Reagent concentrations/volumes

In liquid-liquid extraction, an immiscible liquid—usually an organic solution—is combined with the sample in aqueous solution in an extraction flask and shaken to achieve good contact between the liquids. A reagent that functions as an extractant may have been added to one phase or the other. Information on the distribution ratio D and the extraction yield E that indicate the extent of purification from specified contaminants is available from many studies (Sekine and Hasegaw 1977). The information should describe the extractant, the organic solvent and the conditions of purity, reagent concentrations, volumes, required time, and temperature. The value of D reflects the ratio of the radioelement solubility in the organic phase to that in the aqueous phase, hence the type of solvent and the chemical form of the radionuclide to be extracted may be inferred from radioelement solubility data. If the initial conditions of the extraction procedure are not identical to those for reported extractions, the extent of extraction must be tested. 

In addition to these reactions, metal ions and ligands may participate in many other equilibria reactions such as complex formation, protolysis, and hydrolysis reactions. In order to transfer metal ions quantitatively into the organic phase, the extraction conditions (pH, reagent concentrations, volume ratio of the liquid phases) must be optimized. Figure 146 represents the response of molybdenum as a function of pH in three different organic solvents with toluene-3,4-dithiol and 8-hydroxyquinoline as ligands. According to this plot the determination of molybdenum is most sensitive in MIBK... 

Inspection of Fig. 15.3 reveals that while for jo 0.1 nAcm , the effectiveness factor is expected to be close to 1, for a faster reaction with Jo 1 p,A cm , it will drop to about 0.2. This is the case of internal diffusion limitation, well known in heterogeneous catalysis, when the reagent concentration at the outer surface of the catalyst grains is equal to its volume concentration, but drops sharply inside the pores of the catalyst. In this context, it should be pointed out that when the pore size is decreased below about 50 nm, the predominant mechanism of mass transport is Knudsen diffusion [Malek and Coppens, 2003], with the diffusion coefficient being less than the Pick diffusion coefficient and dependent on the porosity and pore stmcture. Moreover, the discrete distribution of the catalytic particles in the CL may also affect the measured current owing to overlap of diffusion zones around closely positioned particles [Antoine et ah, 1998]. 

A continuous factor is a factor that can take on any value within a given domain. Similarly, a continuous response is a response that can take on any value within a given range. Examples of continuous factors are pressure, volume, weight, distance, time, current, flow rate, and reagent concentration. Examples of continuous responses are yield, profit, efficiency, effectiveness, impurity concentration, sensitivity, selectivity, and rate. 

When attempting to convert a manual method into an automated method, there are certain elements, such as tablet size and solvent selection, which will have an impact on the ease of the conversion from manual to automated. For instance, some of the elements of an assay method that would make it easier to automate would be that the dosage form fits into a test tube the extraction uses neutral media or acid not more concentrated than 0.1 M makes use of nonvolatile, low-toxicity solvents does not use surfactants and uses premixed, room-temperature solvents. Some of the elements of a dissolution method that would make it easier to automate would be that the dosage form fits in the sample carousel, does not use media more concentrated than 0.1 M acid, does not use isopropanol or surfactant in large quantities, uses magnetic sinkers or no sinkers at all, and uses no or minimal reagent addition volumes for pH control. 

Prepare the titration reaction mix in each reaction tube as shown in the following tables. Add all the components except the main counterion that would mediate folding (Mg2-1- for Mg titration and K+ for K titrations). For each reaction mix, prepare a reference solution of slightly excess volume but with identical reagent concentrations, for blank absorbance measurements. [Note For K+ titrations, prepare two tubes with 10 mM MgCl2 for comparison of the final states of the RNA in highest K+ concentration and in 10 mM Mg2 1.]... 

Amperometry — a current (mostly a - faradaic current) is measured as a function of another experimental variable, e.g., concentration, volume of added reagent in analytical applications, or time. When faradaic current is measured as a function of electrode potential the method is called -> voltammetry (derived from - volt and -> ampere), measurement as a function of time is called -> chronoamperometry. See also - amperometric sensor. 

Stock no. Reagent Concentration (M) Total Volume (ml) Amount Needed Actual Amount... 

To understand the theoretical basis of end points and the sources of titration errors, we calculate the data points necessary to construct titration curves for the systems under consideration. Titration curves plot reagent volume on the horizontal axis and some function of the analyte or reagent concentration on the vertical axis. 

Co and Ci are the continuous phase solute concentrations in teed and inside the mixer, respectively, and are the feed rates of the continuous and emulsion phases, respectively, Cir is the internal reagent concentration (based on volume of emulsion), R is the emulsion globule radius, Kr is the emulsion phase holdup volume in the mixer, a is the partition coefficient for solute between external phase and emulsion, is the effective solute diffusivity in the emulsion, and % is the dimensionless reaction front position. Hatton and Wardius [51] also extended their analysis to develop simple graphical and numerical procedures for the prediction of multistage extraction performance of mixer-settler trains operating either cocurrendy or countercurrently without any external recycle over individual stages. For a typical stage i in a cocurrent mixer-settler, they defined the parameter 6 as... 

Internal stripping reagent concentration and the volume fraction of the internal phase... 

This expresses the susceptibility of the analytical procedure to variations in parameters such as flow rates, temperature, reagent concentrations and sample volume [165]. System robustness can be discussed from two perspectives. First, the dependence of the analytical signals on slight variations of relevant system parameters. Second, the dependence on instrumental stability, which can manifest itself as changes in the baseline and/or the analytical signal. The stability of the analytical curve over time and maintenance requirements should also be stated. 

Repeatability. Make small variations in one or more parameters in the experiment that should not proportionally or directly impact the measurement. This could be reagent concentration, the pH, time of reaction, size of measured sample (e.g., increase the injected volume of a standard in a chromatography measurement by 10%, adjusting for the increased quantity injected in calculating the predicted response.)... 

---