Silica base-deactivated

Eor the selective pre-concentration of deactivated phenols a new silica-based material with the grafted 2,3,5-triphenyltetrazole was proposed. This method is based on the formation of molecular chai ge-transfer comlexes of 2,3,5-triphenyltetrazole (7t-acceptor) with picric acid (7t-donor) in the phase of the sorbent. Proposed SPE is suitable for HPEC analysis of nitrophenols after their desorption by acetonitrile. Test-system for visual monitoring of polynitrophenols under their maximum concentration limits was developed using the proposed adsorbent. 

Feibush, B., A new chemically deactivated silica-based reversed phase/ion exchange support, /. Liq. Chromatogr. Relat. Technol, 19(14), 2315, 1996. 

Chepkwony, H., Vanderriest, I., Nguyo, ]., Roets, E., and Hoogmartens, J., Separation of erythromycin and related substances on base-deactivated re-versed-phase silica gel columns, /. Chromatogr. A, 870 (1 2), 227, 2000. 

Imazalil, OPP, and TBZ residues were determined using an HPLC system, consisting of a ternary HPLC pump attached to 250 X 4.6-mm-ID Hichrom RPB 5-/tm column with a 10 X 3.2-mm-ID guard cartridge column. The packing material of both columns was base-deactivated silica, fully endcapped with a bonded phase of Cg/C]8. The mobile phase was methanol/water at a flow rate of 1 ml/min at ambient temperature. Imazalil in the eluate was detected with UV detector at 204 nm a fluorescence detector was used to monitor OPP (excitation 285 nm, emission 350 nm) and TBZ (excitation 296 nm, emission 350 nm) (47). 

Chromatographic column a stainless steel column, 0.25 m long and 4.6 mm internal diameter, packed with base-deactivated octadecylsilyl silica for chromatography R (5 pm particles). The column is maintained at a temperature of 40°C. 

A column consisting of a deactivated silica-based stationary phase is used for the packed-column mode. A packed column allows larger volumes of sample solvent to be injected, thus improving sensitivity. Generally, the column dimensions are 1 x 100-250 mm and the particle size is 5 / m. Commercial SFC instruments are also available that will handle the classical 4.6 x 150-mm or 250-mm columns. With the introduction of electronically controlled variable restrictors to control the back pressure, the packed columns are becoming increasingly more popular. This feature allows the independent flow and pressure control of mobile phases, thus helping in rapid optimization of selectivities. Some of the commonly used packed columns are as follows ... 

We have developed a more efficient method of the silica surface deactivation, based on the liquid phase modification by organosilicon olygomers [35]. The main advantage of this method is that a layer of chemisorbed and sewed together molecules of the hydrophobizer is formed on the surface. This layer not only neutralizes the active OH groups of silica surface, but also covers the surface with the continuous film, making other active ad-sorption-catalytic sites (like coordinately unsaturated Al + or Fe ions) to be sterically inaccessible. The thickness of this layer on silica surface was estimated in [36] to be of about 2 nm. 

Guard column 20 X 4.6 C18 base-deactivated silica (BDS) (Keystone)... 

BDS Base Deactivated Silica, (not activated = suitable for bases)... 

Very recently, Stobo et al. proposed a multiple LC-MS method that allows the detection of YTX together with most of the DSP toxins. The method was set up on a triple quadrupole spectrometer. Chromatographic separation of multiple lipophilic toxins was achieved by using a base deactivated silica C8 column eluted with a 5 mM ammonium acetate-acetonitrile mobile phase under gradient conditions. The method was applied to the analysis of sheUflsh and was validated for the quantitative detection of OA, YTX, PTX-2, and Azaspiracid-1 (AZA-1). 

Table 5 lists two lines of commercially available silica-based gel permeation columns. The selection was limited to the Zorbax and LiChrospher silicas because these materials were specifically developed for gel permeation chromatography. Zorbax silica has a 6 pm particle size for optimum efficiency. The pore sizes were chosen such that a linear calibration curve is obtained when coupling columns of different pore sizes. In addition to plain silicas, Zorbax silicas are also available derivatized with trimethylchlorosilane, providing a surface that is less adsorptive for certain organic soluble polymers. Several important water-soluble industrial polymers, such as polyacrylamide, polyacrylic acid, and polyvinyl alcohol, do not require deactivation of the silica surface to obtain ideal size exclusion behavior. LiChrospher silicas are 10 pm in size they vary in pore size from 100 to 4000 A to allow the separation of very large polymers. 

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