Fundamental Measurements in Online Polymerization Reaction Monitoring and Control with a Focus on ACOMP

Fundamental measurements in online polymerization reaction monitoring and control seek to avoid empirical and inferential models in data interpretation. One such approach making use of multiple detectors is automatic continuous online monitoring of polymerization reactions (ACOMP), wherein a continuous reactor stream is automatically, continuously diluted and conditioned to where measurements reflect intrinsic particle properties and not the interactions that can dominate measurements in concentrated media. Examples where dilute regime measurements are needed include static and dynamic light scattering, and reduced viscosity. This review focuses on ACOMP to illustrate a number of reaction contexts where fundamental measurements are used to gain a comprehensive picture of reaction characteristics.

     

An on-column fracture/end-column reaction interface for chemiluminescence detection in capillary electrophoresis

Chemiluminescence (CL) offers a sensitive detection method for capillary electrophoresis (CE), but the implementation of CE–CL is usually under compromised operating conditions for CE, such as the prerequisite of extreme pH buffer for optimal CL reaction at the capillary outlet. This has sometimes significantly deteriorated the separation of CE. In this study, the development of a new interface makes it possible to optimize the operating conditions for CE separation and CL detection independently. The interface consists of an on-column fracture being installed in a reservoir near the capillary end to create an electrical connection and also serve as reagent addition entrance. The capillary terminal is inserted into an end-column reservoir for CL reaction and detection. In this arrangement, the applied electric field has been decoupled from the CL detection, which is proved to effectively improve CE's performance by allowing the use of optimal CE buffers. At the same time, it enables the optimization of CL detection independently. The applicability of this interface was evaluated by using acridinium ester (AE) and luminol systems. For AE system, the interfering products of CL reagent (⁻OH, HO₂⁻) have been prevented, and the pH range of CE buffer can be independent to the optimal pH value of AE CL reaction, which is usually below 3. The AE was detected using running buffer at pH 8.7, giving a detection limit of 0.1 nM (S/N = 3), and the theoretical plate numbers is as high as 56 000. The on-column fracture based configuration is simple, sensitive and easy to implement.     

Large-scale pesticide testing in olives by liquid chromatography–electrospray tandem mass spectrometry using two sample preparation methods based on matrix solid-phase dispersion and QuEChERS

In this work we have evaluated the performance of two sample preparation methodologies for the large-scale multiresidue analysis of pesticides in olives using liquid chromatography–electrospray tandem mass spectrometry (LC–MS/MS). The tested sample treatment methodologies were: (1) liquid–liquid partitioning with acetonitrile followed by dispersive solid-phase extraction clean-up using GCB, PSA and C₁₈ sorbents (QuEChERS method – modified for fatty vegetables) and (2) matrix solid-phase dispersion (MSPD) using aminopropyl as sorbent material and a final clean-up performed in the elution step using Florisil. An LC–MS/MS method covering 104 multiclass pesticides was developed to examine the performance of these two protocols. The separation of the compounds from the olive extracts was achieved using a short C₁₈ column (50 mm × 4.6 mm i.d.) with 1.8 μm particle size. The identification and confirmation of the compounds was based on retention time matching along with the presence (and ratio) of two typical MRM transitions. Limits of detection obtained were lower than 10 μg kg⁻¹ for 89% analytes using both sample treatment protocols. Recoveries studies performed on olives samples spiked at two concentration levels (10 and 100 μg kg⁻¹) yielded average recoveries in the range 70–120% for most analytes when QuEChERS procedure is employed. When MSPD was the choice for sample extraction, recoveries obtained were in the range 50–70% for most of target compounds. The proposed methods were successfully applied to the analysis of real olives samples, revealing the presence of some of the target species in the μg kg⁻¹ range. Besides the evaluation of the sample preparation approaches, we also discuss the use of advanced software features associated to MRM method development that overcome several limitations and drawbacks associated to MS/MS methods (time segments boundaries, tedious method development/manual scheduling and acquisition limitations). This software feature recently offered by different vendors is based on an algorithm that associates retention time data for each individual MS/MS transition, so that the number of simultaneously traced transitions throughout the entire chromatographic run (dwell times and sensitivity) is maximized.     

发铅检测法的临床应用价值评估

从铅中毒发铅诊断标准、发铅诊断试验及发铅诊断临床应用3个方面论述了发铅检测法在铅中毒诊断、筛查和监督中的实际应用问题。根据临床经验和发铅-血铅比值确定了居民发铅正常值上限及铅中毒发铅诊断分级标准;即使以血铅测定值为"金标准",诊断试验表明,发铅测定在铅中毒诊断中仍有实际应用价值;发铅检测法自上世纪60年代以来一直沿用至今,绝大多数研究者认为,发铅测定是诊断、筛查铅中毒和监督环境铅污染最简单、有效的工具。     

Micro-crack tip fracture of commercial grade aluminum under mixed mode loading

In situ tensile tests were made in a scanning electron microscope (SEM) to investigate the deformation and micro-fracture in the immediate vicinity of a micro-crack tip in commercial pure aluminum with large-size crystal. Examined are the slip line field, stress intensity factor, strain energy density factor and crack tip opening displacement (CTOD) for mixed mode loading. Blunting and sharpening effects are observed. The latter is controlled by localized slip while the former by uniformed slip of the operating slip system with the highest crack tip Schmid factor. The operating slip system depends on the crystallographic orientation of crystal containing micro-cracks.The damage and fracture take place in the blunted region and depend on the coarsening and spacing of uniformed slip lines. The mixed mode micro-crack propagates along the direction where the voids grow and coalesce into the micro-crack. The direction also depends on the orientation of the applied loading. This suggests that the formation of macro-fracture mechanics could be applied. In particular, the minimum strain energy density criterion is suitable for determining the direction of micro-crack instability in the mixed mode. The in situ data were used to yield a nearly constant critical, minimum strain energy density factor for onset of micro-cracking.     

Compressive fracture characteristics of Zr-based bulk metallic glass

The compressive fracture characteristics of Zr-based bulk metallic glass under uniaxial compression tests are studied.The zigzag rheological behavior is observed in the compression stress-strain curves of amorphous alloys.At room temperature the uniaxial compression fracture takes place along the plane which is at a 45-degree angle to the direction of the compressive stress.The microstructure of a typical fracture pattern is the vein network.A unique,finger-like vein pattern is found to exist at the fractur...     

A simple flowcell for reaction monitoring by NMR

A simple, cheap and flexible flowcell based on a standard 5 mm NMR tube, designed for the monitoring of reactions but of wide applicability, is described. No modification of the NMR instrument is needed, allowing the system to be employed with any conventional NMR probe and magnet. The system is robust and economical in use of reagents, and can be used for studying both homogeneous and heterogeneous reactions. Copyright © 2010 John Wiley & Sons, Ltd.     

An overview of sample preparation and extraction of synthetic pyrethroids from water,sediment and soil

The latest developments in sample preparation and extraction of synthetic pyrethroids from environmental matrices viz., water, sediment and soil were reviewed. Though the synthetic pyrethroids were launched in 1970s, to the best of authors’ knowledge there was no review on this subject until date. The present status and recent advances made during the last 10 years in sample preparation including conservation and extraction techniques used in determination of synthetic pyrethroids in water, sediment and soil were discussed. Pre- and post-extraction treatments, sample stability during extraction and its influence upon the whole process of analytical determination were covered. Relative merits and demerits including the green aspects of extraction were evaluated. The current trends and future prospects were also addressed.     

Development and validation of an HPLC‐UV method for the simultaneous determination of the antipsychotics clozapine,olanzapine and quetiapine,several beta‐blockers and their metabolites

A simple, accurate and selective column‐switching high‐performance liquid chromatography (HPLC) method was developed and validated for simultaneous quantification of six beta ‐blockers (metoprolol, timolol, bisoprolol, propranolol, carvedilol and nebivolol), three of their metabolites (α ‐hydroxy metoprolol, N‐ desisopropyl propranolol and 4′‐hydroxy carvedilol 4‐HCAR), three antipsychotics (olanzapine, clozapine and quetiapine) and three of their metabolites (N‐ desmethyl olanzapine, N‐ desmethyl clozapine and N‐ desalkyl quetiapine) in human serum. After pretreatment on a Merck LiChrospher RP‐4 ADS column (25 μm), drugs were separated on a Phenomenex Gemini Phenyl Hexyl 110 A column (250 × 4.6 mm, 5 μm) using a gradient mixture of acetonitrile and potassium dihydrogen phosphate buffer pH 3.1 (containing 10% methanol) as a mobile phase at a flow rate of 1 mL/min. The total analysis time was 40 min. For detection of the analytes, four different UV wavelengths were used: 215, 226, 242 and 299 nm. The method was validated according to the guidelines of the Society of Toxicology and Forensic Chemistry in terms of selectivity, linearity, accuracy, precision and stability and successfully applied for the analysis of the 15 described analytes in human serum.     

Comparison of beaked whale detection algorithms

Due to recent advances in passive acoustic monitoring techniques, beaked whales are now more effectively detected acoustically than visually during vessel-based (e.g. line-transect) surveys. Beaked whales signals can be discriminated from those of other cetaceans by the unique characteristics of their echolocation clicks (e.g. duration >175 μs, center frequencies between 30 and 40 kHz, inter-click intervals between 0.2 and 0.4 s and frequency upsweeps). Furthermore, these same characteristics make these signals ideal candidates for testing automated detection and classification algorithms. There are several different beaked whale automated detectors currently available for use. However, no comparative analysis of detectors exists. Therefore, comparison between studies and datasets is difficult. The purpose of this study was to test, validate, and compare algorithms for detection of beaked whales in acoustic line-transect survey data. Six different detection algorithms (XBAT, Ishmael, PAMGUARD, ERMA, GMM and FMCD) were evaluated and compared. Detection trials were run on three sample days of towed-hydrophone array recordings collected by NOAA Southwest Fisheries Science Center (SWFSC) during which were confirmed visual sightings of beaked whales (Ziphius cavirostris and Mesoplodon peruvianus). Detections also were compared to human verified acoustic detections for a subset of these data. In order to measure the probabilities of false detection, each detector was also run on three sample recordings containing clicks from another species: Risso’s dolphin (Grampus griseus). Qualitative and quantitative comparisons and the detection performance of the different algorithms are discussed.