Separator aminopropyl-bonded silica

Many of the l.c. stationary-phases available may be packed into columns by the user at a fraction of the cost of a commercial column (see Section II,l,f). The most notable of these are the cation-exchange res-ins8.89 and the aminopropyl-bonded silica gels, which can be readily packed to provide high-resolution separations. The Cis-bonded silica gel and cation-exchange resin stationary-phases are especially useful, as large columns (2 x 25 cm) can be accommodated on analytical chromatographs, at flow rates of 1 to 5 mL/min, without any modifications of equipment. 

Sugar analysis by hplc has advanced gready as a result of the development of columns specifically designed for carbohydrate separation. These columns fall into several categories. (/) Aminopropyl-bonded silica used in reverse-phase mode with acetonitrile—water as the eluent. (2) Ion-moderated cation-exchange resins using water as the eluent. Efficiency of these columns is enhanced at elevated temperature, ca 80—90°C. Calcium is the usual counterion for carbohydrate analysis, but lead, silver, hydrogen, sodium, and potassium are used to confer specific selectivities for mono-, di-, and... 

Veuthey and Haerdi reported the separation of amphetamines using packed-column SFC [26]. The amphetamines were derivatized with 9-fluorenylmethyl chloroformate and chromatographed with a methanol or 2-propanol-modified carbon dioxide as the mobil phase. The separations were compared on bare silica and aminopropyl-bonded silica columns. Both columns gave comparable results and the separation of all five amphetamines (methylamphetamine, amphetamine, phenethylamine, ephed-rine, and norephedrine) was achieved in less than 5 min. Both methanol and 2-propanol-modified carbon dioxide gave comparable results. It was observed that the modifier concentration had more effect on the solvating power than the mobile-phase density. 

Later, Klemm and co-workers [86,87] achieved partial resolution of aromatic compounds by low-pressure chromatography on silica gel impregnated with TAPA. The separation was attributed to n-n complexation between TAPA and the enantiomers. Mikes et al. [88] used a column packed with an (i )-(-)-TAPA aminopropyl-bonded silica support to accomplish the full resolution of helicenes. The authors extended their study to other homologues of TAPA (Figure 22-19). These compounds were coated on silica gel or ion-paired to an aminopropyl-bonded phase, and they were used in the HPLC separation of helicenes. To describe the selective interactions that occur between the stationary phase and the helicenes, the authors assumed that the 2,4,5,7-tetranitro-9-fluorenylidene moieties of the selector are laying down on the silica surface, while the X groups point away from the surface and above the plane of the fluorenyl ring. 

Suzuki et al. also separated phospholipids by using a combination of aminopropyl-bonded silica and an unbonded silica SPE to recover PC, PE, cardiolipin, phos-phatidylglycerol, and phosphatidylserine. Phospholipids... 

It is well known that even complex carbohydrate mixtures (found in food or urine samples) can be separated by TLC [10]. Although many different stationary phases are nowadays commercially available, there are in practice only three suitable layers for the separation of carbohydrates cellulose, silica, and aminopropyl bonded silica [3]. 

Pantothenic acid/calcium pantothenate in pharmaceutical products and vitamin premixes was also analyzed using low-wavelength ultraviolet (UV) detection (64,66). The vitamin was extracted from tablets or powdered premixes with 0.005 M NaH2P04 buffer (pH 4.5) and separated from other water-soluble vitamins on an aminopropyl-bonded silica column (LiChrosorb NH2) eluted with an acetonitrile-0.005 MNaH2P04 buffer (pH 4.5) (87 13, v/v) and detected at 210 nm. Quantitative recoveries (>95%) and relative standard deviations 0.79% to 2.2% were obtained for multivitamin tablets, vitamin premixes, fortified yeasts, and raw materials. The limit of sensitivity was approximately 1 mg/g sample. The results were compared with those obtained by the standard microbiological procedure. Low levels of calcium pantothenate (<3 mg per tablet) were more precisely analyzed by the HPLC procedure than by the microbiological method. 

Alvarez, J.G. Touchstone, J.C. Separation of acidic and neutral lipids by aminopropyl-bonded silica gel... 

Surfactants are separated according to adsorption or partitioning differences with a polar stationary phase in NPLC. This retention of the polar surfactant moiety allows for the separation of the ethylene oxide distribution. Of all the NPLC packings that have been utilized to separate nonionic surfactants, the aminopropyl-bonded stationary phases have been shown to give the best resolution (Jandera et al., 1990). The separation of the octylphenol ethoxylate oligomers on an amino silica column is shown in Fig. 18.4. Similar to the capabilities of CE for ionic surfactants, the ethylene oxide distribution can be quantitatively determined by NPLC if identity and response factors for each oligomer are known. 

Carbohydrates are eluted in the order of increasing polarity, and retention decreases when water content increases. With an aminopropyl silica column, Koizumi et al. [54] showed the resolution of d-glycooligosaccharides up to a degree of polymerization of 30-35 under isocratic conditions, with a binary mixture of acetonitrile/water. Similarly, with the use of a polyamine polymer resin-bonded silica or an amino-bonded silica, separation of maltooligosac-charides up to a degree of polymerization of 28 was achieved [55],... 

Polar bonded phases for normal-phase separations have recently gained popularity. These include the dihydroxypropyl propyl ether (diol), aminopropyl, cyanopropyl, and nitrophenyl bonded silicas. These phases are advantageous to silica because they are less active and, yet, produce similar interactions, require shorter equilibration times, and are influenced less by the water content of the mobile phase. The retention of most analytes upon the diol and amino phases is similar to that of the parent silica and alumnia, whereas the cyanopropyl and nitrophenyl phases generally show less retention. 

Chemically bonded silica gels with cyanopropyl, aminopropyl, and diol functional groups are also available and each has been used for normal-phase as well as reversed-phase separations. Polymeric-based packings are available and can be used for ion-exchange or reversed-phase applications. Cross-linked polymeric based packings have been combined with ion-exchange materials to create a more pH-stable stationary phase. Graphitized carbon... 

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