A liquid chromatograph is described which permits rapid separation of metal ions using strongly acidic eluents. The chromatograph is inexpensive to construct and provides for quick changing of eluents.With this equipment, iron(lll) can be separated from other ions and determined spectrophotometrically in less than 6 minutes. The iron is concentrated on a small anion exchange column and then is stripped from the column with dilute hydrochloric acid. The amount of iron is calculated from the peak height of the elution curve. Virtually all chemical and electrochemical methods for determining small amounts of a metal ion are at times subject to interferences that necessitate a chemical separation. Methods such as atomic spectrometry are very selective but their dependency on excitation conditions and matrix composition necessitates frequent calibration and standardization. A separation or concentration is often carried out in conjunction with flame methods.Ion exchange and partition chromatographic methods for separating metal ions from one another are quantitative and selective. However, most of the published methods are slow, often requiring 30 minutes or more to elute each element from the column. Recently a systematic scheme for 27 elements was published (/). By using samples of 25 to 50 mg and relatively small columns, the average elution time was reduced to around 15-20 minutes per element. Clearly a more rapid way to separate inorganic ions by ion exchange and partition chromatography would be useful.

Water hardness is determined by titration with EDTÁ using a mixed indicator containing Arsenazo I and a buffer containing THAM. The end point is sharp and quick; iron, copper, aluminum, and common anions do not interfere in the amounts present in most water samples. A rapid and accurate spectrophotometric titration procedure is also reported. Formation constants for the calcium(ll) and magnesium(ll) complexes with Arsenazo I at pH 10 have also been determined.Few analytical methods compare in importance with the EDTA titration of total hardness in water. Despite this, the existing procedures for water hardness (1-5) have several unfortunate drawbacks. Eriochrome Black T, Calmagite, and other indicators (which are all of similar general structure) change color slowly at the end point and thus require that the end point be approached slowly and carefully. Further, traces of iron, copper, and certain other metal ions dissolved in the water block these indicators and either prevent an end point or seriously reduce its sharpness. Cyanide and other masking agents may be employed, but cyanide is a potential safety hazard.

No abstract

No abstract