecules and surfaces. Mathematical formulas for the evaluation of each type of interactions are presented in this chapter.
Polymeric carbohydrates (polysaccharides) are built by bonding monosaccharide residues through the elimination of a water molecule and the formation of an ether bond. The general formula for monosaccharides is CnH2nOn (n = 3 for trioses, n = 4 for tetroses, n = 5 for pentoses, etc.). They contain a carbonyl group (aldehyde or ketone) and two or more –OH groups. Glyceraldehyde and dihydroxyacetone can be considered the simplest monosaccharides. (Glycolaldehyde or hydroxyacetaldehyde HOCH2–CHO also is considered by some a two-carbon monosaccharide.) Glyceraldehyde has one asymmetric carbon. Consequently, for this compound there are two possible enantiomers indicated as d and l. The d form is shown with the OH to the right of the carbon chain when the CH=O group is at the top, and the l form with the OH to the left, in a so called Fischer formula.
This paper reports the findings of a randomized nicotine pharmacokinetic (PK) study of a closed electronic nicotine delivery system (ENDS). The study evaluated four flavor variants of Vuse Solo ENDS where subjects used their randomized investigational product (IP) for 10 minutes ad libitum and blood samples were collected for PK assessments that included maximum plasma nicotine concentration (C max ) and area under the nicotine concentration-vs-time curve up to 60 minutes (AUC nic0–60 ). Baseline-adjusted mean C max ranged from 6.53 to 8.21 ng/mL, and mean AUC nic0–60 ranged from 206.87 to 263.52 ng*min/mL for all ENDS IPs. Results for C max and AUC nic0-60 values were consistent among the ENDS IP flavor variants tested and results indicate that flavors did not affect nicotine uptake in human subjects.
Since the sample preparation procedures described in this book are dedicated in particular to chromatography, a brief presentation of various core chromatographic techniques was necessary. This presentation is done in this chapter. The basic principles of a chromatographic separation are first discussed. This part also describes the main parameters used for the characterization of a chromatogram and of a chromatographic peak, as well as the qualitative and quantitative evaluation of chromatographic results. Several aspects of gas chromatography and high-performance liquid chromatography, which are the most common chromatographic techniques, are further presented. This includes a brief discussion on instrumentation, the nature and selection of separation media (chromatographic columns), sensitivity of detectors. The relation between the type of core chromatographic technique and the accompanying sample preparation procedure is also examined.
