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

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...

Polymorphism

Display very significant differences in physical properties such as melting point, colour, hardness, density, electrical conductivity, heat of fusion, solubility and dissolution rate, as well as differences in chemical reactivities. Polymorphism is a common phenomenon which has vital ramifications in the crystallization and processing of pharmaceuticals, in food chemistry, explosives manufacture and in crystal engineering. The profusion of polymorphic forms that might be encountered for a...

Countercurrent Distribution

A convenient way of multiextraction is countercur-rent distribution (CCD). Here a number of top phases are sequentially moved over a set of bottom phases and equilibration takes place after each transfer. The process can be seen as a step-wise chromatography. The original two-phase system, number 0, contains the sample and after that a number (n) of transfers have been carried out n 1 systems are obtained and the various proteins in the sample are distributed along the CCD train. The CCD...

Cation Exchangers

HPLC analyses of carbohydrates are most frequently carried out on cation exchange stationary phases consisting of sulfonated polymer-based materials, which can be obtained in various degrees of cross-linking and various particle sizes. Cation exchangers based on poly(styrene-divinyl-benzene) (PS-DVB) copolymers are the most common stationary phases used for carbohydrate separations. Copolymer-based columns offer many advantages for the analysis of carbohydrates and alditols. The PS-DVB...

Future Developments

As current and future separation problems become more difficult due to complex molecular structure of solutes, changes in environmental regulations and demands for material and energy conservation, the solvent selection problem is also becoming more difficult. It is no longer feasible to attempt to solve the solvent selection problem with a single database. Computer-aided techniques provide the necessary framework to solve the current and future solvent selection problems. The current hybrid...

Conclusions Summary of Main Trends

A wide variety of HPLC methods are available to analyse carbohydrates from various complex matrices. Aminopropylsiloxane-bonded silica of small particle diameter (3 im), amine-bonded vinyl alcohol copolymer packings, diol- and cyclodextrin-bonded silica, as well as macroporous cross-linked vinyl-pyridinium polymers, are some of the columns of choice for high selectivity in the HILIC of carbohydrates. Furthermore, a large number of columns may be selected to separate carbohydrates on cation...

Column Development

The development of electrochemically modulated liquid chromatography can be traced back to the early 1950s and 1960s when concepts for the desalination of water and for the separation of metal ions explored a union of liquid chromatographic and electrochemical techniques. These and many subsequent investigations suffered from poor chromatographic efficiency (10-200 plates m-1). As a consequence, interest in this technique has been limited until a few years ago. This limitation reflected the...

Tailor Made Additives

Tailor-made additives are usually organic additives that are especially designed to aid in the crystallization of a particular organic crystal compound. The additive can be designed to work only on a very specific crystal surface. Again, the additive works by blocking the growth of this crystal surface, making the surface morphologically more important. A characteristic tailor-made additive is very similar to a building unit. The interaction energies needed for adsorption of the building unit...

Mass Spectrometry

Mass spectrometry is the method of choice for the detection and characterization of chemical warfare agents, their precursors, degradation products and related compounds. Extensive use has been made of GC-MS and the mass spectra of numerous chemical warfare agents and related compounds have been published, with the most common chemical warfare agent mass spectra being available in the OPCW, commercial or defence community databases. Samples collected for chemical warfare agent analysis...

Alkylsilica Packings

Octadecylsiloxane bonded silica materials, usually designed for reversed-phase (RP) chromatography are nonpolar stationary phases having relatively strong hydrophobic character. The choice of an RP column with pure water as the eluent is an easy method for HPLC analysis of carbohydrates. However, the mechanism governing retention of carbohydrates is not reversed-phase partition but a form of hydrophobic chromatography, involving van der Waals interactions between carbohydrates and the alkyl...

Suspension Growth

In this technique, the crystals form and grow freely suspended in the mother liquor. The heat of crystallization is absorbed by the supercooled liquor. High Figure 6 Heat integration of dynamic falling film crystallizers. (Courtesy of Sulzer Chemtech.) Figure 6 Heat integration of dynamic falling film crystallizers. (Courtesy of Sulzer Chemtech.) specific productivity can be achieved at low growth rates because the crystal surface area is very large (up to 10 000 m2 m 3). Typical growth rates...

Correlation of Vapour Liquid Equilibria VLE

The quality of the available experimental data is the first concern of any VLE correlation. It is known that a considerable proportion of experimental values are not of good quality owing to the impurity of the chemicals and poor equilibrium stills used, equipment set-ups, and operator errors. In many instances there are quantitative discrepancies among the experimental results for the same system investigated under the same thermodynamic conditions by different authors. Therefore, it is...

Heterocyclic Bases

Heterocyclic compounds containing one or more nitrogen atoms have been extensively investigated on thin-layer chromatography as detailed in Table 5. Almost all the heterocyclics are chromatographed on polar stationary phases (silica gel, alumina, cellulose, polyamide) and, to a lesser extent, on hydrophobic layers obtained by impregnating polar adsorbents with nonpolar substances or by using silanized silica gel plates. Chemically modified and impregnated layers with cationic and anionic...

Collection Efficiency

Most important in ESP operation is the particulate collection efficiency, the fraction of particulates removed. Around 1920, Deutsch and Anderson independently derived an expression for r, now commonly referred to as the 'Deutsch equation' no disturbing effects such as erosion, re-entrainment, uneven gas flow distribution, sneakage, or back corona. A number of researchers have adjusted the Deutsch equation to account for neglected factors. Especially questionable is the assumption of complete...

Sample Application as Bands

Sample application in the form of narrow bands provides the highest resolution attainable with a given chromatographic separation method. The sample is typically contained in a syringe, which is emptied by a motor. Delivery speed and volume are electronically controlled. A stream of an inert gas such as nitrogen around the tip of the syringe atomizes the sample and creates a band on the TLC plate if either the syringe or the plate is moving linearly. Because large sample volumes can be applied,...

Cell Launders

Launders in flotation cells are located outside the overflow lip to collect and transport the froth or concentrate product out of the cell tank. Launders are typically located on the top of the cell tank, as shown in Figure 1. Launders are designed with a slope of about 10-15 for smooth transportation of froth without blockage in the launders. The design of launders varies with cell size and type. The launders are located on opposite sides adjacent to the feed and discharge boxes in rectangular...

Theory of Electrophoresis

Harisingh Gour University, Sagar, India Electrophoresis experiments are usually carried out to obtain information on the electrical double layers surrounding the mobile particles, to analyse a mixture, or to separate it into components. Interpretation of experimental results requires a theory connecting the electrophoretic mobility with the fundamental quantities relating to the electric double layer - the electrical potential, charge and structure. The electrical double layer...

Flotation Physics

It is evident that, for effective flotation, the thin liquid films between an air bubble and a target have to be thinned and ruptured (film stability), while association between different species (hetero-coagulation) needs to be avoided to separate one species from another. The physics of the flotation system (i.e. surface forces between various phases) controls such phenomena as thin film stability and coagulation. As a macroscopic process, flotation is often analysed in terms of micro...

Applications

Examples of GC analysis of acids in real-world samples are so numerous and diverse as to permit only representative cases from more significant fields to be cited. Carboxylic acids present at abnormal levels in plasma and urine may indicate various metabolic disorders. Hence, their monitoring is vital for diagnostic purposes. GC has simplified such analysis by expediting the separation and determination of very low concentrations of acids present in these complex matrices (Figure 3). For...

Introduction

The analysis of antibiotics is of primary importance for drug monitoring in pharmacokinetic and health studies, as well as for the quality control of drug production and of numerous food products. As a consequence, the demand for new methods of determination of antibiotics of very different types is continuously increasing. The main methods employed for these analyses include immunoassays and chromatog-raphy, as well as various chemical techniques. Among the chromatographic methods, high...

Sample Preparation

The first step is the most critical in terms of obtaining an adequate recovery for amines, because of the Figure 1 Dual chromatograms of amines as N(O)-isoBOC, O-TBDMS derivatives separated on DB-5 and DB-17 (both 30 m x0.25 mm I.D., 0.11 m film thickness) dual-capillary column system. GC conditions are described in the text. Peaks 1 ethyl-methylamine 2 terf-butylamine 3 diethylamine 4 sec.-butylamine 5 isobutylamine 6 diisopropylamine 7 n-butylamine 8 dipropylamine 9 pyrrolidine 10...

Collection Zone

The collection zone is characterized by a stream of individual bubbles rising against a descending liquid or slurry. This is the zone in which the bubble-particle attachment occurs. The capacity of the column is dictated in part by the intensity of bubble-particle collision (number of collisions per unit time), the probability of attachment, and the bubble surface area flux through the vessel (removal ability) in this zone. When sizing a column, certain assumptions are made. These include that...

Miscellaneous

One novel application of high speed GC has been in the rapid screening of soil gas samples for fuel-related Figure 9 Comparison of high speed screening mode using the photoionization detector (top) and the advanced field analysis mode using the FID (bottom) for a test mixture containing A, n-pentane B, benzene C, toluene D, ethylbenzene E, o-xylene. (Reproduced with permission from Sacks etal., 1996.) hydrocarbons. The gas samples are continuously generated from a cone penetrometer (CPT)...

Vapour Phase

The selection of the vapour space is a variable offered only by planar chromatography. Three important factors have the greatest influence on this parameter - the chamber type, the ratio of the surface of chromatographic plate to the chamber volume, and the temperature. Basically, one can distinguish between normal (N) and sandwich (S) chambers. In the conventional N-chamber there is a distance of more than 3 mm between the layer and the wall lid of the chromato-graphic chamber. If this...

Thiazolidine Derivatization

Hayashi et al. developed a method to determine formaldehyde and methyl glyoxal in foods and beverages. This method is known as the cysteamine method. Volatile aliphatic aldehydes and ketones react with 2-aminoethanethiol (cysteamine) to form thiazolidine compound as follows GC conditions SE-52 capillary column (25 m x 0.25 mm i.d.), Reproduced with permission from Nishikawa H et al. (1987) Determination of aldehydes in exhaust gas and thermal degradation emission using volatile derivatization...

Donnan Dialysis

Donnan dialysis, also referred to as ion exchange dialysis, occurs after placing an ion exchange membrane between two solutions containing different electrolytes. According to the scheme depicted in Figure 2, ions can cross a membrane when their sign is opposite to the sign of the membrane-forming poly-electrolyte. At the same time, the permeation of co-ions is hindered because of their electrostatic exclusion from the membrane phase. Usually, divalent or univalent metal cations are transported...

Synthetic Dialysis Membranes

The monomeric subunits of the various synthetic membranes individually vary and all differ significantly from cellobiose. The absence of surface hydroxyl groups on synthetic membranes is one factor responsible for the reported differences in complement activation between synthetic membranes and either unsubstituted cellulosic membranes or modified cellulosic membranes of low permeability. Subsequent to the introduction of the AN69 (sulfonated polyacrylonitrile) membrane in the early 1970s,...

Full or Normal Scan

The standard GC-MS mode of operation is the full or normal scan mode. On injection of the sample into the GC, the mass spectrometer is set to repetitively scan over a preset mass range. Typically this would involve the mass spectrometer recording a mass spectrum over the scan range 35-500 Da once a second. Figure 3 A quadrupole based GC-MS instrument employing a direct interface for connection between the GC and the MS. Figure 3 A quadrupole based GC-MS instrument employing a direct interface...

Svedala Cells

The former manufacturers of Denver flotation cells (Denver Equipment, USA) and Sala cells (Sala International in Sweden) have merged together to form the Svedala Pumps and Process Division, which is part of the worldwide Svedala Industri group. Both Denver and Sala cells are available through Svedala companies located worldwide. The Svedala flotation cells include mechanical flotation cells in the AS range (previously known as Sala cells), in sizes from 0.03 to 16 m3 the DR range Table 3...

Acidic Compounds of Biosynthetic and Biological Importance

A number of polyfunctional cyclohexanyl derivatives classifiable in several of the above groups are (6) shikimic acid, (7) mevalonic acid and (8) abscisic acid, all of which have biological significance. Their TLC properties in a number of solvents have been described. Table 4 hRF values of keto acids on various layers Table 4 hRF values of keto acids on various layers a, Ethyl formate-light petroleum (60-80 C)-acetic acid (50 50 7), silica gel b, ethanol-concentrated ammonia-water (78 13 20),...

Maldistribution

Liquid maldistribution has a very large effect on column distillation performance. Liquid maldistribution is originated by uneven liquid flow from the distributor to the top section of the packing. Some degree of maldistribution cannot be avoided and it is related to the following factors. Drip points density (total drip points column cross-section area) In principle, a smaller number of drip points equates to a higher initial maldistribution. This could be solved by constructing distributors...

Quantitative Headspace Analysis

Any quantitative method used for HS-GC has to take into account the influence of the sample matrix. The neat matrix should be available to prepare calibration standards, except for gas samples or if the composition of the gas phase only has to be determined, as in aroma research. The calibration techniques of standard addition or multiple headspace extraction (MHE) do not need the pure sample matrix, as opposed to internal or external standard calibration, which do. A neat matrix is also not...

Points to Consider to Obtain Good Separations

A relatively small (1-25 L) measured amount of sample should be carefully added on to the TLC plate, keeping the size of the spot as small as possible. The use of a microlitre syringe pipette, such as a Hamilton syringe, is desirable. When many samples are to be added to the TLC plate, a multi-spotting instrument can conveniently be used to make very small, uniform spots with a minimum of effort. The multi-spotter is also convenient when a relatively large volume, for example 10-25 L, of sample...

Penicillins and Cephalosporins

Many penicillins and cephalosporins are chiral, partly due to the chirality of the side chain. The d-epimers of ampicillin (see Figure 3, structure 13), cephalexin (Figure 3, structure 17) and cephaloglycin are more active than the corresponding l-epimers. Stereo-isomers also exist for amoxicillin (Figure 3, structure 14), azidocillin, cefamandole, cefsulodin and cef-tibuten (Figure 3, structure 16). For these -lactams, commercial preparations contain only a single isomer. For some -lactams,...

High Performance Liquid Chromatography

The term HPLC is appropriate for separations of any size (from microanalytical to preparative) if the particles of the stationary phase are not larger than about 10 im and if the reduced plate height (after Knox) is not larger than 5. This means that the pressure which is necessary in order to force the mobile phase through the column is a parameter of minor importance (the P in HPLC meant pressure when the abbreviation was first coined). It was a long way from pressure to performance with a...

Elution Strength of Micellar Mobile Phases

A disadvantage of MLC techniques is that the eluent strength of micellar mobile phases is quite small. Figure 2 Chromatograms corresponding to the separation of a mixture of 15 benzene and naphthalene derivatives. (A) 0.02 mol L 1 SDS modified with 5 n-butanol. (B) 0.035 mol L 1 SDS modified with 5 n-butanol. (C) 0.035 mol L 1 SDS modified with 10 n-butanol. Key 1, benzene 2, benzylic alcohol 3, benzamide 4, toluene 5, benzonitrile 6, nitrobenzene 7, phenol 8, 2-phenylethanol 9, chlorobenzene...

Fundamentals of Electrophoresis

Unlike chromatography, there is no formal International Union of Pure and Applied Chemistry (IUPAC) definition of electrophoresis, although one is being developed at the time of writing. However, through teaching the subject over the past 10 years, I have developed the following definition 'Electrophoresis is a mainly analytical method in which separations are based on the differing mobilities (i.e. speed plus direction of movement) of two or more charged analytes (ionic compounds) or particles...