.Accuracy and Precision.
ppm
15-
105-
ppm
15-
105-
10 measurements, with
an average
concentration of 12
ppm, yet with <10%
RSD.
Precise Not Accurate
10 measurements,
with an average
concentration of 12
ppm and with
>20% RSD.
Not Accurate and
Not Precise
2
Terms and Definitions
Several Current References on terms and
definitions for analytical methods
Need to understand GLP (Good Laboratory
Practices)
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
sample.
Develop the calibration curve with more evenly
spaced data points.
Include a number of repea
Course Objectives
The overall aim of this course is
to develop an understanding of
the fundamental aspects of
analytical chemistry used in
toxicological considerations:
Target analyte extraction and
concentration
Chromatography and detectors
Mass spec
31
32
A Look At Calibration Curves:
Does r adequately indicate linearity in a
linear least squares regression?
Y
mx b
Conc
resp y int
slope
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
as 3.
Minimum
Distinguishable
Anal
Summary
Significant effort is made to understand the
contribution of noise on the signal from a target
analyte.
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
Binary Code
Data are stored as a series of numbers-encoded as
either 0 or 1, also ON or OFF.
71
Useful Electrical Terms
Resistance
Current
Voltage
Capacitance
Energy
Power
kg m 2
Ohms
Amps
A2 s 3
A
(Charge/sec)
Volts
Farads
Joules
Watts
Coil (Induc
Boxcar Averaging
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
Theorem).
81
Hardware Techniques
to Remove Nois
CLOSED LOOP
Operational Amplifiers
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.
Rf
vi
Ri
ii
if
S
is
+
vo
Point S is t