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Voltammetric behavior of titanium(IV) complexes with chromotropic acid, its azo-derivatives: 2-(4-sulfophenylazo)-1,8-dihydroxy-3,6-naphthalenedisulfonic acid (SPANDS), chromotrope 2B, sulfonazo III and other azo-compounds: calmagite, tropeoline O and kalces was investigated at a hanging mercury drop electrode. These complexes strongly adsorb onto the electrode, thus can be determined by an adsorptive stripping voltammetry (optimal pH about 6). At pH about 3 reduction current enhancement for Ti-kalces complex was observed in the presence of chlorate ions. It is a rare example of a catalytic process with azo-compound as a complexing agent. Signal for Fe-calmagite complex reduction was also observed. Influence of foreign ions and the optimal conditions for titanium determination are described in detail. Additionally, a connection between obtained results and a structure of titanium complexes is discussed.

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A procedure for iron determination in quartz and silica glass materials based on adsorptive stripping voltammetry (AdSV) in the presence of catechol is described. Hanging mercury drop electrode as a working electrode was used. The optimized conditions include pH 7.1, accumulation potential À0.1 V, accumulation time 60 s, scan rate 10 mV s À1, pulse amplitude 25 mV. In case of 60 s accumulation time the obtained detection limit was 2. 2 mg L À1 Fe. The possibility of simultaneous determination of iron and copper in the same solution is shown. ET-AAS technique was applied as a reference method to AdSV measurements.Keywords: Adsorptive stripping voltammetry, Iron, Catechol, Quartz, Silica glass Silica glass is a high purity product containing 99.9 % of silica and even the content of impurities at ppm level can change its optical properties remarkably. Therefore the quality of the raw materials used in its production is of great importance. Within a group of natural materials quartz crystals ®nd the most frequent use. Typical iron content in natural quartz ranges from fractions of ppm to several ppm.Synthetic silica glass practically does not contain any impurities, and for this reason it is transparent for UV radiation up from 180 nm. In case of the silica glass obtained from natural materials this threshold is shifted towards longer waves. This shift as well as the decrease in UV radiation transmittance are generally attributed to iron ions [1]. The absorption of UV radiation by iron ions is probably caused by the absorption bands speci®c for this element (d±d electron transitions). The higher the iron content, the more evident these effects become [2].There are two kinds of analytical methods used for iron determination in quartz and silica glass samples, the ones without a decomposition step and the others requiring sample decomposition. In the ®rst group of methods XRF technique is widely used. Yet, the high detection limit of this method restricts its applications. In the second group, iron content can be measured by means of AAS or spectrophotometric methods. The variation of AAS method which involves sample feeding in form of à slurry' has gained much attention among analytical chemists in the recent years [3,4]. Application of voltammetric stripping techniques for iron determination in quartz or silica glass samples has not been found in the literature. However, AdSV method was applied to determination of titanium in quartz samples [5]. In the presented studies, adsorptive stripping voltammetry with catechol as a complexing agent was used for iron determination, whereas reference measurements were carried out by ET-AAS. The method employing catechol was used to determine iron in a wide range of samples: seawater [6], wine [7], osteoblast-like cell culture medium [8], and simulated PWR coolant [9]. Among other complexing agents used for iron determinations which utilize AdSV methods, the following ones should be listed: 1-nitroso-2-naphthol [10, 11], solochrome violet RS [12].The aim of this article w...