A combined magnetic sector-time-of-flight instrument has been constructed and used with both continuous (liquid secondary ion mass spectrometry and electrospray ionization) and pulsed (matrix-assisted laser desorptionhonization) ion sources. The design includes provision for both low-and high-energy gas collision induced decompositions and orthogonal acceleration of the product ions into the time-of-flight mass analyser. Tandem mass spectra may be acquired for singly and multiply charged precursor ions and reliable mass measurements are easily obtained. Product-ion mass spectra are quite reproducible regardless of any instability in the precursor ion beam intensity.Instrumentation for molecular structure determination studies by tandem mass spectrometry (MSlMS) should ideally be able to provide unit mass selection of the precursor ion with high transmission, and to acquire full product-ion mass spectra within chromatography time scales at the highest achievable sensitivity. The instrumentation should yield reliable mass assignments of product ions, and in addition should ideally operate with both continuous and pulsed ion sources. To date, gas-phase ion/molecule collisions have been the most commonly used and generally most successful method for generating structurally informative decomposition products. Low and high energy collision-induced decompositions (CID) can provide different and complementary information and MSlMS instrumentation should ideally be able to accommodate both types. In particular, high energy CID of peptides generally implies the capability to induce the side-chain cleavages (i.e. 'd', 'v' and 'w' sequence ions) which may be used ?o distinguish isobaric amino acid residues such as leucine and isoleucine, or lysine and glutamine.In 1992 we suggested that the use of a magnetic sector instrument as the first mass analyser (MS-1) of an MUMS instrument offers unit mass precursor ion selection with high transmission, whilst the use of a time-of-flight (TOF) instrument as MS-2 offers the potential for high sensitivity and fast acquisition of full product-ion spectra.' Such an instrument could be smaller and more convenient to operate than foursector instruments equipped with array detectors and yet be comparable in performance. This paper describes a combined magnetic sector-TOF instrument which has been designed for structural determination studies by MSlMS, and which includes provision for both low-and high-energy gas collision-induced decompositions. COLLISION-INDUCED DECOMPOSITIONS (CID)Gas phase ion/molecule collisions have, so far, been the most widely studied method for generating structurally informative decomposition products. To generate * Author for correspondence.side-chain cleavage ions, such as the 'd' fragment ions in peptides, it has been shown that a minimum value of 'centre-of-mass' collision energy (E,,,) of 20 -25 eV is Such collision processes are generally termed 'high energy' collisions. The 'centre-of-mass' collision energy is defined in Eqn ( l ) , where Elab is the laborat...

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Crystals of calcium oxalate in pathological material and artificially precipitated in the absence or presence of citric acid in gelatin models were examined by polarized light and treated with silver nitrate under a variety of conditions. It was found that the intensity of the staining reaction was largely proportional to the strength of the silver solution, and was enhanced in in vitro studies by the presence of citric acid. Staining was also influenced by the crystal form, which was itself related to the absence or presence of citric acid.

A selection of reagents capable of complexing with calcium in various ways was compared by applying them to tissue sections known to contain calcium in a variety of physiochemical states. Their histochemical potential was evaluated according to their sensitivity, specificity, accuracy of localisation and intensity of staining. Murexide, for light microscopy, and 8-hydroxyquinoline, for fluorescence microscopy proved to be the best overall reagents. They failed to demonstrate calcium oxalate, which was well shown by naphthalhydroxamic acid.