Compositions and methods for analyzing disulfide bonds are provided. An exemplary method includes preparing peptide standards having no disulfide bonds, scrambled disulfide bond peptide standards, and native disulfide bond peptide standards according to the sequence of the region of the protein drug product that includes the disulfide bond, digesting a sample of protein drug product into peptides, separating the protein drug product peptides, analyzing the protein drug product peptides and the peptide standards, identifying scrambled and native disulfide bond peptides by retention time, and quantifying the level of scrambled disulfide bond peptides.

Provided are methods of detecting the presence or amount of a vitamin D metabolite in a sample using mass spectrometry. The methods generally directed to ionizing a vitamin D metabolite in a sample and detecting the amount of the ion to determine the presence or amount of the vitamin D metabolite in the sample. Also provided are methods to detect the presence or amount of two or more vitamin D metabolites in a single assay.

Described herein are reagents and methods for improving signal in imaging mass cytometry. Aspects include mass tags with a large number of labeling atoms, chemical modifications to mass tags and additional reagents to reduce background and/or maintain target binding of mass tagged specific binding partners (SBPs), and schemes for associating a plurality of mass tags with a single SBP. As such, embodiments include any combination of one or more reagents and their use. The reagents, kits and methods herein may be used for mass cytometry, including imaging mass cytometry. In some aspects, reagents, kits or methods may be used for delivery of a large number of radioisotopes to a target analyte, for example for therapeutic use or radiometric detection. In certain aspects, only non-radioactive isotopes may be used for mass cytometry.

A method for direct measurement of gradients of patient compliance with a medication regimen by employing a stable non-radioactive isotope taggant compound as part of, bound to, or applied to an endogenous molecule. An assay to determine patient compliance with medication regimens for HIV pre-exposure prophylaxis employing administering a taggant to a pharmacologically active compound, obtaining and collecting a patient tissue or fluid sample analyzing the collected tissue or fluid sample for the taggant concentration and interpreting data from the taggant concentration analysis as an indicator of gradients of patient compliance.

Systems and methods are provided for the analysis of single particles with inductively coupled plasma-time of flight mass spectrometry. An ion compression device is operated in combination with an image current detector to improve a duty cycle of particle analysis. The image current detection device is used to determine a start time and an end time of a separate ion cloud which is derived from a single particle. The ion compression device stores and compresses each ion cloud based on instructions from the image current detector. The duty cycle of the particle analysis can be improved up to nearly 100%. The ion compression device is additionally operated with an ion filtration device to achieve a lower detection limit and a higher signal-to-noise ratio.

Provided are methods for labeling a pharmaceutical product to indicate the origin, and/or intended recipient, and/or a predetermined characteristic (e.g. geographic location) of an intended recipient of the pharmaceutical product. The methods include incorporating certain pharmaceutically inactive marker substances into the pharmaceutical product at manufacture.

Some aspects of this invention provide reagents and methods for the sensitive, quantitative and simultaneous detection of target analytes in complex biological samples by liquid chromatography tandem mass spectrometry (LC MS/MS). Some aspects of this invention provide affinity reagents encoded with mass reporters for the sensitive and quantitative translation of an analyte of interest into a mass tag. The reagents and methods provided herein have general utility in analyte detection and encoding, for example, in biomolecular profiling, molecular diagnostics, and biochemical encoding.

The present invention relates to a method for quantifying a therapeutic antibody in a sample of a human individual comprising a step of adding to a test sample which may contain therapeutic antibodies to be quantified a known amount of two or more labeled forms of said therapeutic antibodies.

The present invention provides a set of novel isobaric chemical tags, also referred herein as SUGAR (Isobaric Multiplex Reagents for Carbonyl Containing Compound). These labeling tags are compact and easy to synthesize at high yield and purity in just a few steps using commercially available starting materials. The tagging reagents of the present invention comprise: a) a reporter group, having at least one atom that is optionally isotopically labeled; b) a balancing group, also having at least one atom that is optionally isotopically labeled, and c) an aldehyde, ketone, or carboxylic acid reactive group. The multiplex SUGAR tags are able to react with an aldehyde, ketone, or carboxylic acid group of the molecule to be tagged, which offers the capability for labeling and quantitation of glycans, proteins/peptides, and fatty acids.

Systems and methods for determining regions of proteins that contribute to self-association of the protein are provided. Methods for modifying the self-association of concentrated protein formulations are also provided.