Refractive index units

Deviation refractometers are the most commonly used. This version of the DRI measures the deflection in the location of a light beam on the surface of a photodiode by the difference in refractive index between the polymer solution and pure solvent. The Fresnel-type refractometers operate on the principle that the intensity of light reflected from a glass-liquid interface is dependent on the incident angle and the RI difference between the two phases. The deviation and Fresnel detectors typically have cell volumes of 5 to 10 pi, detection limits of about 5 x 10-6 refractive index units (RIU), and a range of 10 7 to 10 3 RIU.156 The deflection-type DRI is relatively insensitive to the buildup of contaminants on the sample cell and is therefore of special utility in laboratories that process large numbers of samples, such as industrial laboratories. 

Refractive index detectors are not as sensitive as uv absorbance detectors. The best noise levels obtainable are about 1CT7 riu (refractive index units), which corresponds to a noise equivalent concentration of about 10-6 g cmT3 for most solutes. The linear range of most ri detectors is about 104. If you want to operate them at their highest sensitivity you have to have very good control of the temperature of the instrument and of the composition of the mobile phase. Because of their sensitivity to mobile phase composition it is very difficult to do gradient elution work, and they are generally held to be unsuitable for this purpose. 

As a preliminary test, the experimental setup just described was used to characterize the bare LPG. In Fig. 3.15 it is reported that the central wavelength and the transmission loss peak of the attenuation band centred around 1,300 nm (related to the cladding mode LP06) as a function of the SRI. The refractive index sensitivity of the bare LPG was found to be 5.06 nm/RIU (refractive index units) and 3.59 dB/ RIU, around the water refractive index, in terms of wavelength shift and amplitude... 

One of the main advantages of the optical-based sensors is their high resolution. Integrated optical sensors16, especially the interferometric ones that have been developed in recent years, such as the Mach-Zehnder interferometer (MZI)17 and the Young interferometer 18-21, show an extremely high refractive index resolution in the range of 10 1—10 8 RIU (refractive index units)17,21, which is equivalent to... 

Figure 10.12 shows the phase difference measured between channels of each pair when no phase change was introduced in any of the channels. The phase resolution (S/N =1) for each pair of channels, as determined from these measurements, is 1 xlO 4 x 2n, which corresponds to a refractive index resolution of —8.5 x 10 8 RIU (refractive index units) at a bandwidth of 1 Hz. 

The main objectives in calibrating the SEC detection system in absolute refractive index and absorption units are the estimation of v and E at the normal flow conditions and the standardization of the measurement errors. The first step in the calibration process is the estimation of the instrument s constants to transform the computer units into absorbances and refractive index units. The Waters AAO UV spectrophotometer displays absorbance units. Therefore, step changes in the instrument s balance and sampling of the signal provide the necessary data for the calibration. The equations obtained are ... 

Liquid chromatographs are equipped with a means to continuously monitor the column effluent and recognize the presence of solute. Only small sample sizes are used with most HPLC columns, so a detector must have high sensitivity. The type of detector that has the most universal application is the differential refiractometer. This device continuously monitors the refractive index difference between the mobile phase (pure solvent) and the mobile phase containing sample (column effluent). The sensitivity of this detector is on the order of 0.1 ju,g, which, compared to other detectors, is only moderately sensitive. The major advantage of the refractometer detector is its versatility its main limitation is that there must be at least 10 7 refractive index units between the mobile phase and sample. 

Figure 9.72 Chromatograms of the action patterns of maltoheptaose after the indicated periods of incubation with a-amylase and a-glucosidase. Peaks 1, glucose 2, maltose 3, maltotriose 4, maltotetraose 5, maltopentaose (x) compound A 6, maltohexaose 7, maltoheptaose. (A) Pure maltoheptaose used for the assay. (B) Blank sample before the addition of substrate. (C-H) Chromatograms after 1, 5, 10,15, 20, and 30 minutes, respectively, of incubation. Chromatographic conditions column, 10 jum Nucleosil SA (250 mm X 4 mm) solvent, acetonitrile-water (72.527.5) flow rate, 0.7 mL/min temperature, 27°C detection, differential refractometer, full scale = 2 X 10-6 refractive index units. (From Haegel et aL, 1981.)...

SPR has applications in drag development, medical diagnostics, environmental monitoring, and food and water safety [2]. Typically, the ATR SPR sensitivity is 10 refractive index units (RIU) (i.e., the 7th significant figure after the decimal in refractive index), and the limit of detection is 10 pg/mL. 

Np) usually in millivolts but may be in specific units (e.g. Refractive Index Units)... 

This device has been manufactured by GOW-MAC Inc., who claimed it had a sensitivity of 1 x 10 refractive index units. This would be equivalent to a sensitivity of 9 x 10 g/ml of benzene (refractive index 1.501) eluted in w-heptane (refractive index 1.388). The cell volume was kept to 8 pi, a little large for modern sensors but small enough to work well with normal 4.6 mm I.D. columns. Different cells packed with appropriate materials were necessary to cover the refractive index range of 1.31 to 1.60. A diagram of the Christiansen detector is shown in figure 5. 

Specifications for this detector are not very explicit. It would appear that the sensitivity of the refractive index detector was about 10 refractive index units and the UV detector about 10 absorption units. 

Experimental. The differential refractive indexes of polymer solutions were measured at 25°C with a Waters Scientific R-403 differential refractometer connected on-line with a size exclusion chromatograph. The refractometer was calibrated to refractive index units (Riu) with benzene/carbon tetrachloride solutions. The rationale behind using the refractometer on-line with the chromatograph is the elimination of impurities in the sample (water, residual monomer etc.) which affect the refractive index measurements particularly at low polymer concentrations and to calibrate the detectors at the flow conditions at which they were normally operated. Polymer solutions of several concentrations (0.015-0.0025 wt %) were injected repeatedly to verify the reproducibility of the measurements, which was typically An 0.5 x 10-6 for replicates on the same solutions. 

Abstract Nanophotonic stractures exhibit a large variety of effects on the nanoscale that can be used for biosensing in a biochip format. The resonance nature of these structures then allows high sensitivity to analytes, gases, or other external index perturbations down to the order of 10 refractive index unit. In this chapter, several configurations of nanophotonic structures and their use for sensing are reviewed with special emphasis on grating-based resonant strucmres, metallic nanoparticle, and nano apertures. 

PVA-PAA Polyvynil alcohol-poly aery lie acid RIU Refractive index unit... 

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