Table I.
Analysis of Tin Ore Concentrate in the Turbulent Air-Hydrogen Flame
,
03 0 ~
Samples
W
P 020-
L A
0 000
500 PPM
1000 TIN
1500
Figure 6. Calibration curve prepared from tin ore concentrate absorption readings against actual tin concentration computed from NBS standard analysis Flame, turbulent air-hydrogen; air, 2.5 liters/min; fuel to oxidant ratio, 9.4; heigbt above burner, 40 mm; wavelength, 2246 A; 0 , standard samples; m, A samples; A, B samples
samples from a common stock suspension, a second stock suspension was used to prepare a series of B samples. The working curve is shown in Figure 6 for the tin standard suspensions. The curve was drawn for a best fit through the absorbance values of the standards with absorbance figures also shown for the designated samples a t their normal concentration to indicate the extent of their deviation. Using the
Deviation
A
355 24 1 964
350 24 1 951
-1.4 0.0 -1.3
B
519 1038 1298
525 1045 1334
+1.2 +0.7 +2.8
v
R
Tin concentration, ppm Actual Analysis
working curve in its conventional sense and obtaining apparent concentrations for each sample, Table I was prepared t o indicate that quite reasonable results can be obtained when the standards and samples are closely matched. It is recognized that this represents the ideal case wherein the two are indeed from the same material. However, it does not seem unreasonable to expect that acceptable results could be obtained for ores of similar content. Currently under investigation for other elements are additional types of materials, such as cements, limestones, and geological samples for which more than one standard are available. We feel that the use of suspensions in flame spectrometry has some utility which should be considered. Not only may selected compounds be introduced directly into the flame in the solid state as a possible aid to the study of flame chemistry, but a very practical technique may result for those sample types which involve lengthy sample dissolution procedures. RECEIVED for review July 7, 1970. Accepted October 29, 1970.
High Sensitivity Internal Reflection Spectroelectrochemistry for Direct Monitoring of Diffusing Species Using Signal Averaging Nicholas Winograd' and Theodore Kuwana Department of Chemistry, Case Western Reserve University, Cleveland, Ohio 44106
Internal reflection spectrometry (IRS) at optically transparent electrodes (OTE) appears to be an excellent technique for quantitative studies of species produced or perturbed electrochemically within a distance 6 of the electrode surface. Quantitative applications employing IRS at OTE, however, require an understanding of the sensitivity variation of absorbance. This variation was formulated as a sensitivity factor, Neff,in the quantitative relationships describing absorbance and could be correlated with the optical constants of the system and the Fresnel equations describing the reflectivity. Further, the absorbance as a function of time during an electrochemical potential perturbation could be quantitatively analyzed, and good agreement was found with experimental results. Signal to noise ratios were greatly improved by signal averaging techniques, and small changes (
