Double detection

Bystryakov et al. [36] described a double detection method to determine aliphatic thiols by HPLC. A solution of 0.1-1 mg/mL of such compounds in the mobile phase was analyzed by HPLC using a of Nucleosil C18 micro-column (5 pm 6.2 cm x 2 mm)... 

Chevallet, M., Procaccio, V., and Rabilloud, T. (1997) A nonradioac-tive double detection method for the assignment of spots in two-dimensional blots. Anal. Biochem. 251, 69-72. 

The second system investigated 101) (polystyrene macromonomer and perfluoro-alkyl acrylate) is also of great interest. The polymerization is carried out in trifluoro-benzene with AIBN as the initiator to a conversion of the order of 60 %. The graft copolymer formed is soluble in a number of solvents in which the poly(perfluoro-alkyl acrylate) backbone would be insoluble, e.g. in THF and diethyl ether. The easy formation of foams indicates the low surface energy which is characteristic of fluorinated polymers. Double-detection GPC (UV and refractive index) showed that the distribution of polystyrene branches within the sample was quite uniform. 

The alcohol groups do not absorb in UV and a chemical modification of chain extremities is required. Carbamates are synthesized in a one-step reaction with phenyl isocyanate and allow a double detection in GPC 120, l34). 

The functionality distribution of HTPB 134> can be obtained using the double detection procedure after derivatization of the OH groups with phenyl isocyanate. However, a true fractionation can been obtained by stepwise elution from silica gel n8,120) and, coupled with GPC, it enables establishment of the relationship between functionality and molecular weight distributions. Precipitation fractionation can also be used... 

Gitsov and Frechet [11] reported the syntheses of novel linear-dendritic triblock copolymers achieved via anionic polymerization of styrene and final quenching with reactive dendrimers. For the characterization of the products in the reaction mixture, SEC with double detection was performed at 45°C on a chromatography line consisting of a 510 pump, a U6K universal injector, three Ultrastyragel columns with... 

Because similar retention periods are used for some chlorophenols and polychlorinated gem-dichlorocyclohexadienones a problem of peak times was created and it was necessary to use a double detection method enabling differentiation of both products. In order to obtain the best possible sensitivity and specificity for the polychlorinated gem-dichlorocyclohexadienones, we opted for electrochemical detection based on reduction of gem-dichlorocyclohexadienones at an imposed potential of -0 volt (Fig. 6). 

The limit of detection of polychlorinated gem-dichlorocyclohexadienones by HPLC using equipment fitted with a double detection system, UV and electrochemical, is approximately 0.01 % in a synthetic chlorophenol mixture. 

More recently cyclic acetal-styrene systems were reinvestigated by the GPC technique 154,155). Using double detection (UV and RI), Yamashita et al. showed that products of copolymerization of styrene with tri- and tetraethylene glycol formals have a unimodal molecular weight distribution, and that the maxima of both RI and UV traces coincide indicating that the products are true copolymers. 

G. Schulze, O. Elsholz, and W. Frenzel, Double-Detection Technique for Flow-Injection Analysis [in German]. Fresenius Z. Anal. Chem., 320 (1985) 650. 

P. Betto, G. Ricciarello, M. Giambenedetti, C. Lucarelli, S. Ruggeri and F. Stocchi, Improved high-performance liquid chromatographic analysis with double detection system for L-dopa, its metabolites and carbidopa in plasma of parkinsonian patients under L-dopa therapy, J. Chromatogr., 1988, 459, 341-349. 

A first application of double detection was for the identification of the a/p equilibrium in HPLC chromatography on a Cl8 coliamn (13). Each oligomer of the maltodextrin series gives two peaks in refractive index over a degree of polymerization of 3 (Figure 5). This is one of the disadvantage of HPLC compared with GPC. The oligomers are also well separated for analytical purposes under their reduced form (3) ... 

First, the patient s AF is undersensed by the pacemaker as evidenced by the presence of atrial pacing. The first, second, third, and sixth atrial pacing spikes from the permanent pacemaker are oversensed as ventricular events by the ICD. This causes each of the subsequent paced QRS complexes from the pacemaker to fall into the ICD s VF detection zone. The first QRS is also double detected (sensed by the RV and LV leads at a different time). 

Oliva A, Llabres M, Farifia JB. Estimation of uncertainty in size-exdusion chromatography with a double detection system (light-scattering and refractive index). Talanta 2009 78(3) 781-9. 

But it is clear that single radiogram digitization is not sufficient to detect very thin defects. That is why EDF is working on digital double loading , that means ... 

The obtained results for the magnetic bench have allowed to note that defects situated at 12 mm of depth have been observed clearly. This is explained by the high power furnished by the bench, in addition its induction is double alternation rectified. Dimensions of the defect (height and width) are precisely estimated (figure 1). The defect detection at this depth is due to the application of a rectified field, so skin phenomenon is almost absent. 

This teclnhque can be used both to pennit the spectroscopic detection of molecules, such as H2 and HCl, whose first electronic transition lies in the vacuum ultraviolet spectral region, for which laser excitation is possible but inconvenient [ ], or molecules such as CH that do not fluoresce. With 2-photon excitation, the required wavelengdis are in the ultraviolet, conveniently generated by frequency-doubled dye lasers, rather than 1-photon excitation in the vacuum ultraviolet. Figure B2.3.17 displays 2 + 1 REMPI spectra of the HCl and DCl products, both in their v = 0 vibrational levels, from the Cl + (CHg) CD reaction [ ]. For some electronic states of HCl/DCl, both parent and fragment ions are produced, and the spectrum in figure B2.3.17 for the DCl product was recorded by monitoring mass 2 (D ions. In this case, both isotopomers (D Cl and D Cl) are detected. 

Fehrensen B, Hippier M and Quack M 1998 Isotopomer selective overtone spectroscopy by ionization detected IR + UV double resonance jet-cooled aniline Chem. Phys. Lett. 298 320-8... 

Shallow donors (or acceptors) add new electrons to tire CB (or new holes to tire VB), resulting in a net increase in tire number of a particular type of charge carrier. The implantation of shallow donors or acceptors is perfonned for tliis purjDose. But tliis process can also occur unintentionally. For example, tire precipitation around 450°C of interstitial oxygen in Si generates a series of shallow double donors called tliennal donors. As-grown GaN crystal are always heavily n type, because of some intrinsic shallow-level defect. The presence and type of new charge carriers can be detected by Flail effect measurements. 

Thus we are challenged by the problem of measuring a small signal against the background of one much stronger. The problem is usually solved by one of two means (a) lock-in-amplifier detection and (b) a boxcar type of detection (to some extent we can include double-input optical multichannel detection in this category). 

Por IR-Raman experiments, a mid-IR pump pulse from an OPA and a visible Raman probe pulse are used. The Raman probe is generated either by frequency doubling a solid-state laser which pumps the OPA [16], or by a two-colour OPA [39]. Transient anti-Stokes emission is detected with a monocliromator and photomultiplier [39], or a spectrograph and optical multichannel analyser [40]. 

The unmodified and complementary oligonucleotides were also synthesized, in order to detect thermodynamic and spectroscopic differences between the double helices. Circular dichroism spectra revealed that the covalently bound anthracene does not stack in the centre of the DNA double helix. Mutagenic activity by intercalative binding of the anthracene residue is thus unlikely. Only in vitro and in vivo replication experiments with site-specifically modified... 

Measurement of Unsaturation. The presence of double bonds in a fatty acid side chain can be detected chemically or through use of instmmentation. Iodine value (IV) (74) is a measure of extent of the reaction of iodine with double bonds the higher the IV, the more unsaturated the oil. IV may also be calculated from fatty acid composition. The cis—trans configuration of double bonds may be deterrnined by infrared (59) or nmr spectroscopy. Naturally occurring oils have methylene-intermpted double bonds that do not absorb in the uv however, conjugated dienes maybe deterrnined in an appropriate solvent at 233 nm. 

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