Conductivity Detectors for Column or Paper Chromatography

SUMMARY

A conductivity detector, employing inexpensive operational amplifiers, has been constructed for chromatographic use. The detector is capable of observing conductance changes as small as 1 part in 10⁵ with bridge signals of 100 mV. Detector linearity is good over a wide dynamic range. When used in conjunction with a cell employing mercury strip electrodes, the detector can monitor the elution of ions in paper chromatography. The alkali metals were separated and detected on Whatman No. 1 paper with a sensitivity of less than 10 nmoles. This sensitivity limit was not determined by noise in the detector electronics, but by ionic impurities in the paper. The same detector, and a cell employing platinum electrodes separated from the effluent by ion-exchange membranes, was tested and found suitable for use in column chromatography. Again the sensitivity was not limited by the detector electronics.     

Archaeal nucleosome positioning by CTG repeats

DNA shape recognition determines the preferred binding sites for sequence-independent DNA binding proteins, and here we document that archaeal histones assemble archaeal nucleosomes in vitro centered preferentially within (CTG)6 and (CTG)8 repeats, close to junctions with flanking mixed-sequence DNA. Archaeal nucleosomes were not positioned by (CTG)4-, (CTG)5-, or (CTG)3AA(CTG)3-containing DNA sequences. The features of CTG repeat-containing sequences that direct eucaryal nucleosome positioning may also be similarly recognized by archaeal histones.     

Method for measuring base/neutral and carbamate pesticides in personal dietary samples

Dietary uptake may be a significant pathway of exposure to contaminants. As such, dietary exposure assessments should be considered an important part of the total exposure assessment process. The objective of this work was to develop reliable methods that are applicable to a wide range of base/neutral and carbamate-type pesticides in duplicate diet samples collected as part of dietary exposure assessment studies. The resulting method needed to be sensitive to concentrations below 1 ng/g, accurate and precise, and as simple and cost effective as possible. As a first step, information was gathered on current methods for measuring pesticides in foods. Although the literature methods could serve as a starting point, few had been applied to duplicate diet samples and detection limits were generally high (10 to 100 ng/g). Experimental work was performed to evaluate individual extraction, cleanup, and analysis procedures; link the most promising procedures into analysis methods; and generate performance data on the final method. The final method used Soxhlet extraction with solvent partitioning and gel permeation chromatography cleanup. Gas chromatography/mass spectrometry was used for the analysis of base/neutral pesticides. High performance liquid chromatography analysis was used for the analysis of carbamate pesticides. Results of performance testing showed good accuracy (recovery > 70%), precision (% RSD < 25%), and sensitivity (method detection limits < 1.0 ng/g) for most pesticides targeted for study.     

NMDA receptor-mediated oscillatory activity in the neonatal rat spinal cord is serotonin dependent

The effect of serotonin (5-HT) receptor blockade on rhythmic network activity and on N-methyl--aspartate (NMDA) receptor-induced membrane voltage oscillations was examined using an in vitro neonatal rat spinal cord preparation. Pharmacologically induced rhythmic hindlimb activity, monitored via flexor and extensor electroneurograms or ventral root recordings, was abolished by 5-HT receptor antagonists. Intrinsic motoneuronal voltage oscillations, induced by NMDA in the presence of tetrodotoxin (TTX), either were abolished completely or transformed to long-lasting voltage shifts by 5-HT receptor antagonists. Conversely, 5-HT application facilitated the expression of NMDA-receptor-mediated rhythmic voltage oscillations. The results suggest that an interplay between 5-HT and NMDA receptor actions may be critical for the production of rhythmic motor behavior in the mammalian spinal cord, both at the network and single cell level.     

Clinical and experimental studies on preventing and treating anaphylactic asthma with Zusanli point immunotherapy

We have studied on preventing and treating anaphylactic asthma with Zusanli (S36) point immunotherapy (ZPIT). Sixty-nine patients were observed. The results showed that the clinical curative effect of ZPIT was not only much higher than that of conventional desensitization therapy, but also the patients' total IgE level was reduced, anti-acarid IgE was lowered, SIgA level was raised, the absolute eosinophilic granulocyte level dropped and pulmonary function recovered. Animal experiment results showed that the ZPIT could more effectively suppress the guinea pigs' anaphylactic asthma allergized by albumin and more obviously resist the guinea pigs' bronchial spasm induced by histamine and acetylcholine than the conventional desensitization therapy and injected normal saline. The immunomodulating action of the ZPIT are elucidated from clinical study and animal experiment in the paper.     

Extraction and replacement of permanent pacemaker leads through occluded vessels: use of extraction sheaths as conduits--balloon venoplasty as an adjunct

Patients (pts) may present for lead extraction with symptomatic or asymptomatic subclavian vein or superior vena cava thrombosis. Replacement of permanent pacemaker leads (PPLs) in these pts may be difficult and may require accessing a new site. We examined the utility of replacing PPLs through completely occluded vessels using extraction sheaths as conduits through the total occlusion. Over six years, a total of 210 atrial and/or ventricular PPLs were extracted from 137 pts. Two pts presented with angiographically documented thrombotic occlusion of the subclavian vein. One additional pt. who had presented with a superior vena cava (SVC) syndrome, had a totally occluded innominate vein and SVC occlusion. Balloon venoplasty was used as an adjunct to dilate the SVC. In all pts, after PPLs were removed via a subclavian extraction sheath through the occluded vessel, the retained sheath was used to place a guide wire, then a peel away dilating sheath, to insert new PPLs, in each case on the side of total venous occlusion. Seven PPLs and two lead fragments were extracted, and five new PPLs replaced, ipsilateral to the venous occlusion. These data show that extraction of PPLs through thrombosed veins may be performed successfully and may not require replacing the leads through a new site. This technique spares the pt the need to access the opposite subclavian vein, and it avoids an excessive number of PPLs in the subclavian vein and SVC. The procedure illustrates an efficient means to reintroduce new PPLs with the potential to reduce associated morbidity, since repeat puncture of the subclavian vein is not required. Safety of the procedure as a whole must be considered with regard to the known risks of lead extraction, some complications of which may be substantial using current techniques.