Detectors light scattering

Herslof and Kindmark (105) report the use of the mass detector (light-scattering detector) in this sense. The column used (250 X 4.6-mm ID) was packed with LICHROSPHER RP 100 and thermostated at 22°C. The mass detector oven temperature was 40°C, and the inlet gas pressure was 15 psi. The mobile phase consisted of mixtures of acetonitrile, ethanol, and hexane. Gradients from 0 to 100 of ternary premixtures of the three solvents were used at a flow rate of 1 ml/ min. The sample was dissolved in hexane-isopropanol (1 1), and 12 /A were injected (approx. 150 fj.g total sample). The chromatogram of the standard mixture of TGs is shown in Fig. 35. The separations of soybean oil and a mixture of soybean and coconut oils illustrate the resolution of vegetable oils into TG species (Fig. 36). 

U var possibly as DAD, is still the detector in HPLC. Again, on the top ten list, there is a huge gap before the fluorescence detector, again a gap and then the electrochemical detector, light scattering and FTIR. In carbohydrate, mineral oil and polymer analysis, the RI detector is still widely used. 

This situation also results in the imcertainty of characterization of stmcture of porous bodies with help of SEC designated inverse SEC . In other words, SEC is a relative, non-absolute method. Each column (or column system) must be calibrated, or molar mass of species leaving column must be monitored by special absolute detectors (light scattering measuring devices, viscometers, mass spectrometers, and so on (see sections 11.6.1.4and 11.7.3.2). 

Molar mass-sensitive detector (light scattering, viscometry, MS) + concentration detector (Rl, UV/DAD)... 

The two complicating factors that are encountered most frequently are the linearity of detector response and stray light scattering at low signal levels. DTGS... 

Select the detector. To acquire molecular weight distribution data, use a general detector such as a refractive index detector. To acquire structural or compositional information, employ a more selective detector such as an ultraviolet (UV) or infrared (IR) detector. Viscometric and light-scattering detectors facilitate more accurate molecular weight measurement when appropriate standards are not available. 

FIGURE 6.4 Comparison of Shodex GPC UT column and conventional-type column. Column Left Shodex GPC UT-806M X 2, 8 mm i.d. X 300 mm X 2. Right Conventional type column X 2, 7.8 mm i.d. X 300 mm x 2. Eluent 0.1% BHT in ODCB. Flow rate 1.0 mL/min. Detector Rl, MALLS (multi-angle laser light scattering detector). Column temp. I45°C. Sample High-density polyethylene. 

FIGURE 6.39 Hydroxyethyl cellulose. Column Left Shodex OHpak SB-806 HQ, 8.0 mm i.d. x 300 mm. Right Shodex Asahipak GF-710 HQ, 7.6 mm i.d. x 300 mm. Eluent 100 mA1 NaNOj. Flow rate 1.0 mL/min. Detector Multi-angle laser light scattering detector. Column temp. 40°C. Sample 0.05%, 200 /iL, Hydroxyethyl cellulose. 

FIGURE 12,3 Separation of polyester oligomers, 2 X PLgel 3 jum MIXED-E 300 X 7.5 mm, eluent THE at 1.0 ml/min, evaporative light scattering detector... 

Waters 410 16x, 20/Fitted with a PD2000 Light-scattering Detector 90°... 

The latest trend is to smaller beads in smaller columns, as this saves eluent and shortens the time for a chromatographic analysis. This argument can be correct if only one suitable detector is used. However, these modern small columns are not optimal for a combination of detectors. So-called multiple detection is a combination of some detectors with different measurement principles (differential refractometer, spectral photometer, light-scattering detector, on-line viscometer) behind the last column, mostly in series, seldom in a branched ( parallel ) order. In this way, the tedious preparative fractionation of a polymer sample can often be avoided. 

These combined HDF and GPC separations require the use of detectors such as static light scattering or viscometers to help sort out the convoluted elution profiles seen in those type of experiments. It should also be remembered in these situations that the typical refractive index or ultraviolet detector responses may not be representative of the actual mass fraction of insolubles eluting from the column because of the significant light scattering that can occur with those large particles in the detector cell. 

Detectors Model 410 differential refractive index (Waters Corporation) Model 100 differential viscometer (Viscotek Corporation) Dawn-F multiangle laser light-scattering photometer (Wyatt Technology)... 

A convenient way to examine the light-scattering response from each angle of detection (detector signal versus elution volume) is shown in Fig. 20.5 for a fully hydrolyzed PVA. The chromatograms from all 15 angles of detection from a Dawn-F (Wyatt Technology Corporation, Santa Barbara, CA) are... 

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