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Pyridinoline and deoxypyridinoline crosslinks are biomarkers found in urine for collagen degradation in bone turnover. For the first time, a rapid, sensitive, and ionpairing free method is described for the analysis of pyridinoline and deoxypyridinoline using ultra-high performance liquid chromatography with Cogent Diamond Hydride column and detection by Q Exactive hybrid quadrupole-orbitrap high resolution accurate mass spectrometry. The separation was achieved using both isocratic and gradient conditions and run time <5 min under isocratic conditions of 20% acetonitrile in water containing 0.1% formic acid. Pyridoxine was used as an internal standard and relative standard deviation of the retention times of both pyridinoline and deoxypyridinoline were <1%. The limit of detection was 0.082 ± 0.023 μM for pyridinoline and 0.118 ± 0.052 μM for deoxypyridinoline. The limit of quantitation was 0.245 ± 0.070 μM for pyridinoline and 0.354 ± 0.157 μM for deoxypyridinoline. The method was validated by the detection and quantitation of both pyridinoline and deoxypyridinoline in skin and urine samples. K E Y W O R D Sdeoxypyridinoline, mass spectrometry, pyridinoline, silica hydride column, urine analysis 1482

There is a substantial loss of value in bovine leather every year due to a leather quality defect known as "looseness". Data show that 7% of domestic hide production is affected to some degree, with a loss of $35 m in export returns. This investigation is devoted to gaining a better understanding of tight and loose wet blue leather based on vibrational spectroscopy observations of its structural variations caused by physical and chemical changes that also affect the tensile and tear strength. Several regions from the wet blue leather were selected for analysis. Samples of wet blue bovine leather were collected and studied in the sliced form using Raman spectroscopy (using 532 nm excitation laser) and Attenuated Total Reflectance-Fourier Transform InfraRed (ATR-FTIR) spectroscopy. The purpose of this study was to use ATR-FTIR and Raman spectra to classify distal axilla (DA) and official sampling position (OSP) leather samples and then employ univariate or multivariate analysis or both. For univariate analysis, the 1448 cm − 1 (CH 2 deformation) band and the 1669 cm − 1 (Amide I) band were used for evaluating the lipid-to-protein ratio from OSP and DA Raman and IR spectra as indicators of leather quality. Curve-fitting by the sums-of-Gaussians method was used to calculate the peak area ratios of 1448 and 1669 cm − 1 band. The ratio values obtained for DA and OSP are 0.57 ± 0.099, 0.73 ± 0.063 for Raman and 0.40 ± 0.06 and 0.50 ± 0.09 for ATR-FTIR. The results provide significant insight into how these regions can be classified. Further, to identify the spectral changes in the secondary structures of collagen, the Amide I region (1600-1700 cm − 1) was investigated and curve-fitted-area ratios were calculated. The 1648:1681 cm − 1 (non-reducing: reducing collagen types) band area ratios were used for Raman and 1632:1650 cm − 1 (triple helix: α-like helix collagen) for IR. The ratios show a significant difference between the two classes. To support this qualitative analysis, logistic regression was performed on the univariate data to classify the samples quantitatively into one of the two groups. Accuracy for Raman data was 90% and for ATR-FTIR data 100%. Both Raman and ATR-FTIR complemented each other very well in differentiating the two groups. As a comparison, and to reconfirm the classification, multivariate analysis was performed using Principal Component Analysis (PCA) and Linear Discriminant Analysis (LDA). The results obtained indicate good classification between the two leather groups based on protein and lipid content. Principal component score 2 (PC2) distinguishes OSP and DA by symmetrically grouping samples at positive and negative extremes. The study demonstrates an excellent model for wider research on vibrational spectroscopy for early and rapid diagnosis of leather quality.

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