Detector technologies for comprehensive two-dimensional gas chromatography

The detector is an integral and important part of any chromatographic system. The chromatographic peak profiles (i.e. peak separation) should, ideally, be unaffected by the detector--it should only provide the sensing capacity required at the end of a column separation process. The relatively new technique of comprehensive 2-D GC (GC x GC) extends the performance of GC manyfold, but comes at a price--existing GC systems may not be adequately designed with the requirements of GC x GC in mind. This is primarily the need for precise measurement of very fast peaks entering the detector (e.g. as fast as 50 ms basewidth in some instances). The capacity of the detector to closely track a rapidly changing chromatographic peak profile depends on a number of factors, such as design of flow paths and make-up gas introduction, type of detector response mechanism, and the chemistry of the response. These factors are discussed here as a means to appreciate the technical demands of detection in GC x GC. The MS detector will not be included in this review.     

Dual NPD/ECD detection in comprehensive two-dimensional gas chromatography for multiclass pesticide analysis

A comprehensive 2-D GC (GC x GC) dual detection system, coupled to nitrogen-phosphorus detection (NPD) and electron capture detection (ECD) has been developed for multiclass pesticide analysis in vegetable sample matrices. The second dimension column was connected to the parallel detectors via a microfluidic splitting device. The sample set comprised 17 organochlorine pesticides, 15 organophosphorus insecticides and 9 N-containing fungicides. Selective detection of vegetable sample extracts provides increased information content through simultaneous, correlated GC x GC plots for both ECD and NPD, which demonstrated improved separation of pesticide standards from each other, and from the sample matrix. The efficiency of NPD and ECD modes was investigated and compared; the ECD produced broader peaks, with the ECD generating greater response as measured by S/N ratio. Accuracy and precision of the approach were determined as repeatability and reproducibility for selected pesticides. The RSDs of the intraday (n = 5) and interday (3 days) analyses of the selected pesticides are less than 2.5 and 10%, respectively. The relative ratio of the ECD/NPD response is proposed to offer additional identification of individual pesticides, in addition to the (1)t(R) and (2)t(R) retention coordinates; ratios vary from 19 to over 1000 for selected pesticides that also exhibit ECD and NPD activities.     

Application of comprehensive two-dimensional gas chromatography with nitrogen-selective detection for the analysis of fungicide residues in vegetable samples

Comprehensive two-dimensional gas chromatography (GCxGC) with nitrogen-phosphorus detection (NPD) has been investigated for the separation and quantitation of fungicides in vegetable samples. The detector gas flows (H(2), N(2) and air) were adjusted to achieve maximum response of signal whilst minimizing peak width. The comparison of different column sets and selection of the temperature program were carried out with a mixture of nine N-containing standard fungicides, eight of which were chlorinated. The results from GCxGC-NPD and GCxGC with micro electron-capture detection (muECD) were compared. External calibrations of fungicides were performed over a concentration range from 1 to 1,000 microgL(-1). The peak area calibration curves generally had regression coefficients of R(2)>0.9980, however for iprodione which was observed to undergo on-column degradation, an R(2) of 0.990 was found. The limit of detection (LOD) and limit of quantitation (LOQ) were less than about 74 and 246 ng L(-1), respectively. The intra-day and inter-day RSD values were measured for solutions of concentration 0.100, 0.500 and 1.50 mg L(-1). For the 0.500 mg L(-1) solution, intra- and inter-day precision of peak area and peak height for most of the pesticides were about 2% and 8%, respectively. Excellent linearity was observed for these standards, from 0.001 to 25.00 mg L(-1). The standard mixture peak positions were identified by using GCxGC with quadrupole mass spectrometry (qMS). To illustrate the potential and the versatility of both GCxGC-NPD and GCxGC-muECD, the method was applied to determination of fungicides in a vegetable extract. Decomposition of one fungicide standard (iprodione) during chromatography elution was readily observed in the two-dimensional (2D) GCxGC plot as a diagonal ridge response in the 2D chromatogram between the degrading compound and the decomposition product.     

Protein-Protein Interactions: Insight from Molecular Dynamics Simulations and Nanoparticle Tracking Analysis

Protein-protein interaction plays an essential role in almost all cellular processes and biological functions. Coupling molecular dynamics (MD) simulations and nanoparticle tracking analysis (NTA) assay offered a simple, rapid, and direct approach in monitoring the protein-protein binding process and predicting the binding affinity. Our case study of designed ankyrin repeats proteins (DARPins)—AnkGAG1D4 and the single point mutated AnkGAG1D4-Y56A for HIV-1 capsid protein (CA) were investigated. As reported, AnkGAG1D4 bound with CA for inhibitory activity; however, it lost its inhibitory strength when tyrosine at residue 56 AnkGAG1D4, the most key residue was replaced by alanine (AnkGAG1D4-Y56A). Through NTA, the binding of DARPins and CA was measured by monitoring the increment of the hydrodynamic radius of the AnkGAG1D4-gold conjugated nanoparticles (AnkGAG1D4-GNP) and AnkGAG1D4-Y56A-GNP upon interaction with CA in buffer solution. The size of the AnkGAG1D4-GNP increased when it interacted with CA but not AnkGAG1D4-Y56A-GNP. In addition, a much higher binding free energy (∆GB) of AnkGAG1D4-Y56A (−31 kcal/mol) obtained from MD further suggested affinity for CA completely reduced compared to AnkGAG1D4 (−60 kcal/mol). The possible mechanism of the protein-protein binding was explored in detail by decomposing the binding free energy for crucial residues identification and hydrogen bond analysis.     

Characterization of yellow and colorless decorative glasses from the Temple of the Emerald Buddha, Bangkok, Thailand

Yellow and colorless ancient glasses, which were once used to decorate the Temple of the Emerald Buddha, Bangkok, Thailand, around 150 years ago, are studied to unravel the long-lost glass-making recipes and manufacturing techniques. Analyses of chemical compositions, using synchrotron x-ray fluorescence (SRXRF), indicate that the Thai ancient glasses are soda lime silica glasses (60 % SiO₂; 10 % Na₂O; 10 % CaO) bearing lead oxide between 2–16 %. Iron (1.5–9.4 % Fe₂O₃) and manganese (1.7 % MnO) are present in larger abundance than the other 3d transition metals detected (0.04–0.2 %). K-edge x-ray absorption near edge spectroscopy (XANES) and extended x-ray absorption fine structure spectroscopy (EXAFS) provide conclusive evidence on the oxidation states of Fe being 3+ and Mn being 2+ and on short-length tetrahedral structures around the cations. This suggests that iron is used as a yellow colorant with manganese as a decolorant. L ₃-edge XANES results reveal the oxidation states of lead as 2+. The results from this work provide information crucial for replicating these decorative glasses for the future restoration of the Temple of the Emerald Buddha.     

Electrical responses and dielectric relaxations in giant permittivity NaCu3Ti3TaO12 ceramics

Conductive and highly transparent indium tin oxide (ITO) thin films were prepared on photosensitive glass substrates by the combination of sol–gel and spin-coating techniques. First, the substrates were coated with amorphous Sn-doped indium hydroxide, and these amorphous films were then calcined at 550^∘C to produce crystalline and electrically conductive ITO layers. The resulting thin films were characterized by means of scanning electron microscopy, UV-Vis spectroscopy, X-ray photoelectron spectroscopy and spectroscopic ellipsometry. The measurements revealed that the ITO films were composed of spherical crystallites around 20 nm in size with mainly cubic crystal structure. The ITO films acted as antireflection coatings increasing the transparency of the coated substrates compared to that of the bare supports. The developed ITO films with a thickness of ∼170–330 nm were highly transparent in the visible spectrum with sheet resistances of 4.0–13.7 kΩ/sq. By coating photosensitive glass with ITO films, our results open up new perspectives in micro- and nano-technology, for example in fabricating conductive and highly transparent 3D microreactors.