Chemical suppression

Sodium and chloride may be measured using ion-selective electrodes (see Electro analytical techniques). On-line monitors exist for these ions. Sihca and phosphate may be monitored colorimetricaHy. Iron is usually monitored by analysis of filters that have had a measured amount of water flow through them. Chloride, sulfate, phosphate, and other anions may be monitored by ion chromatography using chemical suppression. On-line ion chromatography is used at many nuclear power plants. 

Chemical Isolation The stopping of a flame hy means of a chemical suppressant. 

Selgrade, M.K., Daniels, M.J. and Dean, J.H., Correlation between chemical suppression of natural killer cell activity in mice and susceptibility to cytomegalovirus rationale for applying murine cytomegalovirus as a host resistance model and for interpreting immunotoxicity testing in terms of risk of disease, J. Toxicol. Environ. Flealth, 37, 123, 1992. 

Sample Reagents Environment Chemical suppression or Elimination Masking agents Precipitation Separation Extraction Volatilization Chromatography Alternate analytical technique... 

Various solutions have been proposed for the reduction or elimination of autofluorescence. One way is to chemically suppress the autofluorescence signal with some reagents such as sodium borohydride, glycine or toluidine blue. However, in many cases, these approaches are either infeasible or ineffective, and none of them fully eliminates the problem. The second way is to use spectral unmixing algorithms subtracting the background fluorescence. This is only possible if you have at your disposal complicated, expensive confocal optics with sophisticated automated software (http //www.cri-inc.com/applications/fluorescence-microscopy.asp). 

Weldon, P. J., Graham, D. P., and Mears, L. P. (1993). Carnivore fecal chemicals suppress feeding by alpine goats (Capra hircus). Journal of Chemical Ecology 19,2947-2952. 

In C albicans, mutations that block cAMP/PKA pathway suppress or delay the apoptotic response to H2O2 and amphotericin B. By contrast, mutations that result in constitutive activation of the RAS pathway accelerate entry into the apoptotic pathway Apoptosis and quorum sensing in filamentous fungi are phenomena associated with stress responses, a recurring motif in morphogenesis and secondary metabolism. The treatment of Colletotrichum trifolii with proline, a known stress relief chemical, suppressed apoptosis associated with Ras as well as apoptosis associated with a variety of other stresses. 

Ion chromatography is a convenient method for simultaneous determination of alkali, alkaline earth and ammonium ion concentrations in solution. The identity of the analytes is set by the retention times and quantation is carried out by a detector. Conductivity is frequently used, after chemical suppression of the eluate, by which chloride counterions were exchanged by hydroxide. UVV spectrophotometric measurement of hydroxide ions at 200 nm was proposed as an alternative method to suppressed conductivity. Both methods... 

In 1C, the election-detection mode is the one based on conductivity measurements of solutions in which the ionic load of the eluent is low, either due to the use of eluents of low specific conductivity, or due to the chemical suppression of the eluent conductivity achieved by proper devices (see further). Nevertheless, there are applications in which this kind of detection is not applicable, e.g., for species with low specific conductivity or for species (metals) that can precipitate during the classical detection with suppression. Among the techniques that can be used as an alternative to conductometric detection, spectrophotometry, amperometry, and spectroscopy (atomic absorption, AA, atomic emission, AE) or spectrometry (inductively coupled plasma-mass spectrometry, ICP-MS, and MS) are those most widely used. Hence, the wide number of techniques available, together with the improvement of stationary phase technology, makes it possible to widen the spectrum of substances analyzable by 1C and to achieve extremely low detection limits. 

Sensitivity and detection levels of analyte ions can be dramatically improved by chemical suppression and auto-suppression techniques (Dionex, 1995). In... 

Acid digestion followed by chemically suppressed ion chromatography. 

Eluent Flow rate Detection 0.05 MNaOH in 40% methanol 1 mL/min Suppressed conductivity, chemical suppression mode... 

Lamb, J. D. and Drake, P. A. (1989) Chemically-Suppressed Anion Chromatography Based On Macrocycle-Cation Complexation, J. Chromatogr. 482, 367-380. ... 

ASTM Standard. 1997. D4327/97 Standard Test Method for Anions in Water by Chemically suppressed... 

Without chemical suppression, the contribution to the total measured conductivity from the eluent is many orders of magnitude higher than that from the analyte, leading to low sensitivity (Fig. 1). 

Eluents for conductivity detection with chemical suppression of the background conductivity... 

In comparing the concentration gradient concept with subsequent chemical suppression, the chromatogram of various inorganic anions in Fig. 3-127 that was obtained with isoconductive eluents clearly shows the limitation of this technique. Although the analysis time for the separation shown is shorter than under isocratic conditions, an improvement in the resolution between the signals, especially in the first part of the... 

While the type of available eluent depends upon the detection method being applied in anion exchange chromatography, a corresponding classification is not necessary in cation exchange chromatography. For the separation of alkali metals, ammonium, and small aliphatic amines, mineral acids such as hydrochloric or nitric acid are typically used as eluents, independent of whether the subsequent conductivity detection is performed with or without chemical suppression. The concentration range lies between 0.002 mol/L and 0.04 mol/L. Bachmann et al. [141] employed cerium(III) nitrate in very low concentrations as the eluent for the indirect fluorescence detection of alkali metals. 

In a system without chemical suppression, the extremely high background conductance would render impossible the sensitive detection of alkaline-earth metal ions via electrical conductivity. 

In a system with chemical suppression, the required reduction of the background conductance cannot be ensured. 

The CMMS micromembrane suppressor also allows the application of concentration gradients in combination with conductivity detection that is indispensable for cation detection. A mixture of hydrochloric acid and 2,3-diaminopropionic acid suitable for chemical suppression is used as the eluent. The gradient technique, however, plays a secondary role in cation analysis, since it can only be applied for the analysis of alkali and alkaline-earth metals as well as a number of short-chain aliphatic amines. It is definitely not suitable for the analysis of heavy and transition metals, where different... 

The latter is a urea derivative in which the three NH2 groups are ordered symmetrically and equidistantly to the central C-atom. Both cations, the separation of which is shown in Fig. 3-141, may be detected either with or without chemical suppression. 

Finally, it should be pointed out that chemical suppression in form of protonation reactions is also applicable to zwitterionic eluents [8,9],... 

Surface thermodynamic considerations can be helpful in an understanding of the complex phenomena which occur in supported metal catalysts. Indeed, the physical and chemical interactions between metal, substrate and atmosphere lead to wetting and spreading phenomena (of the active catalyst over the substrate and of the substrate over the metal) which are relevant for the physical (sintering, redispersion) as well as chemical (suppression of chemisorption, modification of selectivity, enhanced activity) manifestations of supported metal catalysts. 

The eluent used in anion chromatography contains an eluent anion, E". Usually Na" or will be the cation associated with E". The eluent anion must be compatible with the detection method used. For conductivity, the detection E should have either a significantly lower conductivity than the sample ions or be capable of being converted to a non-ionic form by a chemical suppression system. When spectrophoto-metric detection is employed, E will often be chosen for its ability to absorb strongly in the UV or visible spectral region. The concentration of E in the eluent will depend on the properties of the ion exchanger used and on the types of anions to be separated. Factors involved in the selection of a suitable eluent are discussed later. 

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