No abstract

Metabolic profiling of amino acids and acylcarnitines from blood spots by automated electrospray tandem mass spectrometry (ESI-MS/MS) is a powerful diagnostic tool for inborn errors of metabolism. New approaches to sample preparation and data interpretation have helped establish the methodology as a robust, high-throughput neonatal screening method. We introduce an efficient 96-well-microplate batch process for blood-spot sample preparation, with which we can obtain high-quality profiles from 500-1000 samples per day per instrument. A computer-assisted metabolic profiling algorithm automatically flags abnormal profiles. We selected diagnostic parameters for the algorithm by comparing profiles from patients with known metabolic disorders and those from normal newborns. Reference range and cutoff values for the diagnostic parameters were established by measuring either metabolite concentrations or peak ratios of certain metabolite pairs. Rigorous testing of the algorithm demonstrates its outstanding clinical sensitivity in flagging abnormal profiles and its high cumulative specificity.

High efficiency electrically driven separation techniques, such as capillary zone electrophoresis (CZE) and capillary electrochromatography (CEC), yield narrow peak widths of the order of a few seconds. Scanning instruments may have difficulty in obtaining sufficient data points across such narrow peaks (although the use of selected ion monitoring (SIM) mode may overcome this). Orthogonal acceleration time-of-flight ((oa-TOF)) mass analysers have an inherent ability for fast acquisition rates allowing a high number of data points (for example 10 spectra s À1 ) to be collected across a narrow peak and are capable of operation at resolutions in the region of 5000 full width half maxima (FWHM). This enables spectral data to be measured with accuracies greater than 5 ppm, allowing the molecular formula to be predicted / confirmed. We have investigated the use of an oa-TOF mass analyser coupled to CZE. The on-line separation of a drug substance and related impurities has been achieved. Copyright # 1999 John Wiley & Sons, Ltd. Received 20 September 1998; Revised 14 November 1998; Accepted 15 November 1998 In recent years time-of-flight mass spectrometry (TOFMS) has re-established itself as a mainstream technique in mass spectrometry. TOFMS has distinct advantages 1 over scanning instruments, including high duty factors (percentage of ions formed that are detected), fast acquisition rates, sensitivity and large mass range. Recent advances in ion sources (electrospray and matrix-assisted laser desorption/ ionisation) that are capable of dealing with high molecular weight compounds, along with the development of high speed electronics and computers, have allowed TOFMS to develop rapidly in the last decade. Furthermore, the introduction of the ion mirror (reflectron) 2 and orthogonal acceleration time-of-flight 3 (oa-TOF) have increased the development of TOFMS.The reflectron corrects positional and velocity discrepancies in the acceleration region of the TOF mass spectrometer and removes neutral species which may have resulted from in-flight decay.As a result of the reflectron, the spatial spread in the flight direction of ions of given m/z, and thus the detected peak widths, are reduced and this leads to an increase in resolution. Resolution values in excess of 5000 (FWHM) are now readily available.The development of orthogonal acceleration allows continuous ion sources (i.e. electrospray) 3 to be coupled to the TOF mass spectrometer. In the instrument used in the present work, ions generated in the atmospheric pressure ionisation source are transferred to the oa-TOF analyser via two independently pumped frequency (RF) lenses. After entering the analyser the ion beam is focused into the pusher by acceleration, focus, steer and tube lenses. A pusher then pulses a section of the beam towards a reflectron, which reflects ions back to the detector. As ions travel from the pusher to the detector they are separated in mass according to their flight times, with ions of higher mass-to-charge ratio (m/z) arriving later in the ...

The identification of polar microcontaminants in surface water is an important issue in environmental analysis. Liquid chromatography/mass spectrometry (LC/MS) is frequently applied for this purpose. However, even in combination with tandem mass spectrometry (MS/MS), unambiguous identification of the compounds detected is often difficult. The potential of an alternative strategy, based on the ability of an orthogonal-acceleration time-of-flight mass spectrometer to routinely perform accurate mass determination at 10 ppm in on-line LC/MS, is explored. On-line solid-phase extraction LC electrospray orthogonal-acceleration time-of-flight mass spectrometry is shown to enable the determination of pesticides from various compound classes in surface water in the concentration range of 0.1 to 10 micrograms/L. In addition, the ability to discriminate and unambiguously identify pesticides in mixtures of isobaric and/or isomeric compounds is investigated.