Definitions Flashcards
What is absolute error
AE= measured value-true value
What is relative error and the equation
Compares absolute error to the accepted value
RE=AE/true valuex100%
What is an analyze
The substance that needs to be detected/identified or quantified during analysis
What is a bias and what does it affect, and sometimes referred to
The difference between the mean test result and an accepted value
Affects accuracy
Sometimes referred to total systematic error and either positive or negative
What is a blank and where does it come from
Accounts for traces of analyte or another compound that interferes with your analyte
Can come from field, storage and analysis
What are the two types of blanks (3 for each)
Non laboratory
- trip
- field
- equipment
Laboratory
-reagent
-instrumental
-method
What’s a trip blank
Contamination from shipping to and from the lab
Originates from laboratory
What is a field blank
Cross contamination during sampling
Analyzed in lab as a real smple
What’s an equipment blank
Cross contamination during sampling by assessing the effectiveness of decontamination procedures
Analyzed as a real sample
What’s a reagent blank
Contamination of samples by reagents used to process them
What’s a method blank
Sample containing all components except analyzed of interest
What’s a calibration curve
A chemical or physical signal that is proportionate to the amount of analyte in the sample
Shows how the analyte signal changes with the concentration of the analyte
Usually a linear relationship
What’s certified reference material
Material that has had a specific analyte content assigned to it
Assigned concentration is usually the mean value determined from the analyses by many laboratories
What is the detection limit
Detection limit of an analytical procedure is the smallest amount of analyte in a sample that can be detected with confidence\
What is the limit of detection (LOD) and equation
The amount of analyte that is required to produce a signal greater than a prescribed quantity of noise
LOD= Sblank+3x noise
Noise/standard deviation of noise
What is the limit of quantitation (LOQ) and equation
Smallest amount of analyte in a sample that can be quantativley determined with suitable precision and accuracy
LOQ= Sblank +10 x standard deviation of noise
Instrumental detection limit and the equation (ADL)
How to detect it
Smallest amount of analyte that an instrument can detect
Aka. Analytical detection limit
Use analytical standards of analyte and determine how much analyte you can detect with a reasonable degree of certainty
Three types of errors and what they effect
Systematic- affects accuracy, determinate
Random- affects precision, indeterminate
Gross- affects precision and accuracy
What is a systematic error, what is it referred to, can it be identified
Can be identified
A reoccurring error that always has the same sign and magnitude for a given measurement
Referred to as a bias. Constantly misses the true value in the same direction
What’s a random error, can it be identified
Cannot be readily identified
Accounts for variability of individual measurements
Fluctuates in sign and magnitude
Measures of dispersion around central mean value and represented by standard deviation of repeated measurements
What is a gross error
Lab blunders
Recording, calibration errors and contamination
Outliers in data may be an symptom of mistake
Invalidate a good set of data
Linearity
Ability of an analytical procedure to obtain signals that are directly proportional to the amount of analyte in a sample
Method
Application of a technique for a specific analyte in a specific matrix
Interference and what does it cause
A chemical that contributes to the measured signal of the analyte
Causes systematic error in analytical results
What is an interlaboratory test
A series of measurements on an analyte preformed independently by a number of labs on samples of a given material
Material is first homogenize and portions of the homogenization are distributed to participating laboratories
What are performance characteristics
Functional quality that can be attributed to an analytical method
What is proficiency testing and who usually conducts it
Labs analyzing the same samples by their own methods, it assesses the reproducibility of methods
Usually conducted by an international organization, the international standard organization (ISO)
What is recovery and when is it determined and how
The percent of true concentration recovered during an analytical procedure
Determine during method validation
Determined by fortifying an analogue of the analyte into the sample prior to extracting and the analogue must have similar chemical properties as the analyte
What is range
Concentration interval over which linearity, accuracy and precision are all acceptable
What is repeatability
Precision where independent test results are obtained with the same method.
What is replicates
Multiple determinations conducted on identical test portions from one test sample by one laboratory using the same method
What is reproducibility
Precision where independent test results are obtained with the same method on identical test items in different lab, with different operators using different equipment
What is robustness and what does it include
Measure of capacity of procedure to remain unaffected by small but deliberate changes in method parameters
Includes temperature, pH, reagents, and sample storage
What is specificity and when is something specific
Ability of a method to distinguished between the analyte being measured and other substances
Specific if the method only responds to the analyte if interest and not affected by other substances
What is selectivity
If the method responds primarily to the analyte of interest and is little affected by other substancesa
What is sensitivity and how to measure it
The ability to demonstrate that 2 samples have different amounts of analyte
To measure the ability that such differences are signifigant
What is method validation and what comes before and after it
The process of determining the suitability or fit for purpose of an analytical method for providing meaningful analytical data
Method development- method validation- method implementation
Why do we need good quality data (4)
- poor lab data is of little value
- Accurate data is important to public health and safety
- Important for global regulation of man made chemicals
- Lab data is important in litigation
