Lanthanum flame buffer

To determine the instrumental response as a function only of the background matrix of the solution, the effect of perchloric acid on Cr, Mo, and Pd was tested independently of the digestion procedure. The variables were (1) presence of filter matrix in solution (2) presence of perchloric acid (3) presence of lanthanum flame buffer in solution and (4) concentration. The data are presented in Table XI. Slightly high recoveries (4 to 9 percent) were obtained for Cr when the filter matrix was present in solution. Recoveries of approximately 120 percent were obtained from the 1.0 ug/ml samples containing perchloric acid. This was found to be caused by Cr contamination in the perchloric acid. The corrected analytical results showed that the presence of either perchloric acid or lanthanum in solution has essentially no effect on the instrumental response for Cr in a lean air-acetylene flame. 

The filter matrix causes low Mo response (31 to 91 percent). The response of synthetic solutions and solutions containing filter matrix is enhanced approximately 50 percent if perchloric acid is present in solution, and approximately 75 percent if lanthanum is present in solution. When both perchloric acid and lanthanum are present in solution, the enhancement of response is equivalent to that which would be obtained with the lanthanum alone. For two samples which did not contain lanthanum flame buffer, precision of triplicate analysis was poor ( 48 percent). Aliquots of two sample types which contained added lanthanum flame buffer gave much better precision ( 12 percent). It appears that both perchloric acid and lanthanum are acting as flame buffers or "releasing agents" for atomic Mo in the flame. 

TABLE XV. Comparison of single analyte and mixed analyte standard curves obtained with solutions containing 0.5% lanthanum flame buffer... 

The optimization of the atomic absorption method of determining metals in particulates found in the air of workplace is described. The Plackett-Burman Youden-Steiner balanced incomplete block designs as well as single-factor experiments were utilized with ten metals Be, Cd, Co, Cr, Cu, Mn, Mo, Ni, Pb, and Pd. Of the parameters tested, perchloric acid digestion, flame-stoichiometry, and the composition of the calibration standards were the most significant. Perchloric acid affected the recoveries of chromium. This was attributed to the formation of volatile chromylchloride. Flame-related phenomena and interelemental effects were brought under control using lanthanum flame buffer. 

The determination of magnesium in potable water is very straightforward very few interferences are encountered when using an acetylene-air flame. The determination of calcium is however more complicated many chemical interferences are encountered in the acetylene-air flame and the use of releasing agents such as strontium chloride, lanthanum chloride, or EDTA is necessary. Using the hotter acetylene-nitrous oxide flame the only significant interference arises from the ionisation of calcium, and under these conditions an ionisation buffer such as potassium chloride is added to the test solutions. 

One of the most important applications of FAAS in the routine clinical chemistry laboratory is the determination of calcium and magnesium in blood serum and other body fluids. The samples are diluted 1 20 to 1 50 with a buffer such as EDTA, lanthanum, or strontium and analyzed directly in an air-acetylene flame. Paschen [6] describes a micromethod for the determination of sodium, potassium, calcium, and magnesium in a single-serum dilution. One hundred microliters of serum is diluted 1 50 with 0.25% (w/v) strontium chloride solution and analyzed directly. The addition of strontium eliminates the influence of phosphate on calcium and the ionization of sodium and potassium. 

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