Octadecyl silane

Ito et al. [175] used this technique employing octadecyl silane reverse phase columns coated with cetyltrimethyl ammonium chloride for the determination of nitrite and nitrate in seawater. 

Reverse phase HPLC describes methods that utilize a polar mobile phase in combination with a nonpolar stationary phase. As stated above, the nonpolar stationary phase structure is a bonded phase—a structure that is chemically bonded to the silica particles. Here, typical column names often have the carbon number designation indicating the length of a carbon chain to which the nonpolar nature is attributed. Typical designations are C8, C18 (or ODS, meaning octadecyl silane), etc. Common mobile phase liquids are water, methanol, acetonitrile (CH3CN), and acetic acid buffered solutions. 

ECD = electron capture detector GC = gas chromatography IC/SP = ion chromatography/sulfopropyl type column ODS = octadecyl silane... 

These bonded phases are found to be fairly stable between the pH range 2 to 9 and upto temperatures of about 80 °C. The nature of the R group of the silane solely determines the surface polarity of the bonded phase. A fairly common bonded phase is made with a linear C18 hydrocarbon, also known as ODS (octadecyl silane) bonded phases, wherein the groups appear to be protruding out from the silica particle surface just as the bristles on a toothbrush. It takes care of almost 75% of the samples in HPLC. 

The most widely used support substance for the manufacture of packing materials in analytical HPLC columns is silica. Silica can be treated with organochlorosilanes or similar reagents to produce siloxane linkages of any derived polarity similar to what is done for GC columns (stationary phases). The most popular materials are octadecyl silane (ODS), which contains a carbon loading of CIS groups and octyl, which contains C8 groups materials such C2, C6, and C22 are also available. 

HPLC water/ acetonitrile Octadecyl-silane (ODS) (250x10mm) Plumeria acutifolia / leaves methanol extract 15-demethylplumieride [71]... 

The column, filled with 100 mg of octadecyl silane (ODS-3,10.5% carbon load, end capped), is preconditioned with 1 ml of methanol and 2 ml of water. The SPE column is washed with 500 pi of a solution of 5 mM potassium dihydrogenphosphate, 10% (v/v) of methanol. Analytes are eluted with 300 pi of methanol and centrifuged at... 

Cl8 cartridge (with C 8 sorbent bonded on silica C18 Sep-Pak Cartidge (360 mg sorbent), Waters Chromotography ODS-4 Octadecyl Silane (500 mg sorbent), Whatman or equivalent)... 

The following table provides, for comparative purposes, eluotropic values on bonded octadecyl silane (ODS) and octyl silane (OS) for common solvents.12... 

The liquid chromatograph is equipped with a 210-nm detector and a 4.6-mm x 25-cm column containing packing LI (octadecyl silane chemically bonded to porous silica or ceramic 3-10 pm microparticles). The flow rate is about 2 mL/min, and the column temperature is maintained at 40°C. 

Chromatographic System The HPLC system is equipped with a 240-nm detector and a 4.6-mm 25-cm column that contains packing LI (octadecyl silane bound to porous silica particles). The flow rate is about 0.8 mL/min. System Suitability Chromatograph the Standard Preparation, and record the peak responses as directed in the Procedure section. The relative retention times are about 0.8 for benzoylformic acid, 1.0 for mandelic acid, 2.5 for benzoic acid, 2.8 for benzaldehyde, and 3.7 for acetophenone. The tailing factor for each peak is not more than 2.0. The resolution between the benzoylformic acid peak and the mandelic acid peak, and between the benzoic acid peak and the benzaldehyde peak, is not less than 3.0. The relative standard deviation for replicate injections is not more than 1% for the mandelic acid peak. 

Chromatographic System (See Chromatography, Appendix IIA.) Use a suitable high-performance liquid chromatograph equipped with a detector measuring at 210 nm and a 250- x 4.6-mm (id) column packed with octadecyl silanized silica (10-p.m Partisil ODS-3, or equivalent), and operated under isocratic conditions at 40°. The flow rate of the Mobile Phase is about 2 mL/min. 

Procedure (See Chromatography, Appendix IIA.) Use a high-performance liquid chromatograph equipped with an ultraviolet detector that measures absorption at 254 nm and a 25- to 30-cm x 4-mm (id) stainless-steel column, or equivalent, packed with octadecyl silane chemically bonded to porous silica or ceramic microparticles 5 to 10 pun in diameter, or equivalent. Maintain the mobile phase at a pressure and flow rate capable of giving the required resolution (see below). Inject a volume, up to 25 pL, of the System Suitability Solution in a similar manner. Calculate the resolution, R (>3.6), between calcium formyltetrahydrofolate and Folic Acid by the equation... 

Stationary phases for modern, reversed-phase liquid chromatography typically consist of an organic phase chemically bound to silica or other materials. Particles are usually 3, 5, or 10 p,m in diameter, but sizes may range up to 50 p,m for preparative columns. Small particles thinly coated with organic phase allow fast mass transfer and, hence, rapid transfer of compounds between the stationary and mobile phases. Column polarity depends on the polarity of the bound functional groups, which range from relatively nonpolar octadecyl silane to very polar nitrile groups. 

J. Dai, X. Yang, and P. W. Carr, Comparison of chromatography of octadecyl silane bonded silica and polybntadiene-coated zirconia phases based on diverse set of cationic dmgs, J. Chromatogr. A 1005 (2003), 63-82. 

To prove this concept, a set of nanombes were prepared with the green fluorescent silane 7/-(triethoxysilylpropyl)dansyl-amide attached to their inner surfaces, and the hydrophobic octadecyl silane (Cig) to their outer surfaces. These nanombes were added to a vial containing water and the immiscible organic solvent cyclohexane, which were mixed and allowed to separate. Because these nanombes are hydrophobic on their outer surfaces, they partition into the (upper) cyclohexane phase (Figure 24.3B). This may be in contrast to nanombes that were labeled on their inner surfaces with the blue fluorescent silane triethoxysUyl-propylquinineurethan, but were not labeled with any silane on their outer surfaces. When the same experiment is done on these... 

The drug substance is separated from its related substances using a Octadecyl silane column (4 mm ID x 300 mm, 10 pm particle size) and a mobile phase consisting of water, acetonitrile, methanol and acetic acid (650 175 175 1, v/v) at a flow rate of 2.0 mL/minute. Detection of the analytes is achieved at ambient temperafure using UV absorbance at 254 nm. The standard and sample solutions are prepared in a diluent consisting of mobile phase and 5 pL are injected onto the column. All related substances are eluted within 30 minutes and may also be quantitated. The retention time of indapamide is approximately 15 minutes. 

The assay of finished product tablets is accomplished with an HPLC method. The method employs a Octadecyl silane 100 x A.6 mm i.d. column (3 pm particle size) with a mobile phase consisting of 1.08 g octane sulfonic acid, sodium salt in 700 mL of water, 10 mL of glacial acetic acid and 300 mL of acetonitrile. The flow rate is 1.0 mL/minute with UV absorbance detection at 242 nm. 

Figure 33-2 shows plots of plate heights // as a function of average linear velocity u in cm/s for high-performance liquid chromatography and supercritical-fluid chromatography. In both cases, the solute was pyrene, and the stationary phase was a reversed-phase octadecyl silane maintained at 40°C. The mobile phase for HPLC was acetonitrile and water, while for SFC the mobile phase was carbon dioxide. These conditions yielded about the same retention factor (k) for both mobile phases. Note that the minimum in plate height occurred at a flow rate of 0.13 cm/s... 

In this situation, shown in Figure 19-4, the reactive surface of the particle is changed to a nonpolar compound and it is chemically bonded to the -OH group so it cannot be stripped off. A common system is octadecyl silane (ODS). One way to attach these bonded phases is shown on page 184. 

Fig. 2.4. Surface groups used for stationary phases in reversed phase chromatography range from ethyl silane (C2) to n-octadecyl silane (Cig).

Early work in SFC was carried out using absorbants such as alumina or silica, or stationary phases insoluble in supercritical CO2, such as polyethylene glycol. Now, bonded non-extractable stationary phases such as octadecyl-silane and aminopropyl-bonded silicas, are usually used in packed columns. 

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