Estimation and comparison of zeta-potentials of silica-based anion-exchange type porous particles for capillary electrochromatography from electrophoretic and electroosmotic mobility.

Mobilities of different chromatographic particles obtained from two electrokinetic methods were determined and compared. The particles were all based on porous silica, between 3 and 15 microm diameter, and were either native, or derivatized. As intermediate of chemical modification 3-mercaptopropyl-modified silica particles (TP-silica) are obtained. These particles were finally transformed into weakly basic anion exchangers with O-9-(tert-butylcarbamoyl)quinine (tBuCQN) as chiral selector. The electrophoretic mobility of the particles was determined from their migration velocity in an electric field using microelectrophoresis. Electrokinetic chromatography with a capillary column packed with the same particles was used to measure the electroosmotic flow generated. All measurements were carried out in background electrolytes of equal ionic strength (10(-2) mol/L), at pH varying between 3.5 and 9.5. From these data a rough estimation of the zeta-potential was made, taking Helmholtz-Smoluchowski conditions into consideration. With both methods the zeta-potential of the native silica particles is negative throughout, and its value increases with pH. The weakly basic tBuCQN particles have positive zeta-potentials at pH lower than about 7.5, but exhibit a negative zeta-potential above this pH, indicating the dominating effect of residual silanol groups at the silica surface. The zeta-potential for these anion-exchange particles ranged between +30 and -40 mV. The zeta-potentials derived with electrophoresis and electroosmosis agree, showing the adequacy of the approach, although many limitations must be taken into account in the treatment of the electrokinetic phenomena in such porous systems. These restrictions in interpreting mobility and zeta-potential were discussed.

Acute respiratory failure and short-term outcome after premature rupture of the membranes and oligohydramnios before 20 weeks of gestation.

OBJECTIVES: To study the effect of premature rupture of membranes and oligohydramnios before 20 weeks of gestation (PROM20) on acute respiratory morbidity and on short-term outcome in infants with a gestational age >or=24 weeks. STUDY DESIGN: A historic cohort study was performed of all infants born after PROM20 with a gestational age greater-than-or-equal24 weeks between 1990 and 1999. Control infants were matched for year of birth, gestational age, and birth weight. RESULTS: PROM20 infants had an increased acute respiratory morbidity (higher ventilator settings and increased incidence of hypoxemia, hypercapnia, and pulmonary hypertension) and a trend to more air leaks. Although not statistically different, PROM20 infants had more complications (neonatal survival, 68% vs 95%; severe intracranial hemorrhage, 31% vs 6%; chronic lung disease in surviving infants, 46% vs 17%). The relative risk for combined morbidity (death, intracranial hemorrhage, chronic lung disease) was increased (3.0, P =.019) when compared with matched control infants. However, 31% of the surviving PROM20 infants were discharged without apparent morbidity. CONCLUSIONS: Expectant treatment in women with PROM20 and present neonatal intensive care has improved the survival of PROM20 infants despite severe initial respiratory failure. However, chronic morbidity still occurred.