Triple-detection system

The product obtained was analyzed by gel permeation chromatography, GPC, using a Viscotek TDA 302 Triple Detection System with Light Scattering, Viscosity and RI Detection. The columns used were 2x ViscoGel GMPWxl (Mixed Bed), and the eluent was aqueous 0.8 M NaNC>3 at pH 7. The eluent flow rate was 0.6 ml/min. and the oligomer concentration approximately 1 mg/ml. The temperature was 35 °C. 

Present emphasis is being placed on the use of detector combinations in fact, the triple-detection system , SEC-light-scattering-vis-cometry-differential refractometry, is being used more frequently, sometimes with the addition of an on-line UV detector to monitor composition (20). 

The RI constant, which relates the RI units to sample concentration, was determined by the dnjdc method of Wyatt Technology. The RI constant exhibited some variation at times, so that its value hacT to be adjusted in order to match the calculated mass with the injected mass. This variation was attributed to an intermittently faulty RI detector. The triple detection system had sufficient redundancy that accurate values of and [r ] could be obtained even when one component was not working well. 

It appears that for low values of Rg (10-20 nm), the values of Rg that were calculated from the Ptitsyn-Eisner equation were more reliable than those obtained from light scattering in an aqueous medium. Accordingly, for accurate work over a broad range of molecular weights and sizes, a triple detection system is advantageous and recommended. 

FIGURE 9.11 Schematic diagram of an SEC instrumentation with triple detection system. (Courtesy of Polymer Laboratories.)... 

A modern laser Raman spectrometer consists of four fundamental components a laser source, an optical system for focusing the laser beam on to the sample and for directing the Raman scattered light to the monochromator entrance slit, a double or triple monochromator to disperse the scattered light, and a photoelectric detection system to measure the intensity of the light passing through the monochromator exit slit (Fig. 7). 

A useful approach to detection in polymer HPLC presents the on-line hyphenation of different measurement principles. For example, an RI detector combined with a UV photometer produces valuable additional information on the composition of some copolymers. Further progress was brought with the triple detection RI plus LALS plus VISCO [313], which is especially suitable for branched macromolecules and the tetra detection UV plus RI plus LALS plus VISCO, which enables characterization of some complex polymer systems, exhibiting a distribution not only in their molar mass and architecture, but also in their chemical composition such as long chain branched copolymers. 

At present, the most powerful and promising interfaces for drug residue analysis are die particle-beam (PB) interface that provides online EI mass spectra, the thermospray (TSP) interface diat works well with substances of medium polarity, and more recently the atmospheric pressure ionization (API) interfaces that have opened up important application areas of LC to LC-MS for ionizable compounds. Among die API interfaces, ESP and ISP appear to be the most versatile since diey are suitable for substances ranging from polar to ionic and from low to high molecular mass. ISP, in particular, is compatible with the flow rates used with conventional LC columns (70). In addition, both ESP and ISP appear to be valuable in terms of analyte detectability. These interfaces can further be supplemented by preanalyzer collision-induced dissociation (CID) or tandem MS as realized with the use of triple quadrupole systems. Complementary to ESP and ISP interfaces with respect to the analyte polarity is APCI with a heated nebulizer interface. This is a powerful interface for both structural confirmation and quantitative analysis. 

Multiple detection applied to the SEC characterization of copolymers is attractive because it yields both CCD and MWD information. A dual detection system based on two concentration detectors, for example, RI and UV, is useful where narrow standards of the homopolymers are available and where both homopolymers obey universal calibration. However, in other copolymer systems the addition of a third detector, LALLS, can offer the advantage of on-line determination of molecular weight for each eluting species. The triple detection approach gave similar values to the dual detector approach for a model copolymer system (PS-PMMA) studied. It was also applicable to a more difficult copolymer system (PS-PEO), although it appeared that where one homopolymer was present in very small quantities, an average p value gave more consistent results than correction for pi across the distribution. 

Since the [6]radialenes are triple-diene systems, it comes as no surprise that they have been used in multiple Diels-Alder reactions. In fact, after a first 1 1 addition with 150, leading to 161, has taken place, the reaction could proceed in two fashions—a linear course of addition leading to a ara-xylylene 162, and an angular route which produces an crf/ic-xylylene intermediate 163 (equation 19)102-103 Whereas for the hexamethyl compound 150 only products formed by the linear route have been detected with a sizeable number of dienophiles (X=X inter alia TCNE, maleic anhydride, benzoquinone, 1,4-naphthoquinone, acrolein, methyl acrylate ), the parent system 4 undergoes threefold Diels-Alder addition in a star-shaped manner leading to 164 with dimethyl acetylenedicarboxylate and to 165 with fumaroyl chloride followed by methanolysis (equation 20). ... 

Lor analyses, two sets of HPLC conditions were used, depending on whether UV (285 nm) or MS (electrospray ionization on a triple quadrupole system) was to be used for detection. Lor MS detection, analyses were conducted using a 125 x 4 mm (5 pm) Lichrospher 60 RP-Select B column. Eluent A was 800 ml water/200ml acetonitrile/3.08 g ammonium acetate adjusted to pH 6.5 with acetic acid. Eluent B was 500 ml water/500ml acetonitrile/1.93 g ammonium acetate adjusted to pH 6.5 with acetic acid. The gradient was run at 0.5ml/min as follows from 0-25.0 min, 100% A from 25.0-35.0 min, 100% A-100% B from 35.0-45.0 min, 100% B from... 

Accuracy Double, triple etc. injection volume results in double triple etc. peak area Prerequisite pump and detection system OK gravimetric e.g. 500 fll of a solute with a known and large specific weight (e.g. bromine benzene), 20 pi injection, one more weighting 0.2-0.5 %... 

It seems that the homo-Diels-Alder reactions proceed markedly more rapidly than the Diels-Alder reactions since the primary [4-1-2] adducts carmot be detected spectroscopically. Furthermore, it is noteworthy that all 1 -alkynes react regiospecifically in the initial [4-1-2]-cycloaddition process. This addition proceeds in such a way that, independent of the polarity situation of the acetylene, the carbon atom bearing the substituent is positioned in the immediate vicinity of the phosphorus atom of the phosphirane increment. This suggests that steric factors are responsible for the direction of the addition. This is further supported by the observation that 11a does not participate in cycloaddition reactions with any disubstituted triple bond system, except for cyclooctyne, which possesses the necessary reactivity for a cycloaddition on account for the cisoid-dis-... 

In order to validate the system, external sampling under pressure during the reaction was performed. The reactant contents were analyzed by dynamic head space gas chromatography and the polymer molecular weight distribution by size exclusion chromatography with triple detection. 

Traditionally, the design of the injection channel has always been in the form of a cross. A limitation of this configuration is that it is only capable of providing discrete, fixed-volume samples. However, some applications require the delivery of different sample volumes to the detection and separation processes. The unique multi-T configuration injection system [3] has the ability to simulate the functions of the cross, double-T, and triple-T systems through appropriate manipulations of the electric field within its various channels. Figure 7 shows the experimental and numerical simulation results of the proposed multi-T form injection system. 

Triple redundant system In a triple redundant system, there will be three processors operating synchronously. In addition to error detection and... 

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