Automatic refractometers Refractometer

1 automatic refractometers

1.1 influence of wavelength
1.2 influence of temperature
1.3 extended possibilities of automatic refractometers

1.3.1 flow cells
1.3.2 automatic sample feeding
1.3.3 multiparameter measurements


1.4 software features
1.5 pharma documentation , validation

automatic refractometers

schematic setup of automatic refractometer: led light source imaged under wide range of angles onto prism surface in contact sample. depending on difference in refractive index between prism material , sample light partly transmitted or totally reflected. critical angle of total reflection determined measuring reflected light intensity function of incident angle - source of image: anton paar gmbh, www.anton-paar.com

automatic refractometers automatically measure refractive index of sample. automatic measurement of refractive index of sample based on determination of critical angle of total reflection. light source, long-life led, focused onto prism surface via lens system. interference filter guarantees specified wavelength. due focusing light spot @ prism surface, wide range of different angles covered. shown in figure schematic setup of automatic refractometer measured sample in direct contact measuring prism. depending on refractive index, incoming light below critical angle of total reflection partly transmitted sample, whereas higher angles of incidence light totally reflected. dependence of reflected light intensity incident angle measured high-resolution sensor array. video signal taken ccd sensor refractive index of sample can calculated. method of detecting angle of total reflection independent on sample properties. possible measure refractive index of optically dense absorbing samples or samples containing air bubbles or solid particles . furthermore, few microliters required , sample can recovered. determination of refraction angle independent of vibrations , other environmental disturbances.

influence of wavelength

the refractive index of given sample varies wavelength materials. dispersion relation nonlinear , characteristic every material. in visible range, decrease of refractive index comes increasing wavelength. in glass prisms little absorption observable. in infrared wavelength range several absorption maxima , fluctuations in refractive index appear. guarantee high quality measurement accuracy of 0.00002 in refractive index wavelength has determined correctly. therefore, in modern refractometers wavelength tuned bandwidth of +/-0.2 nm ensure correct results samples different dispersions.

modern automatic refractometers - source of image: anton paar gmbh, www.anton-paar.com


influence of temperature

temperature has important influence on refractive index measurement. therefore, temperature of prism , temperature of sample have controlled high precision. there several subtly-different designs controlling temperature; there key factors common all, such high-precision temperature sensors , peltier devices control temperature of sample , prism. temperature control accuracy of these devices should designed variation in sample temperature small enough not cause detectable refractive-index change.

external water baths used in past no longer needed.

refractometer funnel type sampler - flow cell filling funnel - source of image: rudolph research analytical - www.rudolphresearch.com


extended possibilities of automatic refractometers

automatic refractometers microprocessor-controlled electronic devices. means can have high degree of automation , combined other measuring devices

flow cells

there different types of sample cells available, ranging flow cell few microliters sample cells filling funnel fast sample exchange without cleaning measuring prism in between. sample cells can used measurement of poisonous , toxic samples minimum exposure sample. micro cells require few microliters volume, assure recovery of expensive samples , prevent evaporation of volatile samples or solvents. can used in automated systems automatic filling of sample onto refractometer prism. convenient filling of sample through funnel, flow cells filling funnel available. these used fast sample exchange in quality control applications.

automatic sample feeding

automatic refractometer sample changer automatic measurement of large number of samples - source of image: anton paar gmbh, www.anton-paar.com

once automatic refractometer equipped flow cell, sample can either filled means of syringe or using peristaltic pump. modern refractometers have option of built-in peristaltic pump. controlled via instrument‘s software menu. peristaltic pump opens way monitor batch processes in laboratory or perform multiple measurements on 1 sample without user interaction. eliminates human error , assures high sample throughput.

if automated measurement of large number of samples required, modern automatic refractometers can combined automatic sample changer. sample changer controlled refractometer , assures automated measurements of samples placed in vials of sample changer measurements.

multiparameter measurements

measuring combination of automatic refractometer , density meter used in flavors , fragrances industry - source of image: anton paar gmbh, www.anton-paar.com

today’s laboratories not want measure refractive index of samples, several additional parameters density or viscosity perform efficient quality control. due microprocessor control , number of interfaces, automatic refractometers able communicate computers or other measuring devices, e.g. density meters, ph meters or viscosity meters, store refractive index data , density data (and other parameters) 1 database.

software features

automatic refractometers not measure refractive index, offer lot of additional software features, like

instrument settings , configuration via software menu
automatic data recording database
user-configurable data output
export of measuring data microsoft excel data sheets
statistical functions
predefined methods different kinds of applications
automatic checks , adjustments
check if sufficient amount of sample on prism
data recording if results plausible

pharma documentation , validation

refractometers used in pharmaceutical applications quality control of raw intermediate , final products. manufacturers of pharmaceuticals have follow several international regulations fda 21 cfr part 11, gmp, gamp 5, usp<1058>, require lot of documentation work. manufacturers of automatic refractometers support these users providing instrument software fulfills requirements of 21 cfr part 11, user levels, electronic signature , audit trail. furthermore, pharma validation , qualification packages available containing

qualification plan (qp)
design qualification (dq)
risk analysis
installation qualification (iq)
operational qualification (oq)
check list 21 cfr part 11 / sop
performance qualification (pq)