Silica columns samples

Figure 14.20 Comparison between an experimental overloaded elution profile (symbols) and the profiles calculated with the anti-Langmuir isotherm and the FOR and the ED models. Butyl-benzene on a monolithic Cig silica column. Sample concentration, 6.0 g/L injection volume,...

For most samples liquid-solid chromatography does not offer any special advantages over liquid-liquid chromatography (LLC). One exception is for the analysis of isomers, where LLC excels. Figure 12.32 shows a typical LSC separation of two amphetamines on a silica column using an 80 20 mixture of methylene chloride and methanol containing 1% NH4OH as a mobile phase. Nonpolar stationary phases, such as charcoal-based absorbents, also may be used. 

Let us consider the separation of polymethylmethacrylate (PMMA) on a nonmodified silica column as an example. In THE (medium polar eluent) the PMMA eludes in size exclusion mode because the dipoles of the methylmethacrylate (MMA) are masked by the dipoles of the THE. Using the nonpolar toluene as the eluent on the same column, the separation is governed by adsorption because the dipoles of the carbonyl group in the PMMA will interact with the dipoles on the surface of the stationary phase. The separation of PMMA in the critical mode of adsorption can be achieved by selecting an appropriate THF/toluene mixture as the eluent. In this case all PMMA samples... 

Figure 12.8 Mia ocolumn size exclusion chromatogram of a styrene-aaylonitrile copolymer sample fractions ti ansfeired to the pyrolysis system are indicated 1-6. Conditions fused-silica column (50 cm X 250 p.m i.d.) packed with Zorbax PSM-1000 (7p.m 4f) eluent, THF flow rate, 2.0 p.L/min detector, Jasco Uvidec V at 220 nm injection size, 20 nL. Reprinted from Analytical Chemistry, 61, H. J. Cortes et al, Multidimensional chromatography using on-line microcolumn liquid chromatography and pyrolysis gas chromatography for polymer characterization , pp. 961 -965, copyright 1989, with peimission from the American Chemical Society.

Figure 12.10 Microcolumn SEC-LC analysis of an acrylonitrile-butadiene-styrene (ABS) teipolymer sample (a) SEC ti ace (b) EC ti ace. SEC conditions fused-silica column (30 cm X 250 mm i.d.) packed with PL-GEL (50 A pore size, 5 mm particle diameter) eluent, THE at a flow rate of 2.0 mL/min injection size, 200 nL UV detection at 254 nm x represents the polymer additive fraction (6 p-L) tr ansferred to EC system. EC conditions NovaPak CIS Column (15 cm X 4.6 mm i.d.) eluent, acetonitrile-water (60 40) to (95 5) in 15 min gradient flow rate of 1.5 mL/min detection at 214 nm. Peaks identification is follows 1, styrene-acrylonitrile 2, styrene 3, benzylbutyl phthalate 4, nonylphenol isomers 5, Vanox 2246 6, Topanol 7, unknown 8, Tinuvin 328 9, Irganox 1076 10, unknown. Reprinted with permission from Ref. (14).

The preseparation utilized a 5 pim cyano column (250 cm X 4.6 mm i.d.) and a 5 p.m silica column (250 cm X 4.6 mm i.d.) in series, followed by GC analysis on an SE-54 column (25 m X 0.2 mm i.d., 0.33 p.m film thickness). The SFC system separated the aviation sample into two peaks, including saturates and single-ring aromatics as the first peak, and two-ring aromatic fractions as the second peak. These fractions were selectively cut and then transferred to the GC unit for further analysis. (Figure 12.20). 

Zebiihr et al. (29) developed an automated system for determining PAHs, PCBs and PCDD/Fs by using an aminopropyl silica column coupled to a porous graphitic carbon column. This method gives five fractions, i.e. aliphatic and monoaromatic hydrocarbons, polycyclic aromatic hydrocarbons, PCBs with two or more ortho-chlorines, mono-ort/io PCBs, and non-ortho PCBs and PCDD/Fs. This method employed five switching valves and was successfully used with extracts of sediments, biological samples and electrostatic filter precipitates. 

Fig. 4. HPHIC of standard proteins on the weak hydrophobic columns. The SynChro-pack PROPYL column was 25x0.41 cm Poly (alkyl aspartamid)-silicas were packed into 20 x 0.46 cm columns. Sample 25 pi containing 25 pg of each protein in buffer A. Buffer A 1.8 mol/1 ammonium sulphate + 0.1 mol/1 potassium phosphate, pH 7.0. Buffer B 0.1 mol/1 potassium phosphate, pH 7.0. Gradient 40-min linear 0-100% buffer B. Flow rate 1 ml/min. Detection A220 = 1-28 a.u.f.s. Peaks a = cytochrome C, b = ribonu-clease A, c = myoglobin, d = conalbumin, e = neochymotrypsin, / = a-chymotrypsin, g - a-chymotrypsinogen A [48]...

Fig. 10. HPLC of proteins (commercial samples) on the /V-butyl polyacrylamide coated silica gel column. Sample 20 pi of 5-15 mg/ml protein solution in buffer A. Buffer A 10% methanol, 0.2 mol/1 ammonium acetate, pH 4.5. Buffer B methanol. Gradient 50-min linear, 0-100% B. Flow rate 0.8 ml/min. Peaks (/) — lysozym, (2,3) — insulin, (4,5) — myoglobin [57]...

Liver Addition of water to sample followed by homogenization extraction with benzene, clean-up on silica column and HPLC GC/ECD No data No data Demeter and Heyndrickx 1979... 

The catalyst testing was carried out in a gas phase downflow stainless steel tubular reactor with on-line gas analysis using a Model 5890 Hewlett-Packard gas chromatograph (GC) equipped with heated in-line automated Valeo sampling valves and a CP-sD 5 or CP-sil 13 capillary WCOT colunm. GC/MS analyses of condensable products, especially with respect to O-isotopic distribution, was also carried out using a CP-sil 13 capillary column. For analysis of chiral compounds, a Chirasil-CD capillary fused silica column was employed. 

Figure 7. GPC analysis of (A) 312-nm Dow latex sample SE Dupont silica columns—(a) response at 254-nm wavelength (full scale 0.5 A) (b) response at 340-nm wavelength (full scale 0.02 A) (B) 220-nm Dow latex sample E-Linear Watefs silica columns—response at 254-nm wavelength (full scale 0.5 A) (C) 98-nm Polysciences latex sample E-Linear WatePs silica columns—response at 254-nm wavelength (full scale 0.5 A) (D) 183-nm Polysciences latex sample E-Linear Water s silica columns—response at 254-nm wavelength (full scale 0.5 A)...

Cleanup of highly colored samples (e.g., mustard greens) on silica columns may require that only half of the sample extract be passed through the silica columu. 

A polyethylene-coated (PEE) silica column was used with water-methanol eluents to achieve the separation and retention of 27 pesticides.40 The retention times of 33 commercial pesticides were determined on an octadecyl (ODS)-derivatized alumina column using water-methanol eluents and compared with retention properties on an ODS-silica column packing.41 More recently, RP-HPLC was used in combination with diode array detection for the identification and quantification of 77 pesticides (acidic, basic, and neutral) in groundwater samples.42... 

Fig. 3.4f shows an exclusion chromatogram on unmodified silica. The sample is an epoxy resin with an average Mr of 900. Fig. 3.4g shows the determination of pesticide residues in a sample of chicken fat, and is an example of how exclusion can be used to clean up complex samples. First, a pesticide-free sample of the fat is run as a blank, then the blank is spiked with the pesticides to determine their retention volumes. When the sample is injected, the eluent containing the pesticides is collected. The solvent is evaporated, the residue dissolved in acetonitrile and the pesticides are then separated on a reverse phase column. 

Simple and comprehensive 2D HPLC was reported in a reversed-phase mode using monolithic silica columns for the 2nd-D separation (Tanaka et al., 2004). Every fraction from the lst-D column, 15cm long (4.6 mm i.d.), packed with fluoroalkylsilyl-bonded (FR) silica particles (5 pm), was subjected to the separation in the 2nd-D using one or two octadecylsilylated (Cig) monolithic silica columns (4.6 mm i.d., 3 cm). Monolithic silica columns in the 2nd-D were eluted at a flow rate of up to lOmL/min with separation time of 30 s that provides fractionation every 15-30s for the lst-D, which is operated near the optimum flow rate of 0.4-0.8 mL/min. The 2D-HPLC systems were assembled, as shown in Fig. 7.6, so that the sample loops of the 2nd-D injectors were back flushed to minimize band broadening. 

Haglund, P., L. Asplund, U. Jamberg, and B. Jansson. 1990. Isolation of mono- and n o n -o rt ho - po I ych I o ri n atcd biphenyls from biological samples by electron donor acceptor high performance liquid chromatography using a 2-(l-pyrenyl)ethyldimethylsilylated silica column. Chemosphere 20 887-894. 

Cation-exchange resin and C g-bonded silica columns have lower sample capacities than amine-modihed silica-gel columns, but they are more robust, do not covalently interact with sample components, and can be eluted with pure water at low flow-rates. Water is an ideal mobile-phase, because of low cost, solute solubility, and ability to be completely removed from collected samples by evaporation. All mobile phases should have these characteristics—including buffers, which should contain volatile components. ... 

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