Octadecyl bonded phase

Octadecyl-bonded phases Copper silicate gel Cyclodextrin-bonded phases Hydroxyapatite-covered silica Graphitized carbon... 

OS Si-O-Si-C Octyl, n-C8 Bonded, reverse Octylsilane lower resolution than the octadecyl bonded phase useful when separations involve... 

A recent modification of the atmospheric pressure ionization technique involving a special low dead volume interface was described by Thomson etal. [27]. They employed packed microbore columns (170 p, 320 p, and 500 p I. D. with lengths ranging from 5 to 15 cm) in conjunction with a low-volume, wall-coated capillary column as an interface. The total ion current chromatogram of the tryptic digest sample of about 1 picomole of human growth hormone is shown in figure 29. The column was packed with an octadecyl bonded phase... 

Goldberg compared several types of octadecyl columns for their retention of neutral, acidic and basic compounds. Vastly differing chromatographic properties were found. A more extended study of the diversity of octadecyl bonded phases was made by Engelhardt et al. 1. The suitability of the various materials for the analysis of basic compounds is also taken... 

Phillipson et al.77 compared the retention behaviour of nine heteroyohimbine and eight oxindole alkaloids on an octadecyl bonded phase with previously obtained results on straight--phase TLC (Table 8.1). If the retention on silica gel could be explained in terms of the availability of the N-4 lone-pair electrons, such a correlation could not be concluded for the retention in the reversed-phase system. 

Normal-phase chromatography used an amino bonded-phase column (Du Pont Zorbax, 25- X 0.48-cm i.d., 5-p,m spherical particle size) n-hexane and dichloromethane mixtures were used as the mobile phases. Reverse-phase separations used an octadecyl bonded-phase column (Vydac 201TP5, 25- X 0.46-cm i.d. for analytical scale, and 25- X 0.94-cm i.d. for preparative scale, both with 5-p,m spherical particles, Separations Group) methanol and dichloromethane were the mobile phases. As in previous work (5-7, 9), the concentration of strong solvent in the mobile phase was varied from 0% to 100% for reverse-phase studies and from 0% to 30% for normal-phase studies. The peaks isolated from preparative-scale runs were further purified by separation on the analytical-scale octadecyl bonded-phase column. 

I thank C. E. Rechsteiner for the field-ionization mass spectra of the new PAHs and P. Shah and L. B. Rogers (Department of Chemistry, University of Georgia, Athens, GA) for the NMR data on the octadecyl bonded-phase (Vydac) packing. I also thank Chevron Research Company for permission to publish this work. 

RPIP chromatography uses a hydrocarbonaceous stationary phase and either an aqueous or aqueous-organic mobile phase which also contains the counter-ion. The stationary phase is usually an octadecyl bonded phase and the mobile phase is usually an aqueous buffer with either methanol or acetonitrile as an organic modifier. The choice of counter-ions depends on the solutes to be separated, but generally for the separation of acids a hydrophobic organic base is added to the mobile phase, while for the separation of bases a hydrophobic organic acid is added. Separations of other compounds are similarly obtained by the addition of an appropriate counter-ion. 

Conclusion. In conclusion, a simple, rapid set of GC methods based upon hydrofluoric acid digestion and either hexane extraction or head space analysis have been developed which will allow any laboratory equipped with a GC to Identify and quantify the primary ligands and end-capping species present on the most widely used reversed-phase packing materials, l.e., octyl and octadecyl bonded phases. The method has been confirmed against elemental analysis. 

Berthod studied the adsorption of SDS on five different Hypersil stationary phases [11]. Five 10 cm x 4.6 mm i.d. LC columns were specially selected for the study. All experiments were done in a thermostatic bath at 30°C. The amount of SDS adsorbed on the phases was determined by crosschecking the results obtained with (i) the breakthrough method, (ii) controlling the concentration of the effluent solution, and (iii) by the stripping method. The 3 results were in agreement within an 8% experimental error. Figure 4.2 presents the SDS adsorption on bare Hypersil , CPS Hypersil , a cyanopropyl bonded phase, SAS Hypersil , a methyl bonded phase, MOS Hypersil , an octyl bonded phase and ODS Hypersil , an octadecyl bonded phase. The physicochemical properties of these phases are listed in Table 4.1. A very differing behavior was obtained... 

The analysis of mycotoxins, toxic substances produced by some fungi, is essential to guaranteeing the safety of foods such as cereals, nuts, oilseeds, and spices since the discovery of their significance to human health. The main mycotoxins, like aflatoxins and ochratoxin A, are determined using HPLC with octyl-or octadecyl-bonded phases and polar solvents such as methanol, acetonitrile, and water. For detection with the required sensitivity and selectivity, spectrofluori-metric detection is the most common method, with increasing use of mass spectrometric interfaces. 

For further discussion of the R groups see octadecyl bonded phase. 

The side groups R and R are commonly methyl groups but can also be more bulky alkanes (e.g., isopropyl). The identification of these groups is often omitted in the description of the bonded phase, hence, octadecyl-bonded phase and not dimethyloctadecyl-bonded phase. In other instances, the R groups can be reactive fimctional groups such as —OH. These groups are used as points from which to make polymerized supports or are unmodified to add polarity to the surface. 

---