Template:Scanning of spectra

Transcluded in ASMS 1981 and ASMS 1984

Mass spectrum

A spectrum obtained when a beam of ions is separated according to the mass-to-charge (m/z) ratios of the ionic species contained within it.

[Note : A quadrupole mass spectrometer achieves separation of the various ionic species in this way].

Momentum spectrum

A spectrum _obtained when a beam of ions is separated according to the momentum-to-charge ratios of the ionic species contained within it.

[Note: A sector magnetic field achieves separation of the various ionic species in this way. If the ion beam is homogeneous in translational energy, as is the case with sector instruments, separation according to the m/z ratios is also achieved].

Ion kinetic energy spectrum

A spectrum obtained when a beam of ions is separated according to the translational energy-to-charge ratios of the ionic species contained within it.

[Note : A radial electric field achieves separation of the various ionic species in this way].

Magnetic field scan

The usual method of producing a momentum (mass) spectrum in instruments.

Accelerating voltage (high voltage) scan

An alternative method of producing a momentum (mass) spectrum in magnetic deflection instruments. This scan can also be used, in conjunction with a fixed radial electric field to produce an ion kinetic energy spectrum.

Linked scan

A scan, l'.n an" instrument comprising two or more analysers, in which two or more of the analyser fields are scanned simultaneously so as to preserve a predetermined relationship between parameters characterising these fields. often, these parameters are the field strengths, but may also be the frequencies in the case of analysers in which alternating fields are employed_ ..

Linked scan at constant B/E

A linked scan at constant B/E may be performed on a sector instrument incorporating at least one magnetic sector plus one electric sector. It involves scanning the magnetic sector field-strength B and the electric sector field strength E simultaneously, holding the accelerating voltage V constant, so as to maintain the ratio B/E at a constant value. This constant value is determined by the ratio of the two field strengths which transmit main-beam ions of predetermined mass:charge ratio; these preselected main-beam ions are the precursor ions whose fragment-ion spectrum is required. The fragmentation reactions so observed occur in a field-free region traversed before the two sectors scanned in this way.

[Notes: This terms should not be used without prior explanation of the meanings of B and E.

The term "B/E linked scan" is not recommended. It may suggest that the ratio B/E varies during the scan].

Linked scan at constant E2/V

A linked scan at constant E²/V may be performed on a sector instrument incorporating at least one electric sector plus one magnetic sector. It involves scanning the electric sector field E and the accelerating voltage V simultaneously, so as to maintain the ratio E2/V at a constant value, equal to the value of this ratio which transmits the main beam of ions through the electric sector. The magnetic sector field is set at a fixed value such. that main-beam ions of a pre.determined mass:charge ratio are transmitted by the magnet; these preselected main.beam ions are the precursor ions whose fragment-ion spectrum is required. The fragmentation reactions so observed occur in a field-free region traversed before the two sectors scanned in this way.

[Notes : This term should not be used without prior explanation of the meanings of E and V.

The term "E2/V linked scan" is not recommended].

Linked Scan at Constant B2 /V

A linked scan at constant B2 /E may be performed on a sector instrument incorporating at least one electric sector plus one magnetic sector. It involves holding the accelerating voltage fixed, and scanning the magnetic field Band the electric field E simultaneously so as to maintain the ratio 82 /E at a constant value. This constant value corresponds to the ratio of the two fields which 'transmit main-beam ions of predetermined mass:charge ratio; these preselected main-beam ions are the fragment ions whose precursor-ion spectrum is required. The fragmentationreactions thus observed occur in a field-free region traversed before the two sectors scanned in this way.

[Notes : This term should not be used without prior explanation of the meanings of Band E. The term "B2 /Elinked scan" is not recommended] .

Linked Scan at Constant B l[ (E/E0)]l /E A 1 inked scan at constant B[l -(Ee/E0)]'/E may

be performed on a sector instrument incorporating at least one electric sector plus one magnetic sector. It involves holding the accelerating voltage fixed, and scanning the magnetic field Band electric field E simultaneously, so as to maintain the quantityB[l -(E/Eo)]l/E at a constant value. This constant value is equal to B3/E0 , where E0 and B3 are respectively the electric sector field and magnetic sector field required to transmit m; ions in the main ion-beam; me3 represents the mass (m1 -m2) of the selected neutral fragment whose precursor ion spectrum is required. The fragmentationreactions so observed occur in a field-free regio. traversed before the two sectors scanned in this way.

[Note: This term should not be used without prior explanation of the meanings of B, E and E0 .

The term "B [l -(E/E0)] '/E linked scan" is not recommended].

The above three definitions are merely examples of the types of linked scan that might be used. Any other linked scans can readily be defined inna similar manner.

Fixed Precursor Ion Scans

1. Mass Selection followed by Ion .Kinetic Energy Analysis

If a precursor (parent) ion is selected, for example by a magnetic sector, all product ions formed from it in the field-free region between the magnetic sector and a following electric sector can be identified by scanning an ion kinetic energy spectrum.

2. Linked Scan at Constant B/E or at Constant E2 /V

Both of these linked scans give a spectrum of all product (daughter) ions formed from a preselected precursor (parent) ion.

Fixed Product-Ion Scans

1. High Voltage Scan.

2. Linked Scan at Constant B2/E.

Both 1. and 2. give. a spectrum of all precursor (parent) ions that fragment to yield a pre-selected product (daughter) ion.

Fixed Neutral Fragment Scans 1 The linked scan at constant B[l -(E.'E0)]'/E gives a spectrum of all product (daughter)ions that have been formed by loss of a pre-selected neutralfcagment from any precursor(parent) ions.

[Note : The above definitions. have all been given with reference to sector instruments; linked scans to give similar information have also been devised for instruments incorporating one or more quadrupoles].

2E Mass Spectrum Processes of the partial charge-transfer type 2+ + N+

m + N . m + occurring in a collision cell (containing a gas, N) located in a field-free region preceding a magnetic and electric sector combination placed in either order, may be detected as follows.

If the instrument slits are wide, and if the electric sector field Eis set to twice the value required to transmit the main ion-beam, the only ions to be trans.mitted will be those with a kinetic energy/charge ratio twice, or almost exactlytwice, that of the main ion-beam. The product ions of the process shown fulfill this condition. If the magnetic field Bis scanned, a mass spectrum of such singly.charged product ions, and thus of their doubly-charged precursors, is obtained. Such a spectrum is called a 2E mass spectrum.

E/2 Mass Spectrum Processes of the charge-stripping type

m+ + N → m2+ + N + e- occurring in a collision cell (containing a gas N) located in a field-free regionpreceding a magnetic and electric sector combination placed in either order, may be detected as follows. If the instrument slits are wide and if the electric sector field Eis set to half the value required to transmit the main ion-beam, the only ions to be transmitted will be those with a kinetic energy/charge ratio half, or almost exactly half, that of the main ion-beam. The product ions of the charge-stripping process fulfill this condition. If the magnetic field Bis scanned, a mass spectrum of such doubly-charged product ions, and thus of their singly-charged precursors, is obtained. Such a spectrum is called an E/2 mass spectrum.

. [Note Interference from product ions from processes of _the type + m1 + -m2) where m2 . 0.5 m1, can arise in E/2 mass spectra]. Charge Inversion Mass Spectrum Charge inversion processes of the types or m-+ N → m+ + N + 2e. respectively, occurring in a collision cell (containing a gas, N) located in a field.fr_ee region preceding a magnetic and electric sector combination placed in either order, may be detected as followsn.

If the instrument slits are wide, and if the connections to the two sectors, appropriate to transmission of either positive or negative main-beam ionS, are simply reversed, the negative or positive product ions of the two processes,respectively, will be transmitted. If the magnetic field is scanned, a spectrumof such product ions will be obtained, and this spectrum is called a charge-inversion mass spectrum. These spectra are sometimes referred to as -E and +Enspectra, respectively.

[Note : The terms "2E, E/2, -E or +E mass spectrum" should not be used without priorexplanation of the meaning of 2E, E, +E or -E]n.