Unit 1 Flashcards
assay
- process of determining amount of analyte in sample
analyte
- chemical substance being measured
signal
- observable change in some property
Advantages of visual detection
- low cost and maintenance
Disadvantages of visual detection
- subjectivity affects accuracy/precision
- may not be very sensitive
- may require large sample volumes
- often time-consuming
voltage
- electrical potential energy between two points
current
- rate of flow of charge past a point in a circuit (usually electrons moving)
transducer
- device that converts input stimulus into electrical output
Advantages of electrical detection
- objective
- often very sensitive
- often faster
- can analyze smaller sample sizes
Disadvantages of electrical detection
- high cost/maintenance
- calibration required
analog signal
- “real world”
- takes on any value
- transducer input signal
digital signal
- computer world
- recorded as bits
- discrete values
signal
-a measured quantity that is correlated to the amount of analyte
noise
- unwanted variation in a measured quantity
- often takes the form of random fluctuations in a measured signal
signal-to-noise ratio (S/N)
- the magnitude of the signal divided by the magnitude of the noise
- similar term: signal-to-background ratio
detection limit
-the amount of analyte that corresponds to a signal just greater than the mean of the background plus three standard deviations of its noise
background
-an approximately constant signal, measured in the absence of analyte
How can you increase S/N ratio?
- multiple scans
- signal averaging
Determine how many more scans are required to achieve a S/N ratio of 2?4?9?
N=4,16,81
Blank
- a measured sample that lacks the analyte
- contains solvent, reagents, etc. used in the analysis
sample matrix
- all the components of a sample except the analyte
- blank tries to approximate the sample matrix
positive control
- a standard sample that contains a known quantity of the analyte of interest
- prevents false negative results
negative control
- a standard sample that does not contain any analyte
- prevents false positive results
interference
a specific chemical substance in a sample matrix that causes a systematic error in a measured quantity