Attenuated total internal reflectance infrared microspectroscopy as a detection technique for capillary electrophoresis

A novel detector for capillary electrophoresis (CE) using single-bounce attenuated total internal reflectance (ATR) Fourier transform infrared (FT-IR) microspectroscopy is presented. The terminus of the CE capillary is placed approximately 1 microm from the internal reflectance crystal at the focus of an ATR infrared microscope. Using pressure driven flow injection, concentration and volume detection limits have been determined for 25- and 10-microm-i.d. silica capillaries. Upon injection of 820 pL of succinylcholine chloride in a 10-microm capillary, a concentration detection limit of approximately 0.5 parts per thousand (ppt), or 410 pg, is found. The injection volume detection limit using a 108 ppt solution is 2.0 pL (216 pg). Sample separations using a programmed series of pressure, voltage, and again pressure on 25-, 50-, and 75-microm-i.d. capillaries are shown. CE separations of citrate and nitrate, as well as succinylcholine chloride with sodium salicylate using acetone as a neutral marker, are demonstrated. Several advantages of this CE-FT-IR technique include: (1) minimization of postcolumn broadening as a result of a small detector volume; (2) the ability to signal average spectra of the same aliquot, thereby improving the signal-to-noise in a stopped-flow environment; and (3) simplicity of design.     

Capillary electrochromatography-mass spectrometry of zwitterionic surfactants

This work describes the on-line hyphenation of a packed capillary electrochromatography (CEC) column with an internally tapered tip coupled to electrospray ionization-mass spectrometry (ESI-MS) and atmospheric pressure chemical ionization-mass spectrometry (APCI-MS) for the analysis of betaine-type amphoteric or zwitterionic surfactants (Zwittergent). A systematic investigation of the CEC separation and MS detection parameters comparing ESI and APCI is shown. First, a detailed and optimized manufacturing procedure for fabrication of the CEC-MS column with a reproducible internally tapered tip (7-9 microm) is presented. Next, the optimization of the separation parameters by varying the C(18) stationary-phase particle size (3 versus 1.5 microm), as well as mobile-phase composition including acetonitrile (ACN) volume fraction, ionic strength, and pH is described. The optimized separation is achieved using 3-microm C(18) packing with 75% ACN (v/v), 5 mM Tris at pH 8.0. Optimization for on-line CEC-ESI-MS detection is then done varying both the sheath liquid and spray chamber parameters while evaluating the use of random versus structured factorial table experimental designs. The more structured approach allows fundamental analysis of individual ESI-MS parameters while minimizing CEC and MS equilibration time between settings. A comparison of CEC-ESI-MS to CEC-APCI-MS using similar sheath and spray chamber conditions presents new insight for coupling of CEC to APCI-MS. The sheath liquid flow rate required to maintain adequate sensitivity is much higher in APCI source (50 microL/min) as compared to the ESI source (3 microL/min). The on-line mass spectra obtained in the full scan mode show that fragmentation in the two sources occurs at different positions on the Zwittergent molecules. For ESI-MS, the protonated molecular ion is always highest in abundance with minor fragmentation occurring due to the loss of the alkyl chain. In contrast, the APCI-MS spectra show that the highest abundant ion resulted by elimination of propane sulfonate from the Zwittergent molecule. A comparison of the sensitivity between the two sources in positive ionization SIM mode shows that CEC-ESI-MS provides an impressive limit of detection (LOD) of 5 ng/mL, which is at least 3 orders of magnitude lower than CEC-APCI-MS (LOD 100 microg/mL). Finally, the optimized CEC-MS methods comparing ESI and APCI are applied for separation and structural characterization of a real industrial zwittergent sample, Rewoteric AM CAS.     

THE PRODUCTION OF SOME WHITE ENAMELS FOR COPPER1

The investigation deals with the development of some white enamels for copper watch dials, thermometer scale plates, and signs. The effect of varying Na₂O, PbO, cryolite, SiO₂ and B₂O₃ on the properties of the enamels was studied in twenty enamel compositions. The following conclusions were reached: (1) Correct melting is extremely important in the preparation of copper enamels; (a) Slow air cooling of the frit is preferable to quenching in water. (b) Repeated melting tends to promote opacity and to eliminate dissolved gases. (2) A somewhat reducing atmosphere during firing avoids oxidation of the copper. (3) Slight changes in enamel composition have a decided effect on the resultant properties. (4) Sodium oxide promotes gloss but reduces opacity very decidedly. (5) Lead oxide promotes fusibility without materially reducing opacity, except by dilution. (6) Cryolite is not a desirable flux or opacifier as it tends to develop a matt finish. (7) It is desirable to keep the boric oxide content low and good enamels may be produced without it. (8) By using “white arsenic” as an opacifier tin oxide is unnecessary. (9) The following were the best enamels obtained and these appear to be equal to a number of watch dial enamels examined: C-19 and C-20. 20. (10) A second group of compositions which appear to promote results equal to those in use for thermometer scales, advertising letters, etc., are C-10. 10. C-21, C-22, and C-24. In selecting these compositions, all factors such as opacity, gloss, texture, fit and resistance to attack of copper have been considered.     

Improved early morbidity and mortality after Fontan operation: the Mayo Clinic experience, 1987 to 1992

OBJECTIVES: This study sought to evaluate changes in early morbidity and mortality as well as predictors of outcome in our most recent 339 patients undergoing modified Fontan operations. BACKGROUND: The Fontan operation is the preferred definitive palliation for patients with functional single ventricles. Previously reported early mortality rates after Fontan operation have been substantial. METHODS: Records of 339 consecutive patients who had a Fontan operation at the Mayo Clinic between 1987 and 1992 (recent cohort) were reviewed. This cohort was compared with the previous 500 patients who had Fontan operations performed between 1973 and 1986 (early cohort). RESULTS: Recently, overall early mortality after Fontan has decreased significantly compared with that for the early cohort (from 16% to 9%, p = 0.002). This decline occurred despite increased anatomic complexity of patients. Short-term posthospital survival has also improved significantly in recent patients. One-year survival improved to 88% from 79%, and 5-year survival to 81% from 73% (p = 0.006). Patients with common atrioventricular valves and those who took daily preoperative diuretic medication or had either postoperative renal failure or elevated postbypass right atrial pressure were at increased risk for early mortality. Young age was not found to be a risk factor for early mortality. Early mortality for patients with heterotaxia decreased dramatically: recent 30-day mortality was 15% compared with 41% in the early heterotaxy cohort. CONCLUSIONS: Many factors may have contributed to decreased early mortality after Fontan. Improved patient selection, younger age at time of operation, refinements in surgical techniques and postoperative management may all have had important roles. Proposed technical modifications of the Fontan operation must be evaluated in light of these improved results.     

PET studies on brain monoamine transporters with carbon-11-beta-CIT in Parkinson's disease

The cocaine analog 2 beta-carbomethoxy-3 beta-[4-iodophenyl]tropane (beta-CIT) labeled with 11C was used to study dopamine reuptake sites with PET. METHODS: Three normal subjects and nine patients with Parkinson's disease were investigated. Each of them underwent a dynamic PET scan (25 timeframes over 80 min) with [11C]-beta-CIT. A dose of 102.5-211.3 MBq (2.77-5.71 mCi) of this ligand was administered intravenously and a PET examination with an ECAT 931/08 PET camera was carried out. Ratios between the striatal/cortical/thalamic/midbrain and cerebellar uptake of this radioligand were calculated. RESULTS: The highest accumulation of [11C]beta-CIT was observed in the caudate and putamen, though there was some uptake in the thalamus and the midbrain. Cortical uptake was negligible. Carbon-11-beta-CIT accumulated significantly less in the putamen of the Parkinson's patients than in the normal subjects. The putamen-to-cerebellum ratio in the Parkinson's patients was 1.59 +/- 0.04 and 1.80 +/- 0.13s (p = 0.028) in the normal subjects. In the caudate, there was no significant difference between the Parkinson's patients and the normal subjects. CONCLUSION: These results imply that [11C]beta-CIT is a useful compound for carrying out a PET examination of the function of the presynaptic monoaminergic neurons both in normal and pathological brains.     

Studies on the substrate specificity and inhibition of prostaglandin biosynthesis with methyl branched isomers of eicosa-8, 11, 14-trienoic acid

Seven radioactive methyl branched isomers of eicosa-8, 11, 14-trienoic acid, in which a methyl branch was located at carbon 2, 5, 10, 13, 17, 18, or 19, were used as substrates to study their enzymatic conversion into homologues of prostaglandin E1 by microsomes from bovine vesicular glands. The products of this reaction were partially characterized. When the methyl branch was moved towards position 13, the site of sterospecific hydrogen removal by prostaglandin synthetase, the rate of prostaglandin formation decline rapidly. When a methyl branch was a position 10, 13, 17, 18, or 19, the rates of prostaglandin formation were less than 25% of that from eicosa-8, 11, 14-etienoic acid. However, when a methyl branch was at positions 2 or 5, these isomers were converted to prostaglandins at least 50% as rapidly as eicosa-8, 11, 14-trienoic was converted to prostaglandins. The apparent Km and Vmax values for eicosa-8, 11, 14-trienoic acid were respectively 224 muM and 4.62 nmoles/min/mg protein. Kinetic data suggest that the enzyme converted eicosa-8, 11, 14-trienoic acid to prostaglandins 3.6 times faster than the 5-methyl branched isomer, although the enzyme bound the branched isomer twice as firmly as eicosa-8, 11, 14-trienoic acid. The concentration-dependent inhibition of prostaglandin formation from eicosa-8, 11, 14-trienoic acid by the 13-methyl branched isomer was also demonstrated.     

Reactivity of poly(chlorotrifluoroethylene) (PCTFE) oil and PCTFE derivatives with phenyllithium and phenyl Grignard reagents

Summary Poly(chlorotrifluoroethylene) (PCTFE) oil upon reaction with phenyllithium at-78°C formed functionalized products that could be isolated in three fractions by solvent extraction with pentane, ether, and tetrahydrofuran (THF). At-125°C crosslinking of polytrifluoroethylene (PF₃E), and Kel-F 800, a co-polymer of 72% chlorotrifluoroethylene and 28% vinylidene fluoride, with phenyllithium or phenylmagnesium bromide formed glassy black insoluble products. Infrared spectroscopy showed aromatic functional groups had been introduced in all the products. However, alkyl peaks were also evident in the infrared spectra of the lithiated products. Size exclusion chromatography of soluble Kel-F 800 reaction products indicated cracking to lower molecular weight material.