Method for evaluating data from mass spectrometry, mass spectrometry method, and MALDI-TOF mass spectrometer
View Patent ↗The invention relates to a method to evaluate mass spectrometry data for the analysis of peptides from biological samples, particularly MALDI-TOF mass spectrometry data, comprising the steps of: providing expected mass defects; determining measured mass defects, i.e. the mass defects resulting from the mass spectrometry data; and comparing the measured mass defects with the expected mass defects.
1. Method for evaluating mass spectrometry data for the analysis of peptides from biological samples, the method comprising:
a) providing expected mass defects;
b) determining measured mass defects resulting from the mass spectrometry data;
c) determining discrepancies between the measured mass defects and the expected mass defects;
d) determining an actual variance of the discrepancies about a mean thereof; and
e) comparing the actual variance with a defined acceptable variance, an interval of which is formed by limit values
d p 1,2 ( m )=±μ√{square root over ( v ( m ))}
where
v
(
m
)
=
σ
P
2
(
m
)
+
Δ
m
(
m
)
2
1
2
and σ P (m N )=σ 0 +s P m N , where σ 0 ≈0.02 and s P ≈2.0×10 −5 ,
and Δm(m) designates a width of m/z bins at a mass position m,
and m/z bins represent intervals resulting from a discretization of the mass axis,
and μ>0 provides a scaling factor,
and wherein discrepancies data are rejected as defective when the actual variance of the mass defect discrepancies is outside the interval thus specified.
2. The method according to claim 1 , wherein the mass spectrometry data are MALDI-TOF mass spectrometry data.
3. The method according to claim 1 , wherein interquartile ranges of the ascertained discrepancies are determined over subintervals of a mass axis in order to determine the actual variance of the mass defect discrepancies, and wherein discrepancies data are rejected as defective when a limit value of the actual variance is exceeded.
4. The method according to claim 1 , further comprising using at least one of calculatory and visual means in order to assess a quality of the data on a basis of the comparison in step e).
5. The method according to claim 1 , wherein a mass range with a recognizable peptide signal is determined as a totality of subintervals of a mass axis for which a quotient of the actual variance and a maximum permissible variance d P (m) does not exceed a specified threshold value t, and discrepancies data are rejected as defective when a limit value for a lower or upper limit of said mass range or its extent is exceeded or not reached.
6. Method for evaluating mass spectrometry data for the analysis of molecules, which contain the five chemical elements carbon, hydrogen, oxygen, nitrogen and sulfur, from biological samples, the method comprising:
a) providing expected mass defects;
b) determining measured mass defects resulting from the mass spectrometry data;
c) determining discrepancies between the measured mass defects and the expected mass defects;
d) determining an actual variance of the discrepancies about a mean thereof; and
e) comparing the actual variance with a defined acceptable variance an interval of which is formed by limit values
d p 1,2 ( m )=±μ√{square root over ( v ( m ))}
where
v
(
m
)
=
σ
P
2
(
m
)
+
Δ
m
(
m
)
2
1
2
and σ P (m N )=σ 0 +s P m N , where σ 0 is a constant and s P is a scaling factor,
and Δm(m) designates a width of m/z bins at a mass position m,
and m/z bins represent intervals resulting from a discretization of the mass axis,
and μ>0 provides a scaling factor,
and wherein discrepancies data are rejected as defective when the actual variance of the mass defect discrepancies is outside the interval thus specified.
7. The method according to claim 6 , wherein the mass spectrometry data are MALDI-TOF mass spectrometry data.
8. The method according to claim 6 , wherein interquartile ranges of the ascertained discrepancies are determined over subintervals of a mass axis in order to determine the actual variance of the mass defect discrepancies, and wherein discrepancies data are rejected as defective when a limit value of the actual variance is exceeded.
9. The method according to claim 6 , wherein a mass range with a recognizable biological molecule signal is determined as a totality of subintervals of a mass axis for which a quotient of the actual variance and a maximum permissible variance d P (m) does not exceed a specified threshold value t, and discrepancies data are rejected as defective when a limit value for a lower or upper limit of said mass range or its extent is exceeded or not reached.
10. The method according to claim 6 , further comprising using at least one of calculatory and visual means in order to assess a quality of the data on the basis of the comparison in step e).
11. The method according to claim 6 , wherein the method is used for one or more of (i) quality control and (ii) signal correction of the mass spectrometry data.
12. The method according to claim 6 , wherein m/z values or molecular mass are used in daltons (Da) as a multiple of the atomic mass unit (amu).
13. The method according to claim 6 , wherein the biological samples are tissue samples.
14. The method according to claim 13 , wherein the tissue samples (i) are tissue sections or (ii) comprise tissue cells.
15. A mass spectrometer having an ionization mechanism, a mass analyzer and a control unit for the analysis of biological molecules from biological samples using a method according to claim 6 .
16. The mass spectrometer according to claim 15 , wherein the mass analyzer is a time-of-flight (TOF) analyzer.
17. The mass spectrometer according to claim 15 , wherein the ionization mechanism is a matrix-assisted laser desorption ionization (MALDI) source.