Molecular Sieves

Molecular sieves are synthetic and naturally occurring zeolites with well-defined structures that have found extensive use for the separation of permanent (or fixed) gases. Molecular sieves have a pore size that is defined by the particular ion used in the preparation Table 1 General application fields of adsorbents Table 1 General application fields of adsorbents Volatile polar and nonpolar compounds CO and CO2 in air impurities in ethylene hydrocarbon and semipolar impurities of the material...

Separation Strategy and Typical Applications

Operational electrolyte conditions should be optimized to obtain the best quality of separation by changing electrolyte parameters so that the difference of the effective mobilities of the target components should be as large as possible. Strictly speaking, the separability depends on the mobility difference in the mixed zone (see Figure 1). However, to a first approximation, the mobility differences at the steady state or the difference of the RE values may be used for the criterion for...

Advantages of TLE

Thin-layer chromatography has proved to be one of the most successful chromatographic techniques ever devised. This success owes largely to its simplicity and versatility compared with column techniques. The main drawback of TLC is the low solvent velocity achieved through capillary action. This leads to long separation times and means that the optimum flow velocity (for chromatographic efficiency) is seldom reached. Electric fields can be used to cause the migration of the analyte, either by...

Resins

Water treatment The annual production of ion exchange resins has been estimated at 500 000 m3, of which at least 90 goes to industrial water treatment. The various end uses in this area will now be described. Softening The removal of calcium and magnesium ions from water supplies is a requirement for many industries. Laundries, dye-houses and cleansing plants are examples of specific industries but the need can be generalized to many hot water circuits, heat exchangers and low pressure boilers....

Collector Collector Interactions

The use of mixtures of collectors has long been recognized in plant practice and has been shown to enhance flotation performance. These benefits have been reported for a wide range of collector mixtures (anionic, cationic and nonionic) and include lower dosage requirements, improved selectivity and rates and extents of recovery and an increase in the recovery of coarse particles. In many cases an optimum ratio of constituent collectors was shown to exist. Dithiophosphates are a class of thiol...

Freezing Rates

The freezing time can be estimated by an equation developed by Steinbach where tf freezing time AJ enthalpy difference between the initial freezing point and the final temperature AT difference of temperature between the freezing point and the cooling medium d thickness of the product parallel to the direction of prevailing heat transfer ps density of the frozen product thermal conductivity of the frozen product and Ksu surface heat transfer coefficient between cooling medium and the freezing...

Diffusion in Solids

When extracting solutes from solid samples, one must not only overcome the solute-sample attraction, but the solute must diffuse with the solvent back out of the porous solid sample. This diffusion through the pores of a solid sample is influenced by the geometry or tortuosity of the pore structure (e.g. the diffusion path length). Diffusion in solids, assuming weak solute-sample sorption (i.e., a linear isotherm), is expressed by Deff ( D) y(KD + 1), where Deff is the effective (or apparent)...

Sedimentation in a Centrifugal Field

A particle moving in a circular path continuously experiences a centrifugal force, Fc. This force acts in the plane described by the circular path and is directed away from the axis of rotation. The centrifugal force may be expressed as where m is the particle mass (g) a is the acceleration (cm s 2) w is the angular velocity (radians s_1 2n rpm 60) and x is the radial distance from the axis of rotation to the particle (cm). Thus, centrifugal force is proportional to the square of the angular...

Inorganic Oxide Adsorbents and their Applications

The most important adsorbents for extraction and matrix simplification are silica gel, alumina, Florisil and diatomaceous earths. Silica gel, prepared from sodium silicate using the sol-gel procedure, is the most widely used general-purpose adsorbent. Silica gels used for solid-phase extraction have surface areas of about 300-800 m2 g-1, pore sizes from 4-10 nm, and an apparent pH of 5.5-7.5. The apparent sorbent pH is characterized as the observed pH of a 5 (w w) aqueous suspension. Alumina is...

Modes of Paper Chromatography

In most of its practical aspects (e.g. sample application, equipment such as developing tanks and visualization procedures), paper chromatography somewhat resembles TLC. The most noticeable difference is that, as the paper is not rigid, it must either be suspended from an appropriate support during development or arranged in such a way as to be self-supporting. Only the major types of paper chromatography are described below, but it should be noted that there were many minor variants of the...

Hydrocyclones

This device is particularly unique as it separates solids and liquids by centrifugal principles, but contains no moving parts. The principle of the machine is illustrated in Figure 5. The slurry or fluid to be separated is pumped at high speed and enters the conically shaped machine tangentially. The conical shape causes the flowing liquid to swirl or rotate within the cone, with the result that suspended solids move to the wall while clarified liquid remains in the centre of the cone. This...

Synthetic Multiple Interaction Pirkle Stationary Phases

Figure 1 Enantiomer separation on CSPs is made possible by formation of transient diastereomeric adsorbates with differing free energies. In this illustration, the analyte enantiomers are depicted as right and left hands, and the CSP is depicted as immobilized right-handed gloves. Figure 1 Enantiomer separation on CSPs is made possible by formation of transient diastereomeric adsorbates with differing free energies. In this illustration, the analyte enantiomers are depicted as right and left...

Mode of Air Entry

In mechanical cells there are two modes by which air is introduced into the cells one is the forced air entry mode carried out using a blower and the other is the self-induced air entry mode, in which air is sucked into the cell by vortexing. The two cell designs can be distinguished by the difference in vertical location of the impeller in the cell. In the forced air-type machine, the impeller is located close to the cell bottom with a deeper impeller submergence, and an external air blower is...

Solvents

The solvent, besides acting as the medium in which the polymerization is performed, has an important secondary role as a porogen. It controls the porous structure of the polymer matrix to a large extent, and a good porogen is essential if one wants the porous structure in the polymer to be well developed. Sometimes, however, a good porogenic solvent can be a bad solvent for the analyte, so once again a compromise is sometimes required. Common imprinting solvents include toluene, chloroform and...

High Performance Liquid Chromatography HPLC Analysis

The development of sophisticated HPLC instrumentation and of precise pumps with low pulsation as well as improved sensitivity of the detection systems along with new column materials have made this technique well suited for routine laboratory work. Over the last 20 years, a number of different HPLC methods for determination of bile acids in all kinds of biological fluids have been published, each of them with special advantages and disadvantages. Early HPLC work was based on polar column...

Introduction

Ion exchange has been described as the oldest scientific phenomenon known to humanity. This claim arises from descriptions that occur in the Bible and in the writings of Aristotle, but the first truly scientific allusion to ion exchange is attributed to two English agricultural chemists in 1850. These were J. T. Way and H. S. Thompson, who independently observed the replacement of calcium in soils by ammonium ions. This discovery was the precursor to the study of inorganic materials capable of...

Conclusion

Large scale preparative GC is a real purification tool. It is now reliable and economically viable for industrial production. Columns with internal diameter as large as 600 mm are available. The efficiencies Figure 4 Purification cost breakdown for a production of 36 tonnes per year of injected crude on a 400 mm i.d. column. Open segments, investment costs shaded segments, operating costs. Figure 4 Purification cost breakdown for a production of 36 tonnes per year of injected crude on a 400 mm...

Reversal of EOF

The separation of anionic solutes in CE may lead to extended time of analysis due to their migration in the direction opposite to EOF. One method of decreasing the analysis time is to reverse the EOF, thus making the anions migrate in the same direction as the EOF. In aqueous CE, the addition of long alkyl chain trimethylammonium ions is used for this purpose, e.g. in the analysis of inorganic anions and phenols. This principle may also be used in NACE. However, the long alkyl chain...

Control of Batch Crystallizers

Batch crystallizers are used extensively for crystallization procedures that are of small capacity and have a high added value, and often when multipurpose reactors are used for the crystallization process. Therefore the control of a batch process differs considerably from that of a continuous process. In addition, although a batch crystallizer can be described by a similar model to the continuously operated crystal-lizer, because of the inherently nonstationary process conditions and the...

Air Liquefaction Distillation

Herron, Air Products and Chemicals, Hamilton Boulevard, Allentown, PA, USA Copyright 2000 Air Products and Chemicals, Inc Oxygen, nitrogen and argon, the major components of air, have been separated by distillation at cryogenic temperatures for nearly a century. Air was commercially liquefied as early as 1895 by Carl von Linde and also by William Hampson. Linde separated oxygen from air by distillation in a single column in 1902. A commercial plant producing pure nitrogen...

Detector Response to Low Molecular Weight Components

The differential refractive index for a polymer solvent combination is normally independent of molecular weight at high molecular weight. However, while it is generally known that the refractive index detector response varies with low molecular weight polymers this variation is commonly ignored. As a consequence, SEC results for polymers containing low molecular weight material often do not give an appropriate consideration to the low molecular weight components this has important implications...

Attenuation of Sound in a Liquid Medium

The intensity of the ultrasonic wave decreases with increasing penetration into the medium. Molecular vibration induced by the sound wave results in loss of intensity of the wave, which is transformed into heat. Heating occurs in the sites of compression and cooling at the sites of rarefaction. Since the compressibility of liquids is small, there is little heating caused by ultrasound as waves pass through the medium. The heating effect is caused by the degradation of acoustic energy due to...

Intercalation Properties

Over time, research on layered phosphates has moved from the study of their ion exchange properties to that of their intercalation properties in great part determined by the presence of Br+nsted acid groups in the interlayer region. Both a- and y-zirconium phosphates are excellent intercalating agents of Lewis bases. The intercalation chemistry of the former has been more widely investigated and we will be mainly concerned with a-zirconium phosphate. Many molecules belonging to various classes...

Chiral Mobile Phase Additives

There are no fundamental differences between the techniques using chiral stationary phases and chiral Table 3 Chiral selectors used as mobile-phase additives L- or D-Proline Cu(II), L-Phenylalanine Cu(II), W-Methyl-L-phenylalanine Cu(II), W,W-Dimethyl-L-phenylalanine Cu(II), (R, R)-Tartaric acid mono-1-octylamide Cu(II) (R, R)-Tartaric acid mono-1-octylamide Cu(II) 1,1 '-Binaphthyl derivatives of 18-crown-6 Cyclodextrins a-Cyclodextrin -Cyclodextrin Propranolol, pseudoephedrine, salsolinol,...

Silylating Agents

Silylation is the most widely used method for metabolic profiling, especially for urinary organic acids. On the other hand its use for amino acids has a number of disadvantages as already mentioned. For some applications, silylating agents are too powerful in that they are able to react with compounds which will not elute from the column. The most popular reagents are listed in Table 3 and many others are described in detail in the Fluka handbook edited by van Look (see Further Reading). For...

Packed Column Description

Figure 2 illustrates a tower with structured packing. In addition to the packing itself, packed columns require other internals to assure the performance of the packing. These internals are Liquid feed pipes to deliver the fluid to the liquid distributors, as seen at the top of the tower and at the intermediate distributor. Liquid collection and mixing as shown below the top bed. Liquid draw-off sump and pipe as shown below the top bed. Liquid redistributors, as presented between the two beds....

The BOSS and Big Boss Diffusion Denuder Samplers

Diffusion denuder sampling systems for the determination of total fine particulate organic material have been developed at Brigham Young University. The objectives which guided the development of these 1. The sampling system should have a flow rate sufficient to enable measurement of low concentrations of particulate carbonaceous material and to allow the detailed chemical characterization of particulate organic material, e.g. flow rates of from 30 to 300 L min_i were considered desirable. 2....

SEC Concentration Detectors and Sample Concentration

A number of detector types for specific additional information will be considered later but the most basic SEC application requires a concentration detector to monitor the polymer as it emerges from the column. The most common form of concentration detector encountered in SEC is a differential refractive index (DRI) detector. These detectors are a cost-effective option which are nearly universal in application but they have limited sensitivity and require a very good temperature control. Since...

Classification of Chiral Stationary Phases

Enantiomer separation by GC is mainly performed on three types of CSPs chiral amino acid derivatives via hydrogen bonding chiral metal chelates via coordination (complexa-tion GC) cyclodextrin derivatives via inclusion. Initially, the chiral selectors were used as involatile neat liquids or as solutions in squalane or poly-siloxanes, respectively. Subsequently, a number of chiral selectors have been chemically linked to poly-siloxanes (Chirasil-type stationary phases). Chiral Stationary Phases...

Nonlinear Extended pH Gradients

IPG formulations have been given only in terms of rigorously linear pH gradients. While this has been the only solution adopted so far, it might not be the optimal one in some cases. Altering the pH slope in some portions of the gradient might be required in those pH regions overcrowded with proteins. The reasons for resorting to non-linear pH gradients are given in the histogram of Figure 7. With the relative abundance of different species it is clear that an optimally resolving pH gradient...

The Separation Membrane

The dialytic transport across thin membranes can be described in eqn 33 C,MD and ci,MA are the solute concentrations in the membrane at the interfaces with the donor and the Objectives in a microanalytical scale Donor solution Acceptor solution Objectives in a microanalytical scale Donor solution Acceptor solution Flowing or stirred, large sample volume Slowly flowing or gently stirred, small volume Stirred or flowing, large reagent volume Quiescent or slowly flowing, small volume Quiescent or...

Anomalous Migration in Sdspage

The precise structural relationship of SDS to protein during SDS-PAGE is unknown but various studies have indicated that a wide variety of proteins all bind a relatively constant amount of SDS (+1.4 g SDS g_1 protein) and adopt a similar flexible rod shape regardless of their native configuration. It is this supposedly constant very high and uniform charge-mass ratio which allows for reliable molecular weight determination since migration rate therefore depends on molecular sieving alone....

Comparison of Video Technology with Classical Densitometry

Classical densitometry uses the spectral range from 190 to 800 nm with high spectral selectivity. Absorption spectra for substance identification can be recorded within this whole span. In contrast, video technology functions only in the visible range. The UV region - exceptionally productive for planar chromatography - is only indirectly accessible through the use of an UV indicator embedded in the layer and in cases where samples fluoresce. In this respect video technology parallels the human...

Cyclodextrins in Capillary Electrophoresis

In the pharmaceutical industry the importance of capillary electrophoresis is continuously growing. It is a technique which is increasingly used for determination of the optical purity of intermediates and final products. Many different optically pure compounds Figure 12 Capillary GC analysis on cyclodextrin stationary phases. Experimental conditions column (A) 15 m x0.32 mm ID Chiraldex B-PH ((S)-hydroxypropyl- -cyclodextrin (Astec)) (B) 15mmx0.32mm ID Chiraldex B-DA (dipentylated...

Air

The purpose of the air loop is to control a volumetric flow of air through the column or to maintain a three-phase density within the vessel. In basic control systems air rate is controlled manually based on a monitored air flow rate. In slightly more advanced systems, the flow is controlled through an automatic valve to compensate for pressure changes (Figure 2). Figure 2 Example of air control loop. PI, pressure indicator FIT, flow indicator and transmitter FIC, flow indicator and controller...

Indirect method

This method involves reaction of the enantiomeric mixture with a suitable chriral reagent to make the corresponding diastereomeric derivatives prior to chromatography the choice of chiral selector is Table 17 values of amino acids on untreated plates and plates impregnated with metal sulfates Aminoacids Unimpregnated Plate impregnated with Mn2+ Fe2 Co2 Ni2+ Cu2 Zn2 Cd2 Hg2+ T, Tailing SF, migrates with solvent front. hRF values are the average of at least five determinations. Table 18 TLC of...

Determination of Formation Constant of CSEnantiomer Complex

The present technique has an advantage over conventional HPLC by allowing the determination of the formation constant (Kf) for the CS-enantiomer complex which is useful for developing the CS for chiral chromatography. In a schematic view of the portion of the separation column in Figure 5, enantiomers (A+ and A_) are partitioned between the organic stationary phase (upper half) and the aqueous mobile phase (lower half). In the organic stationary phase enantiomers form a CS complex CSA+...

Amino Acids

The scraped layer corresponding to each spot is extracted with 70 ethanol in a known minimum volume, and ninhydrin reaction is performed followed by spectrophotometry. Six to eight standard dilutions in an appropriate concentration range for each amino acid are prepared 2 mL of amino acid solution and 2 mL of buffered ninhydrin are mixed in a test tube, heated in a boiling-water bath for 15 min, cooled to room temperature and 3 mL of 50 ethanol is added. The extinction is read at 570 nm (or 440...

Analytical OPLC Separations

In OPLC, the most frequent modes of development are linear one- and two-directional (Figure 5A,B). Linear OPLC, however, requires a special chromato-graphic plate sealed along the edge, by impregnation, to prevent the solvent from flowing off the layer. The advantage of circular development, in which the mobile phase migrates radially from the centre of the plate to the periphery, is well known for the separation of compounds in the lower RF range, Figure 4 Schematic diagram of long-distance...

Extraction Schemes

Classification schemes are numerous and no one scheme covers all systems. The most common schemes are based on the form of the extracted element that transfers into the organic phase. This simplified classification scheme is adequate for the discussion here. However, even with simple schemes the categories are not exclusive, and some extraction agents could be classified into other categories. The experimental process of inorganic extraction of a neutral complex, regardless of the type of...

Further Reading

Adamovics JA (1990) Chromatographic Analysis of Pharmaceuticals. New York Marcel Dekker. Bieganowska ML and Petruczynik A (1994) Thin-layer reversed-phase chromatography of some alkaloids in ion-association systems. Chemia Analityczna 39 139. Camag Bibliography Service Thin-layer Chromatography. Cumulative CD, Version 1.00. Camag 1997. Deyl A, Macek K and Janak J (1975) Liquid Column Chromatography. A Survey of Modern Techniques and Applications. Amsterdam Elsevier. Golkiewicz W, Gadzikowska M,...

Carbenicillin Sulbenicillin and Ticarcillin

These epimeric, di-anionic -lactams are similar in physicochemical properties and are analysed under very similar conditions. For analysis of carbenicillin (Figure 3, structure 7), plasma and urine samples are loaded onto an anion exchange solid-phase extraction column. Carbenicillin epimers are eluted with 10 lithium chloride-methanol (3 2) and injected into an HPLC. Analysis is on an ODS column with a mobile phase consisting of 0.05 mol L_1 ammonium acetate-methanol (9 1). Carbenicillin...

Flow Cell Sfcftir

The flow cell approach involves connecting a high pressure flow-through cell at the end of the separation column and positioning the flow cell in the FTIR beam so that the analytes can be monitored in real time as they elute from the column and flow through Table 1 Key advances in the development and application of flow cell and mobile elimination interfaces for SFC FTIR Mobile phase elimination approach 1986 First demonstration of flow cell SFC FTIR using carbon dioxide as the mobilephase...

Kataoka S Yamamoto and

Narimatsu, Okayama University, Tsushima, Aliphatic and aromatic mono-, di- and polyamines are naturally occurring compounds formed as metabolic products in microorganisms, plants and animals, in which the principal routes of amine formation include the decarboxylation of amino acids, amination of carbonyl compounds and degradation of nitrogen-containing compounds. Accordingly, amines are important indicators of a wide variety of biochemical, clinical, toxicological and fermentation...

The Principle of Electrodialysis

The principle of electrodialysis is illustrated in Figure 1. A typical electrodialysis cell arrangement consists of a series of anion and cation exchange membranes arranged in an alternating pattern between an anode and a cathode to form individual cells. If an electrolyte solution is passed through these cells and an electrical potential is established between the electrodes, the positively charged cations migrate towards the cathode and the negatively charged anions towards the anode. The...

R2r n

It is seen that the light intensity varies inversely as the square of the distance from the particle, which would be expected from the inverse-square law. Not so obvious is the inverse dependence of the scattered light intensity on the fourth power of the wavelength of the incident light. In practice, the equation does not precisely predict the intensity of the scattered light as there are a significant number of particles present that are not greatly smaller than the wavelength of the incident...

The Ion Exchange Membranes

Ion exchange membranes are the key components in electrodialysis. They consist of highly swollen gel-type polymer structures carrying fixed positive or negative charges. Polymer structures carrying negatively charged groups are referred to as cation exchange membranes, while those carrying positively charged groups are referred to as anion exchange membranes. In a cation exchange membrane, the fixed negative charges are in electrical equilibrium with mobile cations in the interstices of the...

Hi dx a2 ORf dx z ZoRf

Figure 7 Plot of time necessary to ascend 4 cm versus percentage of water in mixtures of methanol water and acetonit-rile water. acetonitrile O, methanol. Plate LiChrosorb RP-18 (7 im). The value of cos 6' decreases rapidly as the percentage of water increases. When 6' is close to 90 the solvent is unable to ascend the plate. Even when using a relatively nonviscous organic solvent such as acetonitrile, 30 of water is the upper limit. In Figure 7, the variation of 4 cm development time with...

Benzyloxime Derivatization

Derivatization of simple aldehydes and ketones to benzyloximes was developed by Magin. The reaction proceeds as follows aPerkin-Elmer F-11 gas Chromatograph equipped with a coiled glass column, 6 ft long and 1 8 in i.d. bRelative retention times of secondary peaks. Reproduced with permission from Kallio H etal. (1972) Gas-liquid chromatographic analysis of 2,4-dinitrophenylhydrazones of carbonyl compounds. Journalof Chromatography 65 355. and a typical chromatogram of DNPHs of carbonyl...

Detection of Alkaloids

Only a few alkaloids are directly visible on the chromatogram as coloured spots and visualization methods have to be applied to detect them. In order to detect the compounds under UV light, fluorescing indicators are added to the adsorbent. Alkaloids become visible in short wavelength UV light (X 254 nm), where they appear as dark zones on a fluorescent background. This is considered to be a nonselective method of detection because, on the layer containing a fluorescent indicator, the emission...

Group IA

As a general rule, most applications concern the brush-type CSPs having a rc-electron acceptor charac ter. This is because many compounds of pharmaceutical interest contain a rc-donor group. CSPs derived from N-(3,5-dinitrobenzoyl)amino acids are among the most widely used for enan-tiomeric separations of numerous compounds. The early commercialization of the well-known CSP ((R)-DNBPG), designed by Pirkle and co-workers in 1980, and the easy and inexpensive preparation of this type of CSP, has...

Preparative OPLC Separations

Whether or not the use of OPLC for preparative separation is necessary depends on the kind of sample to be separated. The potential of linear online OPLC on 20 cm x 20 cm plates with a separation distance of 18 cm as a preparative method is considerable. Because the average particle size of pre-coated preparative plates is too large, not all the advantages of this method can yet be realized. Generally, preparative online OPLC can be used for separation of 6-8 compounds in amounts up to 300 mg....

Like Dissolves Like

A compound will be soluble in, or mix with, another compound that is chemically like it. That is, the two compounds must be from the same, or similar, chemical families. This simple principle is an implied requirement in every analytical extraction. The concept of moving analytes from the matrix to some other location requires them to be transported using some medium in which they are soluble. Therefore, we must carefully consider how the like-dissolves-like concept can help to achieve the...

Focusing FFF

Focusing FFF methods have been classified according to various combinations of the driving field forces and gradients effective property gradient of the carrier liquid, cross-flow velocity gradient, gradient of the non-homogeneous field action. Figure 6 Construction of a channel for thermal FFF (1) electric heating cartridge (2) cooling liquid inlet and outlet (3) foil spacer (4) holes for thermocouples (5) longitudinal flow inlet (6) longitudinal flow outlet. While this classification scheme...

Principles of Chiral Separation Using Chiral Counterions

The chiral counterion may be the only chiral compound needed for separation of enantiomers in a chromatographic system. The solute enantiomers form diastereomeric ion pairs with the chiral counter-ion, also called the selector (Figure 2). In order to achieve enantioselectivity, the ion pairs formed should have different stabilities and or different distribution properties with the stationary phase. If the difference in distribution properties with the stationary phase is responsible for the...

Drugs

Immunoaffinity has been used for the measurement of several drugs and endogenous compounds, including anabolic steroids, betamethasone, bufuralol, clenbut-erol, corticosteroids, dexamethasone, fluoroquinones, leukotrienes, LSD, morphine, S-phenylmercapturic acid, salbutamol, sulphathiazole, tetracyclines, and the thromboxanes TxB1 and TxB2. Matrices include blood, plasma, urine, faeces, liver, milk and honey. In the case of immunoaffinity extraction, this has been used offline (as a form of...

Bubble Attachment

Bubble attachment at a hydrophobic surface occurs due to the instability of the aqueous film that separates the bubble from the surface. As the bubble approaches the surface, to such a separation distance that the bubble may be distorted, there is a thinning of the aqueous film to the point at which rupture occurs. This time of film thinning is called the 'induction time'. After rupture, the film is displaced as it recedes across the hydrophobic surface to establish the equilibrium contact...

Distributor Testing

Water test of assembled distributors at the manufacturer's workshop is always a good practice for all high-efficiency distributors. The test should determine liquid rate gradients under the distributor, liquid level in the distributor itself at design and Figure 12 Vapour distributor. (Courtesy of Sulzer Chemtech.) turndown liquid rate, liquid level gradient in the trough and uniformity of the drip point layout. These parameters should be compared to the distributor design parameters and...

Hydrolysis Products of Chemical Warfare Agents

Both the nerve and blister agents undergo hydrolysis in the environment and methods are required for retrospective detection and confirmation of these hydrolysis products. Hydrolysis products are significant as they are generally compounds that would not be routinely detected in environmental samples and their presence strongly suggests the prior presence of chemical warfare agents. The degradation products of the chemical warfare agents, in particular the nerve agents, are nonvolatile...

Mechanisms of Solute Transfer

Like some of the solid-membrane separation methods, the difference between the chemical potentials of the solute in the donor and acceptor solutions controls the transport of the species. In other words, the concentration difference is the driving force. There are various mechanisms for the selective transfer of solutes in the considered three-liquid-phase system. They can be divided into two groups nonfacilitated and facilitated, or carrier-meditated, transfer mechanisms. In nonfacilitated...

Countercurrent Chromatography and High Speed Countercurrent Chromatography Instrumentation

Employed and the mathematical treatment of each process are quite different. The term CCC was coined by analogy to the earlier CCD process and is considered a misnomer by some because, as usually practised, one phase is stationary in the apparatus. However, the terms are justified by the consideration that if the observer resided in either one of the phases, without reference to the stationary apparatus, it would appear that the phases move in countercurrent fashion. Indeed it is possible to...

Cyclohexane Recovery from Naphtha or Natural Gas Liquid

In recent years, ED technology has also been applied to the separation of paraffins and cyclopara-ffins, a much more difficult separation than aromatics and nonaromatics. One of the major developments was cyclohexane recovery from naphtha or natural gas liquid (NGL) streams. Cyclohexane, an important raw material for the nylon industry, exists naturally in naphtha and NGL streams. However, recovery of high purity cyclohexane from naphtha or NGL through conventional distillation is virtually...

Dual Mode Permeation in Glassy Polymers

Polymers in the glassy state possess 'free volume' as shown in Figure 2 - that is, a polymer quenched below its Tg to a nonequilibrium state in which its molar volume is higher than the equilibrium value. This free volume can be visualized as long-lived molecular-level gaps between the polymer chains. One aspect of free volume is that glassy polymers exhibit excess sorption capacity. Sorption in glassy polymers can be described by eqn 7 Figure 4 Coupling of Langmuir and Henry's mode diffusion...

Preparative ITP Apparatus

Capillary type ITP is useful not only for analytical purposes but also for preparative purposes. Capillary type (CITP) is useful for batch processing of a small amount of sample. In addition to direct cutting of the capillary section containing the target of interest, preparative methods in CITP can be classified into three types, as shown in Figure 4. Figure 4(A) shows a preparative ITP system reported by Arlinger for the fractionation of the entire sample zones. This system was used in the...

The First Followers

A small handful of researchers used chromatography with great success despite the obstacles outlined above Gottfried Kranzlin, Charles Dhere and co-workers, and Leroy Sheldon Palmer. They were all able to isolate pure compounds from natural mixtures. Figure 2 Separation of plant pigments as obtained by Tswett. (Redrawn after Tswett, 1906 see Table 1.) Figure 2 Separation of plant pigments as obtained by Tswett. (Redrawn after Tswett, 1906 see Table 1.) Figure 3 The structures of the...

Quantitative Determination of Carbohydrates

The easiest method of detecting and quantitating carbohydrates on a TLC plate is to use 14C-labelled Figure 8 Densitometric scan of TLC number 3 shown in Figure 2, using a Bio-Rad imaging densitometer. The relative weight per cents for each of the carbohydrates are shown at the top of each peak. The first peak is D-glucose, followed by maltodextrins maltose, maltotriose, maltotetraose, and so forth, down to a maltodextrin with 14 D-glucose residues. Figure 8 Densitometric scan of TLC number 3...

Design Rationale

A valuable approach in biotechnology involves the marriage of several technologies for the production of commercially viable diagnostics and therapeutics. The process of exploiting structural analysis, chemical synthesis and advanced computational tools when combined with rational design makes the technology more powerful, faster and logical. Structure elucidation of proteins by X-ray crystallographic and nuclear magnetic resonance (NMR) studies and improvement in software algorithms to...

The Principle of Electrodialytic Water Dissociation

The process of electrodialytic water dissociation using a bipolar membrane is illustrated in Figure 1, which shows a bipolar membrane consisting of cation and anion exchange layers arranged in parallel between two electrodes. If an electrical potential difference is established between the electrodes, charged species are removed from the interphase between the Figure 1 Schematic diagram illustrating the principle of electrodialytic water dissociation in bipolar membranes. Figure 1 Schematic...

Dissolved Air Flotation DAF

In this method compressed air or gas (nitrogen, carbon dioxide or methane) is dissolved into all or part, of a process liquid under pressure in a retention vessel. The gas-oil-water mixture is then sent to a flotation cell, where the pressure is reduced, causing bubbles to come out of solution. The bubbles then attach to and are possibly nucleated on the oil and suspended particles. The solubility of a gas in water is proportional to its partial pressure and inversely proportional to the water...

Membranes for Diffusion Dialysis

Modern membranes for acid dialysis are made of anion exchange polymers which have an affinity for acids and reject cations other than protons. The anion exchange membranes that are most permeable to acids seem to be those with a very high water content. The water content is important because the high electromobility of protons through water is attributable to a transfer mechanism that is not available to other cations. A proton can transfer from a hy-dronium ion to an adjacent water molecule by...

Selective Dialysis Across Solid and Liquid Membranes

Selective dialysis is defined here as a separation of substances from an aqueous donor phase into an aqueous acceptor phase, the phases being separated by solid and liquid membranes. The analyte transport through such membranes is based on a solva-tion diffusion mechanism in a lipophilic phase. The liquid membranes have to be supported by a micro-porous and hydrophobic layer to enable practical applications to be performed. Again the basic set-up of the flow separation cells shown in Figure 5...

Derivatized Amines

Direct chromatography on thin layers of primary and secondary amines is frequently difficult due to the strong adsorption of the NH2 or NH groups to the adsorbents employed. Derivatives are often used to overcome these difficulties. A series of reagents has been recommended for the formation of derivatives of primary and secondary amines in order to assist in separating, identifying and determining such compounds on thin layers. The formulae of the most important reagents are shown in Figure 2....

Comparisons of Packed and Open Tubular Columns

One thousand plates per foot of column length, or approximately 3000-plates per metre, represents the best that can be expected from a packed column although packed columns rarely achieve this value, it is often exceeded in the open-tubular system. The length of the packed column is limited in practice to about 5 m, because the packing offers a much greater resistance to gas flow than does the open tube. As a result, the packed column can deliver a maximum of about 15 000 theoretical plates,...

Module Design

There are basically six different designs of membrane modules tubular (with channel diameters greater than 3 mm), hollow fibre or capillaries (self-supporting tubes, usually 2 mm or less internal diameters), plates, spiral-wound, pleated sheets and moving modules (e.g. rotating discs or cylinders). Figure 6 shows the more common types of modules. The selection of a particular design depends on (a) the physical properties of the feed stream and retentate, especially viscosity and osmotic...

Solvent Purity

The analysis of impurities in high purity solvents is a very difficult task. By utilizing high speed GC instrumentation which has the ability to control the direction of carrier gas flow through the column this analysis can be greatly simplified. The ability of dual-flow direction instrumentation allows for minor impurities in the solvent to be separated and identified by venting off the solvent peak only. After the majority of the solvent peak has passed off the column and into the detector,...

GCMS Method for Analysis of Alkaloids

Capillary gas chromatography (CGC) analysis has been described for several classes of alkaloids. A ma jor advantage of GC over other methods is its enhanced sensitivity and high resolution. Another advantage is its easy coupling to a mass spectrometer, which allows the identification of new and minor compounds of a mixture without laborious isolation procedures. This makes it a particularly attractive method for thermally stable mixtures. The analysis of pyrrolizidine alkaloids, tropane...

Principle of Reciprocity and its Importance in CSP Development Development of DNB Amino Acid CSPs

The observation that the enantiomers of some DNB derivatives are well resolved on CSP structure I prompted an investigation of the reciprocal situation. As a general rule, if a CSP is useful for separating the two enantiomers of an analyte, then a second CSP derived from one of the enantiomers of that analyte should be useful for separating the enantiomers of compounds which are structurally related to the chiral selector of the original CSP. This concept is known as the 'principle of...

Continuous Linear Development

In conventional continuous development the end of the chromatographic plate is immersed in the eluent and the opposite end is extended out of the chromato-graphic chamber, allowing the solvent to evaporate Figure 5 Densitogram of standard mixture of glycosides separated on silica gel high performance TLC plate wtih stepwise gradient elution (gradient programme given in the text). 1, Acetyl-digitoxine 2, strophantine 3, digitaline 4, desacetylolanatoside 5, lanatoside 6, convalatoxine 7, digoxin...

Characteristics of the Corona Discharge

As voltage applied to a wire discharge electrode is increased, visible discharge points, 'tufts', begin to appear dispersed along the wire. Eventually the tuft pattern stabilizes, appearing as fingers which elongate and retract at 1-10 Hz and remain at somewhat fixed locations along the wire. This stabilization of the corona is indicated by a distinct increase in the slope of the electric field vs. applied voltage curve (Figure 4). Peek determined a semi-empirical expression for the corona...

Influence of Feed Characteristics

Flow rate At low flow rates the tangential velocity is too low to generate an adequate inward radial acceleration. This is reflected in the field results of Meldrum et al. in 1987 which have been converted from tabular results to the plot in Figure 3. These show sharply decreasing values of su for a 60 mm DR hydrocyclone on the Hutton field and for a 35 mm Dr hydrocyclone on the Murchison field for feed flows below & 100 L min1 and 60 L min1, respectively. Figure 3 also shows rapid falls in...

Bubble Particle Collision Dynamics

Interception efficiency - single bubble - particle collision Flint and Howarth observed that for a rational basis for flotation cell design to be achieved it is necessary that methods for the prediction of bubble-particle collision and subsequent adhesion be available. For a single particle falling under gravity in the path of a single rising bubble, they provided a general definition of collision efficiency E, as the ratio of the number of particles which collide with the bubble to the number...

Vaporizer Overflow Interface

The vaporizer overflow interface (Figure 4) is a further development of the stop-flow technique. The transfer valve sends the LC eluent either to waste or into a vaporizer chamber typically thermostatted at around 300 C, replacing the uncoated pre-column. Actuated simultaneously, a separate valve (to avoid contact with solvent) stops the carrier gas supply during transfer. The vaporizer consists of 0.32 mm Figure 4 Vaporizer overflow interface. Figure 4 Vaporizer overflow interface. i.d. fused...

The Christiansen Effect Detector

Refractive Index Detector

This method of measuring refractive index arose from the work of Christiansen on crystal filters. If a cell is packed with particulate material having the same refractive index as the mobile phase passing through it, light will be transmitted through the cell with little or no refraction or scattering. If, however, the refractive index of the mobile phase changes, there will be a refractive index difference between the mobile phase and that of the packing. This difference will result in light...

Fz DxD BxB

Here z is the mole fraction of light component in the feed, and xD and xB are the product compositions. For sharp splits with xD + 1 and xB + 0 we then have that D zF. In words, we must adjust the product split D F such that the distillate flow equals the amount of light component in the feed. Any deviation from this value will result in large changes in product composition. This is a very important insight for practical operation. Example Consider a column with z 0.5, xD 0.99, xB 0.01 (all...

F L XifL

Figure 1 The y-x behaviour of a binary mixture at constant temperature for various values of the relative volatility aij. where f L is the fugacity of pure liquid i at the pressure and temperature of the solution. At constant temperature, the effect of pressure on the pure liquid Integration of eqn 9 from the saturation pressure to the system pressure leads to where f Sat ( SatPSat) is the fugacity of pure i at saturation, Sat is the fugacity coefficient of pure i at saturation, and Psat is the...

Air Sparging Systems

The purpose of the sparging system is to distribute evenly the appropriate-sized bubbles near the bottom of the column. The sparging system is critical and must be designed taking into consideration many elements, including bubble size distribution, maximum air rate, bubble coalescence and induced mix ing uniformity of air hold-up across the vessel, minimization of scale formation, resistance to wear, required air pressure and maintenance considerations. There are many types of spargers used in...

The Air Sparged Hydrocyclone

The ASH was invented by Professor Jan Miller of the University of Utah, and was patented in the USA in 1981. It makes use of the centrifugal forces which arise when air is sparged through the walls of a hydrocyclone. The device consists of a cylinder with a porous wall enclosed in an external chamber (Figure 1). The feed slurry enters tangentially through a conventional hydrocyclone header at the top of the cyclone, to form an annular liquid layer on the inner surface of the porous wall. The...

Cross Linkers Other than Bis and Mixed Polyacrylamide Gels

PA is normally cross-linked with Bis to obtain an electrophoretic matrix. The use of (DHEBA) instead of Bis gives gels that can be solubilized in dilute periodic Figure 8 Electrophoresis of plant (iso)enzymeson ultra-thin PA gradient gels fixed on a polyester film. Gel dimensions 240x120x0.5 (mm) PA gradient from 4 to 28 T. Enzyme source current-year (1989) needles of Norway spruce (Picea abies L., Karst.) sampled from a variety of clones (clone numbers indicated) of the multiple clone variety...

Stateoftheart ED Technologies

The modern state-of-the-art ED technologies for BTX aromatic purification are based on several solvent systems sulfolane, NFM and NMP. Proprietary cosolvents may be blended into the base solvent to enhance the performance in specific applications. Table 3 summarizes the key performance parameters of LLE and ED for aromatics recovery. ED process can provide up to 25 savings in capital investment as compared with the commercially available LLE processes. This saving is attributable to the Table 3...

Detection

Among the different detectors used in gas chromato-graphy for biogenic amine analysis, the four detectors most commonly used are flame ionization detector (FID), electron-capture detector (ECD), nitrogen-phosphorus detector (NPD) and mass spectrometry (MS). Some biogenic amines such as aliphatic mono-, di-and polyamines do not exhibit structural features that permit their specific detection, in this case a nonspecific detector such as flame ionization (FID) can be used, but the lack of...

Hyn hL

From this expression we observe how the vapour flow will vary though a section due to variations in heat of vaporization and molar enthalpy from stage to stage. We will now show one way of deriving the constant molar flow assumption 1. Choose the reference state (where h 0) for each pure component as saturated liquid at a reference pressure. (This means that each component has a different reference temperature namely its boiling point (Tbpi) at the reference pressure.) 2. Assume that the column...

Chemically Bonded Polysaccharide Phases

Over the last few years, various attempts have been made to graft derivatized polysaccharides on to a silica matrix, without losing the chiral recognition properties of these materials. One of the major problems encountered was the limited amount of polysaccharide that could be chemically bonded. For the time being, only the French company Chiralsep (La Fresnaye) has a few chemically bonded polysacchar- ide-based columns (Chirose-bond C1 and Chirose-bond C3) on the market. We were able to test...

Conclusion Of Phl Buffer

Isotachophoresis is a useful analytical technique with high reproducibility. However, ITP is not a very familiar technique to many chromatographers. Possible reasons are absolute sensitivity of ITP is in the sub-nanomole range, which is low in comparison with recent capillary electrophoresis (CE) techniques auto-samples are not available and stepwise recording is not readily accepted by chromatographers. However, it should be noted that the relative sensitivity of ITP is comparable with CE...

Operational Electrolyte System and Separation Principle

Two different electrolytes (a leading and a terminating electrolyte) are used in ITP and this is the important point which distinguishes it from other elec-trophoresis method. A sample solution is injected at the boundary of the two electrolyte solutions as shown in Figure 1(A). The leading electrolyte is usually a pH-buffered electrolyte containing leading ions (L) with the same sign as the sample ions and appropriate counterions with pH-buffering ability. Usually, CP and K+ or NH are used as...

Continuous Centrifugation

These separations are similar to those previously discussed in the sense that separations are based on size or density differences. However, unlike batch-mode separation, in continuous centrifugation the sample mixture is introduced continuously to a spinning rotor as the supernatant stream continuously exits. For pelleting separations, the denser product may either accumulate on the rotor wall from where it is recovered after the rotor capacity is reached (semi-batch) or continuously...

Simplification of Multiresidue Methods

Official laboratories that investigate and analyse pesticide residues usually utilize the established multi-residue methods (MRM) of analysis. One of the most commonly used MRM for pesticide analysis in fruit and vegetables samples is the AOAC (Association of Official Analytical Chemists) method. It involves an aqueous acetone extraction and laborious clean-up employing LLP procedures using organic solvent of limited water capacity, to achieve the removal of the coextractives present in the...

Definition and Classification of Alkaloids

Alkaloids represent a wide variety of chemical structures (Figure 1). More than 16 000 are known and most Dagnino D and Verpoorte R (1994) Gas chromatography in the analysis of alkaloids. In Linskens HF and Jackson JF (eds) Modern Methods of Plant Analysis. Berlin Springer-Verlag. David F and Sandra P (1992) Capillary gas chromtogra-phy-spectroscopic techniques in natural product analysis (Review paper). Phytochemical Analysis 3 145-152. D'Mello JPF, Duffus CM and Duffus JH (eds) (1991) Toxic...

Replacement for Liquid Liquid Extraction

Solid-phase extraction was introduced as a replacement for liquid-liquid extraction to give a practical and economic solution to the real and perceived problems associated with solvent extraction techniques. Liquid-liquid extractions are labour Figure 3 Typical cartridge and vacuum filtration formats for solid-phase extraction using discs. Figure 3 Typical cartridge and vacuum filtration formats for solid-phase extraction using discs. intensive, difficult to automate, and frequently plagued by...

Thermodynamic Aspects of Polymorphism

Thermodynamic treatment of a system displaying polymorphism is based on considerations of the Gibbs free energy, Gi, of each polymorph as well as the variation of Gi with the thermodynamic variables temperature (T) and pressure (p). Furthermore, since each polymorph is distinct, each has a characteristic value for its entropy, Si ( > 0), under any given conditions of T and p. Considering constant pressure, the thermodynamic relationship (3Gl dT)p Si therefore indicates that the slope of the...

Immunoassay IA Methods for Carbamate Determination

In the last few years, the number of enzyme-linked immunosorbent assay (ELISA) methods for the determination of pesticides has increased, but there is still a lack of IA methods for pesticide residue determination in food and crop samples. IA techniques can provide complementary and or alternative approaches in reducing the use of expensive equipment and analysis time while still maintaining reliability and sensitivity. Moreover, IA can be used as a screening method in order to detect food...