PubMed Health⌕ Search

Biomedical subjects

S J Valentine

Publications and source records attributed to S J Valentine.

11 recordsLinked to original sources
PubMed1999

ESI/ion trap/ion mobility/time-of-flight mass spectrometry for rapid and sensitive analysis of biomolecular mixtures.

An ion trap/ion mobility/time-of-flight mass spectrometry technique is shown to be a rapid and sensitive means of analyzing peptide/protein mixtures. In this approach, an ion trap is used to accumulate ions that have been electrosprayed from a mixture into concentrated packets. The ion packets are injected into a drift tube where components of the mixture are separated based on differences in mobility through a buffer gas. Ions that exit the drift tube are dispersed in a time-of-flight mass spectrometer for mass-to-charge (m/z) determination. The gas-phase separation strategy reduces congestion in the mass spectrum, and experimental mobilities complement m/z measurements in assigning peaks. Examples of the application of the approach to identification of peptides (from tryptic digests) and to separation of charge-state distributions from electrospray of a mixture containing ubiquitin and myoglobin are presented. Most peptides that are observed from tryptic digests of proteins such as cytochrome c and myoglobin can be identified from data that are acquired in under 1 min; studies of mixtures with known compositions indicate that detection limits are approximately 0.5-3 pmol for individual components. Factors that may influence the distributions that are observed, such as storage time in the trap, injection voltages used for the mobility experiment, and variations in ion cross section with charge state, are discussed.

Cytochrome c Group↗
PubMed1999

A database of 660 peptide ion cross sections: use of intrinsic size parameters for bona fide predictions of cross sections.

An ion trap/ion mobility/time-of-flight mass spectrometry technique has been used to measure collision cross sections for 660 peptide ions generated by tryptic digestion of 34 common proteins. Measured cross sections have been compiled into a database that contains peptide molecular weight and sequence information. The database is used to generate average intrinsic contributions to cross section (size parameters) for different amino acid residues by solving systems of equations that relate the unknown contributions of individual residues to the sequences and cross sections of database peptides. Size parameters are combined with information about amino acid composition to calculate cross sections for database peptides. Bona fide cross section predictions (made prior to measurement) for peptides observed in tryptic digests of sperm whale myoglobin and yeast enolase are made. Eight of 10 predicted cross sections are within 2% of the experimental values and all 10 are within 3.2%. The utility of size parameters for cross section prediction is explored and discussed.

Algorithms↗
PubMed1998

Three-dimensional ion mobility/TOFMS analysis of electrosprayed biomolecules.

An ion mobility/mass spectrometry technique has been developed to record mass-resolved ion mobility distributions for multiple ions simultaneously. The approach involves a new instrument that couples an electrospray ion source to an injected-ion drift tube/time-of-flight mass spectrometer. Individual components in a mixture of ions are separated by mobility differences in a drift tube and subsequently dispersed by mass-to-charge ratios in a time-of-flight instrument. Flight times in the mass spectrometer are much shorter than residence times in the drift tube, making it possible to record mass-resolved ion mobilities for all ions simultaneously. The result is a three-dimensional spectrum that contains collision cross section, mass-to-charge, and ion abundance information. The instrument and data acquisition system are described. Examples of combined ion mobility/time-of-flight data are presented for distributions of electrosprayed bradykinin and ubiquitin ions.

Bradykinin↗
PubMed1998

High-order structure and dissociation of gaseous peptide aggregates that are hidden in mass spectra.

Injected-ion mobility and high-pressure ion mobility techniques have been used to examine the conformations of bradykinin, insulin chain A, and several other peptide ions in the gas phase. Under the experimental conditions employed, evidence for multimer formation in the mass spectra of peptides is minimal or absent altogether. However, ion mobility distributions show that aggregates of peptides (containing a single charge per monomer unit) are observed at the same mass-to-charge ratios as the singly charged parent ions. Collision cross sections for these clusters show that they have tightly packed roughly spherical conformations. We have bracketed the average density as 0.87 < p < 1.00 g cm-3. In some cases, specific stable aggregate forms within a cluster size can be distinguished indicating that some high order structures are favored in the gas phase. Multimer formation between different sizes of polyalanine peptides shows no evidence for size specificity in aggregate formation. Collisional and thermal excitation studies have been used to examine structural transitions and dissociation of the multimers. Aggregates appear to dissociate via loss of singly charged monomers. The observation that peptide multimers can be concealed in mass spectral data requires that fragmentation patterns and reactivity studies of singly charged monomers be undertaken with care.

Algorithms↗
PubMed1998

Gas-phase separations of protease digests.

A mixture of peptides from a complete tryptic digest of ubiquitin has been analyzed by ion mobility/time-of-flight mass spectrometry techniques. All components of the mixture were electrosprayed and ions were separated in the gas phase based on differences in their mobilities through helium before being dispersed into a time-of-flight mass spectrometer for mass-to-charge analysis. The data show that ions separate into families primarily according to differences in their charge states and, to a lesser extent, differences in conformation. This approach reduces spectral congestion typically associated with electrosprayed mixtures and provides charge assignments for mass-to-charge ratio data. Gas-phase separations of ions appear to provide a new physical basis for characterizing components of biological mixtures.

Endopeptidases↗
PubMed1992

Spinal anaesthesia for caesarean section: comparison of 22-gauge and 25-gauge Whitacre needles with 26-gauge Quincke needles.

We have studied 150 women undergoing elective Caesarean section under spinal anaesthesia. They were allocated randomly to have a 22-gauge Whitacre, a 25-gauge Whitacre or a 26-gauge Quincke needle inserted into the lumbar subarachnoid space. The groups were compared for ease of insertion, number of attempted needle insertions before identification of cerebrospinal fluid, quality of subsequent analgesia and incidence of postoperative complications. There were differences between groups, but they did not reach statistical significance. Postdural puncture headache (PDPH) was experienced by one mother in the 22-gauge Whitacre group, none in the 25-gauge Whitacre group and five in the 26-gauge Quincke group. Five of the six PDPH occurred after a single successful needle insertion. Seven of the 15 mothers in whom more than two needle insertions were made experienced backache, compared with 12 of the 129 receiving two or less (P < 0.001). We conclude that the use of 22- and 25-gauge Whitacre needles in elective Caesarean section patients is associated with a low incidence of PDPH and that postoperative backache is more likely when more than two attempts are made to insert a spinal needle.

Adolescent↗
PubMed1991

Comparative study of the effects of air or saline to identify the extradural space.

Fifty women in labour were allocated randomly to receive either air or saline to assist in the identification of the extradural space by the loss of resistance technique. A study volume of 4 ml of air or saline was used before 0.5% bupivacaine 8 ml and the spread of analgesia was followed for 30 min. The first segment blocked, time of onset, number of blocked segments and height of block were comparable in the two groups. At 30 min, there were eight patients with an unblocked segment in the air group, compared with two in the saline group (P less than 0.01). All unblocked segments were blocked subsequently by further doses of bupivacaine. We conclude that air is more likely than saline to produce unblocked segments in the initiation of extradural analgesia in labour.

Adolescent↗
PubMed1990

Arterial oxygen saturation following premedication for cardiac surgery.

We studied patients scheduled for coronary artery bypass surgery following premedication with lorazepam, morphine and droperidol, using pulse oximetry and serial electrocardiographic (ECG) recordings. Arterial oxygen saturation (SaO2) values were compared with those obtained during two control periods when the patients were awake and asleep. All patients demonstrated progressive arterial oxygen desaturation during the premedication period, statistically significant from both controls (P less than 0.001). Twelve of the 15 patients developed hypoxaemia or severe hypoxaemia which was corrected immediately by administration of oxygen. New ECG changes developed during the premedication period in 33% of patients. It is concluded that additional oxygen should be administered to patients receiving this and similar premedication regimens.

Adult↗
PubMed1990

Preoxygenation in the elderly: a comparison of the four-maximal-breath and three-minute techniques.

To compare the effectiveness of two routinely used methods of preoxygenation in protecting against hypoxia in the elderly, the arterial O2 saturation was measured using an oximeter. Twenty-four elderly patients (greater than or equal to 65 yr) presenting for elective orthopedic surgery were randomly allocated to receive either 3-min or four-maximal-breaths of 100% O2 via a Bain circuit. After preoxygenation, anesthesia was induced, tracheal intubation performed with patients kept apneic, and the endotracheal tube left open to air. The arterial O2 saturation was measured before preoxygenation and continually recorded during desaturation. Although attaining similar arterial O2 saturation values after preoxygenation, patients in the four-maximal-breath group had significantly shorter times (P less than 0.0001) to all levels of desaturation. We suggest that preoxygenation with 3-min breathing of 100% O2 offers more protection against hypoxia due to prolonged apnea after induction of anesthesia in the elderly than does four maximal breaths of 100% O2.

Adult↗
PubMed1981

Many parents think their child is dying when having a first febrile convulsion.

Fifty parents of 36 consecutive children admitted to hospital with their first febrile convulsion were interviewed shortly after the event. Very few parents voluntarily said that they had thought their child was dying, but when asked specifically the majority said they had thought the child was dying or likely to die. This common fear should be kept in mind when discussing febrile convulsions with parents, who are unlikely to volunteer the information.

Adult↗