Reference solutions

Thermodynamically, the activity of a single ionic species is an inexact quantity, and a conventional pH scale has been adopted that is defined by reference to specific solutions with assigned pH(5) values. These reference solutions, in conjunction with equation 3, define the pH( of the sample solution. 

The avadabihty of multiple pH(5) reference solutions makes possible an alternative definition of pH( ... 

Most of ions do not interfere to the determination of P(V) or As(V). Big access of colored transition metals can be tolerated by using those metals solution as reference solution. It was already shown that high selectivity of the proposed method with respect to metal ions gave the opportunity to determine phosphoms in a number of nonferrous (brass, bronze) and ferrous alloys without preliminai y sepai ation. 

For standardization of validation procedure we suggested normalized coordinate system (NCS) X. = 100-C/C", Y. = 100-A/A", where C is a concentration, A - analytical response (absorbance, peak ai ea etc.), index st indicates reference solution, i - number of solution. In this coordinate system recuperation coefficient (findings in per cent to entry) is found as Z = IQQ-Y/X. As a result, coordinates of all methods ai e in the unified... 

Typldsung, /. type (or reference) solution, Typus, m. type, standard. 

In titrimetry certain chemicals are used frequently in defined concentrations as reference solutions. Such substances are referred to as primary standards or secondary standards. A primary standard is a compound of sufficient purity from which a standard solution can be prepared by direct weighing of a quantity of it, followed by dilution to give a defined volume of solution. The solution produced is then a primary standard solution. A primary standard should satisfy the following requirements. 

As with a pH meter, the electrode appropriate to the measurement to be undertaken must be calibrated in solutions of known concentration of the chosen ion at least two reference solutions should be used, differing in concentration by 2-5 units of pM according to the particular determination to be made. The general procedure for carrying out a determination with one of these instruments is outlined in Section 15.16. 

The British standard (BS 1647 1984, Parts 1 and 2) is also based upon potassium hydrogenphthalate and a number of reference solutions of a range of substances, and leads to results which are very similar to the figures given in Table 15.4. When applied to dilute solutions ( < 0.1 M) at pH between 2 and... 

Owing to optical and mechanical imperfections of some makes of colorimeters, it is sometimes found that the same reading cannot be obtained in the adjustment for illumination when the cups are filled with the same solution and balanced. In such a case one of the cups (say, the left one) is filled with a reference solution (which may be a solution containing the component to be determined) of the same colour and approximately the same intensity as the unknown and the... 

Procedure. Use a solution containing 0.15-1.8 mg antimony per 100 mL it should be slightly acidic with sulphuric acid (1.2-1.5M). Transfer a 10 mL aliquot to a 50 mL graduated flask, add 25 mL of the potassium iodide-ascorbic acid reagent, and dilute to the mark with 25 per cent v/v sulphuric acid. Mix thoroughly and measure the absorbance at 425 nm or at 330 nm using a reagent blank as reference solution. 

Prepare an alkaline solution of the phenol concentrate by placing 4.0 mL of a tri-n-butyl phosphate layer in a 5 mL graduated flask and then adding 1.0 mL of the tetra-n-butylammonium hydroxide do this for each of the four solutions. The reference solution consists of 4 mL of the organic layer (in which the phenol is undissociated) plus 1 mL of methanol. Measure the absorbance of each of the extracts from the four test solutions and plot a calibration curve. 

From the difference between the reference solution (taken as the ideal one governed by Raoult s law) and the one with ions, the expression for the activity coefficient for a single ion is... 

As a reference, solutions of alkylbenzenesulfonates at a concentration of I g/L will give a value of 8-10 s. 

For further discussion and for calibration purposes we will have to define a reference solution reaction which would be sufficiently related to the given enzymatic reaction. This will help us in removing the problems associated with concentration effect and in focusing on the actual catalytic advantage of the enzyme. To do this we describe the reference reaction in solution as... 

See also Enzyme cofactors downhill trajectories for, 196,197 mechanism of catalytic reaction, 190-192 metal substitution, 200-204 potential surfaces for, 192-195,197 rate-limiting step of, 190 reference solution reaction for, 192-195,... 

Quantitative estimates of the mass of a particular solute present in a sample are obtained from either peak height or peak area measurements. The values obtained are then compared with the peak height or area of a reference solute present in the sample at a known concentration or mass. In this chapter quantitative analysis by LC will be discussed but the procedures described should not be considered as entirely appropriate for other types of chromatographic analysis. Those interested in general quantitative chromatographic analysis including GC and TLC are referred to the book by Katz (4). 

A pH meter uses a probe to make electrical measurements between a reference solution containing acid at known concentration and the sample being tested. The pH meter is calibrated by dipping the probe in a solution of known pH and adjusting the meter to read the correct value. Then the probe is dipped into the sample solution, and the pH appears on a digital display. Example illustrates how to convert from pH measurements to ion concentrations. 

An ion-selective electrode contains a semipermeable membrane in contact with a reference solution on one side and a sample solution on the other side. The membrane will be permeable to either cations or anions and the transport of counter ions will be restricted by the membrane, and thus a separation of charge occurs at the interface. This is the Donnan potential (Fig. 5 a) and contains the analytically useful information. A concentration gradient will promote diffusion of ions within the membrane. If the ionic mobilities vary greatly, a charge separation occurs (Fig. 5 b) giving rise to what is called a diffusion potential. 

With solid sampling-electrothermal vaporization-inductively coupled atomic emission spectrometry (SS-ETV-ICP-AES), Cu in two environmental CRMs was determined using a third CRM with similar matrix as calibrant. Comparison with a reference solution showed good agreement (Verrept et al. 1993). 

Mercury in various cement products was determined with a special mercury oven for solid samples. Calibration was performed with four BCR CRMs and one NIST SRM with different Hg content as well as with a reference solution and excellent agreement found (Bachmann and Rechenberg 1991). 

Ninhydrin Assays. Ninhydrin tests were performed using a modified procedme of Taylor et al. " APS Silica (10-75 mg) of various loadings (0.857, 0.571, and 0.343 mmol NH2/g Silica) was added to phosphate buffer (5 mL, 100 mM, pH 6.5), and 1 mL of a 5% w/v solution of ninhydrin in ethanol was added to the sluny. After stirring for an hour in a boiling water bath, the mixture was allowed to cool slowly to room temperature. The silica was then filtered and washed three times with 70°C distilled water. The filtrate was collected, added to a volumetric flask, diluted to 100 mL, and the absorbance of this solution at 565 mu was measured using a UV-visible spectrophotometer. The reference solution was prepared as above with unmodified amine-free silica. Calibration standards were prepared with aliquots of a 1 mg/mL solution of APS in ethanol. 

Thiessen and Wilson (1987) presented a modified isopiestic apparatus and obtained osmotic coefficient data for KC1 solutions using NaCl as reference solution. The data are given in Table 15.4. Subsequently, they employed Pitzer s method to correlate the data. They obtained the following values for three Pitzer s... 

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