Titration procedure

Johnson and co-workers [15] found that, in titrating copolymers of methylacrylate and methacrylic acid with standard base to determine carboxyl groups, several deficiencies were encountered. The presence of up to 5% water and unreacted monomer both led to underestimations of acid content. Titration was not applicable to polymers of molecular weight more than one million (or high acid content) because of a tendency to reprecipitate during titration. Titration procedures should therefore be used with caution. 

Most methods for the determination of carboxyl groups in polymers are based on titration techniques including, for example, the following copolymers acrylic acid-itaconic acid [16], acrylic acid-ethyl acrylate [17] and maleic acid-styrene [18]. High-frequency titration has been applied [19] to the analysis of itaconic acid-styrene and maleic acid-styrene copolymers. The method can also be used to detect traces of acidic impurities in polymers, and in the identification of mixtures of similar acidic copolymers. Titration indicates that the acid segments in the copolymers of itaconic acid-styrene, and maleic acid-styrene, and the homopolymer polyitaconic acid, act as dibasic acids. The method has a sensitivity that permits identification and approximate resolution of two carboxylate species in the same polymer, for example  

High-frequency titration gives a precise location of the inflection points related to the polymer carboxyl groups, and is a sensitive method for the determination of the freedom of the copolymer samples from monobasic acid impurities (comonomer acids). This is because mixtures of copolymer acids with monobasic and dibasic acids show definite inflection points that can be related to the individual carboxylate species present. 

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BackTitrations. In the performance of aback titration, a known, but excess quantity of EDTA or other chelon is added, the pH is now properly adjusted, and the excess of the chelon is titrated with a suitable standard metal salt solution. Back titration procedures are especially useful when the metal ion to be determined cannot be kept in solution under the titration conditions or where the reaction of the metal ion with the chelon occurs too slowly to permit a direct titration, as in the titration of chromium(III) with EDTA. Back titration procedures sometimes permit a metal ion to be determined by the use of a metal indicator that is blocked by that ion in a direct titration. Eor example, nickel, cobalt, or aluminum form such stable complexes with Eriochrome Black T that the direct titration would fail. However, if an excess of EDTA is added before the indicator, no blocking occurs in the back titration with a magnesium or zinc salt solution. These metal ion titrants are chosen because they form EDTA complexes of relatively low stability, thereby avoiding the possible titration of EDTA bound by the sample metal ion. 

The equivalent amount of cadmium ion exchanged for the silver ion can readily be determined by EDTA titration procedures. 

Small amounts of moisture (up to about 0.5%) in crystalline sugars can be determined chemically by titration with Kad Fisher reagent. A volumetric Kad Fisher titration procedure for moisture in molasses is accepted by AO AC. Automatic Kad Fisher titrators are available, and as acceptance of pyddine-free reagents increases, their use may increase. 

Two excellent methods (utilising acid-base indicators) are available for standardisation. The first is widely employed, but the second is more convenient, less time-consuming, and equally accurate. A third, back-titration, procedure is also available. 

The theory of titrations between weak acids and strong bases is dealt with in Section 10.13, and is usually applicable to both monoprotic and polyprotic acids (Section 10.16). But for determinations carried out in aqueous solutions it is not normally possible to differentiate easily between the end points for the individual carboxylic acid groups in diprotic acids, such as succinic acid, as the dissociation constants are too close together. In these cases the end points for titrations with sodium hydroxide correspond to neutralisation of all the acidic groups. As some organic acids can be obtained in very high states of purity, sufficiently sharp end points can be obtained to justify their use as standards, e.g. benzoic acid and succinic acid (Section 10.28). The titration procedure described in this section can be used to determine the relative molecular mass (R.M.M.) of a pure carboxylic acid (if the number of acidic groups is known) or the purity of an acid of known R.M.M. 

A simple example of the application of a complexation reaction to a titration procedure is the titration of cyanides with silver nitrate solution. When a solution of silver nitrate is added to a solution containing cyanide ions (e.g. an alkali cyanide) a white precipitate is formed when the two liquids first come into contact with one another, but on stirring it re-dissolves owing to the formation of a stable complex cyanide, the alkali salt of which is soluble ... 

A selection of coulometric titrations of different types is collected in Table 14.2. It may be noted that the Karl Fischer method for determining water was first developed as an amperometric titration procedure (Section 16.35), but modern instrumentation treats it as a coulometric procedure with electrolytic generation of I2. The reagents referred to in the table are generated at a platinum cathode unless otherwise indicated in the Notes. 

A number of commercial titrators are available in which the electrical measuring unit is coupled to a chart recorder to produce directly a titration curve, and by linking the delivery of titrant from the burette to the movement of the recorder chart, an auto-titrator is produced. It is possible to stop the delivery of the titrant when the indicator electrode attains the potential corresponding to the equivalence point of the particular titration this is a feature of some importance when a number of repetitive titrations have to be performed. Many such instruments are controlled by a microprocessor so that the whole titration procedure is, to a large extent, automated. In addition to the normal titration curve, such instruments will also plot the first-derivative curve (AE/AV), the second-derivative curve (A2 E/AV2), and will provide a Gran s plot (Section 15.18). 

Place the prepared copper acetate solution in the beaker and add 10 mL of 20 per cent potassium iodide solution. Set the stirrer in motion and add distilled water, if necessary, until the platinum plate electrode is fully immersed. Use a saturated calomel reference electrode, and carry out the normal potentiometric titration procedure using a standard sodium thiosulphate solution as titrant. 

There are two important hydrogenation (or reduction) — titration procedures for the detn of N as ammonia. The Devarda method involves the quant reduction of nitrates to ammonia in alkaline soln using an Ai-Cu-Zn alloy. The ammonia evolved is distd into standard sulfuric acid... 

A pentane solution of terf-butyllithium (purchased from either Alfa Inorganics, Inc. or Lithium Corporation of America, Inc.) was standardized by one of the previously described titration procedures (Note 1). If possible, it is desirable to use a freshly opened bottle of lert-butyllithium since previously used bottles of this reagent often contain lithium ferf-butoxide which will lead to formation of a contaminant in the final product (Note 10). 

ISO 2271 1989, Surface active agents Determination of anionic-active matter by manual or mechanical direct two-phase titration procedure. 

The most reliable method is probably the potentiometric titration procedure first reported by Dilley [101]. This procedure has the added advantage of avoiding the use of trichloromethane. The procedure for the manufacture of the membrane-indicating electrode has been modified and a simplified description is given below. Commercial variants are also becoming available. 

The technique is especially useful for analysis of low molecular weight AOS (C8, C10), which has greater water solubility, and can be more accurate than the two-phase titration procedures. High molecular weight AOS with poor water solubility can still be analyzed if the ion exchange is performed at elevated temperature. 

Barium perchlorate colorimetric titration. This colorimetric titration procedure is used in the determination of inorganic sulfate impurities in complex systems of water-soluble sulfonates and sulfonic acids. Sulfonates are precipi-... 

Karl Fischer titration. This titration procedure determines the concentration of water present in AOS samples containing 40-70 wt % water. In Karl Fischer titrations, each equivalent of base interferes as 18 g of water. Since AOS samples are basic, water values obtained must be corrected for side reactions of reagent with alkaline material. Alkalinity must be determined to correct for this error. 

The potentiometric titration was carried out in order to determine the functional groups present in the biomass surface. During the titration experiments, the C02-free condition was always maintained to avoid the influence of inorganic carbon on the solution pH. Detailed potentiometric titration procedure and estimation method of functional groups are available in the previous reports [4,6]. 

Micro amounts of sulfur in polymer are usually determined by oxygen flask combustion, sodium peroxide fusion in a metal bomb followed by titration [30], pyroluminescence [36] or ICP-AES. An oxygen flask combustion photometric titration procedure capable of determining total sulfur in polymers in amounts down to 50 ppm was reported. The repeatability of the sulfur determination in polyolefins in the oxygen flask is 40% at 50 ppm level, improving to 2% at the 1 % level [21]. Crompton [31] has also combined Schoniger flask combustion with a colorimetric procedure for the determination of phosphorous in polymers in various concentration ranges (0.01 to 2%, 2 to 13%). 

Applications Basic methods for the determination of halogens in polymers are fusion with sodium carbonate (followed by determination of the sodium halide), oxygen flask combustion and XRF. Crompton [21] has reported fusion with sodium bicarbonate for the determination of traces of chlorine in PE (down to 5 ppm), fusion with sodium bisulfate for the analysis of titanium, iron and aluminium in low-pressure polyolefins (at 1 ppm level), and fusion with sodium peroxide for the complexometric determination using EDTA of traces of bromine in PS (down to 100ppm). Determination of halogens in plastics by ICP-MS can be achieved using a carbonate fusion procedure, but this will result in poor recoveries for a number of elements [88]. A sodium peroxide fusion-titration procedure is capable of determining total sulfur in polymers in amounts down to 500 ppm with an accuracy of 5% [89]. 

Potentiometric titration procedures with sodium methoxide have been reported for non-sulfur-containing organotin compounds in solvent extracts of polymers, and for phenolic antioxidants with sodium isopropox-ide in pyridine medium [21]. Organotin compounds in solvent extracts of PVC can be determined by potentiometric and manual titration procedures [487,488]. 

Titration Procedure, ISO 2771, 1972. Synthetic Anionic Active Matter in Detergents by... 

As has been mentioned previously, the approach to equilibrium can often be slow for macrocyclic complex formation indeed, equilibrium may take days, weeks or even months to be established. This may give rise to experimental difficulties in conventional titration procedures. Under such circumstances, it is usually necessary to carry out batch determinations in which a number of solutions, corresponding to successive titrations points, are prepared and equilibrated in sealed flasks. The approach to equilibrium of each solution can then be monitored at will. 

In some instances, a calorimetric titration procedure may be used to obtain both log K and AH values simultaneously. Thus, the titration curve (heat change versus volume of reactant added) gives a measure of the degree of complex formation at each titration point and, provided... 

On the other hand, nonspecific analytical methods (such as liquid scintillation counting, spectrophotometry, and titration procedures) may not distinguish between the solute under study and certain impurities. When using such methods, the solid state of interest should be highly pure and the amount of solid in excess of that required to saturate the solution should be minimized. 

Ben Yaakov and Lorch [8] identified the possible error sources encountered during an alkalinity determination in brines by a Gran-type titration and determined the possible effects of these errors on the accuracy of the measured alkalinity. Special attention was paid to errors due to possible non-ideal behaviour of the glass-reference electrode pair in brine. The conclusions of the theoretical error analysis were then used to develop a titration procedure and an associated algorithm which may simplify alkalinity determination in highly saline solutions by overcoming problems due to non-ideal behaviour and instability of commercial pH electrodes. 

The titration procedure used was that described by Ben Yaakov et al. [9], in which 100 ml of seawater or brine sample is titrated in 30-50 burette increments with 3 - 5 ml standard 0.1 M hydrochloric acid using a pH electrode. 

After chlorination, beakers were removed from the sunlight at regular (usually 30-min) intervals, placed in a dark box, and the contents analysed for bromate and residual oxidants without delay. Residual oxidants analyses were performed by the Ij spectrophotometric titration procedure described by Carpenter [19] with a pH of 2 and potassium iodide concentration of 4 g/1. Bromate... 

Carpenter et al. [3] proposed that, in order to overcome this difficulty, higher acidity and higher potassium iodide concentrations or a back titration procedure should be used. 

Mascini [653] described a potentiometric titration procedure using an Orion Cu2+ state electrode for the determination of calcium and magnesium in seawater. 

The concentration of acetic anhydride at any time in the CSTR is determined by titration with sodium hydroxide. Because the titration procedure requires time (relative to the hydrolysis reaction time), it is necessary to quench the hydrolysis reaction as soon as the sample is taken. The quenching is achieved by adding an excess of aniline to the sample. The quench reaction is... 

Where the reduction potentials of two analytes are sufficiently different a mixture may be analysed. Titanium(III), = 0-lOV may be titrated with cerium(IV) in the presence of iron(II), =0.77 V usjng methylene blue as indicator. Subsequently the total, iron plus titanium, may be determined using ferroin as indicator. The determination of iron is illustrative of some practical problems which are encountered in direct titration procedures. 

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