Comparison of Chemical Modifiers in Electrothermal Atomization Atomic Absorption Spectrometry with Boron Nitride Tube and Platform Furnaces for Mercury

Abstract

A graphite furnace is often used as a popular atomizer for electrothermal atomization atomic absorption spectrometry (ETAAS) and a popular vaporizer for ICP techniques. There are two types of furnaces: tube and platform. The furnace wall is made with a pyrolytic graphite (PG) to be pore-free and with a non-pyrolytic graphite (NPG) to be pore-rich. The reactivity of the NPG furnace is greater than that of the PG one: reducing power, adsorption of analyte elements on graphite wall, migration of analyte elements into the graphite wall, formation of intercalation compounds and carbide formation. Atomization of the analyte takes place via thermal dissociation of analyte oxide, vaporization of metal and heterogeneous reduction on the hot graphite surface et al. Metal atomizers such as tantalum, tungsten, and molybdenum have a lower reactivity than graphite atomizer. Microtube, boat and coil types are used as well as metal-lined graphite furnace and metal platform. An atomizer with chemically inert ceramic wall would be favorable for ETAAS techniques for unstable oxide forming and stable carbide-forming elements. Our previous letter to the editor 1 is the first report about ETAAS with a ceramic furnace with less reactivity than metal surface, where boron nitride (BN) was used as the ceramic wall. Two types of furnace design, tube and platform, for the laboratorymade ceramic furnaces for ETAAS were reported in the letter.The BN tube and platform was made from two types of BN, pyrolytic boron nitrate (PBN) and non-pyrolytic boron nitride (NBN). Pyrolytic boron nitrate made directly by a chemical vapor deposition technique is pore-free and NBN made by a hot-pressing technique with high-purity BN crystalline powder is pore-rich. The most common form of α-boron nitride, graphite-like hexagonal, is used increasingly in various fields because of its combination of the following properties: low density; hightemperature stability, m.p. near 3000˚C; chemical inertness, especially its resistance to acids and molten metals and its stability in inert gases, like N2, CO and Ar up to 2700˚C; stability to thermal shock; extremely low electrical conductivity and high thermal conductivity. 2 The preliminary data for relative absorbance and standard deviation of 15 elements such as Ag, As, Au, Bi, Cd, Cu, Ga, Hg, In, Pb, Sb, Se, Sn, Te, and Tl, were treated in the letter. 1 In the case of integrated absorbance, both ceramic tube furnaces give a sensitivity enhancement for Bi, Cd, Hg, Se, Sn and Te compared to both graphite tube furnaces. For both ceramic platform furnaces, the sensitivity enhancement was observed for Ag, Bi, Cd, Cu, Hg, Te and Tl. Especially, a remarkable sensitivity enhancement was observed for Hg with all ceramic furnaces. Mercury is a very important element because of its toxicity, presenting a serious environmental and health hazard to humans and animals. Consequently, Hg was selected as an analyte for the BN furnace-ETAAS in the present work.In the present work, the following are reported: (i) the effect of chemical...

Comparative efficacy of platinum group metal modifiers in electrothermal atomic absorption spectrometry

“…With the use of a permanent palladium modifier and calibration against aqueous mercury solutions, da Silva et al [79] successfully analyzed four of five solid SRMs studied. For the determination of mercury with the use of a boron nitride tube, Pd was also the best modifier compared to Rh, Ir and a mixture Pd+Rh modifiers [80].…”

Determination of As, Cd, Cu, Hg and Pb in biological samples by modern electrothermal atomic absorption spectrometry

“…However, if inadequate equipment is used to conduct the acid digestion, unacceptable losses of analytes such as As and Hg may arise by volatilization. The widespread use of microwave assisted acid digestion with elevated pressure and temperature control has alleviated these problems [2,4,[7][8][9][10][12][13][14]17,20,[27][28][29]32,[35][36][37][38]41,43,[45][46][47][48][50][51][52][53][54][55][56][57][59][60][61][62][64][65][66]69,[71][72][73]76] and enabled the use of large sample masses (1-2 g) without the danger of vessel rupture and with a minimal chance for contamination. Microwave assisted processes are particularly important when the determination of As and Hg is targeted as complete mineralization of the sample can be achieved at low temperature preventing losses of these elements.…”

“…Microwave assisted processes are particularly important when the determination of As and Hg is targeted as complete mineralization of the sample can be achieved at low temperature preventing losses of these elements. Nitric acid is the most widely used [4,[8][9][10]12,[15][16][17]20,[24][25][26][27][28][29][30][31][32][33][34][35][36][37][38][39][40][41][42]66] and the addition of H 2 O 2 increases its oxidization power [2,7,13,22,. Mixtures of nitric acid with other acids have also been favored [13,14,22,[67][68][69][70][71][72][73][74][75].…”

“…These problems have been solved by taking advantage of hardware and method improvements. Application of CVG with in situ trapping using various permanent modifiers has achieved good results for acid digested samples and used to concentrate mercury vapor [32,179] or for detection of mercury directly generated from digested or slurried solutions [24,66,82,101,103,119]. Modifiers frequently permits elimination of the pyrolysis stage and use of low atomization temperatures [24,32,82], allowing volatilization of Hg before the corresponding permanent modifier reaches its atomization temperature.…”

“…For this purpose, various matrix modifiers (Table 1), mainly from the Pt group metals, have been used for the collection of CV generated Hg onto Pd-Zr [32], or Au [179], or when utilizing solutions from slurries or extractions relying on Pd [66,119], Pd-Au [66], Pd+Rh [66] or Pd + Ir [66] as permanent modifiers. When several modifiers (Pd, Ph, Ir, Pd + Rh, KMnO 4 and Ag MnO 4 ) were tested for the determination of Hg in human hair using a furnace coated with boron nitride, best recoveries and lowest detection limits were obtained using Pd [66].…”