Multiplexed Mass Spectrometry Research Articles

Screening for proteolytic activities in snake venom by means of a multiplexing electrospray ionization mass spectrometry assay scheme

A multiplexed mass spectrometry based assay scheme for the simultaneous determination of five different substrate/product pairs was developed as a tool for screening of proteolytic activities in snake venom fractions from Bothrops moojeni. The assay scheme was employed in the functional characterization of eight model proteases. Time-resolved reaction profiles were generated and the relative reaction progress at each time point was determined. These were used to semi-quantitatively sort the catalytic activities of each enzyme towards the respective substrates into six classes. The resulting activity pattern served as an activity fingerprint for each enzyme. The multiplex assay scheme was then applied to a screening for proteolytic activities in fractions of the pre-separated venom from B. moojeni. Activity patterns of each fraction were generated and used to sort the fractions into three different categories of activity. By comparison of the fingerprint activity patterns of the venom fractions and the model enzymes, a compound with proteolytic properties similar to activated protein C was detected.

Adsorption and abstraction of H(D) on clean and modified Al(111) and Ni(111) surfaces

The kinetics of adsorption and abstraction for the system H(D) on Al(111) and Ni(111) has been investigated using an efficient atomic beam source, thermal desorption spectroscopy, and multiplexed mass spectrometry. The initial sticking coefficient of atomic hydrogen on Ni(111) is 1.0 and independent of the angle of incidence. For H on Al(111) the initial sticking coefficient is 0.6 and increases with increasing angle of incidence (S(φ)∼cos−0.4 φ). On Al(111) preadsorbed oxygen leads to a decrease of the initial sticking coefficient for H down to 0.1; potassium on the other hand has no significant influence on the initial sticking probability. On both surfaces, Ni(111) and Al(111), abstraction of deuterium proceeds at a surface temperature of 150 K due to impinging H atoms (H+D→HD), with an initial abstraction coefficient of 0.20 on Al(111) and 0.12 on Ni(111). In the case of Al(111) this coefficient is nearly independent of the initial D coverage and therefore the abstraction reaction cannot be described by a simple Eley–Rideal process, but rather by a hot-precursor mechanism. In addition to abstraction there is also a small probability for the removal of an adsorbed species by a collision induced desorption process. Abstraction of deuterium by impinging H-atoms is strongly affected by modification of the Al(111) surface, either by oxygen or by potassium. Oxygen decreases the HD abstraction coefficient, probably by inhibiting the hot-precursor state of H on the surface. Potassium increases the HD abstraction rate, most likely by increasing the lifetime of atomic hydrogen in the precursor state.

Adsorption and abstraction of atomic hydrogen (deuterium) on Al(100)

The kinetics of adsorption and abstraction for the system H (D) on Al(100) has been investigated using an efficient atomic beam source, thermal desorption spectroscope and multiplexed mass spectrometry. Emphasis was put on the quantitative determination of the reaction parameters. The initial sticking coefficient for atomic hydrogen and atomic deuterium is 0.6; the saturation coverage is 1.6 monolayers. On the D(H) saturated surface, abstraction takes place at a surface temperature of 150 K due to impinging H (D) atoms (H+D→HD) with an abstraction coefficient of 0.4 D/H. No significant isotope effect can be observed. The abstraction process cannot be described by a direct Eley–Rideal mechanism, but rather by a hot-precursor mechanism. In addition to abstraction, about 10% of the adsorbed species are removed from the surface by a collision-induced associative desorption process.

End-tidal carbon dioxide pressure in neonates and infants measured by aspiration and flow-through capnography

In 25 anesthetized, intubated, artificially ventilated, and paralyzed healthy neonates and infants, end-tidal PCO2 (PETCO2) measured by remote multiplexed mass spectrometry was 1.86 +/- 1.58 mm Hg lower than arterial PCO2 (PaCO2). PETCO2 measured by a flow-through cuvette was 1.02 +/- 1.64 mm Hg lower than PaCO2. The difference between the two methods of capnography was not significant. Values for PETCO2 obtained by mass spectrometry changed -0.43 +/- 1.43 mm Hg from baseline after 15 minutes of aspiration at a sample flow rate of 240 ml/min. Values for PETCO2 obtained with flow-through capnography changed -0.17 +/- 2.17 mm Hg from baseline after 15 minutes. In both methods, the changes from baseline in PETCO2 over time were not significant. These results suggest that both methods of capnography studied are reliable and may be used safely in neonates despite high sample flow rates and added apparatus dead space (0.6 ml for tracheal tubes less than or equal to 4.0 mm OD and 4.9 ml for tracheal tubes greater than 4.0 mm OD).