Normal-phase HPLC material after

Separation of these spiroacetal isomers was initially achieved using normal phase semi-preparative HPLC, which allowed re-equilibration of the undesired spiroacetal 35 and thereby a method to convert essentially all of the material to the desired isomer 36 after several cycles. The scale-up of this procedure was greatly facilitated by the determination of a simple method for separating the spiroacetal isomers by flash column... 

Evaporation and redissolving. The solvent of the combined upper layer is evaporated under nitrogen flow or low-temperature vacuum distillation. An oily material appears after it is dried. A precisely measured aliquot of mobile phase is normally used to redissolve theextract. These procedures are intended to not only increase the concentration of tocopherols and tocotrienols to the measurable level of the detector, but also to avoid uncertain volume change of organic layer during extraction, which results in inaccurate results. The redissolved sample is transferred to a vial for HPLC analysis. 

Procedure Determination of Unsulfonated Alkylbenzene and Sulfone Content by HPLC (13) A methanol solution of the surfactant, about 10% concentration, is injected on an HPLC system consisting of a Ci8 reversed-phase column, 4.6 x 150 mm, a mobile phase of 94 6 MeOH/H20 at 1 mL/min, and both refractive index and UV detectors. The RI detector is thermostatted at 35 C, while the UV detector is used at 220 nm. In the normal mode of operation, LAS is eluted immediately, followed by unsulfonated material in order of chain length, followed by sulfones over the range 10-35 min. For rapid quantitative analysis, the system is back-flushed after 4.5 min, after elution of the LAS. The total nonpolar material is then eluted through the RI detector, at a retention time of 9 min after injection. 

Precise characterization of surfactants in used formulations, such as the recycled solutions used to remove oil after metal-forming operations, normally requires some preliminary separation. For example, HPLC analysis of alkoxylated surfactants is possible if the sample is cleaned up by solid phase extraction on silica. Water is first removed by azeotropic distillation, then organic material is taken up in methylene chloride and passed through the SPE column. After elution of oil and grease with methylene chloride, the nonionic surfactants are removed with methanol (17). 

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