Refractometer operation

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. 

Most refractometers operate on the concept of the critical angle 4> it this is the angle for which (or 4> ) is exactly 90° (see Fig. 9b). A ray in the medium with any greater angle will be totally reflected at an equal angle as shown in Fig. 9c. The index of refraction is given in terms of the critical angle by... 

Differential refractometers operate by utilizing one of the following principles. In the first type, the measurement is based on an optical displacement of the beam (Figure 19-43). A mirror controls the reflection of the light beam. The light passes through the divided cell the first time without being reflected, and this then is followed by a reflected beam. If there is a difference in the solutions, a deflection will occur. The deflection is the sum of the deflection in the two cells. 

Determination of dn/dc was carried out with a Chromatix KMX-16 differential refractometer operating at 633 nm. For our previous report, dn/dc was measured at only one salt concentration appropriate to the middle of the centrifuge tube (- 6 Na2S0 ), and this one value was used for all calculations of M for a particular type of polymer. Because dn/dc enters... 

The second most widely used detector in HPLC is the differential refractometer (RI). Being a bulk property detector, the RI responds to all substances. As noted in Table 3 the detection limits are several orders of magnitude higher than obtained with the UV detector. Thus, one turns to the RI detector in those cases in which substances are non-UV active, e.g. lipids, prostaglandins. In addition, the RI detector finds use in preparative scale operation. Finally, relative to the UV detector, the RI is significantly more temperature and flow sensitive and cannot be used in gradient elution. 

Ability to analyze unreacted monomers was dependent on detector selectivity. The UV detector was operated at 254 nm for analysis of AN/S latex solutions. Styrene is a strong UV abosrber at this wavelength while acrylonitrile has no measurable absorbance at 254 nm. Thus, the UV detector was entirely selective to monomeric styrene. The refractometer detector was sensitive to both acrylonitrile and styrene when each was present in the desired copolymer proportions (70/30). However,... 

The apparatus employed for this study was a Waters Associates Model ALC/GPC 300 with a differential refractometer as mass detector operated at room temperature. A 2 ml sample loop with polymer concentrations of 0.01-0.1 wt.% cUid a 5 ml siphon were employed with mobile phase flowrates in the reuige 1-8 ml/min. 

Just like refractive index, the °Brix scale is quite dependent on the temperature. Manual Abbe refractometers do not compensate for this temperature effect. Special correlation tables are used to adjust the readings to a standard temperature, 20°C. Digital refractometers, on the other hand, can operate over a fairly wide range of sample temperatures (+15 to +40°C) and automatically apply these temperature corrections. See Workplace Scene 15.2. 

Note If a digital refractometer is used, follow the manufacturer s operating instructions. 

Describe the optical system of Abbe s Refractometer, its optical path for upper prism and its operational procedure. 

Chromatographic System. The isocratic liquid chromatograph used was a Waters Associates (Milford, MA) Model 24A alc which included a Model 6000A Solvent Delivery System, a Model 401 Differential Refractometer and a Model 440 Absorbance Detector operating at 254 nm and was fitted with a WISP automatic injector. The analog outputs of the UV absorbance detector or differential refractometer were recorded with a Model 730 Data Module (printer, plotter, integrator)(Waters). Eluent flow rate was 1.0 ml/min unless otherwise noted. 

Gel Permeation Chromatography (GPC). Waters Associate Model 200 GPC was used with 4 x 3/8" styragel columns with an internal diameter of 0.311" and refractometer detector. The basic characteristics and operation of the instrument have been previously described in detail (19-20). Some of the operating conditions used in this study are outlined below. 

There is a wide variety of instrumentation ranging from simple manually operated devices to completely automated systems. Briefly, the polymer-containing solution and solvent alone are introduced into the system and pumped through separate columns at a specific rate. The differences in refractive index between the solvent itself and polymer solution are determined using a differential refractometer. This allows calculation of the amount of polymer present as the solution passes out of the column. 

The device F is a detector as shown in Fig. 1. Since solutions of tppts and other aryl-group containing water-soluble phosphines absorb UV light strongly, it is better to use a refractometer than usual UV detectors. A refrac-tometer facilitates the detection of inorganic salts such as sodium chloride and sodium sulfate. Here refractometers from Biichi were used and operated with regular x/f-recorders (G). 

A Waters Associates Anaprep GPC fitted with one 4 ft X 2.4 inches od Styragel column having a nominal porosity of 104 A was used for the preparative fractionation of the PMMA blend in tetrahydrofuran at a temperature of 25 °C and at a flow rate of 30 ml/min. The degasser and differential refractometer were operated at 35° and 25 °C, respectively. Samples having concentrations of 0.25 wt-vol % were respectively, automatically injected from a 100 ml loop over a 5-minute period. Ten 125 ml fractions were automatically collected for each sample injection. Upon... 

These include such instruments as opacity monitors, turbidimeters, colorimeters, refractometers and spectrophotometers. A selection of these is described—particularly where the instrument has a more general application as an on-line process analyser and/or to illustrate a general principle of operation. It is likely that development of fibre-optic techniques (Section 6.12.4) will extend the use of this type of sensor in the future(56). 

The separation and purification of ethyl esters of EPA, DHA, and the heretofore-minor unreported polyunsaturate octadecatetraenoic acid (C18 4 3, OTA) on a preparative scale by modification of an analytical RP-HPLC procedure has been described by Beebe et al. (48). They used a liquid chromatograph equipped with a differential refractometer as detector operated at room temperature and an ST Macrobore column (350 X 4.6-mm ID) of C18 reverse-phase material, 25-yum particle size. 

Bellingham and Stanley provide detailed instructions on the operation of the Abbe refractometer the above account is a general outline of the procedure. 

The choice of detectors in LC is often a trade-off between wide scope and high sensitivity. For instance, the refractometer is readily available and easy to operate it can detect most compounds (wide scope), but it often has a lack of sensitivity for many compounds. A variable-wavelength UV detector offers a good choice for solutes that have some UV absorbance capability. Absorption at a specific wavelength results in a more selective and sensitive detection mode than a refractometer, but only for UV-absorbing compounds. In other specific cases the fluorescence or electrochemical detector can be used. These have a high sensitivity for individual compounds but are also limited in the number and type of compounds they can detect (narrow scope). 

The refractive index of a transparent substance is the ratio of the velocity of light in air to its velocity in that material under like conditions. It is equal to the ratio of the sine of the angle of incidence made by a ray in air to the sine of the angle of refraction made by the ray in the material being tested. The refractive index values specified in this Codex are for the D line of sodium (589 nm) unless otherwise specified. The determination should be made at the temperature specified in the individual monograph, or at 25° if no temperature is specified. This physical constant is used as a means for identification of, and detection of impurities in, volatile oils and other liquid substances. The Abbe refractometer, or other refractometers of equal or greater accuracy, may be employed at the discretion of the operator. 

The initial pulse of polymer solution which was injected into the column entry becomes diluted and attenuated as the different species are separated on the gel packing. The column effluent is monitored by detectors which respond to the weight concentration of polymer in the flowing eluant. The most common detector is a differential refractometer. Spectrophotometers, which operate at fixed frequencies, are also used as alternative or auxiliary detectors. Some special detectors which are needed particularly for branched polymers or copolymers are mentioned in Section 3.4.4. 

For proper control in sugar manufacture, the laboratory must be well-equipped with accurate scales, saccharimeter (polariscope), and the Brix spindle or refractometer. The laboratory control of factory operations, from milling to final product, basically depends on the following three operations. 

---