The predawn of paper chromatography

Summary The activities of F.F. Runge, F. Goppelsroeder and R.E. Liesegang are outlined. The technique of capillary analysis is described and its shortcomings elaborated. Tswett's use of filter paper to imitate plant tissues is explained and finally, the considerations of Izmailov and Shraiber eventually leading to thin-layer chromatography are summarized.     

Analytical and experimental aspects of molecular-sieve chromatography

The object of this Review is to give analytical chemists a general introduction to molecular-sieve chromatography, a form of liquid chromatography in which molecular size forms the primary basis for separation, although other effects are also frequently involved. The technique can be used for inorganic and organic molecules, both monomeric and polymeric, in either aqueous or non-aqueous systems. The range of xerogel and aerogel molecular-sieves available at present is described, and the experimental techniques involved in their use are emphasized rather than mechanistic and theoretical considerations. The references cited have been selected critically to form a balanced, up-to-date review and also to indicate the general analytical potential and scope for future development of the technique. An Appendix lists the commercial sources of molecular-sieves and calibration standards.     

Techniques for gas chromatography of volatile terpenoids from a range of matrices.

The commercial importance of the volatile mono- and sesqui-terpenoids has resulted in a wide range of techiques being used for extraction, concentration, chromatography, and characterisation of constituents. The major chromatographic technique is gas chromatography, and tandem techniques of chromatography linked to further chromatography and spectroscopy, allow much increased resolution, and greater ease of characterisation of terpenes. A wide range of extraction techniques are discussed, and suitability for particular matrices and sample sizes outlined. Chromatography operating conditions and stationary phases, and techniques for solute identification are laid out. A number of applications of terpene analysis in many different matrices are discussed.     

Isolation of biologically active plant constituents by liquid chromatography

Strategies are outlined for the separation of biologically active products of plant origin. The techniques involved include low-pressure liquid chromatography, semi-preparative high-performance liquid chromatography, flash chromatography and droplet counter-current chromatography. Their application to the isolation of compounds from Sesamum angolense (Pedaliaceae), Psorospermum febrifugum (Guttiferae) and Cordia goetzei (Boraginaceae) is described.     

Simple calibration procedure for comprehensive two-dimensional gas chromatography

Mass transfer from the first-dimension to the second-dimension column in comprehensive two-dimensional gas chromatography (GC x GC) is normally quantitative, which means that the peak areas produced by GC x GC are equal to those obtained in one-dimensional gas chromatography (GC). In view of this relationship, it was investigated whether normal GC calibration could be used to quantify compounds analysed by GC x GC. Quantification of polycyclic aromatic hydrocarbons (PAHs) in sediment was used as a test case. It was concluded that more laborious and time-consuming GC x GC area calibration can be replaced by GC area calibration if separation quality and quantity prerequisites are met.     

Determination of 6-acetylmorphine in urine as a specific marker for heroin abuse by high-performance liquid chromatography with fluorescence detection

A sensitive method is described for the determination of 6-acetylmorphine in urine, to detect the use of heroin by drug addicts participating in a morphine-dispensing experiment. The method is based on an extraction procedure, reaction of the isolated 6-acetylmorphine with excess of morphine to give a highly fluorescent mixed dimer, and determination by normal-phase high-performance liquid chromatography (h.p.l.c.) with fluorescence detection. The calibration graph was linear at low 6-acetylmorphine concentrations and the absolute detection limit was 0.4 ng. In urine samples, 6 μg l^?1 of 6-acetylmorphine could be detected. A reversed-phase system is also outlined.     

Day-dream on process and laboratory gas chromatography

Three main problems have to be solved in process gas chromatography: psychological, technical and economic. A simple concept already used with success for fifteen years by the author, called the Deferred Standard, is an answer for process GC and, to some extent, laboratory GC as well. That the injection of a pure compound in each analytical sequence is reproducible demonstrates the good working order of PGC. Accurate quantitative results may be obtained because the gas density balance is used as a calibrator detector for determining the relative response factors of the components of interest with respect to the Deferred Standard. By suppressing any calibration standards in process and laboratory chromatography, the Deferred Standard may reveal itself as a time and money saving technique.     

Simultaneous determination of five different food proteins by high-performance liquid chromatography and partial least-squares multivariate calibration

A method is described for the simultaneous determination of food proteins originating from different raw food materials. The proteins are hydrolysed to amino acids which are labelled with dansyl chloride and finally separated by reversed-phase high-performance liquid chromatography. Partial least-squares multivariate calibration is used to resolve and quantify the overlapping amino-acid patterns. The method enables muscle protein, collagen, soy protein (both texturate and isolate), casein and milk protein to be quantified in both heated and raw samples from the same calibration set. The accuracies for the raw and heated samples averaged 3% and 6% relative total protein content, respectively.     

Developments in the application of gas chromatography with atomic emission (plus mass spectrometric) detection

Capillary gas chromatography with atomic emission detection is a highly element-selective and sensitive detection technique for many non-metal as well as metallic elements. A 3-5 order of magnitude element/carbon selectivity, compound-independent calibration and the possibility to calculate (partial) molecular formulae are some of the attractive features of the technique. In the present review, the emphasis is on real-life applications for non-metals such as sulphur, phosphorus, nitrogen and the halogens, and on the potential of combined atomic emission/mass spectrometric detection.     

Calibration of ultrafiltration membranes against size exclusion chromatography columns

Using the extension of the concept of universal calibration parameter, yielding a relation between the hydrodynamic volume of molecules and the elution volume in size exclusion chromatography (SEC), to retention coefficients in ultrafiltration (UF), we propose a direct calibration of UF membranes against chromatography columns. Plotting the retention coefficient by one given UF membrane of a series of probe molecules versus their elution volume in SEC chromatography provides a calibration curve for this membrane. For a wide range of retentions, such calibration can be directly used to predict the retention of any molecule: one only needs to measure its exclusion volume by the SEC column, and read the retention by the calibrated membrane on the calibration curves.     

Characterisation of polymers by size exclusion chromatography using multiple detection. Investigations on the determination of structural differences of hydroxyethyl starches

Summary An aqueous size exclusion chromatography system is outlined using dual detection by a multi-angel laser light scattering photometer (MALLS) and a concentration detector (RI). This system makes possible the determination of the molecular weight distribution of water soluble polymers in conjunction with the radius of gyration. The differences in the radii of gyration at the same molecular weights of two hydroxyethyl starches with different molecular structure are presented qualitatively. The determination of the Mark-Houwink relation for these polymers leads to a qualitatively similar result.     

Calibration of thin-layer chromatography with flame ionization detection for the analysis of natural lipid samples

Thin-layer chromatography coupled with flame ionization detection has been used to develop a method to quantitate fish lipids. Quantitation of fractionated lipid classes is usually accomplished through calibration with standards. Our work shows that various standards within a class, such as triglycerides or free fatty acids give substantially different responses to the detector. A method has been developed in which a composite sample of salmon lipid is prepared with an internal standard. This technique eliminates the variable detector response observed for compounds within a class and provides more accurate quantitation of oils from which the calibration samples were prepared. The lipid classes quantitated were triglycerides, free fatty acids, phosphatidylethanolamine and phosphatidylcholine.     

Fractionation of polyethylene by gel permeation chromatography

The performance of the gel permeation chromatography (GPC) technique was studied with several commercial samples of linear high density polyethylene. A comparison of these data was made with those obtained from the elution column technique based on fractional dissolution. GPC gave reproducible fractionation data in the molecular weight range of 10³–10⁶. These data were obtained from two columns in series with nominal capacity of 1–10⁴ and 1–10⁶A. Polyethylene fractions of known molecular weights are required as calibration standards and for many commercial polyethylenes it is necessary to increase sensitivity at molecular weight higher than 10⁶.     

Polymer characterization by coupling gel-permeation chromatography and automatic viscometry

A method is proposed for use of the universal calibration curve, i.e., the product of molecular weight and intrinsic viscosity versus retention volume, in calculating the molecular weight distribution of a polymer from gel-permeation chromatography (GPC) when the Mark-Houwink relation of the polymer in the solvent used for the GPC is unknown. This is achieved by measuring the viscosity of each fraction with an automatic capillary tube viscometer. Application of this technique to poly(vinyl chloride) and poly(vinyl acetate) proved to be successful.     

Determination of composition distribution of acrylonitrile-styrene copolymers by thin-layer chromatography

Determination of chemical composition distribution of acrylonitrile-styrene copolymers was carried out by thin-layer chromatography (TLC). A mixture of benzene and methyl ethyl ketone gave the most suitable calibration curve of R_f values versus acrylonitrile (AN) contents, where a concentration gradient technique was applied for development. Average AN contents obtained by TLC are coincident with those found by elemental analysis. The copolymers extracted from ABS resins are sufficiently arranged in the order of breadth of composition distribution by using the data from TLC. The agreement between the composition distribution curve and that from the theory of copolymerization is good.     

Evaluation of size-exclusion chromatography and size-exclusion electrochromatography calibration curves

Size-exclusion chromatography (SEC) and size-exclusion electrochromatography (SEEC) are chromatographic techniques used to determine molecular mass (weight) distributions (MWD) of polymers. One important step in the data treatment to derive MWD parameters is the modelling of the calibration curves. The calibration curves applied in SEC and SEEC are generally not linear. In this study the modelling of calibration curves is being examined. Different polynomial models have been evaluated and compared, not only for model fit but also for their predictive properties. It was found that sometimes a straight line and sometimes a third-order polynomial model were best. The best model across the effective range (also called linear range) is not always found to be a straight line. The SEEC curves were found to have considerably higher prediction errors than the SEC ones. Reduction of the number of calibration standards to five or six did not greatly affect the predictive properties of the calibration curves, neither in SEC nor in SEEC.     

Analysis of polyamides by size exclusion chromatography and laser light scattering

The molar mass analysis of polyamides is complicated due to the fact that only a limited range of solvents can be used and association and aggregation phenomena have to be screened by adding electrolytes to the mobile phase. Optimum SEC behaviour is obtained when hexafluoroisopropanol + 0.05 mol/L potassium trifluoroacetate is used as the mobile phase. The calibration of the SEC system can be conducted in different ways. While a calibration with narrow disperse polymethyl methacrylate standards does not yield accurate molar mass information, the quantification can be done using an “artificial” calibration curve. This calibration curve is obtained by correcting the PMMA calibration curve with polyamide molar mass data from light scattering. The resulting molar mass distributions for different types of polyamides are compared with molar masses that are determined by size exclusion chromatography with a light scattering detector and an excellent correlation is obtained.     

High-performance affinity chromatography

High-performance affinity chromatography is a new technique for the fast and efficient purification of biologically active molecules. It combines the biospecificity of affinity chromatography with the high speed and resolution obtained in high-performance liquid chromatography. In particular, the immobilization of ligands to different silica derivatives and their suitability for high-performance affinity chromatography are discussed.     

Spectroscopic quantifiication of preservatives in different food matrices using QuEChERS extraction and multivariate calibration with comparison against liquid chromatography

The application of QuEChERS (Quick, Easy, Cheap, Effective, Rugged and Safe) extraction procedure has recently received significant attention, particularly for quantifying food additives in complex food matrices. A reliable analytical method based on QuEChERS extraction, UV spectroscopic measurement at 200–320 nm and partial least square regression PLS1 was outlined to determine two classes of preservatives in different processed food products. Examined additives were sodium benzoate SB, potassium sorbate PS, propylparaben PP, and methylparaben MP which showed highly overlapping UV spectra. The method indicated high detection of preservatives down to 1.1–2.4 mg/kg, recoveries between 97 and 102%, and RSD ≤ 7.0%. The efficient extraction of preservatives by QuEChERS from real matrices has improved the snentivity of spectral measurement and the detection of the analytical procedure. Methylparaben, MP, was detected in most samples with levels of 24.5, 74.3 and 393.7 mg/kg in liquid drinks, corn flakes, and soya sauce, respectively. The levels of preservatives were found to be within the regulated limits in all tested items. The outlined QuEChERS along with PLS1 calibration of spectroscopic data is proved to be a suitable alternative for liquid chromatography to monitor different types of preservatives in complex food matrices. The validity of the proposed method was checked against standard liquid chromatography.     

Progress in liquid chromatography of synthetic electroneutral polymers

Recent achievements and anticipated future progress in high performance liquid chromatography of synthetic electroneutral polymers (polymer HPLC) are briefly reviewed. Basic retention mechanisms of polymer HPLC are explained and corresponding separation procedures are discussed. Advantages, drawbacks and pitfalls are presented of the most important polymer HPLC method, namely size exclusion chromatography. Principles of polymer HPLC methods combining various separation mechanisms within one chromatographic column (coupled procedures) or in a set of different chromatographic columns (two- and multi-dimensional procedures) are outlined.