.Accuracy and Precision.
10 measurements, with
concentration of 12
ppm, yet with <10%
Precise Not Accurate
with an average
concentration of 12
ppm and with
Not Accurate and
Terms and Definitions
Several Current References on terms and
definitions for analytical methods
Need to understand GLP (Good Laboratory
All analytical methods used for defining analyte
concentrations of significance are moving
toward GLP st
How to avoid some of the pitfalls
with calibration curves
Calibration curves must appropriately reflect the
analyte concentration range of interest in the
Develop the calibration curve with more evenly
spaced data points.
Include a number of repea
The overall aim of this course is
to develop an understanding of
the fundamental aspects of
analytical chemistry used in
Target analyte extraction and
Chromatography and detectors
A Look At Calibration Curves:
Does r adequately indicate linearity in a
linear least squares regression?
resp y int
R is often used to describe linearity, but
be very careful, since extreme bias can
be realized at low concentrati
.Noise and Detection Limit.
ACS - basic definition of detection limit (see
equation below). The ACS approach is generally
accepted; however, it has numerous limitations
which we will explore. Note that k is usually taken
Significant effort is made to understand the
contribution of noise on the signal from a target
Chapter 5 (Skoog) brings us into the next level of
understanding noise, how to manage it, and how to
pull out signals from what would otherwise
Data are stored as a series of numbers-encoded as
either 0 or 1, also ON or OFF.
Useful Electrical Terms
kg m 2
A2 s 3
Assumes that noise is random, and that the signal varies
slowly with time.
Average of a small number of adjacent data points, yields
a response this is better than 1 point. (Nyquist Sampling
to Remove Nois
This operational amplifier uses negative feedback.
It has the effect of making the Gain of the circuit
independent of the OP AMP (proof later).
Output is 180 out of phase with input.
Point S is t