Refractive index chromatogram

Lecacheux et al.240 have examined xanthan samples from various suppliers using SEC and refractive index detection coupled with on-line LALLS (Table 5, XCPS-2). Figure 13 shows LALLS and refractive index chromatograms... 

NMR mass chromatogram corresponds to a one-dimensional UV or refractive index chromatogram. The second peak consists of methyl methacrylate and ethyl acrylate, which is evident from the different chemical shifts provided from the on-line experiment. A clear differentiation is available from the chemical shift of the methyl group of both compounds. The chemical shift at 1.9 ppm indicates the methyl group at the double bond of methyl methacrylate, whereas the signal at 1.22 ppm is from the terminal methyl group of ethyl acrylate. Thus, the second dimension of the SFC-NMR run, provided by the H chemical shifts, enables the separation of co-eluting compounds. 

Figure 7.1. HPLC analysis of carbohydrates (simple sugars) in soft drink using resin column and refractive index detection. HPLC conditions column BioRad Aminex HPX-87C (300 x 7.8mmi.d.) injection volume 10 pL mobile phase water, flow rate 0.6mL/min at 85°C detection refractive index. Chromatogram courtesy of PerkinElmer, Inc.

Different liquid chromatography modes in polymer analysis were successfully interfaced with electrospray ionisation time-of-flight mass spectrometry in a single experimental set-up the mass spectrometry data from size exclusion chromatography/mass spectrometry of PMMA were used as absolute calibration points in the size exclusion chromatography/refractive index chromatogram, and monomer mass and end groups were inferred from the isotopically resolved mass spectra. 44 refs. 

The refractive index detector, in general, is a choice of last resort and is used for those applications where, for one reason or another, all other detectors are inappropriate or impractical. However, the detector has one particular area of application for which it is unique and that is in the separation and analysis of polymers. In general, for those polymers that contain more than six monomer units, the refractive index is directly proportional to the concentration of the polymer and is practically independent of the molecular weight. Thus, a quantitative analysis of a polymer mixture can be obtained by the simple normalization of the peak areas in the chromatogram, there being no need for the use of individual response factors. Some typical specifications for the refractive index detector are as follows ... 

Figure 13 Low-angle, light-scattering (LALLS) and refractive index (DRI) chromatograms for two xanthan samples. The xanthan samples were supplied by Shell (-...

Infrared spectra were recorded on a Perkin Elmer Model 567 Spectrophotometer. Ultraviolet spectra were obtained on a Cary 1756 Spectrophotometer. Gas chromatograms were recorded on a Tracor Model 220 with electron capture detector. High pressure liquid chromatography studies were conducted with a Waters Model ALC-200 with ultraviolet and refractive index detectors. 

Figure 2.10 Chromatograms of ( + )-trans-stilbene oxide. Conditions column, Chiralpak OP( + ), 25 cm x 4.6 mm i.d. eluent, methanol column temperature, ambient flow rate, 1 ml min -detector A, polarimeter B, refractive index.

Figure 6. Chromatograms of polydisparse dextran calihra-tion standard and dextran T-1 0 sample. Detector refractive index.

Figure 8. Gel permeation chromatograms with refractive index, UV 254, and photoconductivity detectors. Key top, 2 -chlorohiphenyl and bottom, decachlorobiphenyl.

The MOLWT-II program calculates the molecular weight of species in retention volume v(M(v)), where v is one of 256 equivalent volumes defined by a convenient data acquisition time which spans elution of the sample. I oment of the molecular weight distribution (e.g., Mz. Mw. Mn ) are calculated from summation across the chromatogram. Along with injected mass and chromatographic data, such as the flow rate and LALLS instruments constants, one needs to supply a value for the optical constant K (Equation la), and second virial coefficient Ag (Equation 1). The value of K was calculated for each of the samples after determination of the specific refractive index increment (dn/dc) for the sample in the appropriate solvent. Values of Ag were derived from off-line (static) determinations of Mw. 

Gel permeation chromatograms were generated from a Waters Associates, Inc. GPC equipped with a refractive index detector. The following operating conditions were employed mobile phase, THF flow rate 1 ml/min., columns ICP, 10, 500, 100 A . Sample concentrations were prepared at 0.2% (w/w) a 100 microliter aliquot was used for molecular weight analysis. Standard polystyrene samples (Polymer Laboratories, Inc.) were used to create a calibration curve. 

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]. 

In SEC the concentration by weight of polymer in the eluting solvent may be monitored continuously with a detector measuring refractive index, UV absorption, or infrared (IR) absorption [17]. The resulting chromatogram is therefore a weight distribution of the polymer as a function of retention volume, VR. 

The refractive index detector, considered to be almost universal, is often used in series with a UV detector in the isocratic mode to provide a supplementary chromatogram. This detector, which is not highly sensitive, has to be temperature controlled, as does the column (0.1 °C). The baseline of the chromatogram has to be set to an intermediate position because it can lead to either positive or negative signals (Fig. 3.18). The detector can only be used in the isocratic mode because in gradient elution the composition of the mobile phase changes with time, as does the refractive index. Compensation, which is easily obtained in the case of a mobile phase of constant composition, is difficult to carry out when the composition at the end of the column differs from that at the inlet. 

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.

Fig. 27, using an acetone/acetonitrile mobile phase and refractive index detection, the chromatogram in Fig. 28 appears remarkably similar for TGs of high retention times. However, peaks corresponding to the lower retention times appear to be enhanced, presumably due to the higher molar absorptivity of these species. 

Fig. 33 NARP-HPLC chromatogram of typical palm olein at room temperature (about 27°C) LaLaLa, lauric-lauric-lauric LaLaM, lauric-lauric-myristic MMLa, myristic-myristic-lauric MMM, myristic-myristic-myristic MPO, myristic-palmitic-oleic MPL, myristic-palmitic-linoleic PPO, palmitic-palmitic-oleic PPL, palmitic-palmitic-linoleic LLL, linoleic-linoleic-linoleic POS, palmitic-oleic-stearic POO, palmitic-oleic-oleic PLO, palmitic-linoleic-oleic OOS, oleic-oleic-stearic SOS, stearic-oleic-stearic SLS, stearic-linoleic-stearic OOO, oleic-oleic-oleic and OOL, oleic-oleic-linoleic. R.I.D., refractive index detector.

Fig. 3 Chromatogram of a red wine using Shodex S-801/S and S-802/S columns at 75°C with a mobile phase of water at a flow-rate of 1 ml/min and using a refraction index detector. Peaks A = compounds with the highest molecular mass and with an acid character 1 = glucose 2 = fructose 3 = glycerol 4 = butan-2,3-diol (= 0.8 g/L added to the initial wine) 5 = ethanol. (Reprinted from Ref. 30 with the kind permission of Elsevier Science—NL, Sara Burgerhartstraat 25, 1055 KV Amsterdam, The Netherlands.)...

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