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A determinação sequencial de cromo, tálio, cádmio, chumbo, cobre e antimônio em concentrados polieletrolíticos para hemodiálise (DCs) é apresentada. Cromo foi determinado usando voltametria adsortiva de redissolução catódica e tálio, cádmio, chumbo, cobre e antimônio por meio de voltametria de redissolução anódica. O novo método desenvolvido para testar estas amostras se baseia no efeito do gradiente de pH do eletrólito na resposta voltamétrica. Os limites de detecção variaram de 0,03 mg L -1 para cádmio a 0,27 mg L -1 para cobre. Recuperações das amostras variaram de 92,0 a 117,5%. Este método foi aplicado para a análise de DCs comerciais, nos quais as concentrações encontradas dos analitos variaram de 0,16 mg L -1 para antimônio até 140,00 mg L -1 para cobre. Interferências e método de referência são discutidos.The sequential voltammetric determination of chromium, thallium, cadmium, lead, copper and antimony in dialysate concentrates (DCs), is presented herein. Chromium was quantified by adsorptive cathodic stripping voltammetry and thallium, cadmium, lead, copper and antimony were assayed by anodic stripping voltammetry. The novel method developed to test these samples exploits the effect of electrolyte pH gradient on voltammetric response. The limits of detection (LOD) ranged from 0.03 mg L -1 for cadmium to 0.27 mg L -1 for copper. Recoveries from spiked samples were 92.0-117.5%. This method was applied to the analysis of commercial DCs, where the investigated metals were found in some samples at concentrations between 0.16 mg L -1 for antimony and 140.00 mg L -1 for copper. Interferences and the reference method are discussed.

1IntroductionTheo cean is ad ynamic system operating in different time scales,g overning important global processes,s uch as ore formation, bioproductivity and climate changes.D ue to their extremely low concentrations in seawater, trace elements are the key to understanding many of thesep rocesses.T race elements and their isotopes have been explored as proxies for the movement of aquatic masses [1]. Thep rimarys ourceso fd issolveda nd particulatet race metals into the oceans are dust, riverinei nput and continental shelf, i.e., theiri nputsare controlled by continental sources, whereas hydrothermal fluxes are significant for some elementss uch as Mn, and according to newer studies,even Fe [2,3].Thet ransition metalso fg roups IV and Vare characterized by as mall ionic radius and high charges (typically, tetravalent and pentavalent), and despite their relative immobility during processes of rock formation,i th as been shown that in geological systems involving water, such as seawater, estuaries,a nd marine sediments,t hey could become mobileu nder certain conditions [4][5][6][7][8][9].Zirconium occurs as an egatively charged species,s uch as Zr (OH) [11].Z irconium is grouped as aH igh-Field Strength Element (HFSE),w ith as ignificant tendency towards hydrolysis.Z irconium is strongly particle-reactive and is rapidly depleted from solution by interaction with the surface of sinking particles.T his behaviorl eads to al ow truly dissolved concentration of this element in natural waters and as ignificant effect of particles and colloids in its dissolved concentrations [1,4,5,12]. In contrast to HFSEs, whichtypically have only one oxidation state,v anadiumc an present variable oxidation states,V (IV) and V(V). Different redoxs pecies show different affinitiest owards particles and ligands in solution, leading to variations with respect to their biodisponibility and biogeochemistry reactivity.H ence,r edox conditions represent am ajor control over the distribution of these redox-sensitive trace elements. ForV ,o nly the oxidation state + 5i ss table in oxic waters at an eutral pH [13].T he vanadatea nion species, whicha re completely hydrolyzed, such as HVO 4 2À,H 2VO 4 À and the complexN aHVO 4 À , are predominant [ 13].Voltammetric determinations of Zr(IV) as well as V(V) at trace levels are more properly done as complexes of organic compounds [14][15][16][17][18][19][20][21][22][23][24][25][26][27][28].I nap revious paper [29] the adequacy of some of theseligands towards the Zr(IV) determination in natural waters was critically discussed. Thel igand COD showedt he best results for Zr(IV) determination at trace levels.I nt he presents tudy,w ed escribe the sequential determination of Zr(IV) and V(V) in natural waters using adsorptive voltammetric methods based on the accumulation of Zr(IV) and V(V) as cupferron-oxalic acid-1,3-diphenylguanidine (COD) complexes at the HMDE surface.N om ethodu sing the ligandC OD as complexing agent for V(V) was published yet neither individually nor in combinationw ith Zr(IV).Ther...

A voltammetric method was developed for zirconium determination as Zr(IV)-cupferron-oxalate-diphenylguanidine complex based on adsorptive accumulation at the HMDE (E peak = À0.95 V). The supporting electrolyte was a mixture of acetate/acetic acid (pH 4.6) and ammonium acetate (pH 5.7) solutions. E ads = À0.6 V (vs. Ag/AgCl), t ads = 400 s, 10 mV s À1 scan rate, and DP mode were the main parameters. The linear range was 0.033 to 3.3 10 À9 mol L À1, and the LOD and LOQ (t ads = 400 s) were 0.77 and 1.6 10 À11 mol L À1, respectively. The method was adequate for seawater samples, although not sufficiently sensitive for surface waters.