Carl M. Selavka

Derivatization and post-column reactions for improved detection in liquid chromatography/electrochemistry

Abstract A summary Is provided of most of Che reported derlvatizations that have been used for improved analyte detection in liquid chromatography with electrochemical detection (LCEC). These approaches include pre-column derivatizations and postcolumns chemical, photochemical or enzymatic reactions for oxidative EC detection. This review covers the literature up to early 1985, and includes information gathered from books, technical articles, previous reviews and scientific journal publications. Specific reagents, methods and instrumentation are described for those classes of compounds studied by derlvatization-LCEC, and suggestions for future experiments are included, where applicable. It is concluded that the future will likely Include the development of a great number of derivatizations which may be used in conjunction with LCEC for trace analysis.

The Trace Analysis for Explosives and Related Compounds Via High Performance Liquid Chromatography-Photolysis-Electrochemical Detection

Organic nitro compounds, such as explosives, are amenable to high performance liquid chromatographic (HPLC) analysis with a variety of appropriate, selective or general, detectors. Although such compounds have been studied recently by electrochemical detection (EC) in the reductive mode, virtually nothing has been reported on the application of oxidative EC for such compounds. Since the parent compounds themselves cannot be electrochemically oxidized, nitrite (NO2−) released post-column, on-line, in real time, by photolysis of the HPLC effluent, can very readily be detected at trace levels by oxidative EC methods and techniques. A wide variety of organic nitrate esters (R-O-NO2), N-nitro (N-NO2) nitramine derivatives, as well as aliphatic/aromatic C-nitro (C-NO2) compounds, can all be analyzed at trace levels by this HPLC-photolysis-EC (HPLC-hv-EC) approach. A large number of explosives and certain drugs have been studied by these approaches. The basic high performance liquid chromatography-photolysis-electrochemical detection (HPLC-hv-EC) system has been optimized with regard to minimum detection limits (MDLs), linearity of responses as a function of concentration/amounts injected, specific HPLC separations and mobile phases compatible with hv-EC derivatization-detection, dual detector EC response ratios for individual analytes, and other suitable analytical parameters of importance and interest. Some applications of this method to real world samples of explosive debris are also described.

Analysis for penicillins and cefoperazone by HPLC—photolysis—electrochemical detection (HPLC—hv—EC)

Continuous, post-column, on-line, real-time photolytic derivatization or degradation can now be used following HPLC separation of various penicillin derivatives prior to conventional thin-layer, amperometric electrochemical detection using oxidative working potentials. Beta-lactam derivatives are separated by conventional reversed-phase HPLC, and each separated penicillin is then photolytically degraded to form, it is presumed, stable anionic species, which are then conveyed to the on-line electrochemical detector for qualitative and quantitative determinations. These methods of trace drug analysis have been applied to four separate penicillins or prodrugs, as well as one typical cephalosporin, viz. cefoperazone. Analytical parameters of the analysis have been determined, including dual electrode response ratios, sensitivity, minimum detection limits, linearity of calibration plots and the range of linear calibration. Finally, the analysis of cefoperazone-spiked saline solutions for i.v. administration has been performed in a single-blind study, as well as the determination of bacampicillin HCl in formulations obtained from a drug manufacturer in the United States. The overall method of analysis for these drugs has been demonstrated as being reproducible, accurate, and precise for at least five beta-lactam analogs. It is suggested that other beta-lactams will be amenable to these newer methods of analysis in a wide variety of sample matrices, including solid or liquid formulations, aqueous infusion solutions, and biological media, such as blood and urine.

The Forensic Determination of Drugs of Abuse Using Liquid Chromatography with Electrochemical Detection: A Review

Abstract The identification and quantitation of drugs of abuse in biological fluids, bulk pharmaceuticals and illicit preparations requires a large commitment of manpower and time within most full service forensic science laboratories. Funding levels within such laboratories rarely allow for large expenditures for very expensive or esoteric equipment, so the majority of the analyses of controlled substances must be performed using techniques which are relatively inexpensive, yet which provide for accurate and sensitive determinations of such compounds in a variety of matrices. Chromatographic methods provide an inexpensive, yet powerful, approach for the identification and quantitation of controlled substances. Liquid chromatography (LC) is particularly well suited for the analysis of a number of important controlled substances which are relatively nonvolatile, or thermally unstable. However, the full potential of LC in the forensic analysis of drugs has not been met to date, due to the lack of suitably s...

Solvent systems for intracarotid 1,3-bis(2-chloroethyl)-1-nitrosourea (BCNU) infusion.

The agent, 1,3-bis(3-chloroethyl)-1-nitrosourea (BCNU), when given by arterial infusion for brain tumor chemotherapy is usually dissolved in an alcohol/saline solution. The authors compared the osmolality of and drug recovery from solvent systems of alcohol/saline, dimethyl sulfoxide (DMSO)/water, and dextrose/water. Recovery of drug was adequate from all solvent systems, although variability of drug recovery from the alcohol/saline and DMSO/water systems was greater than from the dextrose/water system. The alcohol/saline system was significantly hyperosmolar. The alcohol/saline and DMSO/water solvent systems offer no advantage over the dextrose/water system and may be associated with significant disadvantages.

Do Forensic Science Graduate Programs Fulfill the Needs of the Forensic Science Community

This research project was designed to address a number of issues which were felt to be vital to the construction of a meaningful graduate program in forensic chemistry. The purpose of the project was threefold: (1) to determine the current status of the graduate forensic science educational service in the United States; (2) to determine the effectiveness of forensic science graduate programs in providing new employees having appropriate skills and educational background; and (3) to assess the roles of local, state, national, and academic laboratories in forensic science research. The results indicate that graduate degree programs are generally well-focused, but that many managers do not require such training background for applicants. It was also found that, in the perception of forensic science practitioners, forensic science research should be performed in all settings including the practicing labs and academic and Federal research labs, but that funding and release time should be increased to allow for greater efforts and better research.

Improved Determination of Nitrotoluenes Using Liquid Chromatography with Photolytically Assisted Thermal Energy Analysis (LC-PAT)

A post-column, on-line, photolysis unit is incorporated in a normal phase, high-performance liquid chromatography (LC) system to improve the thermal energy analyzer (TEA) detectability of mono-, di- and tri-nitrotoluenes. The construction of this photolytically assisted TEA (PAT) detection approach includes the use of an ultraviolet lamp and a knitted open tubular (KOT) reaction chamber of Teflon®. The mechanism for improved detection using PAT is explored, using batch irradiations followed by LC-TEA and gas chromatography/mass spectrometry, and is postulated to involve photochemically induced isomerization leading to homolytic cleavage of the C-NO2 bond, followed by hydrogen abstraction. After optimization of photolytic residence time and cooling bath temperature, PAT allows for an improvement in the TEA detectability of trinitrotoluene and dinitrotoluene by factors of 30 and 16, respectively. Mononitrotoluene, which is not responsive under conventional TEA conditions, may be detected with good sensitivity using LC-PAT. The use of LC-PAT does not interfere with the determination of other nitro-based high explosives which exhibit adequate responses under conventional LC-TEA conditions.

Liquid chromatography with photolysis–electrochemical detection for nitro-based high explosives and water gel formulation sensitizers

Abstract The use of high performance liquid chromatography with photolysis–electrochemical detection (LC-hv-EC) for conventional high explosives has been improved through the use of a knitted open tubular (KOT) photolysis chamber geometry. Improvements in the analytical figures of merit and selectivity of this hybrid analytical technique are a direct result of the improved radial mass transfer of analyte in the KOT reactor, as demonstrated in comparisons with the coiled reactor geometry previously used. Using the KOT photolysis chamber geometry in LC-hv-EC, the limits of detection for aromatic C-nitro compounds, nitramines and nitrate esters are in the range of 120- to 250- pg injected. In addition, an off-line, pre-column chemical derivatization has been developed to convert water gel sensitizer residues to a form which will allow for their determination using LC-hv-EC. In a rapid, single-step process, 2,4-dinitrofluorobenzene (Sangers reagent) is used to derivatize residues of monomethylamine and monoe...