Ion concentration measurements with

Positive-ion concentrations measured with 2 X 10 atoms cm of metal added to 034 C2H4/O.O4 C HJ2.0 O2/4.O N2 flame (from Addecott and Nutt )... 

A three-dimensional modular setup for a miniaturized analysis system for flowing streams is presented The system uses silicon micromachined pumps and flow manifolds in combination with electrochemical sensors or optical detection Applications range from simple ion concentration measurements with ISFETs to a multi-step chemical analysis of phosphate Miniaturization of the flow systems leads to a substantial reduction in reagent consumption... 

Ion concentration measurements with ion sensitive field effect transistors (ISFETs)... 

Table 13.2 shows the concentrations of Cu2+ in tap water and lake water determined by the MPA-Gly-Gly-His modified electrode and compared with those of inductively coupled plasma mass spectrometry (ICP-MS). The measured concentration of Cu2+ in tap water when dilutions were accounted for using the MPA-Gly-Gly-His modified electrode was 0.55 +0.08 pM (95% confidence interval). This value is much lower than the copper concentration measured by ICP-MS of 1.70+0.15 pM (95% confidence interval). The peptide-modified electrode measures free Cu2+ or weakly bound copper complexes rather than the total metal-ion concentration measured by ICP-MS. Hence the use of peptides has the ability to measure metal-ion bioavailability for specific species. The results are consistent with others who have also shown that the labile fraction of copper is much less than the total copper [7]. 

Limits of quantitative analyses were in the range of 0.5 ng/L (signal to noise ratio of 5 1 in real samples) in case of full scan analyses and for single-ion mode measurements. With respect to vaiying matrix influences no attempt was made to quantify components with concentrations less than 1 ng/L. The data on concentrations are recovery corrected according to spiking experiments with concentrations of 1 pg/L to 1.25 pg/L of the respective reference compounds (Dsikowitzky et al. 2002). 

Different approaches are available for determining the chemical speciation of a soil solution. Excellent discussions of this subject have been presented by Sparks (1984), Amacher (1984), Baham (1984), and Sposito (1984). The speciation of dissolved Mo in soil solutions is not well understood, partly because of the difficulty of measuring low concentrations of individual Mo species (at the level of micrograms per liter). For example, specific ion electrodes are often used to determine the concentrations of the ionic species in soil solutions. Specific ion electrodes work well when the concentrations of dissolved ionic species of interest are above 10 pM, but below that concentration, measurements with specific ion electrodes are not very reliable. 

Even univalent ions can be sequestered, and part of the Na" " in living animal tissue is in an osmotically inactive form. It is held by polymers whose repeating units carry at least one acidic group (examples nucleic acids, mucopolysaccharides). These sequestered sodium ions can instantly be liberated by ions of a higher valency, and the concentration measured with a sodium-responsive electrode (Palaty, 1966). 

The relative ion intensities of the sodium ion hydrates measured with such apparatus at various water pressures are shown in Fig. 9. At equilibrium the relative intensities should reflect the stabilities of the clusters. The results show that two, three, or even four clusters with different number of water molecules may coexist with concentrations of the same order of magnitude. Increase of water pressure leads to increase of cluster size. The number of coexisting clusters also increases with pressure, showing that the stabilities of clusters become more similar as the number of molecules in the cluster increases. The regular change of cluster intensities with pressure indicates that the number of ligands is not restricted to any fixed coordination number like four, six, or eight. 

The hydrolysis of the mesionic 4,5-diphenyl-l,3,4-thiadiazole (211) has been studied kinetically in aqueous ethanol over a wide pH range, by measuring the decreasing intensity of its absorption maximum at 382 nm. The rate, which is first order with respect to the hydroxide-ion concentration, increases with the polarity of the medium. The reaction is characterized by its small entropy. A proposed mechanism consistent with the observed results accounts for the formation of A -benzoyl-iV-phenyl-hydrazine as the final product of the hydrolysis." ... 

Thus, by the end of the nineteenth century the electromotive force from high resistance sources could be measured with a relatively high precision. The introduction of the glass membrane electrode for the hydrogen-ion concentration measurement presented a challenge and a test of instrument capabilities. The State of the Art (1905) for the measurement of membrane potentials had been described by Max Cremer in the paper entitled (14.) ... 

The activation volumina for the solutions at the lower polarity are lacking because in this region the relaxation time is predominantly determined by triple-ion formation even at the lowest TBAP concentration measurable with the field modulation technique. If the ionisation equilibrium is treated as the association-dissociation of hard, charged, spheres subjected to Brownian motion in a continuous medium of dielectric constant D and viscosity n it is possible to give theoretical expressions for and k ... 

A connnon approach has been to measure the equilibrium constant, K, for these reactions as a fiinction of temperature with the use of a variable temperature high pressure ion source (see section (Bl.7.2)1. The ion concentrations are approximated by their abundance in the mass spectrum, while the neutral concentrations are known from the sample mlet pressure. A van t Hoff plot of In K versus /T should yield a straight Ime with slope equal to the reaction enthalpy (figure B1.7.11). Combining the PA with a value for basicityG at one temperature yields a value for A.S for the half-reaction involving addition of a proton to a species. While quadnipoles have been tire instruments of choice for many of these studies, other mass spectrometers can act as suitable detectors [19, 20]. 

Fig. 4.1. Variation of NO2+ ion concentration with the concentration of mixed acid (nitric sulphuric, i mole i mole) inorganic solvents (a) in sulpholan (6)in aceticacid (c) in nitromethane. Curves (a) and (6) were determined by Raman measurements using the 1400 cm band while curve (c) was derived from infra-red measurements on the 237s cm band. Unity on the NO2+ concentration scale was determined to be 5-6 molar ( 2S 8 weight %). (From Olah et...

The sodium hydroxide is titrated with HCl. In a thermometric titration (92), the sibcate solution is treated first with hydrochloric acid to measure Na20 and then with hydrofluoric acid to determine precipitated Si02. Lower sibca concentrations are measured with the sibcomolybdate colorimetric method or instmmental techniques. X-ray fluorescence, atomic absorption and plasma emission spectroscopies, ion-selective electrodes, and ion chromatography are utilized to detect principal components as weU as trace cationic and anionic impurities. Eourier transform infrared, ft-nmr, laser Raman, and x-ray... 

Chlorate Analysis. Chlorate ion concentration is determined by reaction with a reducing agent. Ferrous sulfate is preferred for quaHty control (111), but other reagents, such as arsenious acid, stannous chloride, and potassium iodide, have also been used (112). When ferrous sulfate is used, a measured excess of the reagent is added to a strong hydrochloric acid solution of the chlorate for reduction, after which the excess ferrous sulfate is titrated with an oxidant, usually potassium permanganate or potassium dichromate. 

Fig. 10-11. The pH scale is a measure of hydrogen ion concentration. The pH of common substances is shown with various values along the scale. The Adirondack Lakes are located in the state of New York and are considered to be receptors of acidic deposition. Source U.S. Environmental Protection Agency, Acid Rain—Research Summary," EPA-600/8-79-028, Cincinnati, 1979.

This method involves very simple and inexpensive equipment that could be set up m any laboratory [9, 10] The equipment consists of a 250-mL beaker (used as an external half-cell), two platinum foil electrodes, a glass tube with asbestos fiber sealed m the bottom (used as an internal half-cell), a microburet, a stirrer, and a portable potentiometer The asbestos fiber may be substituted with a membrane This method has been used to determine the fluoride ion concentration in many binary and complex fluondes and has been applied to unbuffered solutions from Willard-Winter distillation, to lon-exchange eluant, and to pyrohydrolysis distil lates obtained from oxygen-flask or tube combustions The solution concentrations range from 0 1 to 5 X 10 M This method is based on complexing by fluonde ions of one of the oxidation states of the redox couple, and the potential difference measured is that between the two half-cells Initially, each cell contains the same ratio of cerium(IV) and cerium(tll) ions... 

Throughout this section the hydronium ion and hydroxide ion concentrations appear in rate equations. For convenience these are written [H ] and [OH ]. Usually, of course, these quantities have been estimated from a measured pH, so they are conventional activities rather than concentrations. However, our present concern is with the formal analysis of rate equations, and we can conveniently assume that activity coefficients are unity or are at least constant. The basic experimental information is k, the pseudo-first-order rate constant, as a function of pH. Within a senes of such measurements the ionic strength should be held constant. If the pH is maintained constant with a buffer, k should be measured at more than one buffer concentration (but at constant pH) to see if the buffer affects the rate. If such a dependence is observed, the rate constant should be measured at several buffer concentrations and extrapolated to zero buffer to give the correct k for that pH. 

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