Chromatographic identification of pesticides

The chromatographic properties of 51 common pesticides have been measured using seven different chromatographic systems involving gas-liquid chromatography (GLC), high-performance liquid chromatography (HPLC) with diode-array spectrophotometric detection and thin-layer chromatography (TLC) with different spray reagents. Correlation coefficients were calculated for combinations of all systems. The best combination of the chromatographic systems examined for the identification of an unknown compound is GLC on OV-17, HPLC on ODS-Hypersil with acetonitrile-water as eluent and TLC using an isooctane-ethyl acetate solvent system.     

Paper electrophoretic separation of some diastereomers

Summary Gas chromatography (GC) and thin-layer chromatography (TLC) have received most attention as techniques for separation of stereoisomers. Indirect separations by GC of diastereomers have been extensively reviewed by Gil-Av and Nurok [1] while Lochmüller and Souter recently reviewed direct GC resolution methods [2]. TLC work involving diastereomeric compounds of various classes: -methyltryptophans [3], di- and tripeptides [4], some aliphatic compounds [5], and thymidine hydrates [6] have been reported. Although much attention is given to diastereomer separations by GC and TLC, no reports exist of such applications by electrophoresis. This report describes some high voltage electrophoretic separations of diastereomers of several pharmaceutically and biochemically useful compounds.     

Behavior of peptides and computer-assisted optimization of peptides separations in a normal-phase thin-layer chromatography system with and without the addition of ionic liquid in the eluent

The addition of an ionic liquid into the mobile phase appeared to be useful in optimization of chromatographic separation of peptides. Different behavior of peptides in thin-layer chromatography (TLC) was observed after addition of 1-ethyl-3-methylimidazolium tetra fluoroborate to the eluent in comparison to the system without the ionic liquid. Nonlinear dependence of the retention coefficient, R(M), of peptides on the volume percentage of acetonitrile in the eluent was found in normal-phase TLC with and without immidazolium tetra fluoroborate in the mobile phase. In general, R(M) increased with increasing concentration of acetonitrile. In TLC systems without the ionic liquid, R(M) can be described well with a quadratic function. On the other hand, in a TLC system with an ionic liquid as the additive to the mobile phase, the retention behavior is better described with a third-degree polynomial function. The potential usefulness of ionic liquids for optimization of separation of peptides was demonstrated. Optimization of the separation conditions was supported by a commercially available computer program.     

Use of evaporative light scattering detection for the quality control of drug substances: Influence of different liquid chromatographic and evaporative light scattering detector parameters on the appearance of spike peaks

High performance liquid chromatography (HPLC) with evaporative light scattering detection (ELSD) is a versatile, easy to use and inexpensive alternative when it comes to the analysis of substances lacking a chromophor for UV detection. However, in pharmaceutical analysis injection of highly concentrated test solutions are normally required to control impurities at low levels. Under these conditions spike peaks were observed in the chromatograms of the test solutions making a proper evaluation of the impurity profile impossible. The influence of different eluent and ELSD parameters such as eluent composition, eluent flow-rate, ELSD scavenger gas flow-rate and evaporation temperature on the appearance of spike peaks was investigated. It could be shown that spike peaks can be avoided when selecting elevated eluent flow-rates and ESLD scavenger gas flow-rates. Moreover, eluents containing high amounts of organic modifier seem to foster the appearance of spike peaks.     

Determination of n-acetylmuramoyl-l-alanyl-d-isoglutamine in liposomes by HPLC

A method using reversed-phase high-pressure liquid chromatography (with spectrometric detection at 218nm) is described for the determination in new pharmaceutical preparations (liposomes) of a new immunostimulating agent (N-acetylmuramoyl-l-alanyl-d-isoglutamine). Separation was achieved with a mu-bondapak column and phosphate buffer (pH 2.5)-methanol mixture (93:7 v/v) as eluent, at a flow-rate of 2 ml min . Sodium acetate was used as an internal standard. The detector response at 218 nm was linear in the range 10-170 mug ml . The method is simple and accurate.     

Reversed-phase partition high-pressure liquid chromatography of trace amounts of inorganic and organic mercury with silver diethyldithiocarbamate

Inorganic and organic mercury diethyldithiocarbamates have been separated by reversedphase partition high-pressure liquid chromatography. The mercury chelates were formed by an exchange reaction with silver diethyldithiocarbamate in chloroform, in the presence of acetate buffer (pH 5.0). The inorganic and organic mercury chelates in the extract were separated within 30 min on a 3.9 x 300 mm mu-Bondapak C(18) column. EDTA (10(-4)M) in methanol-water mixture (78:22 v v ) was used as eluent at a flow-rate of 0.5 ml min .     

离子色谱用于标准物质硫酸根定值的方法研究

对离子色谱用于测定标准物质硫酸根定值的方法进行了研究。采用阴离子分析柱IonPac AS19(2 mm×250 mm),抑制型电导检测,进样体积25 μL,NaOH为等度淋洗液,通过正交设计表安排试验,确定了优化的色谱条件。SO2-4的检出限是0.005 mg/L,方法的精密度（RSD）为0.44%,方法的线性范围是1.0～50.0 mg/L, 样品的平均加标回收率为95.5%～105%。利用校正曲线的稳定性检查,质控样的可靠性检查和回收率试验证明该分析方法是可靠的。该方法操作简单、速度快、灵敏度高、重复性好,已用于标准物质硫酸根的定值。     

New TLC/HPTLC commercially prepared and laboratory prepared plates: A review

Thin-layer chromatography (TLC) had its initial growth in the 1950s when TLC sorbents and devices for making TLC plates in the analytical laboratory became available. A resurgence in TLC use occurred when commercially prepared plates became available around 1965. Their advantage was greater reproducibility because of their uniformity and convenience of use. Having just passed the 50th anniversary of this date, TLC still finds wide application as a useful analytical tool throughout the world. The introduction of high-performance TLC (HPTLC)-prepared plates was also a welcome addition to the chromatography laboratory. Today, advances in TLC instrumentation that aid in sample application, plate development, qualification, and quantification continue to evolve and improve. The TLC/HPTLC plate manufacturers have continued to add new prepared plates to meet the greater demands for higher purity or special applications for these newer devices. More recently, researchers have experimented with new sorbents or preparation techniques that have resulted in special properties for thin-layer-prepared plates, particularly for use in TLC–MS applications. This article will discuss not only some classical TLC plates but also these newer thin layers, their advantages, and some of their applications.     

Class Fractionation of Acidic Glycolipids and Further Separation of Gangliosides by OPTLC

Abstract

The use of the OPTLC method has been extended to the separation of the acidic fraction of the total lipid extract derived from a given blood element. This newly developed method is suitable for the interclass separation of sulphatides and gangliosides and further intraclass separation of gangliosides on the same TLC plate with step gradient development. The elutions can be performed on 10 × 10 cm (or larger) HPTLC plates with 13 parallels on each one. The chromatograms were stained either with orcinol-H₂SO₄ to show class separation (in this case only a single isocratic elution was performed) or with rescrcinol-HCl reagent to visualize the ganglioside intraclass separation. The chromatograms were evaluated by spectrodensitometric scanning and the reproducibility of the separation was determined.     

Superheated water as eluent in high-temperature high-performance liquid chromatographic separations of steroids on a polymer-coated zirconia column

High-temperature liquid chromatography (HTLC), with a superheated water mobile phase, has been shown to be a feasible replacement for medium-polarity acetonitrile-water mixtures as an eluent in reversed-phase HPLC. Instrumental parameters of flow-rate, injection volume and mobile phase preheating were shown to have significant effects on the quality of the chromatographic peaks. The selectivity and retention patterns of testosterone and several related compounds were investigated on a porous zirconia, polybutadiene-coated column at temperatures up to 200 degrees C and compared with that of a porous silica, octadecylsilane-coated column and the zirconia column under traditional reversed-phase conditions of an acetonitrile-water mobile phase at 40 degrees C. The selectivity differences observed for testosterone and related compounds show that the separation mechanisms are complementary and unique selectivity is obtained with the zirconia column under HTLC conditions.     

Chromatographic analysis of chemical warfare agents

The usefulness and applications of the particular types of chromatography in the analysis of chemical warfare agents have been reviewed. A major problem in the chromatographic analysis of chemical warfare agents is the collection and preparation of the samples. The importance of this problem differs for the various types of chromatography. Significant differences occur in the way in which samples are collected from air, water, soil, vegetables or animal organisms. The analyses are characterized by the main groups of chemical warfare agents, e.g., organophosphorus, vesicants, irritants, etc. Account has been taken of the relationships between their properties and the possibilities of their chromatographic analysis. The advantages and disadvantages of particular types of chromatography in the analysis of the particular groups and individual agents have been considered. The detectability of particular chemical warfare agents has been assessed, together with the separating efficiency for their mixtures. Examples of applications of chromatographic systems and conditions of chromatographing are summarized in tables. It is concluded that chromatography is a very useful tool in the analysis of chemical warfare agents; GC and TLC have the most advantageous properties, HPLC being slightly inferior.     

On the signal response of various pesticides in electrospray and atmospheric pressure chemical ionization depending on the flow-rate of eluent applied in liquid chromatography-tandem mass spectrometry.

The API-MS signal response of several pesticides (atrazine, simazine, isoproturon, diuron, chlorfenvinphos, chlorpyrifos, alachlor, trifluralin) depending on the flow-rate of eluent entering the MS interface was investigated. The investigations were based on API-MS-MS analyses of standard pesticide mixtures in the flow injection mode (FIA) at systematically varied eluent flow-rates using both an ESI interface (Turboionspray) and a heated nebulizer type APCI source. In the result, the individual compounds included in this study showed significant differences in their signal response behaviour depending on the flow-rate of eluent applied. The most hydrophobic compounds among the investigated pesticides (chlorpyrifos and trifluralin) showed drastic losses of sensitivity with increasing eluent flow-rate in both ESI and APCI, while more hydrophilic compounds like atrazine, simazine and isoproturon showed the expected signal response (concentration-sensitive in ESI, mass-flow-sensitive in APCI) at least within a certain range of flow-rates (200-600 microl/min in ESI, 200-2000 microl/min in APCI). These findings lead to the conclusion that application of a programmed HPLC eluent flow-rate may be advantageous to achieve maximum sensitivity of API-MS detection for all pesticides of interest. This is exemplified by the implementation of a flow gradient into an online SPE-HPLC-APCI-MS/MS method for improved analysis of pesticides in drinking water.     

Macromolecular prodrugs. V. Simultaneous determination of high-molecular-weight dextran metronidazole monosuccinate ester prodrugs and the hydrolysis products metronidazole and the corresponding monosuccinate ester on nucleosil diol

A high-performance size-exclusion chromatography procedure using Nucleosil Diol has been developed which provides the simultaneous determination of macromolecular dextran metronidazole monosuccinate ester prodrugs and the hydrolysis products metronidazole and metronidazole monosuccinate. Various factors influencing the chromatographic behaviour of the compounds are discussed. Baseline separation of the three substances was achieved within 8 min by using a 0.05 M phosphate buffer pH 7.5 eluent at a flow-rate of 2 ml min-1. The detection limit at 320 nm for a conjugate with a degree of substitution of 4.61 was found to be 3.5 micrograms ml-1.     

Determination of Trialkyl and Triaryl Phosphates by Narrow-bore Liquid Chromatography with On-line Thermionic Detection

Abstract

The potential of a previously reported on-line reversed-phase liquid chromatography-thermionic detector (LC–TID) system has been further evaluated. Several trialkyl (trimethyl to tri-octyl) and triaryl (triphenyl and tri-o-cresyl) phosphates were chosen as model compounds. LC was done on an alkyl-bonded silica column with methanol-water (80:20) at a flow-rate of 35—70μ/min as eluent. The band broadening in the interface-TID unit increased with decreasing volatility of the compounds and for the relatively non-volatile compounds, the band broadening decreased with increasing eluent flow-rate.

For most of the test compounds, detection limits of 40–100pg were obtained. As an illustration of the high selectivity of the LC[sbnd]TID system, the trace-level determination of two aryl phosphates in sediment samples is reported.     

Stationary phases for thin-layer chromatography

This paper presents a review of the literature concerning development of the stationary phases for thin-layer chromatography (TLC) in the last ten years. The silica gel remains the most important adsorbent for TLC separation. The kinetic properties of the silica-gel thin layer and the new TLC plates have been presented. Other materials used as stationary phase were alumina, zirconium oxide, Florisil, and ion-exchanger. Chemically new bonded stationary phase development is also discussed. The improvement of the separations of some organic mixtures by impregnation of silica gel, cellulose, or polyamide plates (with transition metal ions and silver salts) and their applications is presented. The impregnation of the thin layer with organic stationary phase and inclusion complexes is another method used for the enhancement of the separation efficiences. Another modality to improve the selectivity in TLC using ion-pairing as reagent of impregnation is described as well. The actual state of chiral separation by TLC is discussed with concrete references to recent advances in chiral stationary phases. The use of nonpolar chemically bonded stationary phases impregnated with transitional metal ions is presented as chiral stationary phases. The cellulose, modified cellulose, chitin, chitosan, and their derivatives are presented and their potential for the analysis of the racemates is discussed. The cyclodextrines and macrocyclic antibiotics were used with very good results for enantiomeric separation by TLC. A new separation approach with molecular imprinting polymers was reported as a chiral stationary phase in TLC. The examples provide a wide range of structural types that can be readily resolved enantiomerically by TLC.     

Methods of identification and confirmation of abusive drugs in human urine

A thin-layer chromatography (TLC) procedure is described to be used as the initial drug detection method for urine surveillance in a drug abuse treatment program. While the TLC method is sufficiently sensitive, it is prone to false-positive results. For this reason, two other drug detection methods (gas—liquid chromatography and radioimmunoassay) have been incorporated to confirm positive results obtained with TLC. The combined methodologies result in a urine surveillance procedure that is versatile, sensitive and highly reliable.     

Optimization of artificial neural networks used for retention modelling in ion chromatography

The aim of this work is the development of an artificial neural network model, which can be generalized and used in a variety of applications for retention modelling in ion chromatography. Influences of eluent flow-rate and concentration of eluent anion (OH-) on separation of seven inorganic anions (fluoride, chloride, nitrite, sulfate, bromide, nitrate, and phosphate) were investigated. Parallel prediction of retention times of seven inorganic anions by using one artificial neural network was applied. MATLAB Neural Networks ToolBox was not adequate for application to retention modelling in this particular case. Therefore the authors adopted it for retention modelling by programming in MATLAB metalanguage. The following routines were written; the division of experimental data set on training and test set; selection of data for training and test set; Dixon's outlier test; retraining procedure routine; calculations of relative error. A three-layer feed forward neural network trained with a Levenberg-Marquardt batch error back propagation algorithm has been used to model ion chromatographic retention mechanisms. The advantage of applied batch training methodology is the significant increase in speed of calculation of algorithms in comparison with delta rule training methodology. The technique of experimental data selection for training set was used allowing improvement of artificial neural network prediction power. Experimental design space was divided into 8-32 subspaces depending on number of experimental data points used for training set. The number of hidden layer nodes, the number of iteration steps and the number of experimental data points used for training set were optimized. This study presents the very fast (300 iteration steps) and very accurate (relative error of 0.88%) retention model, obtained by using a small amount of experimental data (16 experimental data points in training set). This indicates that the method of choice for retention modelling in ion chromatography is the artificial neural network.