Water-soluble salts of copper(ll), nickel, chromium(lll), iron(lll), aluminium, cobalt, manganese(ll), cadmium, zinc and lead(l1) are determined titrimetrically in amounts down to 0.1 mequiv. in the presence and absence of hydrochloric, nitric and sulphuric acids. Ammonium salts are determined in the absence of free acids. When the mixture of metal salt and acid is titrated with aqueous potassium hydroxide, the end-point corresponding to the neutralisation of the free acid is determined by the onset of turbidity caused by precipitation of the hydroxide of the metal by the first excess of titrant. The titration is continued, and when all of the metal hydroxide is precipitated the final excess of titrant initiates the thermometric indicator reaction. The thermometric indicator, acetaldehyde, is diluted 1 + 1 with water to ensure solubility of the metal salts.The method has been used to analyse four representative electroplating solutions for free acid and total metal content, the free acids being boric, acetic, succinic and glycollic acids.
Dihydroxamic acids contain two bidentate ligand groups and are very powerful chelating agents for metal ions. Five water-soluble acids of the general formula HONHCO(CH2),-CONHOH were examined by differential-pulse voltammetry (DPV), cyclic voltammetry (CV) and microcoulometry (MC).The acids were prepared by J. Glennon at Cork University using procedures of Brown and co workers.1.2 The acids listed in Table 1 were investigated.A series of Prideaux buffers were used as supporting electrolytes, with suitable amounts of potassium nitrate added,
Dimethoxymethane, 1,3,5-trioxane, 1,3-dioxoIane and alicyclic ethers with three-to seven-membered rings were evaluated as thermometric end-point indicators in the non-aqueous titration of weak organic bases including some basic drugs, in the free form and as hydrochlorides, phosphate and tartrate, with perchloric acid in acetic acid.All the indicators except the three and four-membered-ring cyclic ethers give sharp end-point inflections in titrations of quinuclidine and 8-hydroxyquinoline, but for caffeine only the acetal indicators are satisfactory. Relative standard deviations obtained in replicate determinations of 0.1-mequiv. amounts range from 0.1 0 to 0.66%, with sample and titrant delivery errors making a significant contribution.In the drug titrations, the acetal indicators give the sharpest end-point inflections for chloroquine phosphate. Only 1,3-dioxoIane is a suitable indicator for the adrenaline hydrogen tartrate titration. The perchloric acid titrant is effective only in the presence of acetic anhydride, when it functions as acetyl perchlorate. Boron trifluoride etherate in 1,4-dioxane can also be used as the titrantkatalyst but is less effective in terms of end-point sharpness.
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