Primary standard solutions

The list given below includes the substances that are most used and most useful for the standardization of solutions for precipitation titrations. Primary standard solutions are denoted by the letter (P) in Column 1. 

The IUPAC Commission on Analytical Nomenclature refers to (3) and (4) respectively as Primary Standard Solutions and Secondary Standard Solutions. 

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. 

A secondary standard is a substance which may be used for standardisations, and whose content of the active substance has been found by comparison against a primary standard. It follows that a secondary standard solution is a solution in which the concentration of dissolved solute has not been determined from the weight of the compound dissolved but by reaction (titration) of a volume of the solution against a measured volume of a primary standard solution. 

The IUPAC definition of pH39 is based upon a 0.05M solution of potassium hydrogenphthalate as the reference value pH standard (RVS). In addition, six further primary standard solutions are also defined which between them cover a range of pH values lying between 3.5 and 10.3 at room temperature, and these are further supplemented by a number of operational standard solutions which extend the pH range covered to 1.5-12.6 at room temperature. The composition of the RVS solution, of three of the primary standard solutions and of two of the operational standard solutions is detailed below, and their pH values at various temperatures are given in Table 15.4. It should be noted that the concentrations are expressed on a molal basis, i.e. moles of solute per kilogram of solution. 

Procedure Transfer 20 ml of the primary standard solution (Mohr s salt) to the titration flask and add 20 ml of 2 N sulphuric acid. Take the potassium dichromate solution in the burette. Put drops of freshly... 

Procedure. A primary standard solution of benzidine in methanol was prepared. Standards of lower concentrations were prepared by dilution of the primary standard. Typical liquid chromatograph calibration curves were linear in the region from .38 to 30.6 yg/mL. The standards were stable for several months when stored in the dark. Aqueous solutions of known dye-formulation concentration were prepared. 

An international inter-laboratory study recently compared quantitative methods used for measuring short chain (C10-C ) PCAs [70]. In this study, the samples to be quantified consisted of a standard solution of a commercially available PCA product containing 70% chlorine by mass (PCA-70), a synthetic PCA mixture consisting of purified products derived from the chlorination of 1,5,9-decatriene (PCA-1) and two fish sample extracts. The fish samples consisted of a cleaned up extract (lipid-free) of muscle tissue from a yellow perch fish, collected at the mouth of the Detroit River at Lake Erie, in 1995. All participating labs were asked to quantify the PCA-1 and PCA-70 mixtures and at least one fish extract against a primary standard solution which contained a known concentration of a second short chain commercial PCA product containing 60 mass % chlorine (PCA-60) and, if desired, by using other commercially available C10-C13 PCA mixtures. 

All standards were prepared by dilution of Alfa Inorganics Ventron primary standard solutions using acidified filtered surface Gulf Stream seawater (salinity ca. 36% ) or distilled water. Sample injections were made with Eppendorf microliter pipets with disposable plastic tips. 

Under certain conditions regarded as ideal, j is probably actually close to zero. This should be the case when solution X matches closely the primary standard solutions S in pH, composition, and ionic strength (which must not exceed 0.1). Then pH(X) doubtless approaches —log (mHyn), where mn is the molality (mol/kg of water) of hydrogen ion and 7h is its conventional activity coefficient on the numerical scale defined by the convention adopted for the assignment of values to pH(S). When, as in seawater, these conditions do not prevail, the meaning of the experimental pH(X) in terms of concentrations and activities becomes unclear. 

A primary standard solution of Na2COs was prepared and used to standardise a solution of H2S04 of unknown concentration. 25.0 mL of 1 m (f = 1.000) Na2COs was added by pipette to a conical flask and 24.60 mL of H2S04 was required for neutralisation. Calculate the factor of the H2S04 solution. 

This is the process of determining the volume of a substance (usually of a primary standard solution or a standardised secondary standard solution) required to just complete the reaction... 

Secondary standard solutions are those which cannot be prepared by direct weighing in a chemical balance. These are usually prepared by standardising against some primary standard solution. Examples are solution of NaOH, KOH, HCl, HgSO, KMnO. ... 

A solution standardized by titrating a primary standard is itself a secondary standard. It will be less accurate than a primary standard solution due to the errors of titrations. 

Wx mass of sample X added to the spike Y to prepare the blend B (g or kg) mzc mass of primary standard solution Z added to the spike Y to make calibration blend Be (g or kg)... 

The same principle can be applied to characterise the concentration of a spike in this case, the labelled analyte is blended with a primary standard solution Z, which is well characterised. This will give a reverse IDMS equation ... 

To prepare primary standard solutions, weigh out separately 100 mg of each alkaloid (nicotine, 4-ethenylpyridine, etc.) into individual 100-ml volumetric flanks and dilute to volume with solvent. To prepare secondary standard solutions, pipet 1ml of nicotine primary standard into 100-ml volumetric flask. Also, pipet 0.50ml of 4-ethenylpyridine into the same volumetric flask (along with appropriate volume of any additional alkaloid primary solutions) and dilute with solvent. 

A stock solution was prepared by dissolving the enriched isotope. Diluted solutions were prepared from this stock solution on a weight basis. The isotopic composition of this solution was determined experimentally by GC-MS analysis of the chelate. The internal standard solution was calibrated by reverse isotope dilution GC-MS using the atomic absorption primary standard. Weighed amounts of the primary standard solution were mixed with weighed amounts of the enriched isotope solution. Chelates were prepared from the spiked samples (as described below) and were used for mass spectrometric determination of isotope ratios. Concentration of the trace metal in the spike solution was calculated using the experimentally determined isotope ratios, the weights of the standard and... 

The properties of the proposed primary standard solutions are listed in Table 7.1. The table is taken from the report of lUPAC 2002 [35]. 

Table 7.1 pH values of primary standard solution at different temperature... 

Operational pH The determination of sample pH by relating to pH measurements in a primary standard solution. This relationship assumes that electrode errors such as sensitivity and changes in asymmetry potential can be disregarded or compensated for, provided the liquid junction potential remains constant between standard and sample. 

Secondary standard pH buffer solutions which do not meet the requirements of primary standard solutions but provide coverage of the pH range not covered by primary standards. Used when the pH value of the primary standard is not close to the sample pH value. 

A primary standard solution is prepared simply by weighing the reagent in the pure state (called for this goal a primary standard), by dissolving it into the solvent, and making up the solution to a known volume. A secondary standard is a substance that can also be used for standardizations. However, its solution content in the active substance has been found by comparison with a primary standard. 

Standardized solutions of 13 ions are stable, but they lose iodine by vaporization. Hence, they cannot be used as primary standard solutions. In the presence of 1.2 X 10 mole of iodide ions, 5 x 10 mole of iodine can be dissolved in one liter of water. 

As iodine and tri-iodide ions solutions are not primary standard solutions, the standardization of thiosulfate solutions may be achieved with the help of iodine solutions extemporaneously prepared from primary standards. Iodine is usually prepared by the iodate/iodide reaction or by the oxidation of iodides with potassium dichromate, but other possibilities exist. 

Hence iron (II) solutions can be titrated against standard potassium dichromate solution. Because of the high purity of the purest solid, it can be considered as a primary standard. Solutions are made up by weighing the finely ground solid and making up in a volumetric flask. A redox indicator is necessary for dichronate titrations. 

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