Chapter 1 - What is mass spec? Flashcards
First mass spec was created
by JJ Thomson in 1906.
The basic principle of MS is to
generate ions from inorganic or organic compounds, separate these ions by their m/z ratio, and detect them qualitatively and quantitatively by their m/z ratio and abundance.
An MS consists of
an ion source, a mass analyzer, and a detector.
MS can be regarded as practically nondestructive because
the amount of analyte needed is so small.
Y-axis
ordinate
X-axis
abscissa
Base peak
The most intense peak of a mass spectrum.
In most representations, the intensity of the base peak is normalized to
100% relative intensity.
Minimum amount of sample
1 attomol (10^-18 moles) = 6.022 X 10^5 molecules
Unified atomic mass (u)
1/12 mass of a single carbon-12 atom (same thing as Da)
Profile mode
Gaussian peaks
Centroid mode
Straight line vertical peaks
Total ion chromatogram (TIC)
Summation of peak intensities of each mass spectrum as successively acquired during analysis.
Extracted Ion Chromatogram (EIC)
A chromatogram created by plotting the intensity of the signal observed at a chosen m/z value or set of values in a series of mass spectra recorded as a function of retention time.
Sensitivity is defined as
the slope of a plot of analyte amount vs. signal strength.
Sensitivity units
C/ug for solids
A/Pa for gases
Limit of detection (LOD)
The smallest flow or the lowest amount of analyte necessary to obtain a signal that can be discerned from the background noise.
Signal to noise ratio (S/N)
describes the uncertainty of an intensity measurement.
Noise results from the
electronics of an instrument.
Noise is present
between the signals and also on the signals.
The reduction of noise is proportional to the
square root of acquisition time or number of single spectra that are averaged (reduced by a factor of 10 by averaging 100 spectra)
Signals are regarded to be clearly visible at S/N > or = to
10
S/N greater than 1000 means
that noise is essentially invisible in the spectral plot.
The abscissa of a mass spectrum is to be labelled only as
m/z
