Exam 1 Study Guide Flashcards
Transducer
Devices that convert information from no electrician domains to information in electrical domains and the converse
Detector
a mechanical, electrical or chemical device that identifies, records, or indicates a change I one of the variables in its environment, such as pressure, temperature, electrical charge, electromagnetic, radiation, nuclear radiation, particulates, or molecules.
Sensor
class of analytical instruments that are capable of monitoring specific chemicals species continuously and reversibly (PH electrode, ion selective electrodes)
Precision
Refers to how close two or more measurements are to each other, regardless of whether those measurements are accurate or not.
Bias
Is a quantitative term describing the difference between the average of measurements made on the same object and its true value
Accuracy
Refers to how close a measurement is to its standard known value
Random errors
(indeterminate error) caused by uncontrollable variables, which can not be defined/eliminated but can
Systematic errors
(determinate error) has a definite value and as assignable cause and are of the same magnitude for replicate measurements made in the same way. This error leads to bias, is reproducible and can be discovered and corrected.
Sensitivity
the detector is a measure of its ability to discriminate between small differences in analyte concentration. It is actually the slope of the calibration curve. It is also dependent on the standard deviation of the measurement
Selectivity
refers to the extent to which a method can determine particular analytes in mixture or matrices without interferences from other components.
Dynamic range
the concentration range between the LOQ and LOL
Detection limit
is the lowest quantity of a substances that can be distinguished from the absence of that substance (a blank value) with a stated confidence level (generally 99%)
2) Be familiar with and be able to discuss the issues involved in selecting an appropriate analytical method for a proposed analysis.(section 1E)
- What accuracy is required?
- How much sample is available?
- What is the concentration range of the analyte?
- What components of the sample might cause interference?
- How many samples are to be analyzed?
- Vital importance because it determines how much time and care will be needed for the analysis
- Determine how sensitive the method must be and how wide the range of concentrations must be accommodated.
- Same as above.
- Determines the selectivity require of the method
Important because some analytical methods in table 1-1 are applicable to solutions (usually aqueous) of the analyte. Other methods are more easily applied to gaseous samples and still other methods are suited to the direct analysis of solids.
The number of samples is important consideration from an economic standpoint, if number is large, considerable time and money can be spent on instrumentation, method development and calibration.
Be able to discus the various calibration methods and when would it be most appropriate to use each.
a. External standard - prepare separately from the sample; assume no matrix interference or instrumental drift. This can be used to calibrate instruments and procedures when there are no interference effects from matrix components in the analyte solution.
b. Internal standard – used to compensate for instrumental drift; something that would not be expected to be found in the sample. A substance that is added in a constant amount to all samples, blanks, and calibration standards in an analysis. IF properly chose and used, can compensate for several types of both random and systematic error.
c. Standard additions – used to compensate for matrix interference; calibration standards are prepared in sample itself. USEFUL for analyzing complex samples in which the likelihood of matrix effects is substantial. “spiking”
Be able to discuss types various types of errors (random and systematic) and how to detect and correct for them.
a. Instrumental: caused by nonideal instrument behavior, faulty calibrations or by use under inappropriate conditions. Detected/Corrected: calibration with suitable standards.
b. Personal: introduced into a measurement by judgements the experimentalist has to make (ex: include reading a pointer, reading color change) Most personal errors can be minimized by care and self-discipline.
c. Method: often introduced from nonideal chemical or physical behavior of reactions and regents on which the analysis is based
