Interferences in graphite furnace atomization

D. C. Baxter and J. Ohman, Multi-component standard additions and partial least squares modelling, a multivariate calibration approach to the resolution of spectral interferences in graphite furnace atomic absorption spectrometry, Spectrochim. Acta, Part B, 45(4 5), 1990, 481 491. 

Substances Added to the Sample for the Removal of Interference in Graphite Furnace Atomic Absorption Method... 

In the case of flame atomization (Section 3.4) general interference effects involved in atomic absorption have been discussed. In this section only those interferences in graphite furnace atomic absorption occurring during the atomization process are described. 

Maia S. M., Welz B., Ganzaroijj E. and CuRTius A. J. (2002) Feasibility of eliminating interferences in graphite furnace atomic absorption spectrometry using analyte transfer to the permanently modified graphite tube wall, Spectrochim. Acta, Part B 57 473—484. 

Two colorimetric methods are recommended for boron analysis. One is the curcumin method, where the sample is acidified and evaporated after addition of curcumin reagent. A red product called rosocyanine remains it is dissolved in 95 wt % ethanol and measured photometrically. Nitrate concentrations >20 mg/L interfere with this method. Another colorimetric method is based upon the reaction between boron and carminic acid in concentrated sulfuric acid to form a bluish-red or blue product. Boron concentrations can also be deterrnined by atomic absorption spectroscopy with a nitrous oxide—acetjiene flame or graphite furnace. Atomic emission with an argon plasma source can also be used for boron measurement. 

Principles and Characteristics Flame emission instruments are similar to flame absorption instruments, except that the flame is the excitation source. Many modem instruments are adaptable for either emission or absorption measurements. Graphite furnaces are in use as excitation sources for AES, giving rise to a technique called electrothermal atomisation atomic emission spectrometry (ETA AES) or graphite furnace atomic emission spectrometry (GFAES). In flame emission spectrometry, the same kind of interferences are encountered as in atomic absorption methods. As flame emission spectra are simple, interferences between overlapping lines occur only occasionally. 

Koide et al. [537] have described a graphite furnace atomic absorption method for the determination of rhenium at picomolar levels in seawater and parts-per-billion levels in marine sediments, based upon the isolation of heptavalent rhenium species upon anion exchange resins. All steps are followed with 186-rhenium as a yield tracer. A crucial part of the procedure is the separation of rhenium from molybdenum, which significantly interferes with the graphite furnace detection when the Mo Re ratio is 2 or greater. The separation is accomplished through an extraction of tetraphenylarsonium perrhenate into chloroform, in which the molybdenum remains in the aqueous phase. 

Tominaga et al. [682,683] studied the effect of ascorbic acid on the response of these metals in seawater obtained by graphite-furnace atomic absorption spectrometry from standpoint of variation of peak times and the sensitivity. Matrix interferences from seawater in the determination of lead, magnesium, vanadium, and molybdenum were suppressed by addition of 10% (w/v) ascorbic acid solution to the sample in the furnace. Matrix effects on the determination of cobalt and copper could not be removed in this way. These workers propose a direct method for the determination of lead, manganese, vanadium, and molybdenum in seawater. 

Willie et al. [17] used the hydride generation graphite furnace atomic absorption spectrometry technique to determine selenium in saline estuary waters and sea waters. A Pyrex cell was used to generate selenium hydride which was carried to a quartz tube and then a preheated furnace operated at 400 °C. Pyrolytic graphite tubes were used. Selenium could be determined down to 20 ng/1. No interference was found due to, iron copper, nickel, or arsenic. 

The major anions and cations in seawater have a significant influence on most analytical protocols used to determine trace metals at low concentrations, so production of reference materials in seawater is absolutely essential. The major ions interfere strongly with metal analysis using graphite furnace atomic absorption spectroscopy (GFAAS) and inductively coupled plasma mass spectroscopy (ICP-MS) and must be eliminated. Consequently, preconcentration techniques used to lower detection limits must also exclude these elements. Techniques based on solvent extraction of hydrophobic chelates and column preconcentration using Chelex 100 achieve these objectives and have been widely used with GFAAS. 

The recommended procedure for the determination of arsenic and antimony involves the addition of 1 g of potassium iodide and 1 g of ascorbic acid to a sample of 20 ml of concentrated hydrochloric acid. This solution should be kept at room temperature for at least five hours before initiation of the programmed MH 5-1 hydride generation system, i.e., before addition of ice-cold 10% sodium borohydride and 5% sodium hydroxide. In the hydride generation technique the evolved metal hydrides are decomposed in a heated quartz cell prior to determination by atomic absorption spectrometry. The hydride method offers improved sensitivity and lower detection limits compared to graphite furnace atomic absorption spectrometry. However, the most important advantage of hydride-generating techniques is the prevention of matrix interference, which is usually very important in the 200 nm area. 

Baucells [53] applied graphite furnace atomic absorption spectrometry to the determination of cadmium in soils with a precision of 0.4% at the 69 p,g/g cadmium level. The loss of cadmium during the charring cycle was high, preventing the use of any char in the atomisation process in order to remove the organic matrix or minimise interference effects. 

Palladium. Flame AAS analysis of Pd is described in P CAM 173 however, it would probably be preferred to use graphite furnace atomization as in S-191 Pt, soluble salts. An oxidizing air-acetylene flame is used for Pd AAS to minimize interferences from Al, Co, Ni, Pt, as well as Rh and Ru. These interferences may be minimized by complexation of Pd as the bis-pyridine-dithiocyanate (13) and extraction into hexone (3). Interferences may be minimized by the addition of 1000 ppm La. The 244.8 and 247.6 nm lines have equal sensitivity however, the 247.6 nm line is generally preferred ( 3). No Federal standard exists for Pd however, in analogy to Ni and Pt, Pd should be treated with caution. 

Graphite Furnace Atomic Absorption Spectrometry Graphite furnace atomic absorption spectrometry (GFAAS), the most popular form of ET-AAS, is today a common technique widely used in routine laboratories and has become a powerful tool for the analysis of trace and ultratrace elements in clinical and biological samples [61]. The main advantages of this technique are low cost, simplicity, excellent detection power, and the fact that it allows very low sample volumes to be used (5-20 p,L). In this sense, this technique allows LoDs for many elements in the order of 0.01 pgl-1 in solution or 1 pg g-1 in solid samples to be achieved [62]. However, the technique is prone to spectral and matrix interferences. 

With electrothermal evaporation from a tungsten filament and quartz fiber optics, detection limits are at the 50-100 pg level for many elements, except for Fe which is subjected to spectral interferences from tungsten lines. This was established from the use of different working gases and especially from experiments with the addition of H2 to the argon. In the case of coupling with graphite furnace atomization Cu, Mg and Fe can be determined in serum samples without dilution for Fe and Cu and with a 1 100 fold dilution for Mg [434]. 

The determination of Se03- and SeOc in water with graphite furnace atomic absorption detection was investigated by Chakraborti et al. [22]. Some interference by Cl" and F was reported. DCPAE detection was used by Urasa and Ferede [23]. Results were 1000 times more sensitive than conductivity detection. One of the advantages of atomic emission detection was described in this work. Identical molar sensitivity was obtained for both species. Mehra et al. [24] developed a novel singlecolumn IC method to determine selenium species in seleniferous soil samples. The separation took about 14 minutes and there were no reported interferences. 

The potential interfering ions Cu2+ and Pb2+ were deposited on the cathode and anode, respectively, while Cd2+ was maintained in solution. The processed sample zone then passed through an AG1-X8 resin minicolumn for in-line analyte concentration as [CdCh]2 The eluted analyte was spectrophotometrically determined using the malachite green-iodide method. With a 60 s electrolysis time and a 0.25 A applied current, Pb2+ and Cu2+concentrations up to 50 and 250 mg L 1 respectively did not interfere and the detection limit for Cd was 0.23 pg L-1. Precise results (r.s.d. = 3.85%) in agreement with those obtained by graphite furnace atomic absorption spectrometry were obtained at a sampling rate of 20 h-1. 

The determination of technetium by atomic absorption spectrophotometry was studied with a Tc hollow-cathode lamp as a spectral line source. The sensitivity for technetium in aqueous solution was 3-10 g/ml in a fuel-rich acetylene-air flame for the unresolved 2614.23-2615.87 A doublet. Cationic interferences were eliminated by adding aluminum to the sample solutions. The applicability of atomic absorption spectrophotometry to the determination of technetium in uranium and a uranium alloy was demonstrated [42]. A detection limit of 6 10 g w as achieved for measuring technetium by graphite furnace atomic absorption spectrometry. In using the same doublet and both argon and neon as fill gases for the lamp, 6-10 to 3 10 g of technetium was found to be the range of applicability [43]. 

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