Abstract: A model system with blue dextran, potassium hexacyanoferrate(III) and heparin as analytes was used to generate second-order FIA data. The system incorporated a gel-filtration column (2.5 cm x 16 mm i.d.) packed with Sephadex G-25 Superfine. Photodiode array detection was at 220-594 nm with scanning at 1 s intervals for 75 s, starting 20 s after injection. The tri-linear parallel factor analysis (PARAFAC) algorithm (Smilde et al., J. Chemom., 1994, 8, 21) c ombined with multiple linear regression and tri-linear partial least-squares regression (tri-PLS; Bro, Ibid., 1996, 10, 47) were used for data processing. The prediction abilities of the two methods were satisfactory for two-component mixtures and the detection of unknown interferents. The tri-PLS method was slightly better.

Abstract: Sulfated polysaccharides, including heparin and carrageenans, were determined by the formation of fluorescent complexes with Ce3+. The reaction system incorporated a strong cation-exchange tubular membrane reactor (SciTech, Umea, Sweden). In one mode, Ce2(SO4)3 was added to the carrier solution flowing in the internal channel, and 50 mM H2SO4 flowed in the external channel; the anionic polymers were equilibrated initially with aqueous Ce(SO4)2 of the same concentration. as the carrier, and unreacted Ce3+ was removed by the H2SO4. In the other mode, the carrier was 50 mM ammonium acetate pumped through the reactor, and Ce3+ was introduced from 2 to 4 mM Ce2(SO4)3 in 50 mM H2SO4 flowing in the external channel. The fluorescence of the products was measured at 350 nm (excitation at 250 nm). Either mode could be used in flow injection analysis; the second mode was used in conjunction with size-exclusion LC on a column (30 cm x 1 cm) of Superdex (13 µm) in which the carrier also constituted the mobile phase. Samples could be desalted on a Biosil guard column (8 cm x 7.8 mm; 5 µm particles) for flow injection analysis. Response to anionic polymers was high and that to low-mol.-wt. acids was small or absent; there was a small negative response to oxalic acid. The detection limit in flow injection analysis was 1 pmol with 50 mM ammonium acetate and 0.1 pmol with water as carrier for heparin, and response was rectilinear over three decades of concentration.

Abstract: The electrochemical oxidation of full-size heparin (13-15 kDa) is demonstrated in 1 M H-3PO-4 at a glassy carbon electrode coated with a ruthenium oxide film. The pathway apparently is analogous to chemical oxidation by periodate. By comparison to currents from inorganic species. it is apparent that only about 2 electrons per mole are involved. Flow injection analysis (FIA) allowed determinations down to 2 µM heparin, but the calibration plot was nonlinear. Low molecular weight heparin (5-6 kDa) was not electroactive with this system. In basic solution at a glassy carbon electrode that is modified with a film of Cu-2O, both full-size and low molecular weight heparin are oxidized. The pathways involved oxidative desulfation and attack on saccharide units with evolution of CO-2. Linear calibration plots which extended into the sub µM level were obtained by FIA. The detection limits, which were based on a value of 3 for the ratio of the signal to the standard deviation of replicates, were 9 nM for full-size and 20-30 nM for various low molecular weight heparin samples.