Determination of niobium with p-arsonophenylazochromotropic acid and cetylpyridinium bromide

Abstract

Color stabilization and modification of the visible spectrum of the p-arsonophenylazochromotropic acid (L) and Nb(V) binary complex by the addition of surfactants has been studied In the course of a search for improved spectrophotometric methods for niobium. Addition of cationic surfactants resulted in an effective means of color stabilization and brought about a drastic improvement in the intensity of the absorption band maximum (sensitized reactions). The surfactant which gave the most intense absorption band maximum was cetylpyridinium bromide (CPAB). Spectrophotometric measurements indicate the formation of two Nb-L-CPAB ion-association ternary complexes: a complex with the stoichiometry 1:2:4 was formed in approximately 1 M HCI. The other complex had the stoichiometry 1:l:Z and formed in 2-4 M HCI mediums. Both ternary complexes mentioned can be applied to the spectrophotometric determination of niobium and two different analytical methods have been established: the complex formed in a 1.0 M HCI medium provides a method less selective than the complex formed in 2-4 M HCI. The method provided by the former complex is sensitive ( t = 1.87 X lo4 L mol-' cm-I), has a working range of 0.5-5 ppm Nb, and has a relative standard deviation of 0.5 YO. The complex formed in the higher acidity range provides a less sensitive method. The working range is 1-9 ppm and t = 7.40 X lo3 L mol-' cm-I. This latter method is most adequate for a selective spectrophotometric determination of niobium (relative standard deviation being 0.5 YO).Recent research into increasing the absorptiometry sensitivity for trace metal analysis in the visible region has investigated the use of colored metal chelate systems "sensitized" by the presence of a third component (ternary systems).The use of binary metal ion complexes of organic dyestuffs such as Catechol Violet, "sensitized" by the addition of long-chain cationic surfactants such as cetyltrimethylammonium bromide (CTAB) is claimed to be a mode of analytical reaction more generally applicable to the determination of tin ( 1 ) and one of the most sensitive methods available for the absorptiometric determination of' metal ions. Although some attempts have been made to define the mechanisms and associated color changes of such reactions, much more work is needed to elucidate them.Bayley et al. ( I ) concluded from their study that ternary complexes are formed by ion association of the quaternary ammonium group with the metal dyestuff chelate. However. in aqueous solution, this occurs only when micelles are formed. It is thus necessary to form micelles t o obtain the ternary system because the critical micelle concentration (CMC) of the surfactant turned out also to be a critical reaction concentration ( I ) .The work of Ashton et al.(2) on the Sn(1V)-Catechol Violet system in the presence of surfactants of different nature confirmed that the Sn(1V)-Catechol Violet-CTAB system is a ternary ion association system which is probably formed in colloidal solution and dispersed by the excess surfact...

Metal chelate fluorescence enhancement in micellar media and its applications to niobium and tantalum ultratrace determinations

“…If epoxides were converted to S-alkylated derivatives with sodium sulfide and then subsequently treated with a suitable fluorogenic reagent for thiols, it seems that epoxides can be determined. Recently, the o-phthalaldehyde (OPA) reaction for primary amino compounds in the presence of thiols at basic pH (5), was applied to the precolumn (6) and postcolumn (7,8) derivatization reaction in high-performance liquid chromatographic analysis of some thiols. The stability of isoindole fluorophores has been also well-studied (9)(10)(11).…”

“…Efforts in our laboratory to develop more sensitive and selective methods for the traditionally difficult niobium trace determination initially focused on the use of micelles to sensitize colored Nb(V) reactions (5,6). We extended this "micellar principle" to enhance the analytical fluorescence Of several chelates of niobium (7,8) and of the chemically similar element tantalum.…”

Metal chelate fluorescence enhancement by nonionic micelles: surfactant and auxiliary ligand nature influence on the niobium-lumogallion complex

“…Reagents. A 100 ppm stock solution of Nb(V) was prepared from Nb205 (Scharlau) as described in the literature (17).…”

Hexadecylpyridinium-phosphotungstate ion association in construction of a hexadecylpyridinium cation selective electrode

“…Figure 3. Long-term stability of aspartame electrode when stored In buffer solution at 5 °C. theless, Diet Coke samples exhibited a very high background, and a compensating electrode was necessary.…”

“…Donoso et al (4) determined titanium(IV) even at a concentration below 5 X 10"6 M in a solution of iV-benzoyl-N-phenylhydroxylamine in an acidic water-ethanol mixture. The sensitivity of titanium(IV) de-termination was increased to 1 X 10"7 M by using the catalytic maximum wave in the differential pulse polarographic analysis of copying paper and carbon steels in a supporting electrolyte composed of 1 mM ethylenediaminetetraacetic acid (EDTA), 5 mM KBrOa, and 40 mM HB02 dissolved in a Britton Robinson buffer (5). Differential pulse polarography was also employed for the determination of titanium(IV) in bone tissue (6) and biological samples (7)…”