Differential refractive index detector

Detectors Differential refractive index (Waters), Mini-Dawn multiangle laser lightscattering photometer (Wyatt Technology) ... 

RID Refractive index detector Differential refractive index... 

Degassed and preswelled Bio-Gel P-6 and Sephacryl S-200 were packed in self-made glass columns (70 X 1.5 cm 140 X 1.5 cm) and equilibrated for 20 hr with H20(dest.) -t- 0.002% NaN3 to prevent microbial growth. The mass of eluted fractions was detected with a differential refractive index detector (Waters 403 RI, sensitivity 8). 

FIGURE 16.23 Inulln isolated from small (—). medium ( ) and large (A) tubers separated on P-6 (140 X 1.5 cm) flow rate 0.33 ml/min eluenf. H20(dest) + 0.002% NaNa mass detection Waters 403 R differential refractive index detector, sensitivity 8X applied sample solution volume I ml of a 20-mg/ml aqueous inulin solution. 

Synthetic, nonionic polymers generally elute with little or no adsorption on TSK-PW columns. Characterization of these polymers has been demonstrated successfully using four types of on-line detectors. These include differential refractive index (DRI), differential viscometry (DV), FALLS, and MALLS detection (4-8). Absolute molecular weight, root mean square (RMS) radius of gyration, conformational coefficients, and intrinsic viscosity distributions have... 

Detection is also frequently a key issue in polymer analysis, so much so that a section below is devoted to detectors. Only two detectors, the ultra-violet-visible spectrophotometer (UV-VIS) and the differential refractive index (DRI), are commonly in use as concentration-sensitive detectors in GPC. Many of the common polymer solvents absorb in the UV, so UV detection is the exception rather than the rule. Refractive index detectors have improved markedly in the last decade, but the limit of detection remains a common problem. Also, it is quite common that one component may have a positive RI response, while a second has a zero or negative response. This can be particularly problematic in co-polymer analysis. Although such problems can often be solved by changing or blending solvents, a third detector, the evaporative light-scattering detector, has found some favor. 

Differential refractive index detectors measure the difference in refractive index between the solvent and the eluting polymer solution. The DRI can be used with almost any polymer-solvent combination, as long as the incremental increase in refractive index of the polymer solution with increase in polymer concentration is sufficient. Although a large number of differential refractometers are available in the market,167168 they usually conform to three main types, namely... 

Gel permeation chromatography was performed in tetrahydrofuran using a Waters pump system and a Model 410 differential refractive index detector for the eluant. Five Ultrastyragel columns with nominal porosities ranging from 500 to 105 angstroms were used for all the samples and the polystyrene standards. 

GPC analyses were performed with a Waters Model 244 chromatograph using Microstyragel columns. Both differential refractive index and UV (254 nm) detectors were used. THF was the eluant with a flow rate of 2 ml min-1. A benzene internal standard was employed to correct for flow variations and for normalization of the integrated peak areas. The column set was calibrated using nearly monodispersed polystyrene standards and all molecular data are reported as polystyrene-equivalent molecular weights. 

The FALLS or MALLS detector measures r-related values a differential refractive index (DRI) detector is used to measure concentration, and the SEC supplies samples containing fractionated polymer solutions allowing both molecular weight and MWD to be determined. Further, polymer shape can be determined. This combination represents the most powerful one, based on ease of operation, variety of samples readily used, cost, means to determine polymer size, shape, and MWD available today. 

The use of multidetector GPC greatly increases the power of SEC, particularly in the case of copolymers. For copolymers of styrene-maleic anhydride (SMA), not only can the molecular weight distribution be determined, using a differential refractive index (DRI) detector, but also the compositional information of SMA (styrene content or acid number) by combining chromatograms from DRI and UV detectors [9]. 

Figure 3.18—Example of a differential refractive index detector. Opticalpath through the cell. Control of the position of the refracted beam is obtained with a dual stage photodiode. Chromatogram of a mixture of sugars obtained with this type of detector.

Procedure Use a liquid chromatograph equipped with a differential refractive index detector and a 20-cm x 10-mm (id) column (Phenomenex Rezex 4% silver oligosaccharide, or equivalent). Maintain the column at 80° and the Mobile Phase flow rate at 0.3 mL/min. 

Separately inject about 50-p.L portions of the Assay Solution and Standard Solutions into the chromatograph, record the chromatograms, and measure the responses for the major peaks. The elution order for the standards is maltose, maltitol, dextrose, and sorbitol. The differential refractive index detector should show similar response factors. 

Gel Permeation Chromatography - The GPC data were obtained in dimethylformamide solution using a Waters Associates Model 100 GPC equipped with a differential refractive index detector and five Styragel columns having he following nominal exclusion limit designations 10 10 A, 10 A, 3 x 10 A,... 

The combination of the differential refractive index (RI) detector and on-line viscometer allows the direct use of the universal calibration and thus true molecular weight determination. The RI detector is concentration-sensitive, and the viscometer records specific viscosity. The ratio of the specihc viscosity to the concentration is equivalent to intrinsic viscosity (as discussed in Section 6.1), and the continuous dependence of this ratio versus the retention volume could be related to the universal calibration curve, thus allowing the correlation of each point on the chromatogram with the true molecular weight. 

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