Abstract: The present invention provides methods for improved label-free absolute quantification of relatively low abundant polypeptides by liquid chromatography/mass spectrometry analysis of peptide products obtained from simple or complex polypeptide mixtures. The methods for absolute quantification include MS signals from a set of qualified ions of peptide products of a relatively high abundant polypeptide to improve quantification of a relatively low abundant polypeptide.

Abstract: The present invention provides methods for improved label-free absolute quantification of relatively low abundant polypeptides by liquid chromatography/mass spectrometry analysis of peptide products obtained from simple or complex polypeptide mixtures. The methods for absolute quantification include MS signals from a set of qualified ions of peptide products of a relatively high abundant polypeptide to improve quantification of a relatively low abundant polypeptide.

Abstract: The present invention provides methods for improved label-free absolute quantification of relatively low abundant polypeptides by liquid chromatography/mass spectrometry analysis of peptide products obtained from simple or complex polypeptide mixtures. The methods for absolute quantification include MS signals from a set of qualified ions of peptide products of a relatively high abundant polypeptide to improve quantification of a relatively low abundant polypeptide.

Abstract: A method for identifying a polypeptide a specimen can include (i) treating a specimen suspected of including an insulin with a base; (ii) extracting a first fraction of the treated specimen by solid phase extraction using a mixed mode or polymeric reversed-phase media and a first solvent including an acid; (iii) separating a component of the first fraction by liquid chromatography using a chromatographic surface including a hydrophobic surface group and one or more ionizable modifiers, and a second solvent including an acid; and (iv) analyzing the component of the first fraction by mass spectroscopy, thereby identifying the polypeptide, if present, using a signal corresponding to a sequence fragment ion from the polypeptide. The signal can correspond to an intact multiply charged precursor fragment selected in a first quadrupole and its corresponding sequence fragment ion selected in a final quadrupole.

Abstract: The present invention provides methods for improved label-free absolute quantification of relatively low abundant polypeptides by liquid chromatography/mass spectrometry analysis of peptide products obtained from simple or complex polypeptide mixtures. The methods for absolute quantification include MS signals from a set of qualified ions of peptide products of a relatively high abundant polypeptide to improve quantification of a relatively low abundant polypeptide.

Abstract: A method for identifying a polypeptide a specimen can include (i) treating a specimen suspected of including an insulin with a base; (ii) extracting a first fraction of the treated specimen by solid phase extraction using a mixed mode or polymeric reversed-phase media and a first solvent including an acid; (iii) separating a component of the first fraction by liquid chromatography using a chromatographic surface including a hydrophobic surface group and one or more ionizable modifiers, and a second solvent including an acid; and (iv) analyzing the component of the first fraction by mass spectroscopy, thereby identifying the polypeptide, if present, using a signal corresponding to a sequence fragment ion from the polypeptide. The signal can correspond to an intact multiply charged precursor fragment selected in a first quadrupole and its corresponding sequence fragment ion selected in a final quadrupole.

Abstract: A method for identifying a polypeptide a specimen can include (i) treating a specimen suspected of including an insulin with a base; (ii) extracting a first fraction of the treated specimen by solid phase extraction using a mixed mode or polymeric reversed-phase media and a first solvent including an acid; (iii) separating a component of the first fraction by liquid chromatography using a chromatographic surface including a hydrophobic surface group and one or more ionizable modifiers, and a second solvent including an acid; and (iv) analyzing the component of the first fraction by mass spectroscopy, thereby identifying the polypeptide, if present, using a signal corresponding to a sequence fragment ion from the polypeptide. The signal can correspond to an intact multiply charged precursor fragment selected in a first quadrupole and its corresponding sequence fragment ion selected in a final quadrupole.

Abstract: A method for identifying a polypeptide a specimen can include (i) treating a specimen suspected of including an insulin with a base; (ii) extracting a first fraction of the treated specimen by solid phase extraction using a mixed mode or polymeric reversed-phase media and a first solvent including an acid; (iii) separating a component of the first fraction by liquid chromatography using a chromatographic surface including a hydrophobic surface group and one or more ionizable modifiers, and a second solvent including an acid; and (iv) analyzing the component of the first fraction by mass spectroscopy, thereby identifying the polypeptide, if present, using a signal corresponding to a sequence fragment ion from the polypeptide. The signal can correspond to an intact multiply charged precursor fragment selected in a first quadrupole and its corresponding sequence fragment ion selected in a final quadrupole.

Abstract: A method for identifying a polypeptide a specimen can include (i) treating a specimen suspected of including an insulin with a base; (ii) extracting a first fraction of the treated specimen by solid phase extraction using a mixed mode or polymeric reversed-phase media and a first solvent including an acid; (iii) separating a component of the first fraction by liquid chromatography using a chromatographic surface including a hydrophobic surface group and one or more ionizable modifiers, and a second solvent including an acid; and (iv) analyzing the component of the first fraction by mass spectroscopy, thereby identifying the polypeptide, if present, using a signal corresponding to a sequence fragment ion from the polypeptide. The signal can correspond to an intact multiply charged precursor fragment selected in a first quadrupole and its corresponding sequence fragment ion selected in a final quadrupole.

Abstract: A method for identifying a polypeptide a specimen can include (i) treating a specimen suspected of comprising an insulin with a base; (ii) extracting a first fraction of the treated specimen by solid phase extraction using a mixed mode or polymeric reversed-phase media and a first solvent comprising an acid; (iii) separating a component of the first fraction by liquid chromatography using a chromatographic surface including a hydrophobic surface group and one or more ionizable modifiers, and a second solvent comprising an acid; and (iv) analyzing the component of the first fraction by mass spectroscopy, thereby identifying the polypeptide, if present, using a signal corresponding to a sequence fragment ion from the polypeptide. The signal can correspond to an intact multiply charged precursor fragment selected in a first quadrupole and its corresponding sequence fragment ion selected in a final quadrupole.