We present here the instrument design and first experimental results from a multipass millimeter/submillimeter spectrometer designed to probe dissociative reaction dynamics. This work focuses on benchmarking the instrument performance through detection of the CH3O and H2CO products from methanol dissociation induced by a high-voltage plasma discharge. Multiple rotational lines from CH3O and H2CO were observed when this plasma discharge was applied to a sample of methanol vapor seeded in an argon supersonic expansion. The rotational temperature of the dissociation products and their abundance with respect to methanol were determined using a Boltzmann analysis. The minimum detectable absorption coefficient for this instrument was determined to be αmin ≤ 5 × 10(-9) cm(-1). We discuss these results in the context of future applications of this instrument to the study of photodissociation branching ratios for small organic molecules that are important in complex interstellar chemistry.

A new approach to wavelength-modulation photoacoustic spectroscopy is reported, which incorporates diode lasers in the near infrared and optical fiber amplifiers to enhance sensitivity. We demonstrate the technique with ammonia detection, yielding a sensitivity limit less than 6 parts in 10(9), by interrogating a transition near 1532 nm with 500 mW of output power from the fiber amplifier, an optical pathlength of 18.4 cm, and an integration time constant of 10 s. This sensitivity is 15 times better than in prior published results for detecting ammonia with near-infrared diode lasers. The normalized minimum detectable fractional optical density, alphaminl, is 1.8 x 10(-8); the minimum detectable absorption coefficient, alphamin, is 9.5 x 10(-10) cm(-1); and the minimum detectable absorption coefficient normalized by power and bandwidth is 1.5 x 10(-9) W cm(-1)/square root Hz. These measurements represent what we believe to be the first use of fiber amplifiers to enhance photoacoustic spectroscopy, and this technique is applicable to all other species that fall within the gain curves of optical fiber amplifiers.

OBJECTIVE:

To isolate and purify pulmonary surfactant-associated protein A(SP-A) from human amniotic fluid.

METHODS:

Human amniotic fluid was collected from 11 parturients and SP-A was isolated by extraction and dialysis followed by purification procedures. The specificity of SP-A was detected by Western blotting and the bioactivity assessed by MTP-1 film balance.

RESULTS:

An amount of 12 mg (20 ml) purified SP-A was obtained, and the protein presented a single band upon SDS-PAGE with relative molecular mass of 31 000. Western blotting also displayed one specific band. Film balance demonstrated that the minimum surface tension alphamin of Exosurf, an synthetic pulmonary surfactant, was 7.7+/-0.3, significantly higher than alphamin of Exosurf and SP-A mixture(1.5+/-0.22, P<0.05), indicating enhanced bioactivity of the mixture.

CONCLUSION:

Dialysis can effectively purify SP-A from human amniotic fluid with little damage of its biological activity.

The influence of temperature on retention and separation of estrogens, progesterone derivatives and beta-cyclodextrin in reversed-phase high-performance liquid chromatography has been studied. Steroids were detected using direct UV detection at 240 and 280 nm. Detection of beta-cyclodextrin was achieved using a post-column indirect photometric method. Chromatographic experiments were performed using an acetonitrile-water mobile phase (30%, v/v) and a wide range of column temperatures from 0 to 80 degrees C with 20 degrees C steps. Linear Van't Hoff plots were observed for steroids and beta-cyclodextrin when an unmodified binary mobile phase was applied. The retention of steroids was strongly influenced by temperature when the mobile phase was modified with beta-cyclodextrin at a concentration of 12 mM. Particularly, for 17beta-estradiol and 20alpha-hydroxyprogesterone a strong deviation from the linear Van't Hoff plots and a remarkable affinity for beta-cyclodextrin was observed. Polynomial regression calculations were performed to fit the set of experimental data points. Using third-order polynomial equations, minimum separation factor values (alphamin) were calculated for temperatures from -10 to + 100 degrees C with 1 degrees C steps. The best chromatographic conditions for separation of multicomponent samples were chosen. A possible retention mechanism for solutes in the presence of macrocyclic additives is discussed. The results presented describe the role of temperature in high-performance liquid chromatography systems in which the mobile phase is modified with an inclusion agent.