Indirect laser-induced fluorescence detection of explosive compounds using capillary electrochromatography and micellar electrokinetic chromatography

Abstract

Indirect laser-induced fluorescence detection of explosive compounds using capillary electrochromatography and micellar electrokinetic chromatographyMixtures of nitroaromatic and nitramine explosive compounds and their degradation products were analyzed using electrokinetically driven separations with both indirect laser-induced fluorescence (IDLIF) and UV absorption detection. Complete separations of the 14-component mixture (EPA 8330) were achieved using both capillary electrochromatography (CEC) and micellar electrokinetic chromatography (MEKC). IDLIF detection was performed using an epifluorescence system with excitation provided by a 635 nm diode laser and micromolar concentrations of the dye Cy-5 as the visualizing agent. While the sensitivity of the two detection methods was similar for the nitroaromatic compounds, the nitramines could only be detected using UV absorption due to their low fluorescence quenching efficiency of Cy-5. The detection sensitivity using IDLIF was limited by low frequency oscillations in the fluorescence background. The oscillations increased with higher electric field strength and were attributed to thermal fluctuations caused by Joule heating. Due to the more conductive running buffer and higher separation currents used in MEKC, sensitive IDLIF detection could only be achieved using low (~100 V/cm) field strengths, resulting in long analysis times. CEC separations, which are typically run with low conductivity mobile phases to avoid bubble formation, are less sensitive to this effect. In CEC separations with IDLIF detection a stable fluorescence background using Cy-5 could be established using only a nonporous stationary phase. In capillaries packed with porous silica particles, anomalous migration behavior was observed with charged dye molecules and a stable fluorescence background could not be established under electrokinetic flow. This is the first demonstration of IDLIF in packed channel CEC.

Investigation of common fluorophores for the detection of nitrated explosives by fluorescence quenching

“…In industrial quality control, manufacturers of explosive materials must assure consumers that their products are safe, effective, and free from contamination by monitoring the composition throughout the manufacturing process. Because the requirements in each of these fields are [8][9][10]24,29], indirect laser-induced fluorescence [4,19,20,30], and fluorescence quenching [16,[31][32][33][34][35][36][37][38][39][40]. Unfortunately, many of these methods are difficult to adapt for field use owing to the size of laboratory-scale instrumentation and the need for other accessories that limit portability.…”

The application of single particle aerosol mass spectrometry for the detection and identification of high explosives and chemical warfare agents

“…12 Explosives are commonly identified using colorimetry, 13 UV-absorption spectroscopy, 14,15 laser-induced fluorescence (LIF), 16,17 immunoassay, 18 ion mobility spectrometry (IMS), [19][20][21][22][23] and mass spectrometry (ion trap and time-of-flight (TOF)). [24][25][26][27][28][29][30][31][32][33] It should be noted that research into explosives detection is performed on gas, liquid, and/or solid phase explosives, and that the sampling methods and concepts of operation vary widely between the different techniques.…”

“…whereas the nitroamines had much higher LODs due to their low quenching efficiencies. 16 Bailey and Wallenborg's detection scheme was also adapted into a microchip device capable of on-site analysis. 17 By performing indirect LIF with MEKC on the microchip, LODs of 1 ppm (mg/L) for the nitroaromatic compounds were achieved, albeit with a narrow linear dynamic range.…”

Enhanced Indirect Fluorescence Detection of p-Nitrophenol, 2,4-Dinitrophenol and Trinitrophenol by Micellar Electrokinetic Capillary Chromatography with In-column Optical-fiber LED-induced Fluorescence Detection

“…3,4 The detection mechanism can be explained by the displacement of a visualizing reagent from the sample zone to maintain local charge neutrality. 1,[5][6][7] Currently, one of the most sensitive detection techniques in CE is laser-induced fluorescence (LIF) detection, 8 which was first introduced into CE by Zare et al 9 In order to detect compounds without native fluorescence, indirect LIF [10][11][12][13][14] can be applied to determine these compounds. However, most indirect LIF detections possess the disadvantages of high background noise, using single-wavelength detection and requiring relatively expensive laser equipment.…”