Miniaturization of solid-phase reactors for on-line post-column derivatization in narrow-bore liquid chromatography

Derivatization, an Applicable Asset for Conventional HPLC Systems without MS Detection in Food and Miscellaneous Analysis

One of the most valuable practices for analyzing not-so-analytical-friendly analytes in complex, heterogenous matrices is derivatization. Availability of numerous derivatizing reagents (DRs) makes the modification of analyte more exploitable in terms of an analytical perspective. A wide array of derivatization techniques like pre or post-column, in-situ, enzymatic, ultrasound-assisted, microwave-assisted, photochemical derivatization has added much-needed methodological strength in analyzing intricate analytical matrices (food, water, and soil). In recent years, analytical chemistry has achieved greater heights through the development of new sensitive methods with simple conventional instruments like High-Performance Liquid Chromatography (HPLC) devoid of Mass detectors. The prompt availability of these straightforward instruments also makes it a favorable option for routine analysis in food, environmental, bioanalytical chemistry. Analyzing food, environmental or bioanalytical specimen has some of the most problematic aspects, like the low concentration of the analytes accompanied by not too suitable analytical properties. Even though conventional HPLC lacks the required sensitivity but merger with derivatization can lead to a remarkable increase in sensitivity. In recent years there has been a lot of application of diverse derivatizations to increase the sensitivity and selectivity of the analyte for available instruments, resulting in notable findings. Therefore, this review describes the application of derivatization principles in the analysis of analytes in food and additional matrices using conventional HPLC instruments such as HPLC-UV, HPLC-DAD, and HPLC-FD. In this article, we will briefly review the different modes and multiple types of derivatizing reagents with their mechanisms and importance for encouraging the use of established HPLC instruments.

Recent Applications of Derivatization Techniques for Pharmaceutical and Bioanalytical Analysis through High-performance Liquid Chromatography

Background:

Derivatization of analytes is a quite convenient practice from an analytical perspective. Its vast prevalence is accounted by the availability of distinct reagents, primarily pragmatic for obtaining desired modifications in an analyte structure. Another reason for its handiness is typically to overcome limitations such as lack of sensitive methodology or instrumentation.The past decades have witnessed various new derivatization techniques including in-situ, enzymatic, ultrasound-assisted, microwave-assisted, and photochemical derivatization which have gain popularity recently.

Methods:

The online literature available on the utilization of derivatization as prominent analytical tools in recent years with typical advancements is reviewed. The illustrations of the analytical condition together with the structures of different derivatizing reagents (DRs) are provided to acknowledge the vast capability of derivatization to resolve analytical problems.

Results:

The derivatization techniques have enabled analytical chemists throughout the globe to develop an enhanced sensitivity method with the simplest of the instrument like High-Performance Liquid Chromatography (HPLC). The HPLC, compared to more sensitive Liquid chromatography coupled to tandem mass spectrometer, is readily available and can be readily utilized for routine analysis in fields of pharmaceuticals, bioanalysis, food safety, and environmental contamination. A troublesome aspect of these fields is the presence of a complex matrix with trace concentrations for analyses. Liquid chromatographic methods devoid of MS detectors do not have the desired sensitivity for this. A possible solution for overcoming this is to couple HPLC with derivatization to enable the possibility of detecting trace analytes with a less expensive instrument. Running cost, enhanced sensitivity, low time consumption, and overcoming the inherent problems of analyte are critical parameters for which HPLC is quite useful in high throughput analysis.

Conclusion:

The review critically highlights various kinds of derivatization applications in different fields of analytical chemistry. The information primarily focuses on pharmaceutical and bioanalytical applications in recent years. The various modes, types, and derivatizing reagents with brief mechanisms have been ascribed briefly Additionally, the importance of HPLC coupled to fluorescence and UV detection is presented as an overview through examples accompanied by their analytical conditions.

Stability studies of propoxur herbicide in environmental water samples by liquid chromatography-atmospheric pressure chemical ionization ion-trap mass spectrometry

Liquid chromatography-atmospheric pressure ionization ion-trap mass spectrometry has been investigated for the analysis of polar pesticides in water. The degradation behavior of propoxur, selected as a model pesticide belonging to the N-methylcarbamate group, in various aqueous matrices (Milli-Q water, drinking water, rain water, seawater and river water) was investigated. Two interfaces of atmospheric pressure ionization, atmospheric pressure chemical ionization (APCI) and electrospray ionization (ESI), were compared during the study. Propoxur and its transformation product (N-methylformamide) were best ionized as positive ions with both APCI and ESI, while another transformation product (2-isopropoxyphenol) yielded stronger signals as negative ions only with APCI. In addition, the effects of various pH, matrix type and irradiation sources (sunlight, darkness, indoor lighting and artificial UV lamp) on the chemical degradation (hydrolysis) were also assessed. From the kinetic studies of degradation, it was found that the half-life of propoxur was reduced from 327 to 161 h in Milli-Q water with variation of irradiation conditions from dark to sunlight exposure. Degradation rates largely increased with increasing pH. The half-life of the target compound dissolved in Milli-Q water under darkness decreased from 407 to 3 h when the pH of Milli-Q water was increased from 5 to 8.5. These suggest that hydrolysis of propoxur is light-intensity and pH-dependent. In order to mimic contaminated natural environmental waters, propoxur was spiked into real water samples at 30 microg/l. The degradation of propoxur in such water samples under various conditions were studied in detail and compared. With the ion trap run in a time-scheduled single ion monitoring mode, typical limits of detection of the instrument were in the range of 1-10 microg/l.

Sensitive Determination of Propoxur by Spectrophotometry Using 3-Aminopyridine

A simple spectrophotometric method for the determination of propoxur, a widely used insecticide, in various environmental samples and pesticide formulations is described. The method is based on the coupling of the hydrolysis product of propoxur with diazotized 3-aminopyridine in an alkaline medium, to form an azo-dye which has a maximum absorbance at 463 nm. Beer's law is obeyed over the concentration range of 0.05 to 1.2 microg ml(-1) of propoxur. The molar absorptivity and Sandell's sensitivity are found to be 3.10 x 10(4) l mol(-1) cm(-1) and 0.007 microg cm(-2), respectively. The important analytical parameters and optimum reaction conditions were evaluated. The method is free from the interference of other commonly used pesticides and inorganic metal ions.

Solid-phase derivatization reactions for biomedical liquid chromatography

Polymeric reagents have been developed for performing off- and on-line derivatizations of numerous organic analytes in HPLC-detection modes. Such reagents utilize ionic or covalent attachment of labile tags that possess specific detector enhancement properties: ultraviolet, electrochemical, fluorescence, and so forth. Specific synthetic procedures have evolved to generate various linkages of the tag to the underlying, polymeric support, usually involving activated ester connections (leashes). The polymer itself may play a number of roles in the nature of the overall reactions, such as hydrophobic-hydrophillic exclusion, pore size restriction, stabilization of the attachment leashes, and protection of the tags from hydrolysis in aqueous media. The basic, underlying chemistry of polymeric reagents has evolved to the point where it is possible to engineer the polymer support itself, the attachment leash, and the various tags that are then transferred to the analyte molecules. These procedures have now reached the stage of commercialization and practical applicability for real-world drugs and bioorganics in complex biofluid type samples. Polymer supported reagents can now be used for direct injection of biofluids with solid-phase (hydrophobic) extraction of the analytes of interest, followed by sample cleanup, derivatization, elution onto the HPLC column, peak compression, gradient HPLC elution, multiple detection, and final data interpretation with quantitation. This review summarizes much or most of what has been described in the scientific literature over the past decade in the various areas where polymeric reagents are being used for derivatization in HPLC and in capillary electrophoresis as well.

Derivatization reactions applicable to pesticide determination by high-performance liquid chromatography

The literature dealing with HPLC analytical methods for pesticides employing derivatization reactions is reviewed. Included are methods for insecticides, acaricides, nematicides, antimicrobials, herbicides and a rodenticide. Derivatization reactions are employed mainly for the purpose of increasing sensitivity or selectivity for the UV or, more frequently, fluorescence detectors. Of the pre-column and post-column derivatization methods reviewed, post-column methods are the more commonly used.

Determination of carbaryl and some organophosphorus pesticides in drinking water using on-line liquid chromatographic preconcentration techniques

Reversed-phase high-performance liquid chromatography (HPLC) was adapted for the determination of trace concentrations of carbaryl and seven organophosphorus pesticides in drinking water. Between 100 and 300 ml of water sample is passed through a 1.5-cm precolumn, packed with C18-bonded silica or styrene-divinylbenzene copolymer (PRP-1) sorbent at a flow-rate of 3 ml/min. The HPLC system is then switched to an acetonitrile-water gradient elution programme. The analytes that have been concentrated on the precolumn are eluted and separated on a 15-cm C18 analytical column and are determined by measuring their UV absorption at 254 nm. This wavelength was selected as the optimum for the simultaneous determination of these pesticides. The preconcentration yields of the examined solutes obtained with the two types of precolumn are almost identical. Band broadening is avoided by a suitable choice of the C18 precolumn and the analytical column. With 200 ml of tap water, the recoveries for most of the examined pesticides were ca. 90%, except for carbaryl (54%). The detection limits are in the range 0.03-0.2 micrograms/l.

Polymeric benzotriazole reagent for the off-line high-performance liquid chromatographic derivatization of polyamines and related nucleophiles in biological fluids

A polymeric benzotriazole reagent containing a 9-fluorenylmethyleneoxycarbonyl (FMOC) group has been synthesized, characterized, and its derivatizations, off-line, for three polyamines, have been optimized with regard to solvent, time, and temperature. An authentic FMOC derivative of cadaverine has been prepared, characterized, and used as the external standard for quantitation of off-line derivatizations and identification of final derivatives. Actual percent derivatizations have been determined, rather than just percent disappearance of starting material. The polyamines in urine or other biological fluids can be derivatized without organic solvent or solid phase extraction, but rather in situ by the simple addition of the polymeric reagent to the fluid, incubation for a few minutes at room or elevated temperature, filtration and direct injection. Derivatizations could also be performed by transferring a small volume of the hydrolyzed and filtered biological fluid to a disposable pipette containing the polymeric reagent. Derivatization was then followed by elution, filtration, and direct injection onto the high-performance liquid chromatographic (HPLC) system. Automation of the overall polymeric derivatization, filtration, HPLC injection, separation, detection, quantitation, and data acquisition-interpretation is suggested. The polymeric reagent has been utilized for the qualitative and quantitative determination of cadaverine and putrescine, normally occurring polyamines, in human urine. These levels were compared with the corresponding literature values for healthy human subjects, and the values were found to be in excellent agreement. This novel derivatization approach, though off-line, provides for a much simpler, more rapid, and more efficient conversion of these and related polyamines or nucleophiles to derivatives having vastly improved chromatographic detection properties in HPLC. The final derivatives contain the FMOC group, making them extremely chromophoric and fluorophoric, and providing trace detection at ppb (microgram/l) and sub-ppb levels. The overall approach is recommended for these and other biologically occurring polyamines, in fluids and tissues, as well as related bioorganic and biologically active nucleophiles, including drugs and their metabolites.

Parallel column ion exchange for post-separation pH modification in liquid chromatography. Application to barbiturates and miniaturization

A new approach to the UV detection of barbiturates in high-performance liquid chromatography is demonstrated. The analytical system comprises an anion-exchange column inserted parallel to the injection valve and analytical column. One part of the acetate-containing mobile phase flows through the injection valve and analytical column to achieve the separation, the other part flows through the anion-exchange column where the acetate ions cause the release of hydroxide ions from this column. Finally, the alkaline stream from the anion-exchange column is recombined with the analytical column effluent. This results in an alkaline medium which can be favourable for many detection processes. A series of barbiturates, which show enhanced UV detectability at 254 nm in alkaline solution, was chosen to demonstrate the potential of such a method. Applications of this principle to the analysis of urine and plasma samples are described. In the system only one pump is needed for the separation and the post-column pH modification. A critical comparison between conventional scale and narrow-bore systems is made.