Bicarbonate sensor

Stimulation of the platelets by prostacyclin (prostaglandin I2 see Chapter 22) leads to a 10- to 40- fold increase in cAMP concentration and a 4- to 5-fold increase in the rate of lsO incorporation.178 A quite different soluble adenylate cyclase is present in spermatozoa. It is stimulated directly by bicarbonate ions. It may be a bicarbonate sensor in sperm cells and in some other bicarbonate-responsive tissues as well as in cyanobacteria.178a,178b... 

Fluorescent pH indicators offer much better sensitivity than the classical dyes such as phenolphthalein, thymol blue, etc., based on color change. They are thus widely used in analytical chemistry, bioanalytical chemistry, cellular biology (for measuring intracellular pH), medicine (for monitoring pH and pCC>2 in blood pCC>2 is determined via the bicarbonate couple). Fluorescence microscopy can provide spatial information on pH. Moreover, remote sensing of pH is possible by means of fiber optic chemical sensors. 

In this case, an internal pH sensor is the choice. Because 1 mol of CO2 yields 1 mol each of hydrogen and bicarbonate ion (6.77), after substitution from (6.76), becomes... 

The most widely used sensor for chloride ions in clinical analyzers is based on an ion-exchanger, a quaternary alkylammonium chloride, dispersed in a plastic membrane. It is not an ideal sensor due to the interference of lipophilic anions (e.g., salicylates, bromides) and lip-ophylic cations (e.g., bacteriostatic agents, anesthetics) and a relatively poor selectivity towards hydrogen carbonates (bicarbonates). However, compared to charged anion- and neutral carrier-based membranes that have been tested, it is still the best-suited for automated analyzers. 

A good sensor for the direct measurement of bicarbonates has not yet been invented. However, an electrode selective to carbonate ions, based on triflouroacetophenone derivates, has been used. This electrode is non-selective for a number of ions, and unless substantial improvements or inventions are made, it is unlikely that it will become a commonly used sensor in routine instruments [32],... 

Nitrate in water may be analyzed by a nitrate selective sensor. Chloride and bicarbonate ions at concentrations about ten times greater than nitrate interfere in this test. Sulfide, cyanide, and halide ions are eliminated by using a buffer solution containing AgS04. The buffer — boric acid at pH 3 — removes bicarbonate. 

Figure 6 shows the selectivity behavior of this NOx gas sensor. The sensor had a sub-Nernstian response toward nitrite, with slopes in the range of -45 to -50 mV/decade. Further, the response observed with salicylate and thiocyanate was diminished substantially, as compared to that obtained with the original nitrite-selective electrode (Figure 3). In addition, the gas sensor described here does not suffer interferences from nitrate, bicarbonate, acetate, benzoate, or chloride. These excellent selectivity properties of the sensor are a combination of the selectivity characteristics of the nitrite-selective electrode and the additional discrimination provided by the GPM.

Figure 6. Selectivity pattern of the NOx gas sensor. The sensor was exposed to 0.010 M H2SO4 containing the following anions nitrite (1), salicylate (2), thiocyanate (3), benzoate (4), nitrate (5), chloride (6), bicarbonate (7), acetate (8). (Adapted from ref. 15.)...

Sodium, potassium and chloride sensors were evaluated using undiluted serum specimens with no sample pretreatment of any kind. The performance data set, summarized by Table II, comprises a minimum of 8 sensors and 60 samples. The bicarbonate assays were performed separately on serum specimens buffered at pH 9.0. Clinical efficacy is normally judged by the response linearity, precision and... 

Chromogenic octamethyl calix[4]pyrrole-based sensors (e.g., 165-167) for antipyretic carboxylates such as naproxen, ibuprofen, and salicylate, without bias by bicarbonate or carboxy termini of blood plasma proteins, have been described <2005JA8270>. The formation of a sensor-anion complex results in partial charge transfer and a dramatic change in color. 

The respiratory response to metabolic alkalosis is hypoventilation, which resnlts in an increased PaC02. Respiratory compensation is initiated within honrs when the central and peripheral chemoreceptors sense an increase in pH. The PaC02 increases 6 to 7 mm Hg for each 10-mEq/L increase in bicarbonate, np to a PaC02 of abont 50 to 60 mm Hg (see Table 51M) before hypoxia sensors react to prevent fnrther hypoventilation. If the PaC02 is normal or less than normal, one shonld consider the presence of a snperimposed respiratory alkalosis, which may be secondary to fever, gram-negative sepsis, or pain. 

The Severinghaus-type carbon dioxide sensor measures CO2 concentration by monitoring the resultant pH change when ambient CO2 dissolves into an internal electrolyte to form bicarbonate ions ... 

Sensors for Pcoj ate usually based on a pH sensor material with added bicarbonate ion (HCOp encased in a gas-permeable, ion-impermeable material... 

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