Relative molar response factors for thermal conductivity detectors

This paper describes an investigation into the universal nature of relative molar response factors for thermal conductivity detectors. Relative molar response factors are measured on multiple gas chromatographs equipped with thermal conductivity detectors, and the values are compared with values in the literature. As was observed previously, relative molar responses obtained on a single instrument for a homologous series vary linearly with respect to the number of carbon atoms in the hydrocarbon chain. However, significant differences are observed for the slope of this line depending on the instrument studied. This contradicts previous literature results that demonstrated an indepedence of the relative molar response with regard to the detector. The current results show that the calibration of thermal conductivity detectors using literature values for relative molar response factors could produce significant errors in the concentrations measured by the laboratory chromatograph.

Receptor-mediated binding of milk lactoferrin to nursing piglet enterocytes: a model for studies on absorption of lactoferrin-bound iron.

Lactoferrin, an iron-binding glycoprotein that is abundant in milk of some species, has been suggested to play a key role in the absorption of iron in human infants. This hypothesis is based on the dominant role of lactoferrin as an iron-binding component in human milk and on the occurrence of lactoferrin receptors in brush-border membranes in infants' intestines. The piglet may be a useful model to evaluate the biological activity of lactoferrin because we have previously found the presence of a lactoferrin receptor in brush-border membranes from suckling piglets. In this study, viable enterocytes were isolated from 6- to 20-day-old suckling piglets. Binding studies were performed at 4 degrees C using 125I-labeled porcine lactoferrin. Scatchard analysis of equilibrium binding data showed an apparent binding constant (Kd) of 2 x 10(-6) M (SD = 0.6 x 10(-6)). This affinity is in close agreement with previous results obtained using isolated brush-border membrane vesicles. Bovine lactoferrin inhibited the binding of porcine lactoferrin. Porcine transferrin, however, did not affect porcine lactoferrin binding significantly. Thus, lactoferrin binding is highly specific. When enterocytes were incubated with 125I-labeled lactoferrin at 37 degrees C, the amount of cell-associated radioactivity exceeded the surface binding capacity of the cells by almost fivefold. This finding agrees with the continuous binding and subsequent internalization of 125I-labeled lactoferrin. The isolated piglet enterocyte seems to provide a useful model for further studies of the mechanism of receptor-mediated absorption of lactoferrin.

Iron absorption differs in piglets fed extrinsically and intrinsically 59Fe-labeled sow's milk.

Iron bioavailability from species-specific milk is assumed to be high for the offspring, possibly due to species-specific iron-binding proteins in the milk. To assess this bioavailability using radioisotopes, the validity of extrinsic labeling technique needs to be proven. Using the suckling piglet as an animal model, we have compared iron bioavailability from sow's milk labeled extrinsically and intrinsically. During intrinsic labeling transfer into milk of 59Fe given intramuscularly was slow and was found to be at maximum 14 h post-injection. Recovery of isotope in the milk was only 0.00014%. Extrinsic and intrinsic labels were distributed differently among milk fractions; intrinsic iron bound primarily to the fat fraction but the extrinsic iron bound primarily to the casein fraction. Iron retention from intrinsically labeled milk was considerably higher than from extrinsically labeled milk. These results show that the extrinsic tag method is not valid for studies on iron absorption from sow's milk and suggest that the situation may be the same for human milk.

Studies of the spatial distribution of firearms discharge residues.

Fingerprint lifting tape has been applied to the lifting of firearms discharge residue from various surfaces. Lifting efficiencies from coarse fabric ranged from 30 to 70%. Use of the technique has been demonstrated in identifying a bullet hole and in measuring residue patterns on floor and firing hand surfaces. In hand lifts it has been shown that autoradiography alone does not uniquely distinguish the hand of someone who has fired a revolver from the hand of someone who has not. Neutron activation analysis of lifts from selected hand areas may, however, provide such a distinction.