Rapid detection of nitroaromatic and nitramine explosives on chromatographic paper and their reflectometric sensing on PVC tablets

Rapid and inexpensive sensing of explosive traces in soil and post-blast debris for environmental and criminological purposes with optical sensors has recently gained importance. The developed sensing method for nitro-aromatic and nitramine-based explosives is based on dropping an acetone solution of the analyte to an adsorbent surface, letting the solvent to dry, spraying an analytical reagent to produce a persistent spot, and indirectly measuring its reflectance by means of a miniature spectrometer. This method proved to be useful for on-site determination of nitro-aromatics (trinitrotoluene (TNT), 2,4,6-trinitrophenylmethylnitramine (tetryl) and dinitrotoluene (DNT)) and nitramines (1,3,5-trinitro-1,3,5-triazacyclohexane (RDX) and octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX)) pre-adsorbed on a poly vinyl chloride (PVC) surface, with the use of different spray reagents for each group of explosives producing different colors. The calibration equations of the tested compounds as reflectance vs. concentration showed excellent linearity (correlation coefficient: 0.998-0.999). The linear quantification interval in terms of absolute quantity of analyte was 0.1-0.5 μg. The developed method was successfully tested for the analysis of military explosives Comp B and Octol, and was validated against high performance liquid chromatography (HPLC). The reflectometric sensing method could also be used for qualitative identification of the nitrated explosives on a chromatographic paper. The reagent-impregnated paper could also serve as sensor, enabling semi-quantitative determinations of TNT and tetryl.     

1-Butyl-3-methylimidazolium-based ionic liquids and an anionic surfactant: Excellent background electrolyte modifiers for the analysis of benzodiazepines through capillary electrophoresis

In this study, we found that adding 1-butyl-3-methylimidazolium-based ionic liquids (ILs) and sodium dodecyl sulfate (SDS) as modifiers in the background electrolyte (BGE) for capillary electrophoresis enhanced the separation of benzodiazepines. In particular, 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide ([BMIM][NTf₂]) was the best IL additive for the separation system because its anionic moiety interacted favorably with the benzodiazepines. We added SDS because of its known effect on the separation of hydrophobic analytes. We optimized the separation conditions in terms of the concentrations of the IL, SDS, and organic solvent, the pH, and the BGE's ionic strength. The optimal BGE, containing 170 mM [BMIM][NTf₂] and 10 mM SDS, provided baseline separation, high efficiency, and satisfactory peak shapes for the benzodiazepines. The separation mechanism was based on heteroassociation between the anionic moiety of the IL and the benzodiazepines, with SDS improving the resolution of the separation. The limits of detection for the seven analytes ranged from 2.74 to 4.42 μg/mL. We subjected a urine sample to off-line solid phase extraction (SPE) prior to the analysis of its benzodiazepine content. Our experimental results reveal that the combination of [BMIM][NTf₂] and SDS provides adequate separation efficiency for its application to CE analyses of benzodiazepines after SPE concentration.     

A fast and highly sensitive detection of cholesterol using polymer microfluidic devices and amperometric system

In this work, the rapid detection of cholesterol using poly(dimethylsiloxane) microchip capillary electrophoresis, based on the coupling of enzymatic assays and electrochemical detection, was developed. Direct amperometric detection for poly(dimethylsiloxane) (PDMS) microchip capillary electrophoresis was successfully applied to quantify cholesterol levels. Factors influencing the performance of the method (such as the concentration and pH value of buffer electrolyte, concentration of cholesterol oxidase enzyme (ChOx), effect of solvent on the cholesterol solubility, and interferences) were carefully investigated and optimized. The migration time of hydrogen peroxide, product of the reaction, was less than 100 s when using 40 mM phosphate buffer at pH 7.0 as the running buffer, a concentration of 0.68 U/mL of the ChOx, a separation voltage of +1.6 kV, an injection time of 20 s, and a detection potential of +0.5 V. PDMS microchip capillary electrophoresis showed linearity between 38.7 μg/dL (1 μM) and 270.6 mg/dL (7 mM) for the cholesterol standard; the detection limit was determined as 38.7 ng/dL (1 nM). To demonstrate the potential of this assay, the proposed method was applied to quantify cholesterol in bovine serum. The percentages of recoveries were assessed over the range of 98.9-101.8%. The sample throughput was found to be 60 samples per hour. Therefore, PDMS microchip capillary electrophoresis, based on the coupling of enzymatic assays and electrochemical detection, is very rapid, accurate and sensitive method for the determination of cholesterol levels.     

Comparison of an antibody and its recombinant derivative for the detection of the small molecule explosive 2,4,6-trinitrotoluene

Antibodies are commonly used as recognition elements in immunoassays because of their high specificity and affinity, and have seen extensive use in competitive assays for the detection of small molecules. However, these complex molecules require production either in animals or by mammalian cell cultures, and are not easily tailored through genetic manipulation. Single chain antibodies (scFv), recombinantly expressed molecules consisting of only the antibody's binding region joined via a linking peptide, can provide an alternative to intact antibodies. We describe the characterization of a new monoclonal antibody (mAb), 2G5B5, able to detect the small molecule explosive 2,4,6-trinitrotoluene (TNT) and the scFv derived from its variable regions. The mAb and scFv were tested by surface plasmon resonance to determine their affinity for an immobilized TNT surrogate; dissociation constants were determined to be 1.5 × 10⁻¹³ M and 4.8 × 10⁻¹⁰ M respectively. Circular dichroism was used to determine their melting temperatures. The mAb is more stable melting at ∼75 °C while the scFv melts at ∼65 °C. The recognition elements were incorporated into a competitive assay format using a bead-based multiplexing platform to examine their sensitivity and specificity. The scFv was able to detect TNT ∼10-fold more sensitively than the mAb in this assay format, allowing detection of TNT concentrations down to at least 1 μg L⁻¹. The 2G5B gave similar detection limits to a commercial anti-TNT mAb, but was less specific, recognizing 1,3,5-trinitrobenzene (TNB) equally well as TNT.     

Analysis of explosives using electrospray ionization/ion mobility spectrometry (ESI/IMS)

The analysis of explosives with ion mobility spectrometry (IMS) directly from aqueous solutions was shown for the first time using an electrospray ionization technique. The IMS was operated in the negative mode at 250°C and coupled with a quadrupole mass spectrometer to identify the observed IMS peaks. The IMS response characteristics of trinitrotoluene (TNT), 2,4-dinitrotoluene (2,4-DNT), 2-amino-4,6-dinitrotoluene (2-ADNT), 4-nitrotoluene (4-NT), trinitrobenzene (TNB), cyclo-1,3,5-trimethylene-2,4,6-trinitramine (RDX), cyclo-tetramethylene-tetranitramine (HMX), dinitro-ethyleneglycol (EGDN) and nitroglycerine (NG) were investigated. Several breakdown products, predominantly NO₂⁻ and NO₃⁻, were observed in the low-mass region. Nevertheless, all compounds with the exception of NG produced at least one ion related to the intact molecule and could therefore be selectively detected. For RDX and HMX the [M+Cl⁻]⁻ cluster ion was the main peak and the signal intensities could be greatly enhanced by the addition of small amounts of sodium chloride to the sprayed solutions. The reduced mobility constants (K₀) were in good agreement with literature data obtained from experiments where the explosives were introduced into the IMS from the vapor phase. The detection limits were in the range of 15–190 μg l⁻¹ and all calibration curves showed good linearity. A mixture of TNT, RDX and HMX was used to demonstrate the high separation potential of the IMS system. Baseline separation of the three compounds was attained within a total analysis time of 6.4 s.     

Micellar electrokinetic chromatography of organic and peroxide-based explosives

CE methods have been developed for the analysis of organic and peroxide-based explosives. These methods have been developed for deployment on portable, in-field instrumentation for rapid screening. Both classes of compounds are neutral and were separated using micellar electrokinetic chromatography (MEKC). The effects of sample composition, separation temperature, and background electrolyte composition were investigated. The optimised separation conditions (25 mM sodium tetraborate, 75 mM sodium dodecyl sulfate at 25 °C, detection at 200 nm) were applied to the separation of 25 organic explosives in 17 min, with very high efficiency (typically greater than 300,000 plates m⁻¹) and high sensitivity (LOD typically less than 0.5 mg L⁻¹; around 1–1.5 μM). A MEKC method was also developed for peroxide-based explosives (10 mM sodium tetraborate, 100 mM sodium dodecyl sulfate at 25 °C, detection at 200 nm). UV detection provided LODs between 5.5 and 45.0 mg L⁻¹ (or 31.2–304 μM), which is comparable to results achieved using liquid chromatography. Importantly, no sample pre-treatment or post-column reaction was necessary and the peroxide-based explosives were not decomposed to hydrogen peroxide. Both MEKC methods have been applied to pre-blast analysis and for the detection of post-blast residues recovered from controlled, small scale detonations of organic and peroxide-based explosive devices.     

Micellar extraction and high performance liquid chromatography-ultra violet determination of some explosives in water samples

An analytical method based on the cloud point extraction combined with high performance liquid chromatography is used for the extraction, separation and determination of four explosives; octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazine (HMX), hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX), 2,4,6-trinitrotoluene (TNT) and pentaerythritol tetranitrate (PETN). These compounds are extracted by using of Triton X-114 and cetyl-trimethyl ammonium bromide (CTAB). After extraction, the samples were analyzed using a HPLC-UV system. The parameters affecting extraction efficiency (such as Triton X-114 and CTAB concentrations, amount of Na₂SO₄, temperature, incubation and centrifuge times) were evaluated and optimized. Under the optimum conditions, the preconcentration factor was 40 and the improvement factors of 34, 29, 61 and 42 with detection limits of 0.09, 0.14, 0.08 and 0.40 (μg L⁻¹) were obtained for HMX, RDX, TNT and PETN, respectively. The proposed method was successfully applied to the determination of these compounds in water samples and showed recovery percentages of 97-102% with RSD values of 2.13-4.92%.     

Design and development of microfabricated capillary electrophoresis devices with electrochemical detection

Our efforts have been focused on developing a self-contained and transportable microfabricated electrophoresis (CE) system with integrated electrochemical detection (ED). The current prototype includes all necessary electrodes “on-chip” and utilizes miniaturized CE and ED supporting electronics custom designed for this purpose. State-of-the-art design/modeling tools and novel microfabrication procedures were used to create recessed platinum electrodes with complex geometries and the CE/ED device from two patterned ultra-flat glass substrates. The electrodes in the bottom substrate were formed by a self-aligned etch and deposition technique followed by a photolithographic lift-off process. The microchannels (20 μm deep×65 μm wide (average)) were chemically etched into the top substrate followed by thermal bonding to complete the microchip device. CE/ED experiments were performed using 0.02 M phosphate buffer (pH 6), an analyte/buffer solution (2.2 mM dopamine, 2.3 mM catechol) and varying separation voltages (0-500 V) with a custom electronics unit interfaced to a laptop computer for data acquisition. Detection limits (S/N=3) were found to be at the micromolar level and a linear detection response was observed up to millimolar concentrations for dopamine and catechol. The microchip CE/ED system injected 50 pl volumes of sample, which corresponded to mass detection limits on the order of 200 amol. For the first time, an integrated “on-chip” multi-electrode array CE/ED device was successfully designed, fabricated and tested. The majority of the electrodes (six out of eight) in the array were capable of detecting dopamine with the amplitude of the signal (i.e., peak heights) decreasing as the electrode distance from the channel exit increased.     

Determination of triazine compounds in ground water samples by micellar electrokinetic capillary chromatography

In this work, a capillary electrophoresis (CE) method for the determination of a group of eleven triazine compounds by micellar electrokinetic capillary chromatography (MEKC) with diode array detection was developed. The eleven herbicides studied were: desethylatrazin-2-hydroxy (DEA), simazine, prometon, atrazine, simetryn, ametryn, propazine, prometryn, trietazine, terbutylazine, and terbutryn The separation of these compounds was optimised as a function of buffer concentration and pH, concentration of sodium dodecyl sulphate (SDS) and voltage applied. To increase the selectivity of the separation and the resolution of the solutes, different organic solvents were tested as buffer additives, obtaining the best results when 1-propanol was used. The optimised buffer (24 mM of sodium borate, 18 mM of disodium hydrogen phosphate, 25 mM of SDS, pH 9.5, and 5% of 1-propanol) provides the best separation in terms of resolution and migration time. This method allowed the determination of these compounds at concentrations of 0.05 μg l⁻¹ in ground water samples pretreated using solid-phase extraction (SPE).     

Strategies for the on-line preconcentration and separation of hypolipidaemic drugs using micellar electrokinetic chromatography

Three strategies were investigated for the simultaneous separation and on-line preconcentration of charged and neutral hypolipidaemic drugs in micellar electrokinetic chromatography (MEKC). A background electrolyte (BGE) consisting of 20 mM ammonium bicarbonate buffer (pH 8.50) and 50 mM sodium dodecyl sulfate (SDS) was used for the separation and on-line preconcentration of the drugs. The efficiencies of sweeping, analyte focusing by micelle collapse (AFMC), and simultaneous field-amplified sample stacking (FASS) and sweeping, were compared for the preconcentration of eight hypolipidaemic drugs in different conductivity sample matrices. When compared with a hydrodynamic injection (5 s at 50 mbar, 0.51% of capillary volume to detection window) of drug mixture prepared in the separation BGE, improvements of detection sensitivity of 60-, 83-, and 80-fold were obtained with sweeping, AFMC and simultaneous FASS and sweeping, respectively, giving limits of detection (LODs) of 50, 36, and 38 μg/L, respectively. The studied techniques showed suitability for focusing different types of analytes having different values of retention factor (k). This is the first report for the separation of different types of hypolipidaemic drugs by capillary electrophoresis (CE). The three methods were validated then applied for the analysis of target analytes in wastewater samples from Hobart city.     

Statistical evaluation of an analytical GC/MS method for the determination of long chain fatty acids

In-depth evaluation of an analytical method to detect and quantify long chain fatty acids (C₈-C₁₆) at trace level concentrations (25-1000 μg/l) is presented. The method requires derivatization of the acids with methanolic boron trifluoride, separation, and detection by gas chromatography-mass spectrometry. The calibration experiments passed all the tested performance criteria such as linearity, homoscedasticity, and ruggedness. The detection limits and related quantities were computed by applying the method detection limit, and the calibration line approximation. The values obtained by applying the latter approach were more reliable and consistent with the actual statistical theory of detection decisions and yielded the following concentrations: C₈, 87.6 μg/l; C₁₀, 45.2 μg/l; C₁₁, 39.9 μg/l; C₁₂, 37.7 μg/l; C₁₄, 41.4 μg/l and C₁₆, 40.6 μg/l. Two different gas-liquid chromatographic columns were tested and similar results achieved, which shows the ruggedness of the method.     

Determination of glyphosate using off-line ion exchange preconcentration and capillary electrophoresis-laser induced fluorescence detection

An enrichment method for the herbicide glyphosate is presented based on ion exchange solid phase extraction (SPE) technique. A 200-μl micro-pipette tip packed with 50 mg of Bio-Rad AG1-X8 anion exchanger beads was used for offline extraction of glyphosate from 50 ml of spiked river water sample. The retained glyphosate was eluted with 10 mM HCl and then converted quantitatively to the corresponding amine (glycine) using hypochlorite. Subsequent fluorescent labeling using naphthalene-2,3-dicarboxaldehyde (NDA)-cyanide allowed micellar electrokinetic chromatography (MEKC) separation and laser-induced fluorescence detection (LIF) with a violet diode laser. Optimization of the sample clean-up, extraction, elution, conversion and labeling steps enabled analysis of glyphosate in river water in the nanomolar range. Detection limits were 0.04 nM glyphosate in standards and 1.6 nM in spiked river.     

An end-channel amperometric detector for microchip capillary electrophoresis

An end-channel amperometric detector with a guide tube for working electrode was designed and integrated on a home-made glass microchip. The guide tube was directly patterned and fabricated at the end of the detection reservoir, which made the fixation and alignment of working electrode relatively easy. The fabrication was carried out in a two-step etching process. A 30 μm carbon fiber microdisk electrode and Pt cathode were also integrated onto the amperometric detector. The characteristics and primary performance of the home-made microchip capillary electrophoresis (MCCE) were investigated with neurotransmitters. The baseline separation of dopamine (DA), catechol (CA) and epinephrine (EP) was achieved within 80 s. Separation parameters such as injection time, buffer components, pH of the buffer were studied. Relative standard deviations of not more than 6.0% were obtained for both peak currents and migration times. Under the selected separation conditions, the response for DA was linear from 5 to 200 μM and from 20 to 800 μM for CA. The limits of detection of DA and CA were 0.51 and 2.9 μM, respectively (S/N=3).     

Identification and quantitation of iodotyrosines and iodothyronines in hydrolysate of iodinated casein by capillary electrophoresis

In this paper, a new method for separation, identification and quantitation of iodotyrosines and iodothyronines [3-monoiodo-L-tyrosine (MIT), 3,5-diiodo-L-tyrosine (DIT), L-thyronine (T₀), 3,5-diiodo-L-thyronine (T₂), 3,5,3′-triiodo-L-thyronine (T₃) and 3,3′,5,5′-tetraiodo-L-thyronine (T₄)] was described by using capillary electrophoresis with photodiode-array ultraviolet-visible detection (CE-UV). The certain influence factors were systematically investigated, including the type, concentration and pH of buffer, and additive. We found that 10 mM sodium borate running buffer (pH 8.5) containing 0.10 mM β-CD as additive reagent allowed the best instrumental conditions for the optimum separation of the iodotyrosines and iodothyronines. Under optimized conditions, the analytical time was within 6 min, using an uncoated fused-silica capillary of 75 μm inner diameter with an effective length of 30 cm. The reproducibility of the migration time and peak area was less than 0.6% and 6.8%, respectively. A linear range from 10-1000 μg/mL and low limits of detection from 1.3-3.4 μg/mL were obtained at the detection wavelength of 280 nm. Our preliminary results show that the method is well suitable for determination of the hydrolysate of iodinated casein.     

Selective spectrophotometric determination of TNT using a dicyclohexylamine-based colorimetric sensor

Because of the extremely heterogeneous distribution of explosives in contaminated soils, on-site colorimetric methods are efficient tools to assess the nature and extent of contamination. To meet the need for rapid and low-cost chemical sensing of explosive traces or residues in soil and post-blast debris, a colorimetric absorption-based sensor for trinitrotoluene (TNT) determination has been developed. The charge-transfer (CT) reagent (dicyclohexylamine, DCHA) is entrapped in a polyvinylchloride (PVC) polymer matrix plasticised with dioctylphtalate (DOP), and moulded into a transparent sensor membrane sliced into test strips capable of sensing TNT showing an absorption maximum at 530 nm when placed in a 1-mm spectrophotometer cell. The sensor gave a linear absorption response to 5-50 mg L⁻¹ TNT solutions in 30% aqueous acetone with limit of detection (LOD): 3 mg L⁻¹. The sensor is only affected by tetryl, but not by RDX, pentaerythritoltetranitrate (PETN), dinitrotoluene (DNT), and picric acid. The proposed method was statistically validated for TNT assay against high performance liquid chromatography (HPLC) using a standard sample of Comp B. The developed sensor was relatively resistant to air and water, was of low-cost and high specificity, gave a rapid and reproducible response, and was suitable for field use of TNT determination in both dry and humid soil and groundwater with a portable colorimeter.     

Miniaturized capillary electrophoresis system with a carbon nanotube microelectrode for rapid separation and detection of thiols

Multi-walled carbon nanotube (CNT) was mixed with epoxy to fabricate microdisc electrode used as a detector for a specially designed miniaturized capillary electrophoresis (CE)-amperometric detection system for the separation and detection of several bioactive thiols. The end-channel CNT amperometric detector offers favourable signal-to-noise characteristics at a relatively low potential (0.8 V) for detecting thiol compounds. Factors influencing the separation and detection processes were examined and optimized. Four thiols (homocysteine, cysteine, glutathione, and N-acetylcysteine) have been separated within 130 s at a separation voltage of 2000 V using a 20 mM phosphate running buffer (pH 7.8). Highly linear response is obtained for homocysteine, cysteine, glutathione, and N-acetylcysteine over the range of 5-50 μM with detection limits of 0.75, 0.8, 2.9, and 3.3 μM, respectively. Good stability and reproducibility (R.S.D. < 5%) are obtained reflecting the minimal adsorption of thiols at the CNT electrode surface. The new microchip protocol should find a wide range of bioanalytical applications involving assays of thiol compounds.     

Microchip capillary electrophoresis with electrochemical detector for precolumn enzymatic analysis of glucose, creatinine, uric acid and ascorbic acid in urine and serum

An integrated multiple-enzymatic assay was performed on a (microchip capillary electrophoresis) μCE-EC chip capable of precise intake of sample or reagents in nanoliters. Incorporating multiple-enzyme assay into the μCE chip is relatively new—rendering simultaneous analysis of creatinine and uric acid a snap.Added to the list of merits in this study are the enhanced sensitivity down to 1 μM and a broader spectrum of analytes—inclusive of glucose for the long-time sufferers of diabetes. The performance was orchestrated to attain the claimed level: employing the end-channel electrode mode to tame the noises and the precolumn enzymatic reaction to stabilize the baseline. The 10 μm embedded Pt electrode, deposited at the end of the 30 μm wide separation channel, benefited chip fabrication besides noise reduction. The optimized conditions were 20 mM phosphate buffer (pH 7.5), +1.5 kV separation voltage and +1.0 V detection potential (versus Ag/AgCl). The migration time was repeatable within the deviation of 0.5% R.S.D. (n=7), but the peak currents ranged from 1.5 to 2.2% R.S.D. The detection limits (S/N=3) ranged from 0.71 μM for ascorbic acid to 10 μM for glucose. The calibration curve was linear from 10 to 800 μM (R²>0.995). Glucose, creatinine, uric acid and ascorbic acid as model analytes, in pure form or in serum and urine samples, were tested to verify its feasibility.     

Determination of nitroaromatic, nitramine, and nitrate ester explosives in soil by gas chromatography and an electron capture detector

Hazardous waste site characterization, forensic investigations, and land mine detection are scenarios where soils may be collected and analyzed for traces of nitroaromatic, nitramine, and nitrate ester explosives. These thermally labile analytes are traditionally determined by high-performance liquid chromatography (HPLC); however, commercially available deactivated injection port liners and wide-bore capillary columns have made routine analysis by gas chromatography (GC) possible. The electron-withdrawing nitro group common to each of these explosives makes the electron capture detector (ECD) suitable for determination of low concentrations of explosives in soil, water, and air. GC-ECD and HPLC-UV concentration estimates of explosives residues in field-contaminated soils from hazardous waste sites were compared, and correlation (r>0.97) was excellent between the two methods of analysis for each of the compounds most frequently detected: 2,4,6-trinitrotoluene (TNT), hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX), 2,4-dinitrotoluene (2,4-DNT), 1,3-dinitrobenzene (1,3-DNB), 1,3,5-trinitrobenzene (TNB), and octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX). The analytes were extracted from soils with acetonitrile by 18 h of sonication in a cooled ultrasonic bath. Two soil-to-solvent ratios were evaluated: 2.00 g:10.00 ml and 25.0 g:50.0 ml. GC-ECD method detection limits were similar for the two soil-to-solvent ratios and were about 1 mug kg(-1) for the di- and trinitroaromatics, about 10 mug kg(-1) for the mono-nitroaromatics, 3 mug kg(-1) for RDX, 25 mug kg(-1) for HMX, and between 10 and 40 mug kg(-1) for the nitrate esters (nitroglycerine [NG] and pentaerythritol tetranitrate [PETN]). Spike recovery studies revealed artifacts introduced by the spiking procedure. Recoveries were low in some soils if the amount of soil spiked was large (25.0 g) compared to the volume of spike solution added (1.00 ml). Recoveries were close to 100% when 2.00-g soil samples were spiked with 1.00 ml of solution. Analytes most frequently found in soils collected near buried land mines were the microbial transformation products of TNT (2-amino-4,6-dinitrotoluene [2-Am-DNT] and 4-amino-2,6-dinitrotoluene [4-Am-DNT]), manufacturing impurities of TNT (2,4-DNT, 2,6-DNT, and 1,3-DNB), and TNT. The microbial reduction products of the isomers of DNT and of 1,3-DNB were also detected, but the ECD response to these compounds is poor.     

Stacking and separation of aspartic acid enantiomers under discontinuous system by capillary electrophoresis with light-emitting diode-induced fluorescence detection

We describe the stacking and separation of d- and l-aspartic acid (Asp) by capillary electrophoresis (CE) with light-emitting diode-induced fluorescence detection (LEDIF). In the presence of cyanide, d- and l-Asp were derivatized with naphthalene-2,3-dicarboxaldehyde (NDA) to form fluorescent derivatives prior to CE-LEDIF. The separation of NDA-derivatized d- and l-Asp was accomplished using a discontinuous system - buffer vials contained a solution of 0.6% poly(ethylene oxide) (PEO), 150 mM sodium dodecyl sulfate (SDS), and 60 mM hydroxypropyl-β-cyclodextrin (Hp-β-CD), while a capillary was filled with a solution of 150 mM SDS and 60 mM Hp-β-CD. The role of PEO, Hp-β-CD, and SDS is to act as a concentrating media, as a chiral selector, and as a pseudostationary phase, respectively. This discontinuous system could be employed for the stacking of 600 nL of NDA-derivatized d- and l-Asp without the loss of chiral resolution. The stacking mechanism is mainly based on the difference in viscosity between sample zone and PEO as well as SDS sweeping. The limits of detection at signal-to-noise of 3 for d- and l-Asp were down to 2.4 and 2.5 × 10⁻¹⁰ M, respectively. Compared to normal sample injection volume (25 nL), this stacking approach provided a 100- and 110-fold improvement in the sensitivity of d- and l-Asp, respectively. This method was further applied for determining d- and l-Asp in cerebrospinal fluid, soymilk, and beer.     

Fast haptoglobin phenotyping based on microchip electrophoresis

A new and fast method for haptoglobin phenotyping was developed based on microchip electrophoresis with laser induced fluorescence detection. Haptoglobin phenotypes 1-1 and 2-2 were labeled with fluorescein isothiocyanate. The analyses were performed on glass microchip which was simply treated with sodium dodecyl sulfate. After the optimization of the separation conditions, Hp 1-1 and Hp 2-2 could be differentiated in 150 s and the detection limits for Hp 1-1 and Hp 2-2 were 0.39 and 0.62 μg/mL, respectively. Finally, the method was applied to human serum samples from healthy people and liver cancer patients. A decrease in Hp concentration for liver cancer patients was confirmed. Featuring high efficiency, speed, simplicity, the method reveals great potentials for the diagnosis of diseases and proteome research.