Advances in the detection of azodicarbonamide and the metabolic product semicarbazide.

In the present work, capillary electrophoresis (CE) was used for the first time for the simultaneous analysis of azodicarbonamide (ADA) and semicarbazide (SEM), and the capillary electrophoresis separation conditions, extraction agents, and derivatization conditions were investigated. In 20 mmol L−1 sodium tetraborate, 30 mmol L−1 β-cyclodextrin (β-CD), 17 % isopropanol (v/v), and 25 mmol L−1 sodium dodecyl sulfate (SDS) running buffer, ADA and SEM previously derivatized with 9-fluorenylmethyl chloroformate (FMOC) were separated in less than 25 min with good sensitivity. The linear ranges were 8.3 × 10−4∼6.6 × 10−2 mmol L−1 and 1.9 × 10−3∼3.4 × 10−2 mmol L−1, and detection limits (S/N = 10) were 0.5 and 0.15 mg kg−1 for ADA and SEM, respectively. The proposed method was successfully applied for the simultaneous analysis of ADA and SEM in five flour samples with satisfactory recovery data from 88.0 to 93.0 % for ADA and 98.0 to 106.0 % for SEM, indicating the valuable potential application of this method for food analysis.

Analysis and Detection by Capillary Electrophoresis

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Conductivity detection in capillary electrophoresis

Azodicarbonamide (ADA) in flour products can be converted into carcinogenic biurea and semicarbazide hydrochloride after baking. Thus, it is mandatory to determine ADA in flour. We herein developed a colorimetric method for the rapid and visual detection of ADA in flour based on glutathione (GSH)-induced gold nanoparticles (AuNPs) aggregation and specific reaction between ADA and GSH. The GSH can react to AuNPs via Au-SH covalent bond to form a network structure, which leads to AuNPs aggregation to produce color change, whereas ADA can specifically react with GSH to lead to the coupling of two GSH molecules, which makes GSH lose a -SH group and thus decreases the aggregation degree of AuNPs induced by GSH. This provided a platform for field-portable colorimetric detection of ADA. The colorimetric sensor can be used to detect as little as 0.33 μM (38.3 ppb) of ADA by naked eye observation and 0.23 μM (26.7 ppb) of ADA by spectrophotometry within 2 h. The method was successfully used to detect ADA in flour with a recovery of 91-104% and a relative standard deviation (RSD) < 6%. The visual detection limit of sensor is lower than the ADA limitation in flour (45 mg/kg), which makes the sensor a potential approach for the instrument-free visual and on-site detection of ADA in flour.

Analytical potential of mid-infrared detection in capillary electrophoresis and liquid chromatography: A review

The microwave hydrolysis and derivatization coupled with capillary electrophoresis detection were developed for the separation and determination of the amino acids in Panax notoginseng. The experimental conditions for the microwave hydrolysis and derivatization were examined and optimized. Several parameters of capillary electrophoresis, such as pH value of background electrolyte, borate concentration and applied voltage were optimized. Under the selected conditions, 11 amino acids were completely separated. The real sample was analyzed and the results were satisfactory. Compared with that of conventional heat hydrolysis and derivatization, the analytical time of this method was significantly shortened.

Raman spectroscopy can be an alternative to near-infrared spectroscopy (NIR) for nondestructive quantitative analysis of solid pharmaceutical formulations. Compared with NIR spectra, Raman spectra have much better selectivity, but subsampling was always an issue for quantitative assessment. Raman spectroscopy in transmission mode has reduced this issue, since a large volume of the sample is measured in transmission mode. The sample matrix, such as particle size of the drug substance in a tablet, may affect the Raman signal. In this work, matrix effects in transmission NIR and Raman spectroscopy were systematically investigated for a solid pharmaceutical formulation. Tablets were manufactured according to an experimental design, varying the factors particle size of the drug substance (DS), particle size of the filler, compression force, and content of drug substance. All factors were varied at two levels plus a center point, except the drug substance content, which was varied at five levels. Six tablets from each experimental point were measured with transmission NIR and Raman spectroscopy, and their concentration of DS was determined for a third of those tablets. Principal component analysis of NIR and Raman spectra showed that the drug substance content and particle size, the particle size of the filler, and the compression force affected both NIR and Raman spectra. For quantitative assessment, orthogonal partial least squares regression was applied. All factors varied in the experimental design influenced the prediction of the DS content to some extent, both for NIR and Raman spectroscopy, the particle size of the filler having the largest effect. When all matrix variations were included in the multivariate calibrations, however, good predictions of all types of tablets were obtained, both for NIR and Raman spectroscopy. The prediction error using transmission Raman spectroscopy was about 30% lower than that obtained with transmission NIR spectroscopy.

On-the-fly fluorescence lifetime detection (OFLD) in capillary electrophoresis (CE) was previously demonstrated using a commercial multiharmonic Fourier transform (MHF) spectrofluorometer interfaced to a commercial CE system. This paper discusses optimization of the interface design for minimization of background fluorescence and scattered light, thereby maximizing the signal-to-background ratio (S/B) of the dynamic measurement. Strategies included using various combinations of optical filters including a holographic filter and longpass or bandpass filters, tilting the capillary relative to the incident laser beam, employing a confocal design and adding an iris to remove out-of-focus light, using a microscope objective in the emission beam to increase the collection efficiency, and using square instead of ciruclar capillary columns. Significant improvements in S/B for on-column, on-the-fly detection of fluorescein in CE were achieved with most modifications.

Identification of anisodamine tablets by Raman and near-infrared spectroscopy with chemometrics

Two applications of a near-field thermal lens capillary electrophoresis detector in the deep ultraviolet region (pump beam 257 nm wavelength) will be presented: (1) Capillary electrophoretic determination of the pharmaceuticals Tramadol, Verapamil, and Papaverin. Direct separation techniques were used for the different classes of substances with characteristic absorbance spectra. The combination of capillary electrophoresis and the highly sensitive detection with thermal lens spectroscopy permits the analysis of nanoliter volume samples common in biomedical diagnostics without any preconcentration step. (2) The determination of (nonfluorescent) nitro aromatic explosives in contaminated soil. These compounds are detected with the laboratory built thermal lens detector after their separation by micellar electrokinetic chromatography. Its shown that this type of detection makes it possible to obtain limits of detection 1–2 orders of magnitude lower than those obtained with classical absorption spectrometric detection.

It is shown that organo-aqueous separation buffers show much promise when used in capillary electrophoresis separations with photothermal (thermal lens) detection systems. Acetonitrile-water and methanol-water mixtures were selected, as conventionally used in capillary electrophoresis. It is shown that, despite more sophisticated experimental conditions (significant heat outflow from the capillary body) and peak detection, the theoretical ratio of the thermal lens signal for a binary mixture to the thermal lens signal for an aqueous solution (or the corresponding ratio obtained experimentally under bulk batch conditions) can be used to predict the sensitivity of thermal lens detection in capillary electrophoresis. The limits of detection for 2-, 3-, and 4-nitrophenols selected as model compounds in 70% v/v acetonitrile separation buffers are 1 x 10(-6) M, 1 x 10(-6) M and 3 x 10(-7) M, respectively, and are therefore decreased by a factor of six compared to thermal lens detection in aqueous separation buffers. The overall increase in the thermal lens detection sensitivity in a 100% ACN buffer is a factor of 13.

Electrochemical detection has been shown to be a sensitive method of detection in capillary electrophoresis (CE). The small sample volume required for CE makes it ideal for the analysis of microdialysis samples. In this paper, capillary electrophoresis with electrochemical detection is utilized in the analysis of samples obtained during continuous monitoring of the pharmacokinetics of L‐dopa in the rat. The detection limit for L‐dopa was 98 attomoles or 3.9 ng/mL. The elimination half‐life was calculated to be 10.3 ± 1.1 minutes. Voltammetric characterization was used to verify the identity of L‐dopa and its metabolites. The effects of electrochemical pretreatment on the detector performance was also investigated.

Capillary electrophoresis (CE), with its advantage of high resolution power, has attracted much attention. But CE has another advantage of needing only a small sample volume, which is expected to make it a useful tool for ultramicroscale analysis as well. However, conventional absorbance detectors are not sensitive enough because the optical light-path is that of the diameter of a capillary, which is several tens of microns. A highly sensitive detector is indispensable to application of CE to ultramicroscale analysis. Several sensitive detection methods have been developed, such as laser-induced fluorometry (LIF), electrochemical detection, mass spectrometry, etc. To make the best use of the high separation efficiency of CE, an on-column detection scheme, which can easily reduce the detection volume needed by using a focused laser beam as a probing beam, seems to be more preferable than other detection schemes including off-column or end-column detection schemes, and LIF seems to be more suitable than electrochemical detection and mass spectrometric detection. However, LIF cannot be applied to nonfluorescent analytes, and fluorescent derivatization is usually needed, which is not suitable for ultramicroscale analysis. Laser-induced photothermal spectrometry is another highly sensitive on-column detection approach, and differing from LIF, nonfluorescent species are also detectable. As a kind of photothermal effect, we found the capillary vibration induced by laser (CVL) effect [1], and proposed it as a highly sensitive on-column detection method of CE [2]. Like other photothermal detection methods, the CVL method is based on light absorption by a sample and successive heat generation due to nonradiative relaxation. This heat changes the capillary tension. Because the excitation laser beam is periodically irradiated onto the capillary, the tension fluctuation occurs periodically, resulting in vibration of the capillary. The amplitude of the capillary vibration has been found to be proportional to sample concentration. Therefore, quantitative analysis can be performed by detecting the amplitude of the capillary vibration.

The purpose of this study was to investigate the dehydration of piroxicam monohydrate (PRXMH) in compacts using terahertz pulsed spectroscopy (TPS), Raman spectroscopy, and reflectance near-infrared (NIR) spectroscopy. Compacts were prepared by using PRXMH and poly(tetrafluoro)ethylene powders and combining them in three different manners before compression to produce compacts in which the PRXMH was dispersed throughout the compact, deposited on one face of the compact, or included as a layer within the compact. TPS was a suitable technique to assess the effect of sample preparation on dehydration, whereas Raman and NIR spectroscopy were limited by their sampling depth and the interference of the polymer matrix. TPS revealed that the dehydration behavior depended largely on the compact preparation method. Non-isothermal dehydration was investigated with all three spectroscopic techniques, combined with principal component analysis (PCA) on samples where the PRXMH was deposited on one face of the compact. In addition, variable temperature X-ray powder diffractometry (VT-XRPD) was used to verify the transformation from PRXMH to anhydrous PRX form I, while thermogravimetric analysis (TGA) was used to monitor the water loss. All three spectroscopic techniques allowed in situ monitoring of the dehydration from the surface layers of the compacts. TPS and Raman spectroscopy detected structural changes of the crystal, while NIR spectroscopy was more sensitive to water loss. PCA of the TPS, Raman spectroscopy, and XRPD data revealed similar dehydration profiles. In contrast, the NIR spectroscopy profile was more similar to the TGA results. The spectroscopic techniques were more suitable than slower techniques such as VT-XRPD for monitoring rapid structural changes that occurred during the dehydration.