Instrumental Ch1-3,5

Data Domain
way of encoding an Analytical response in electrical or non electrical signals
Detector
device that indicates change in environment
Transducer
device that converts non electrical signals to electrical data
Sensor
device that is capable of monitoring a specific chemical species continuously and reversibly
Examples of non electrical domains
light, color, scale position, number(objects)
Examples of electrical domains
current, voltage, charge, frequency
Analog domains
record the magnitude of electrical quantities
Time domains
record things that vary with time frequency, phase, pulse width
Digital domains
record discrete values count,serial, parallel
Precision
is a measure of random of indeterminate error associated with an analysis
Accuracy
measure of determinate errors (operator, method)
Detection limit
the minimum concentration or mass of analyte that can be detected at a known confidence level-which is dependent on the ratio of magnitude of analyte signal to the size of the statistical fluctuations of the blank
Figures of merit
A numerical quantity based on one or more characteristics of a system that represents a measure of the systems efficiency or effectiveness
On a calibration plot the ________ the slope the more sensitive the machine
Higher
Two things that can limit sensitivity
slope of the calibration curve and the reproducibility or the precision of the measure device
Selectivity
degree at which the method is free from interference by other species in the sample matrix
Circuit
a closed path that may be followed by and electrical current
Kirchhoff’s current law
sum of current around any point in a circuit is zero
Kirchhoff’s voltage law
sum of voltages around closed electrical loop is zero
Power
the amount of work done by an electrical current
Voltage divider
a device that provides potentials that are variable functions of an input voltage
Potentiometer
a device that provides potential that’s continuously variable
A/D converter
a device that converts the input analog signal to a number proportional to the magnitude of input voltage
Sinusoidal wave
the most common periodic electrical signal
Dielectric
A substance that contains no current carrying or charged species, it resists a change in voltage
Impedance
expression which in applied to any electrical system which impedes the flow of current
Operational Amplifiers
a device used in precise measurement of voltage, current, and resistance- can also be used to provide a constant current and constant voltage
Feed back circuit
A special type of OP amp- the output signal is connected to one of its inputs reading a signal feed back
Signal
Gives you information about your analyte
Noise
degrades accuracy and precision -can limit amounts of analyte detected
Chemical noise
A type of noise that is caused by temperature, pressure variations, changes in humidity, and light
Types of Instrumental noise
Thermal noise, Shot noise, Flicker noise
Thermal noise
a noise that is random and periodically produces voltage fluctuations that appear as readout noise
Thermal noise is dependent on what? and independent on what?
dependent on frequency bandwidth independent of frequency
Thermal noise is also known as
white noise or Johnson noise
Shot noise
A noise that is caused when electrons or other charge particles cross a junction
Flicker noise
A noise whose cause is not understood but is characterized by the fact that its magnitude is inversely proportional to the frequency of the signal observed
Environmental noise
a noise that occurs when parts of the instrument act as an antenna which can pick up electromagnetic radiation and convert it to an electrical signal
Ways to improve signal to noise
Analog filtering, Modulation, signal chopping, lock in amplifiers, various software programs…… add math ways
Analog filtering
uses a low pass filter to remove high frequency components of the signal- this includes thermal and shot noise
Modulation
a process where the signal is either brought up or down- in an effort to separate it from noise- the noise filtered out and then the signal brought back to its original place
Signal chopper
Converts the signal into a square wave
lock in amplifiers
can be used when the S/N ratio is bad- but requires a reference signal with the same frequency and phase to work