Universal response

A nearly universal response to organic compounds, high sensitivity, long term stability, sli liclty of operation and construction, low dead volume and fast signal response, and... 

As the reaction temperature is increased, chemiluminescence is observed in the reactions of ozone with aromatic hydrocarbons and even alkanes. Variation of temperature has been used to control the selectivity in a gas chromatography (GC) detector [35], At room temperature, only olefins are detected at a temperature of 150°C, aromatic compounds begin to exhibit a chemiluminescent response and at 250°C alkanes respond, giving the detector a nearly universal response similar to a flame ionization detector (FID). The mechanisms of these reactions are complex and unknown. However, it seems likely that oxygen atoms produced in the thermal decomposition of ozone may play a significant role, as may surface reactions with 03 and O atoms. 

The reactions of fluorine atoms with hydrocarbons are similar to those of active nitrogen in that they provide an essentially universal response. Fluorine atoms abstract H atoms from hydrocarbons at near-collisional reaction rates. Reactions with fluorine are highly exothermic, forming strong H—F (=570 kJ mol-1) and C—F (=485 kJ mol-1) bonds while breaking much weaker C—H (=414 kJ mor1) and C—C (=368 kJ mol-1) bonds. The hydrogen abstraction reaction... 

Fig. 11.2 Universal response curve for a two port interferometer as a function of phase offset. The positions of quadrature occur at the points of largest slopes where phase to intensity transduction is largest...

Raicu, V. 1999. Dielectric dispersion of biological matter Model combining Debye-type and universal responses. Phys. Rev. E 60 4667-80. 

Refractive index detectors are useless in gradient elution because it is impossible to match exactly the sample and the reference while the solvent composition is changing. Refractive index detectors are sensitive to changes in pressure and temperature (—0.01 °C). Because of their low sensitivity, refractive index detectors are not useful for trace analysis. They also have a small linear range, spanning only a factor of 500 in solute concentration. The primary appeal of this detector is its nearly universal response to all solutes, including those that have little ultraviolet absorption. 

A short guard column containing the same stationary phase as the analytical column is placed before the analytical column to protect it from contamination with particles or irreversibly adsorbed solutes. A high-quality pump provides smooth solvent flow. The injection valve allows rapid, precise sample introduction. The column is best housed in an oven to maintain a reproducible temperature. Column efficiency increases at elevated temperature because the rate of mass transfer between phases is increased. Mass spectro-metric detection provides quantitative and qualitative information for each substance eluted from the column. Ultraviolet detection is most common and it can provide qualitative information if a photodiode array is used to record a full spectrum of each analyte. Refractive index detection has universal response but is not very sensitive. Evaporative light scattering responds to the mass of each... 

A common feature, and also a puzzle, of vesicular signaling is the nearly universal response to calcium ions. Exocytosis is usually triggered by a rise in the concentration of Ca2+, and most receptor signaling also leads to an increase in cytosolic Ca2+.388-391 Tire puzzle lies in the ability of cells to use a common mechanism for so many specific purposes. This topic is considered further in Section B,8. There are also many other factors that can control exocytosis. Recent evidence suggests that NO may play a role.392... 

The popularity of GC as an analytical technique in many areas depends on the fact that all of the compounds of interest in an important sample can be detected. For instance, in petroleum and petrochemical labs, it is the rule that all of the compounds can be measured at very low levels with the flame ionization detector. In this case, the detector is "universal." In a natural gas analysis, however, the same detector would not have universal response. This is because several of the important constituents, such as N2 and CO, give little or no response on the FID. In this case a TCD is used, which is "universal" for this analysis. 

AA. It is characteristic that the baseline value. A, is very large compared to sample responses, AA. The reason a large baseline response is so common is that these detectors are intended to have almost universal response. When a property is chosen so that any sample will make it change, it is difficult to avoid having sensitivity to pure carrier gas as well. Thus the baseline response. A, is due to the "response" of carrier gas, and as a result, is usually sensitive to variations in things that affect this for instance, temperature and pressure variations anywhere in the system. 

Pufferfish toxin, isolated from a dozen or more species, has heen identified as having the empirical formula CjiHnNiO , bul the structure is not well-eslablished. nor is it certain lhat the same structure is universally responsible for poisoning, although this is assumed lo be the case. The so-called paralytic shelllish poisoning reported in many areas of the world has a microbiological etiology, and is thus more accurately a contamination rather than a natural toxicosis. 

The detector converts a change in the column effluent into an electrical signal that is recorded by the data system. Detectors are classified as selective or universal depending on the property measured. Selective (solute property) detectors, such as fluorescence detectors, measure a physical or chemical property that is characteristic of the solute(s) in the mixture only those components which possess that characteristic will be detected. Universal (bulk property) detectors measure a physical property of the eluent. Thus, with refractive index (RI) detectors, for example, all the solutes which possess a refractive index different from that of the eluent will be detected. Selective detectors tend to be more sensitive than universal detectors, and they are much more widely used. Universal detectors are more commonly used in preparative chromatography, where a universal response is desired and sample size is large. 

Tadeusz G, Frederic L, Roman S, Pat S. 2006. Universal response in liquid chromatography using charged aerosol detection. Anal. Chem. 78 3186-3192. 

Since the degradation products are not yet identified in this stage, it is advisable to use detection systems, which have universal response and also provide high sensitivity. MS is probably the most sensitive detector that also... 

Detectors may be classified on the basis of selectivity. A universal detector responds to all compounds in the mobile phase except carrier gas. A selective detector responds only to a related group of substances, and a specific detector responds to a single chemical compound. Most common GC detectors fall into the selective designation. Examples include flame ionization detector (FID), ECD, flame photometric detector (FPD), and thermoionic ionization detector. The common GC detector that has a truly universal response is the thermal conductivity detector (TCD). Mass spectrometer is another commercial detector with either universal or quasi-universal response capabilities. 

The katharometer detector [sometimes spelled cath-erometer and often referred to as the thermal conductivity detector (TCD) or the hot-wire detector (HWD)] is the oldest commercially available gas chromatographic (GC) detector still in common use. Compared with other GC detectors, it is a relatively insensitive detector and has survived largely as a result of its almost universal response. In particular, it is sensitive to the permanent gases to which few other detectors have a significant response. Despite its relatively low sensitivity, the frequent need for permanent gas analysis in many industries probably accounts for it still being the fourth most commonly used GC detector. It is simple in design and requires minimal electronic support and, as a consequence, is also relatively inexpensive compared with other detectors. 

One of the drawbacks of using modifiers is their response in some of the detectors. The flame ionization detector (FID) is very popular with capillary and micropacked columns in SFC because of its near-universal response and high sensitivity and the lack of response of CO2 as the most popular mobile phase. The low mass flow rate of the mobile phase in small columns allows for a direct interfacing of the column to the FID and other detectors without flow splitting or back-pressure regulation. 

Scouting/discovery Find substances present in a sample of unknown composition Sensitive, specific, with broad scope and range, universal response... 

Quantification Determine the concentration at which a substance is present in a sample Accurate, precise, specific, sensitive, universal response, known response function... 

We have documented the main stress response pathways responsible for the majority of homeostatic changes encountered in stressed cells and therefore of major importance as measurable factors in in vitro toxicity models. There are others however, which may have important regulatory functions not only in a universal response capacity but also in specific cell systems or in response to particular stress conditions. We will briefly describe some of these pathways and key targets which may indicate their regulation in testing strategies. 

UV at 220 nm was chosen as the method for purity determination. U V detectors interface seamlessly as in-line detectors with LC-MS systems, are extremely robust, reproducibile and sensitive at the required sample concentrations. No HPLC detector has uniform response across all compounds [38 1]. Evaporative light-scattering detection (ELSD) is reported to offer a more universal response factor [38], but the response factors compared to UV at 220 nm were... 

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