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Temperature Effects in Reversed-Phase Liquid Chromatography
Published in Nelu Grinberg, Peter W. Carr, Advances in Chromatography Volume 57, 2020
Anthony R. Horner, Erin P. Shields, Michael T. Rerick, Stephen G. Weber
Solute focusing during injection results in the solute’s occupying a smaller volume on column than the volume injected. Minimizing the volume on column requires the solute to have a high retention factor, k, during the injection. Further, it is also wise to avoid larger diameter columns. Capillary-scale columns are often essential for the analysis of low volume, low concentration samples because they avoid radial dilution of the sample.61 Both temperature and solvent composition during the injection can be manipulated to temporarily increase solute retention during injection. It is this concentration enhancement effect that has made capillary-scale columns such an invaluable tool when applied to the fields of metabolomics,62–64 proteomics,65,66 and online monitoring of neurotransmitters.67–69 However, the enhancement from decreasing the column diameter may not be observed if the analyte retention during injection is low or if injection volume is large in relation to the total column fluid volume.70,71 In these cases, injecting more sample only results in a broader peak at a constant peak height. This effect is known as volume overload.72 To maximize the concentration sensitivity of a method, inject the largest volume of sample that increases the ultimate peak width only marginally given the retention factor, k, of the solute under the conditions during the injection and the column radius.
Should we overcome the resistance to bioelectrical impedance in heart failure?
Published in Expert Review of Medical Devices, 2020
Stephen J. Hankinson, Charles H. Williams, Van-Khue Ton, Stephen S. Gottlieb, Charles C. Hong
Decompensated HF is characterized by elevated diastolic pressures and symptoms of volume overload including dyspnea, fatigue, rales, and peripheral and pulmonary edema [7]. Available data suggest the symptoms of volume overload due to elevated cardiac filling pressures are the most common precipitant for hospitalization and readmission for worsening HF [8]. Volume overload in HF is defined as a high left ventricular diastolic pressure (LVDP) and symptoms of HF [9]. Elevation of LVDP in patients with HF without overt clinical volume overload is called hemodynamic congestion [10]. Hemodynamic congestion often precedes clinical volume overload by days or even weeks; therefore, volume overload may represent the end result of complex hemodynamic derangements that precede HF symptoms [9,11]. Considering that decompensated HF is often preceded by a gradual increase in fluid over weeks, numerous monitoring strategies have been proposed to improve detection of impending volume overload. Guidelines recommend patients with HF benefit from regular follow-up and monitoring of biomedical parameters in order to maintain euvolemia, ensure the safety and optimal dosing of medicines, and monitor for disease progression in order to avoid decompensated HF [12]. The most common method to detect impending volume overload in patients with HF is regular monitoring of body weight (BW). Guidelines recommend that in the case of unexpected weight gain greater than 2 kg in three days, then patients should increase their diuretic dose and alert their health-care team [12]. Unfortunately, the sensitivity of BW to detect HF decompensation is low [13]. Moreover, markers of volume removal such as weight loss, fluid loss, and natriuretic peptides have a poor correlation with dyspnea relief [14]. Therefore, additional means of fluid status monitoring is needed for HF evaluation in the acute care and ambulatory care settings.