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WHITE PAPER. Sensitivity, Background, Noise, and Calibration in Atomic Spectroscopy: Effects on Accuracy and Detection Limits. Introduction. Proper calibration in atomic spectroscopy and an understanding of uncertainty is fundamental to achieving accurate results.
- 1MB
- 11
- The Spectral Background
- Background Equivalent Concentration
- The Limit of Detection
- Signal-To-Background and Signal-To-Noise Ratios
- Additional Relationships of Interest
- Summary
- Appendix I: Compton Effect Derivation in Energy Terms
- Appendix II: Deriving Bec from The Calibration Curve
We consider here the spectral background radiation in the optical and X-ray regions of the electromagnetic (EM) spectrum. Also, the change in spectral background resulting from the presence of neighboring spectral lines is addressed. Optical Background Radiation The radiant energy given off by an object is dependent on both the temperature and natu...
The BEC provides a quantitative measure of the amount of background radiation at a specified spectral line. It is defined as the analyte concentration that produces a net signal (peak minus background) equal to the background. That is, an analyte concentration for which the signal-to-background ratio is one. Example 2:A practicing spectrochemist me...
The analytical chemist defines detection limitas three times the standard deviation of the blank. But just what does this mean? The problem, as already noted above, is one of signal and noise. If the signal is so low or small that it can't be distinguished from the noise, then it is not detectable. In spectrochemistry, the noise is due to the spect...
In the measurement process it is important to distinguish between these two ratios. First, the signal-to-noise ratio (S/N): Whether we consider a strip-chart recording, a wavelength scan (Figure 6), or repeated measurements made on the same sample, the noise is determined by the statistical fluctuations of the signal. The standard deviation is a me...
BEC and Sensitivity The sensitivity (S) was defined as the change in measured spectral line per unit concentration in equation 5. Note that this is just the inverse of the first term in equation 3a. Therefore, the relationship between the BEC and sensitivity is simply Or, using the conditions already noted above, (CL = 0, so that IL = IB , and DC <...
The concept of spectral background radiation and its quantification in the BEC is important in analytical atomic emission spectrometry, whether the excitation be by ICP, arc/spark, or XRF. For any given spectrometric system with a defined resolution and excitation condition, the BEC is a characteristic of the spectral lines. The LOD, however, depen...
An X-ray photon of energy E0 and momentum P = E0/c moving along the x axis collides with electron initially "at rest" at the origin (rest energy E = m0 c2). After the collision, the photon heads off at an angle a to the horizontal (x axis) and the electron goes off at an angle β. This is shown in Figure 3. The photon has an energy EF and momentum E...
Refer back to Figure 5 in the text above. Let the coordinates of the first point (lowest on curve) be (IL , CL ) and the second (IH , CH ). Because the equation of a straight line is y = mx + b, we can write CL = mIL + b and CH = mIH + b Subtracting the first equation from the second gives CH – CL = m(IH – IL ) or m = (CH – CL )/(IH – IL) = ΔC/ΔI S...
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