Sensitivity Versus Detection Limit - For The Better
Sensitivity Versus Detection Limit
Technical Note
Atomic Absorption
The earliest atomic absorption (AA) spectrometers provided results in terms of percent absorption (%A = 100 ? %T). Those early instruments were significantly less stable than today's modern equipment, and virtually all analyses were performed with no scale expansion. For most elements, the smallest concentration which could be detected was that which produced a percent absorption signal of about 1%A (0.0044 absorbance units) which became accepted as a rough measurement of performance known as "sensitivity", a term used with emission spectroscopy and other techniques. However, improvements in AA systems soon permitted the use of high degrees of scale expansion, allowing the determination of concentrations much lower than that represented by the sensitivity value. The term "detection limit" was coined to mean the lowest concentration that could be detected by atomic absorption.
The change in the terminology used to describe the smallest detectable quantity by AA had an unfortunate side effect ? the frequent (and erroneous) interchangeable use of the terms "sensitivity" and "detection limit".
The difference between sensitivity and detection limit Sensitivity is a measure only of signal magnitude, the solution concentration or weight of an element that produces a signal of 0.0044A (1%A) for continuous or peak height measurements or 0.0044 A?s for integrated peak area. It is also known as characteristic concentration with flame AA or characteristic mass with furnace AA.
Detection limit is a measure of the smallest concentration which can be determined with a specified precision or reproducibility. Most frequently, the specified precision is defined in terms of the concentration producing a signal equivalent to three times the standard deviation of a series of blank (baseline) readings or readings for a standard with a concentration close to the anticipated detection limit. This definition is equivalent to a 99% confidence level. That is, the answer obtained under these conditions will be correct 99 times out of 100.
As defined, the detection limit is a function of both signal strength (or sensitivity) and signal stability.
For a visual representation of the difference between sensitivity and detection limit, refer to the signals below. Signals A and B represent the same concentration and give comparable absorbances or signal (S). The sensitivities are, therefore, the same. However, the better signal stability or
lower "noise" level (N) of signal B will provide better reproducibility (precision) and allow smaller concentrations to be accurately measured. Signal B will provide better precision and detection limits because it has a better (i.e., higher) signal-to-noise ratio (S/N).
Greater sensitivity alone will not provide better detection limits or precision as illustrated by signals C and D, which again are for the same concentration. The system which produced signal C provided twice the signal or sensitivity of that which produced signal D but also generated twice the noise level. The signal-to-noise ratios for the two signals are therefore the same (S/N = 8 for each). As a result, performance should also be the same for the two systems.
Sensitivity alone cannot be related to system performance, since it is only an indication of signal strength. Detection limits are direct indicators of system performance, since both detection limits and performance are functions of the signalto-noise ratio.
PerkinElmer, Inc. 940 Winter Street Waltham, MA 02451 USA P: (800) 762-4000 or (+1) 203-925-4602
For a complete listing of our global offices, visit ContactUs
Copyright ?2004-2011, PerkinElmer, Inc. All rights reserved. PerkinElmer? is a registered trademark of PerkinElmer, Inc. All other trademarks are the property of their respective owners.
006953A_01
................
................
In order to avoid copyright disputes, this page is only a partial summary.
To fulfill the demand for quickly locating and searching documents.
It is intelligent file search solution for home and business.
Related download
- sanitizing and disinfecting is there a difference
- the facts differences between pex a b and c
- the difference between different and better
- mandatory and best efforts committing two great
- blanket insurance coverage vs specific coverage
- choosing between a ppo and hmo dental plan los angeles
- sensitivity versus detection limit for the better
- understanding best s credit ratings
- maximize the value of your enterprise application delivery
Related searches
- for the better synonym
- legal limit for alcohol
- income limit for va healthcare
- what is the legal limit for alcohol
- what is the income limit for medical
- drug detection chart for urine
- income limit for fafsa
- parent income limit for fafsa
- income limit for obamacare 2019
- income limit for pell grant
- weight limit for nexplanon use
- max 401k wage limit for 2020