Detectors, HPLC refractive index detector

Hplc techniques are used to routinely separate and quantify less volatile compounds. The hplc columns used to affect this separation are selected based on the constituents of interest. They are typically reverse phase or anion exchange in nature. The constituents routinely assayed in this type of analysis are those high in molecular weight or low in volatility. Specific compounds of interest include wood sugars, vanillin, and tannin complexes. The most common types of hplc detectors employed in the analysis of distilled spirits are the refractive index detector and the ultraviolet detector. Additionally, the recent introduction of the photodiode array detector is making a significant impact in the analysis of distilled spirits. 

For acrylate polymers with higher levels of carboxylic acids, THF can be modified by the addition of acids such as acetic, phosphoric, or trifluoroacetic. Levels as high as 10% acetic acid are considered acceptable by most manufacturers for their styrene/DVB columns. If such a modified mobile phase is used, it may need to be premixed rather than generated using a dynamic mixing HPLC pump because on-line mixing often leads to much noisier baselines, particularly when using a refractive index detector. 

Thin-layer chromatography (TLC) is used both for characterization of alcohol sulfates and alcohol ether sulfates and for their analysis in mixtures. This technique, combined with the use of scanning densitometers, is a quantitative analytical method. TLC is preferred to HPLC in this case as anionic surfactants do not contain strong chromophores and the refractive index detector is of low sensitivity and not suitable for gradient elution. A recent development in HPLC detector technology, the evaporative light-scattering detector, will probably overcome these sensitivity problems. 

Sodium dodecyl sulfate present in hydrophilic ointments has been determined by TLC on silica gel with flame ionization detection, which was considered better than the colorimetric method. TLC is preferred to HPLC in this case due to the low sensitivity of the refractive index detector that makes difficult the analysis of small amounts of sodium dodecyl sulfate [284]. 

The choice of detector is often crucial to the success of a particular HPLC method. A number are in routine use, including the UV, fluorescence, electrochemical, conductivity and refractive index detectors, and each has particular advantages and disadvantages, details of which can be found elsewhere [2-4],... 

Another variation of the preceding method is to apply HPLC to fractionate the cleaned-up aliphatic-aromatic fraction from flash colurim separation of soluble organic matter as it is performed in the Chevron laboratory, for example, as described in Reference 2. A Waters HPLC system equipped with a preparative Whatman Partisil 10 silica column (9.4 X 500 mm), a HPLC pump, and two detectors for separation monitoring (a UV and refractive index detector) are used, giving three fractions of aliphatic hydrocarbons, mono-, di-, and triaromatics and polar compounds. The hrst two fractions are eluted with hexane, whereas polar compounds are eluted with... 

Sample preparation, injection, calibration, and data collection, must be automated for process analysis. Methods used for flow injection analysis (FLA) are also useful for reliable sampling for process LC systems.1 Dynamic dilution is a technique that is used extensively in FIA.13 In this technique, sample from a loop or slot of a valve is diluted as it is transferred to a HPLC injection valve for analysis. As the diluted sample plug passes through the HPLC valve it is switched and the sample is injected onto the HPLC column for separation. The sample transfer time typically is determined with a refractive index detector and valve switching, which can be controlled by an integrator or computer. The transfer time is very reproducible. Calibration is typically done by external standardization using normalization by response factor. Internal standardization has also been used. To detect upsets or for process optimization, absolute numbers are not always needed. An alternative to... 

Specifications for modem detectors in HPLC are given by Hanai [538] and comprise spectroscopic detectors (UV, F, FUR, Raman, RID, ICP, AAS, AES), electrochemical detectors (polarography, coulometry, (pulsed) amperometry, conductivity), mass spectromet-ric and other devices (FID, ECD, ELSD, ESR, NMR). None of these detectors meets all the requirement criteria of Table 4.40. The four most commonly used HPLC detectors are UV (80%), electrochemical, fluorescence and refractive index detectors. As these detectors are several orders of magnitude less sensitive than their GC counterparts, sensor contamination is not so severe, and... 

HPLC analysis for succinic acid, succinamic acid, succinamide, succinimide, N-methylsuccinimide, butyric acid, and propionic acid was performed with a Waters Model 515 HPLC pump equipped with a Waters Model 2410 Refractive Index Detector. Separations were performed with an Aminex HPX-87H 300mm column (Bio-Rad Laboratories, Hercules, CA) operated at 35°C, and using 0.005 M H2S04 elluent. 

Products were analyzed via Waters Model 515 HPLC Pump fitted with a Waters model 2410 refractive index detector. Separations was performed via an Aminex HP-87H 300mm column at 65°C using 0.005M H2SO4 as the mobile phase. Compounds calibrated for this work included xylitol, arabitol, erythritol, threitol, PG, EG, glycerol, lactate, 1-propanol, 2-propanol, ethanol, methanol, and the butanetriol isomers. Any compounds not visible by RID were not quantified in this work. 

There are many HPLC detectors that can turn the presence of your compound into an electrical signal to be written on a chart recorder. Time was the refractive index detector was common. Clean eluent, used as a reference, went through one side of the detector, and the eluent with the samples went through the other side. A difference in the refractive index between the sample and reference caused an electrical signal to be generated and sent to a chart recorder. If you ve read the section on gas chromatography and looked ahead at infrared, you shouldn t be surprised to find both a sample and a reference. I did tell you the reference/sample pair is common in instrumentation. 

Separation and quantitation of carbohydrate mixtures may be achieved using HPLC, a method that does not necessitate the formation of a volatile derivative as in GLC. Both partition and ion-exchange techniques have been used with either ultraviolet or refractive index detectors. Partition chromatography is usually performed in the reverse phase mode using a chemically bonded stationary phase and acetonitrile (80 20) in 0.1 mol U1 acetic acid as the mobile phase. Anion- and cation-exchange resins have both been used. Carbohydrates... 

Refractive index detectors are not suitable for use in the HPLC of carbohydrates... 

A comparative study of the analysis of aliphatic amines by GC-FID, GC-TSD and HPLC with refractive index detector (RID), using isopropylamine as internal standard, gave good results in all cases. Determination of trimethylamine oxide by HPLC with a pulsed amperometric detector was problematic136. 

Manufacturers publish their product s performance characteristics as specifications, which are often used by the customer for comparison during the selection process. Table 1 shows the specifications of an Agilent 1100 Series Quaternary Pump, which is quite representative of other high-end analytical pumps. Note pulsation is particularly detrimental to the performance of flow-sensitive detectors (e.g., mass spectrometer, refractive index detector). Differences in dwell volumes and composition accuracy between HPLC systems might cause problems during method transfers. 

Experimental Techniques. Chromatography was performed on a Varian model 5060 HPLC equipped with a RI-3 refractive index detector. A Vista Plus Gel Permeation Chromatography (GPC) data system was used consisting of a Vista 401 chromatography data system serially connected to an Apple II microcomputer. The Vista 401 performs data acquisition and allows data storage and automations capability while all SEC data processing is performed on the Apple II by means of user-interactive GPC software for automated, on-line calibration and polymer analysis. 

Figure 1. The Ranges and Contents of Each Species of PEG as Related to Mns. PEG materials used were products graded for laboratory use. They were analyzed by HPLC with a Hitachi Liquid Chromatograph 655 with a refractive index detector (Erma ERC-7510). The operational conditions were as follows column, Toyo Soda TSK-GEL G3000PW 7.5 x 600 mm sample size, 1%, 20 yl eluent, distilled water flow rate, 0.5 ml/min pressure, 80 kg/cm temperature, room temperature (16.5 0.5 C). (Reproduced with permission from Ref. 1. Copyright 1987 CRC Press, Inc.)...

An HPLC system, equipped with a Waters solvent delivery system (M-45), two PLgel 20 p,m Mixed-A columns (300 x 7.5 mm) with 20 p,m guard column (50 x 7.5 mm) (Polymer Laboratories, Amherst, MA) and a refractive index detector (model 2410) (Waters, Milford, MA), can be used to study the molecular size and size distribution (e.g. molecular weight and weight distribution) of starch. 

The HPLC was equipped with a refractive index detector, and a 150 mm x... 

While lactose may be determined by gas liquid chromatography, high performance liquid chromatography (HPLC), using a refractive index detector, is now usually used. 

High-performance liquid chromatography (HPLC) system with refractive index detector and HPLC column (e.g., Aminex HPX-87H, Bio-Rad) fitted with suitable guard column... 

Improved separation of natural oil TGs using short columns packed with 3-//m alkyl bonded-phase particles was reported by Dong and DiCesare (88). The HPLC columns used were HS-3 high-speed columns packed with 3-/um C18 bonded-phase particle (100 X 4.6-mm ID) with a column void volume of ca. 0.8 ml and efficiencies in the range of 13,000-15,000 theoretical plates (measured under optimized conditions) and HS5 C,8 columns (125 X 4.6-mm ID packed with 5-yttm particles). Two detectors were used a modified refractive index detector having an 8-/rl flow cell and 0.007-in. ID inlet tubing and a variable-wavelength UV/visible detector. 

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.

Reversed-phase HPLC has been used to analyze the oxidation products of triacylglycerols in edible oils. The detection is often based on monitoring the conjugated dienes with an ultraviolet detector (234-235 nm). However, the UV detector provides no information about oxidation products without a conjugated diene structure, e.g., products of oleic acid. Information about these compounds is important when oils with a high oleic acid content are studied. The most common universal detector types—refractive index and flame ionization detectors—are not sensitive enough to detect small amounts of oxidation products. 

Whether eluted from columns or from thin-layer plates, the quantitative determination of sugars was traditionally based on colorimetric reactions involving the use of chemical reagents, e.g., anthrone. These detection methods have been largely replaced in modem HPLC by the refractive index detector, although ultraviolet detectors are also employed. Recently we have also seen the introduction of other types of detector (e.g., the mass detector), as will be discussed later. 

Fig. 3 HPLC separation of carbohydrates in chickpeas. Column (200 X 4.6-mm ID) LiChrosorb NH2 flow rate 1 ml min-1 mobile phase 20% water in acetonitrile. Refractive index detector. Peak assignment 1, fructose 2, glucose 3, sucrose 4, rafflnose 5, maninotriose 6, stachyose 7, verbascose.

Fig. 4.3. High performance liquid chromatography (HPLC) of the monosaccharides obtained from a partially purified preparation of microbubble glycopeptide surfactant from forest soil. Following hydrolysis (in 2 N HC1 for 6 hr at 100°C) and filtration, the carbohydrate mixture was charged on a Bio-Rad HPX-87 cation exchange column. For comparison, part A shows the chromatogram (using the same HPLC column) of a standard solution, which contained 4 pg of each of three different monosaccharides (i.e., the last three peaks shown are glucose, xylose and fiicose, in the order of increasing retention times). Part B shows the chromatogram obtained from hydrolysis of the partially purified (see text) microbubble surfactant (approximately 30 pg). All other experimental conditions were identical in the two cases, i.e., water eluent, 0.5 ml/min flow rate, 85°C, refractive index detector attenuation -2x. (Taken from ref. 322.)...

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