Probability-Based Library Search Algorithm (ProLS)

Patent metadata

Field	Value
Publication number	US-2018166264-A1
Application number	US-201615576875-A
Country	US
Kind code	A1
Filing date	May 26, 2016
Priority date	Jun 18, 2015
Publication date	Jun 14, 2018
Grant date	—

Abstract

One or more known compounds of a sample are ionized. At least one precursor ion corresponding to a compound of the one or more known compounds is selected and fragmented, producing a product ion mass spectrum for the precursor ion. An m/z tolerance probability function that varies from 1 to 0 with increasing values of an m/z difference between two mass peaks and that includes one or more values between 1 and 0 is received. A library product ion mass spectrum for the at least one compound is retrieved from a memory. An m/z difference between at least one experimental product ion mass peak in the product ion mass spectrum and at least one library product ion mass peak in the library product ion mass spectrum is calculated. An m/z tolerance probability that determines if the two peaks are corresponding peaks is calculated from the m/z difference using the probability function.

First claim

What is claimed is:

1 . A system for determining corresponding mass peaks in experimental and library product ion spectra using a mass-to-charge ratio (m/z) tolerance probability function with values between 1 and 0, comprising:
an ion source that ionizes one or more known compounds of a sample, producing an ion beam of precursor ions; a tandem mass spectrometer that receives the ion beam from the ion source and that selects at least one precursor ion from the ion beam corresponding to at least one compound of the one or more known compounds and fragments the at least one precursor ion, producing a product ion mass spectrum for the at least one precursor ion; and a processor in communication with the tandem mass spectrometer that
receives the product ion mass spectrum from the tandem mass spectrometer,
receives an m/z tolerance probability function that varies from 1 to 0 with increasing values of an m/z difference between two mass peaks and that includes one or more values between 1 and 0,
retrieves from a memory a library product ion mass spectrum for the at least one compound,
calculates an m/z difference between at least one experimental product ion mass peak in the product ion mass spectrum and at least one library product ion mass peak in the library product ion mass spectrum,
calculates an m/z tolerance probability, (p m/z ) 1 , from the m/z difference using the m/z tolerance probability function, and
determines if the at least one experimental product ion mass peak and the at least one library product ion mass peak are corresponding peaks based on the m/z tolerance probability, (p m/z ) 1 .

2 . The system of claim 1 , wherein the processor further calculates a score for a comparison of the product ion mass spectrum and the library product ion mass spectrum that includes calculating a product of the m/z tolerance probability, (p m/z ) 1 , an intensity of the at least one experimental product ion mass peak, U 1 , and an intensity of the at least one library product ion mass peak, L 1 .

3 . The system of claim 2 , wherein the processor calculates the score using (p m/z ) 1 , U 1 , and L 1 and any other (p m/z ) i , U i , and L i according to:

score
=

100

%
×

(

∑



(

p

m
/
z

)

i



U
i



L
i

)

2

∑



U
i



U
i

×

∑



L
i



L
i

where U i is the intensity of ith unknown or experimental peak, L i is the intensity of ith library peak, and (p m/z ) i is probability that two peaks with intensities U i and L i are corresponding peaks.

4 . The system of claim 3 , wherein U i and L i include a weighting factor or are transformed mathematically from the original values measured by the mass spectrometer.

5 . The system of claim 1 , wherein the processor further
receives an intensity ratio threshold probability function that varies from 1 to 0 with increasing values of a ratio of intensities of two mass peaks and that includes one or more values between 1 and 0, calculates an intensity ratio from an intensity of the at least one experimental product ion mass peak and an intensity of the at least one library product ion mass peak, calculates an intensity threshold probability, (p ratio ) 1 , from the intensity ratio using the intensity ratio threshold probability function, and modifies an intensity, U 1 , of the at least one experimental product ion mass peak or an intensity, L 1 , of the at least one library product ion mass peak based on the intensity threshold probability, (p ratio ) 1 .

6 . The system of claim 5 , wherein the processor modifies the intensity, L 1 , of the at least one library product ion mass peak according to
modified L 1 =L 1 +( p ratio ) 1 ×( U 1 −L 1 ).

7 . The system of claim 6 , wherein the processor further calculates a score for a comparison of the product ion mass spectrum and the library product ion mass spectrum using modified L 1 , and any other modified L i according to:

score
=

100

%
×

(

∑



(

p

m
/
z

)

i



U

i


Assignees

• Dh Technologies Dev Pte Ltd

Inventors

• Burton Lyle Lorrence
• Ivosev Gordana

Classifications

• H01J49/0036 Primary

  Step by step routines describing the handling of the data generated during a measurement · CPC title

• H01J49/0072

  by ion/ion reaction, e.g. electron transfer dissociation, proton transfer dissociation · CPC title

• G06F19/709

  Physics · mapped topic

• H01J49/004

  Combinations of spectrometers, tandem spectrometers, e.g. MS/MS, MSn · CPC title

• G16C20/90

  Programming languages; Computing architectures; Database systems; Data warehousing · CPC title