Analysis of trace volatile metabolites in serum and plasma
Abstract A method is described for analyzing volatile constituents in 5- to 10-ml samples of human serum and plasma. A headspace sampling technique was employed by which volatile sample constituents are carried in a stream of ultra-pure nitrogen and adsorbed onto a porous polymer with subsequent heat desorption. The concentrated volatiles were separated on highly efficient capillary columns. Mass spectrometric identifications were made with 55 ml of serum. Characteristic components in normal serum are: ethanol, 4-methyl-2-pentanone, hexanal, 1-butanol, 2-hexanol, 2-heptanone, and benzaldehyde.
Traditional multivariate quality control charts are based on independent observations. In this paper, we explain how to extend univariate residual charts to multivariate cases and how to combine the traditional statistical process control (SPC) approaches to monitor changes in process variability in a dynamic environment. We propose using Alt's (1984) W chart on vector autoregressive (VAR) residuals to monitor the variability for multivariate processes in the presence of autocorrelation. We study examples jointly using the Hotelling T2 chart on VAR residuals, the W chart, and the Portmanteau test to diagnose the types of shift in process parameters.