Abstract: Methods of evaluating molecular isomers of branched-chain amino acids are featured. The methods can include: derivatizing one or more molecular isomers of branched-chain amino acids in a sample comprising a branched-chain amino acid labeled with one or more heavy atoms as a first standard; adding, to the sample, after derivatization, a nonderivatized or derivatized branched chain amino acid that is labeled with one or more heavy atoms, as a second standard; evaluating the sample using tandem mass spectrometry; and detecting peaks indicative of derivatized and nonderivatized forms of one or more branched-chain amino acids in the sample.

Abstract: Methods of evaluating molecular isomers of branched-chain amino acids are featured. The methods can include: derivatizing one or more molecular isomers of branched-chain amino acids in a sample comprising a branched-chain amino acid labeled with one or more heavy atoms as a first standard; adding, to the sample, after derivatization, a nonderivatized or derivatized branched chain amino acid that is labeled with one or more heavy atoms, as a second standard; evaluating the sample using tandem mass spectrometry; and detecting peaks indicative of derivatized and nonderivatized forms of one or more branched-chain amino acids in the sample.

Abstract: This invention relates, inter alia, to detecting and/or measuring succinylacetone and one or more additional biological analytes using mass spectrometry.

Abstract: A fiber optic array is miniaturized in a configuration that includes an input collimator, a first birefringence crystal, a waveplate, a Faraday rotator, a second birefringence crystal and a second collimator. The elements are aligned along a common optical axis. A light beam along the optical axis that is passed through the first collimator emerges off of the optical axis and through the remaining elements. It re-emerges from the fiber optic array on axis. The configuration provides substantial attenuation in a backward direction.