Continuous efforts implemented by government agencies such as the United States Geological Survey (USGS) aim to
manage and protect the integrity of the environment's natural resources. RDX is one of the most frequently utilized
nitramine explosives for mining, demolition and munitions purposes in the United States (US). The degradation of RDX
in natural environments is of particular importance as a result of the accumulation of consequential degradation products
in nature. Specifically, RDX has the potential to be degraded by microorganisms resulting in hazardous levels of harmful
degradation products in soil and groundwater. The necessity for the detection of these particular degradation products is
emphasized as a consequence of their toxicity as these products are recognized as potential mutagens.
Photo-assisted electrochemical detection (PAED) following HPLC-UV is used to develop an analytical method qualified
for the assessment of RDX and degradation products. The technique offers unique selectivity possessed by the
photochemical reactor coupled to EC detection serving to eliminate the need for repetitive analysis using different
column technologies. Furthermore, on-line sample pretreatment is developed and optimized specifically for the
preparation of samples consisting of RDX and degradation products. Analytical figures of merit determined for all
target analytes using on-line SPE-HPLC-UV-PAED revealed detection limits in the sub part per billion range for RDX
and degradation product MEDINA. The effectiveness of the method is exemplified in collaborative studies with the
USGS in monitoring the degradation of RDX and formation of degradation products once the nitro explosive is subject
to anaerobic microorganisms WBC-2.
High-performance liquid chromatography with ultra violet and photo-assisted electrochemical detection (HPLC-UV-PAED) has been applied to the sensitive and selective determination of organic nitro compounds. The system was first developed for the determination of nitro explosives, and PAED has shown superior sensitivity over UV detection for these compounds (i.e., <1 part-per-trillion for HMX). The system also shows enhanced selectivity over the traditional UV method in that two detectors can be used for improved analyte identification. Also, having two detectors permits chemometric resolution of overlapping peaks, and this is not addressed in the UV method. Because this method is applicable to a wide range of nitro explosives, it was predicted that PAED would show the same sensitivity and selectivity toward other types of nitro compounds. Since its development, the system's use has been expanded to include the determination of nitro-containing pharmaceuticals and glycosylated nitro compounds in biological matrices. Model compounds were chosen, specifically nitroglycerin and related compounds and nitrophenyl-glucoside, to represent these classes. PAED showed superior detection limits over low wavelength UV detection for nitroglycerin (PAED = 0.3ppb, UV at 220nm = 48ppb), demonstrating PAED’s applicability to determining nitro-pharmaceuticals. Conversely, UV detection at 220nm proved to be more sensitive than PAED for nitrophenyl-glucoside (UV at 220 = 0.6ppb, PAED = 3.6ppb). However, when nitrophenyl-glucoside was spiked into urine, PAED determination resulted in 99+0.3% recovery, while UV at 220nm resulted in 116+0.2% recovery, suggesting that UV determination may suffer from matrix interference.
DNA damage is caused by a variety of foreign and endogenous compounds. There are endogenous photosensitizers in cells, such as porphyrins and flavins, which may create damage in the presence of UV-A light. Typically, samples are analyzed by <sup>32</sup>P-postlabelling and electrophoretic separation or by LC-MS separation and detection. Separation by HPLC is common; however, in all instances, the DNA sample is hydrolyzed down to nucleosides prior to analysis. It will be shown here that ion-pairing reversed phase high performance liquid chromatography (IP-RPLC) has the ability to provide biophysical information concerning the sites of UV-A induced photosensitizer damage on an intact oligonucleotide concurrent with the separation. IP-RPLC is less labor intensive and faster than electrophoretic methods and it is less costly than LC-MS. IP-RPLC can also be used to purify modified oligonucleotides for further use and analysis. This technique is sensitive to the charge, conformation, and sequence characteristics of the nucleic acid sample and may be used to determine the damage or modifications made to DNA by a variety of compounds.
Pulsed Electrochemical Detection (PED) is a revolutionary approach to the simple, sensitive, and direct detection of numerous polar aliphatic compounds, especially carbohydrates. This technique exploits the electrocatalytic activity of noble metal electrode surfaces to oxidize various polar functional groups. In PED, multi-step potential-time waveforms at Au and Pt electrodes realize amperometric/coulometric detection while maintaining uniform and
reproducible electrode activity. The response mechanisms in PED are dominated by the surface properties of the electrode, and, as a consequence, members of each chemical class of compounds produce virtually identical voltammetric responses. Thus, the full potential is realized when combined with high performance liquid chromatography (HPLC). This paper reviews the fundamental aspects of PED and details a novel approach to the chemical "fingerprinting" of natural products. Applications include the characterization of tobacco, peptones, and bacteria.
High-performance liquid chromatography with ultra violet and photo-assisted electrochemical detection (HPLC-UV-PAED) has been developed for the sensitive and selective detection of explosives in ground water and soil extracts. Fractionation and preconcentration of explosives is accomplished with on-line solid phase extraction (SPE),
which minimizes sample pretreatment and enables faster and more accurate on-site assessment of a contaminated site. Detection limits are equivalent or superior (i.e., <1 part-per-trillion for HMX) to those achieved using the Environmental Protection Agency (EPA) Method 8330. This approach is more broadly applicable, as it is capable of determining a wider range of organic nitro compounds. Soil samples are extracted using pressurized fluid extraction (PFE), and this
technique is automatable, field-compatible, and environmentally friendly, adding to the overall efficiency of the methodology.
Conference Committee Involvement (1)
Smart Medical and Biomedical Sensor Technology II
25 October 2004 | Philadelphia, Pennsylvania, United States