Biomedical subjects

B S Broyles

Publications and source records attributed to B S Broyles.

8 recordsLinked to original sources

PubMed2001

Visualization of solute migration in chromatographic columns influence of the frit porosity.

The dual-perspective, on-column detection method previously described was used to observe the effects of the inlet frit on the profiles of chromatographic bands. Visualization of bands of iodine was achieved by injecting its dilute solutions in carbon tetrachloride into a glass column packed with a C18-bonded silica and eluted with carbon tetrachloride, which has the same refractive index as the packing material. The bands were photographed on-column with two standard 35-mm SLR cameras oriented at right angle. The photographs were scanned and the digitized images of the sample bands analyzed with proper software. A number of columns, as similar as possible, were fitted with different 2- and 10-microm porosity stainless steel frits. Subsequent analysis of the digitized band images revealed irregularities in the band shape resulting from frit contributions to band dispersion. The 2-microm frits produced more dramatic effects overall than the coarser frits. Local axial dispersion coefficient values, expressed as local reduced plate height, were calculated. The results demonstrate the possibly damaging effects of the frit on the band shape.

Chromatography, Liquid↗

PubMed2000

Physical evidence of two wall effects in liquid chromatography.

Using optical on-column visualization for the study of the migration of sample bands, the radial variations of the local migration rate were studied in the region near the column wall. Photographs of small sample bands migrating along the column at various radial locations were obtained. On-column chromatograms extracted from these photographs showed evidence of two wall effects. The first of these effects was present only within the immediate vicinity of the wall. It is a direct result of the inability of the packing material to form a close packed configuration against the rigid column wall surface. The second wall effect causes a systematic variation of the migration rate of the sample band in the region of the wall, this rate increasing from the wall to the central region of the column. The corresponding images portrayed the classical "wall effect" that chromatographers have long discussed. They also show that this effect extends further into the column than anticipated. As to what are the relative contributions to the results of our observations of the wall effect and of a frit effect discussed in previous publications, this could not be ascertained.

Artifacts↗

PubMed2000

Evaluation of the secondary consolidation of columns for liquid chromatography by ultrasonic irradiation.

The consolidation of packed analytical chromatography columns was carried out under ultrasonic irradiation. Columns were first packed using a conventional high pressure downward slurry method. Then, they were subjected to further bed consolidation in the presence of ultrasonic vibration. This process of further bed consolidation is referred to as secondary consolidation. Secondary consolidation was observed to occur more readily in solvents of low viscosity and at low flow-rates (low pressures). Column efficiency was not observed to be a factor affecting the process of secondary consolidation of the packed bed.

Chromatography, Liquid↗

PubMed2000

Visualization of solute migration in chromatographic columns quantitation of the concentration in a migrating zone.

The concentration distribution across a zone of iodine migrating along a column made of glass, packed with C18-bonded silica, and eluted with carbon tetrachloride was derived from a quantitative analysis of the photographs of the zone. The photographs were scanned and turned into digital images. The intensity distributions obtained from the measurement of the grayscale intensity were converted into concentration profiles using a calibration method. This procedure is illustrated and suitable corrections are introduced to account for the transverse variation of the optical path length, as a result of using a cylindrical detector cell (the column itself), and for the refraction of light due to the differences between the refraction indices of the glass wall and the liquids involved. An error analysis is also reported. It shows that the method can reliably produce results with a precision of a few percent, allowing on-column evaluation of column performance and the derivation of the radial distributions of the column efficiency, the migration velocity of the zone, and the sample distribution at the head of the column.

Calibration↗

PubMed2000

On-column visualization of sample migration in liquid chromatography.

A quantitative on-column visualization technique for evaluating solute migration in liquid chromatography columns was described. This technique employed a matched refraction index phase system in high-pressure glass columns. In this case, the mobile phase was carbon tetrachloride and the stationary phase was a C18 silica. Because the refractive indexes of the two phases were the same, the column bed, otherwise opaque, was transparent to the eye. Zones of colored solutes could be injected (iodine for instance) and their migration studied along the column. Photographing the sample band during its migration allowed chromatographic information to be extracted using digital technology. As an example of applications for this technique, we show the sample entry through various inlet fittings. The results demonstrate that chromatographers should pay more attention to the selection of inlet frits. Importantly, the frit porosity should be matched to the particle size of the packing.

Calibration↗

PubMed1999

Visualization of sample introduction in liquid chromatographic columns. Contribution of a flow distributor on the sample band shape.

The contributions to the radial distribution of the sample concentration across the column inlet and to the axial band dispersion resulting from a column header containing a distributor were evaluated using a band-visualization process entailing matching the refractive indices of the stationary and mobile phases in a glass column. This study illustrates graphically how a distributor fitted to the column can increase the axial dispersion of the sample band compared to an inlet containing only a frit. The distributor did not provide a uniform sample distribution across the column. In fact, for 17-mm inner diameter columns and high-porosity frits, the distribution was no better than with the frit having no distributor. However, when low-porosity frits were employed, improved peak shapes were obtained with a distributor. In addition, we observed that the inlet header configuration influenced dramatically the flow stream established along the column. The radial distribution of the efficiency of the columns was nearly homogeneous for those having only a frit but not for those having also a distributor. For the latter, the efficiency decreased from the column axis to its wall.

Chemical Phenomena↗

PubMed1999

Visualization of viscous fingering in high-performance liquid chromatographic columns. Influence of the header design.

Using an on-column visualization technique, band profiles of solutes migrating along an HPLC column were studied. The study showed that, under conditions where viscous fingering is prevalent, the design of the inlet header has little influence on the outcome of the viscous fingers. Two types of headers were studied. The first contained a small diameter inlet frit, which localized the majority of the sample in or near the central region of the column. The second header contained a wide frit and produced a more uniform radial distribution of the sample. In both cases, the extent of viscous fingering was essentially the same.

Chemical Phenomena↗

PubMed1999

Visualization of sample introduction in liquid chromatography columns. The effect of the frit diameter.

A previously developed on-column detection technique using 35 mm SLR cameras [J. Chromatogr. A 826 (1998) 1] was employed to visualize colored sample bands as they elute through frits of differing diameter. Head fittings containing a 4.0 mm frit and a 15.9 mm frit were mounted in a 17 mm I.D. glass column packed with C18 silica with an average particle size of 21 microns. A carbon tetrachloride mobile phase of matching refractive index to that of the silica provides clarity along the column diameter during band migration. The photographs of the migrating sample zones were scanned and analyzed with appropriate imaging software. The smallest diameter frit induced severely parabolic sample distributions at the column inlet compared to the larger frit. Local axial dispersion coefficient values, expressed as local reduced plate height, were calculated as well as local zone velocities at the column inlet. The results demonstrate clearly the need to match the diameter of the inlet frit to the I.D. of the column so as to avoid the initial onset of zone broadening due to the frit.

Chromatography, Liquid↗