At least one molecule is ionized and a mass spectrometer mass analyzes an m/z range, producing an m/z mass spectrum. A range of N sequential charge states is received. A copy of the m/z mass spectrum is created for each of the N charge states, producing N m/z spectra. Each spectrum of the N spectra is converted to a neutral mass mass spectrum using a different charge state of the N charge states, producing N neutral mass mass spectra. The N neutral mass mass spectra are aligned by neutral mass. When two or more spectra of the N neutral mass mass spectra corresponding to two or more different and sequential charge states include a neutral mass peak above a predetermined intensity threshold at a neutral mass value within a predetermined neutral mass tolerance, the neutral mass value is identified as a neutral mass of the at least one molecule.

Methods for quantitation of fC1-INH from dried blood spot are provided herein. Such methods may comprise spotting and drying a blood sample on a support member, extracting protein from the dried blood sample and measuring the level of fC1-INH in the extracted proteins.

The present disclosure relates to a method of analyzing a sample comprising a hydrophobic molecule. The method includes preparing an aqueous solution comprising the sample. The method also includes placing the solution in contact with a polypropylene substrate having a deactivated surface that reduces adsorption of the hydrophobic molecule relative to a polypropylene substrate that has not been deactivated. The method also includes analyzing the sample.

Provided herein are methods and systems directed to stable, isotopically labeled internal calibrators for use in mass spectrometry analysis for quantifying a target analyte in a sample. The present disclosure relates more particularly to mass spectrometry analysis where a single sample includes at least three isotopically labeled internal calibrators and the target analyte. The methods and systems described herein allows accommodation of isotope interferences arising from the use of isotopically labeled internal calibrators in quantification a target analyte. As a result, smaller quantities (e.g., lesser concentration) of isotopically labeled internal calibrators are utilized in the present technology in the generation of a calibration curve to quantify a target analyte.

The present invention generally pertains to methods of identifying and characterizing host cell proteins. In particular, the present invention pertains to the use of size exclusion chromatography in non-denaturing or denaturing conditions to enrich a sample for host cell proteins and characterize the binding of host cell proteins to a protein of interest.

Provided is a method for simultaneously detecting Vitamin K1 and Vitamin K2 in traces of blood. The method includes: constructing a two-dimensional liquid chromatography-tandem mass spectrometer, establishing an analytical method, and detecting at least three mixed standard solutions using the constructed two-dimensional liquid chromatography-tandem mass spectrometer to obtain a first detection result; fitting standard curve equations respectively corresponding to Vitamin K1 and Vitamin K2; and mixing and centrifuging a blood sample to which an extraction reagent and a certain amount of internal standard substance are added, collecting a supernatant, blowing the supernatant to dry with nitrogen, redissolving the residue, and detecting the dry supernatant using the constructed two-dimensional liquid chromatography-tandem mass spectrometer to obtain a second detection result. In this manner, concentrations of Vitamin K1 and Vitamin K2 in the blood sample are obtained.

A detection system for the interaction between known molecules and proteins based on covalent connection and an identification or verification method thereof are disclosed. The detection system comprises: a) streptavidin-short peptide tetramer; b) PafA enzyme; and c) Biotin-modified known molecules. After a known molecule interacts with a protein, streptavidin-short peptide tetramer can efficiently capture interacting proteins of known molecules under mild conditions. Then, under the catalysis of PafA enzyme, the interaction between short peptides and known molecules is made into protein covalent binding, so that the non-covalent binding between known molecules and proteins is converted into covalent binding between streptavidin and protein, and then analysis, separation and identification are carried out. This method can capture weak interaction and instantaneous interaction on the basis of keeping the natural structure of known molecules, which can be used to verify and discover known molecules and interacting proteins.

Systems, computer-readable media, and methods using mass spectrometry to analyze a sample are provided. For example, a method includes: acquiring a precursor ion spectrum; analyzing the precursor ion spectrum to identify precursor ions that preliminarily match one or more peptides that each belong to at least one protein of interest for the analysis; selecting each of the identified precursor ions in an order according to a ranking protocol for maximizing the number of proteins that are identified in the sample; for each selected precursor ion: acquiring a corresponding product ion spectrum, determining whether the acquired product ion spectrum matches one of the peptides that belong to the set of proteins of interest, and identifying a matched peptide as being present in the sample; and identifying proteins of interest that are present in the sample based on the peptides that are identified as being present in the sample.

The invention relates to a method of diagnosing or screening for 27-hydroxylase (CYP27A1) deficiency in an animal comprising: determining in a biological sample the intensity signal by mass analysis of at least a bile alcohol glucuronide and a C24- or C27-bile acid or a conjugate thereof, comparing the intensity signals to a control sample or control value, and determining 27-hydroxylase (CYP27A1) deficiency based on said comparison.

An isobaric stable isotope-containing phosphorylated protein labeling reagent, and a preparation method and application thereof are provided. The protein labeling reagent is a phosphorylated dipeptide organophosphorus reagent labeled by a stable isotope such as deuterium-2, carbon-13, oxygen-18, or nitrogen-15. The preparation method includes: (1) preparation of an isobaric stable isotope-containing amino acid with N-terminal protection, (2) preparation of an isobaric stable isotope-containing amino acid activated ester Fmoc/Boc-R.sub.1-NHS with N-terminal protection, (3) preparation of an isobaric stable isotope-containing dipeptide, (4) preparation of an isobaric stable isotope-containing phosphite, (5) preparation of an isobaric stable isotope-containing phosphite dipeptide, and (6) preparation of a stable isotope-labeled N-phosphorylated amino acid activated ester. The present protein labeling reagent can realize the quantitative analysis of polypeptides, standard proteins, proteins in cells, and proteins in urine samples and blood samples, and has the advantages of good accuracy, high sensitivity, no interference of isotope effect and wide applicability.