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Berger T.A.,SFC Inc
Journal of Chromatography A | Year: 2015

Analytical scale supercritical fluid chromatography (SFC) is largely a sub-discipline of high performance liquid chromatography (HPLC), in that most of the hardware and software can be used for either technique. The aspects that separate the 2 techniques stem from the use of carbon dioxide (CO2) as the main component of the mobile phase in SFC. The high compressibility and low viscosity of CO2 mean that pumps, and autosamplers designed for HPLC either need to be modified or an alternate means of dealing with compressibility needs to be found. The inclusion of a back pressure regulator and a high pressure flow cell for any UV-Vis detector are also necessary. Details of the various approaches, problems and solutions are described. Characteristics, such as adiabatic vs. isothermal compressibility, thermal gradients, and refractive index issues are dealt with in detail. © 2015 Elsevier B.V.


The first systematic study of the performance of a porous shell, hydrophylic interaction liquid chromatography (HILIC) column in supercritical fluid chromatography (SFC) is presented. Observed efficiency on 2.6-μm porous shell particles exceeded all reports using UHPLC on 100-mm long columns packed with <2-μm totally porous particles. A Kinetex 4.6×150mm, 2.6μm HILIC column significantly outperformed a 3μm Luna totally porous silica of the same length and diameter. A 17 component, low molecular weight test mix, consisting of a range of small drug-like molecules was separated isocratically on each column, with similar selectivity, but the porous shell column required 1\2 the time (≈2min vs. 4min), with almost 50% higher efficiency. Even little retained compounds (k<0.5) exhibited more than 30,000 plates under some conditions. Reduced plate heights were higher than previously reported on porous shell particles in both HILIC and rHPLC, with the lowest value of 1.62. Significant fronting was sometimes observed. The cause of the fronting was not determined. The least symmetrical peaks showed the highest apparent efficiency. Pressure drop at optimum velocity (2.5ml/min) and low modifier concentrations was <60bar, and only exceeded 250bar at near double optimum flow and 65% modifier. Peak widths were mostly just over 0.01min (20Hz) wide. There was a loss of efficiency when the injection volume was increased. The chromatograph was shown to have extremely low extra-column dispersion, on the order of 5-10μL 2, which is also the lowest reported in an SFC, in spite of using standard components. This is likely due to turbulent flow in the tubing and fittings. © 2011 Elsevier B.V.


The preservatives benzoate and sorbate, plus caffeine were rapidly separated and quantified, in just over 2 min, in a wide range of beverages and foods, using supercritical fluid chromatography (SFC). Fifteen beverages and 10 semi-liquid foods were evaluated. The benzoate and sorbate were originally present in the samples as the acid, or the sodium, or potassium salt. The aqueous samples were diluted 3:1 with acidified methanol, to insure the acids were protonated, then directly injected. The solutes were isocratically eluted from a 4 × 250 mm, 5 μm Diol column with 3.5 mL min-1 of 8.5 % methanol containing 0.3 % acetic acid at 50 C and a column outlet pressure of 150 bar. The real samples exhibited remarkably little interference. All the beverages were accurately labeled. However, many of the foods, such as salad dressings, mustard, etc., were mislabeled. The method was linear over a wide range with correlation coefficients for all three solutes >0.999. RSD's were generally less than 1 %. The results agreed with the caffeine content on the labels within a few percent. Surprisingly, this appears to be the first published separation of benzoic and sorbic acid preservatives in food, and beverages using SFC, and one of a very few SFC applications where aqueous samples were simply diluted and injected. Compared to published references, the SFC method was found to be up to 7 times faster than HPLC, and eliminated the use of acetonitrile. © 2013 Springer-Verlag Berlin Heidelberg.


The concept of peak fidelity was shown to be helpful in modeling tubing and detector cell dimensions. Connection tubing and flow cell variances were modeled to determine appropriate internal ID's, lengths, and volumes. A low dispersion plumbing configuration, based on these calculations, was assembled to replace the standard plumbing and produced the reported results. The modifications made were straightforward using commercially available parts. The full theoretical efficiency of a 3 × 100 mm column packed with 1.8 μm totally porous particles was achieved for the first time in supercritical fluid chromatography (SFC). Peak fidelity of >0.95 was maintained to below k = 2. A reduced plate height as low as 1.87 was measured. Thus, true "ultra high performance" SFC was achieved, with the results a major improvement from all previous SFC reports.Since there were no efficiency losses, none could be attributed to thermal gradients caused by the expansion of the fluid over large pressure drops, under the conditions used. Similarly, changes in diffusion coefficients caused by significant decreases in density during expansion are apparently balanced by the increase in linear velocity, keeping the ratio between the diffusion coefficient and the linear velocity a constant. Changing modifier concentration to change retention was shown to not be a significant problem. All these issues have been a concern in the past.Diffusion coefficients, and viscosity data needs to be collected at high pressures before the actual limits of SFC can be discovered. © 2016 Elsevier B.V.


Berger T.A.,SFC Inc | Berger B.K.,SFC Inc
Journal of Chromatography A | Year: 2011

Pressure fluctuations and resulting refractive index changes, induced by the back pressure regulator (BPR) can be a significant source of UV detector noise in supercritical fluid chromatography (SFC). The refractive index (RI) of pure carbon dioxide (CO 2) changes ≈0.2%/bar at the most commonly used conditions in supercritical fluid chromatography (SFC) (40°C and 100bar), compared to 0.0045%/bar for water (CO 2 IS 44× worse). Changes in RI cause changes in the focal length of the detector cell which results in changes in UV intensity entering the detector. The change in RI (ΔRI/bar) of CO 2 decreases 8-fold at 200bar, compared to 100bar. A new back pressure regulator (BPR) design representing an order of magnitude improvement in the state of the art is shown to produce peak to peak pressure noise (PN p-p) as low as 0.1bar, at 200bar, and 20Hz, compared to older equipment that attempted to maintain PN p-p<1bar, at <5Hz. With this lower PN p-p, changes in baseline UV offsets could be measured as a function of very small changes in pressure. A pressure change of ±1bar at 100bar, common with some older BPR's, produced a UV baseline offset >0.5mAU. A pressure change of ±0.5bar representing the previous state-of-the-art, resulted in a UV offset of 0.3mAU. Baseline noise <0.05 is required to validate methods for trace analysis. The new BPR, with a PN p-p of 0.1bar, demonstrated UV peak to peak noise (N p-p)<0.02mAU with a >0.03min (10Hz) electronic filter under some conditions. This new low noise level makes it possible to validate SFC methods for the first time. © 2011 Elsevier B.V.


Berger T.A.,SFC Inc
Journal of Chromatography A | Year: 2016

Reduced plate heights (hr) of <2 were observed for the first time during the chiral separation of enantiomers, on sub-2μm particles with supercritical fluid chromatography (SFC). The enantiomers of trans-stilbene oxide, were separated on a 4.6×50mm, 1.8μm R,R-Whelk-O1 column, with hr as low as 1.93. The plumbing of a commercial SFC instrument was modified to create a low dispersion version. Without the modification performance was considerably worse.vanDeemter like plots of reduced plate height vs. flow rate, for trans-stilbene oxide, indicate that the optimum flow varied with% modifier. On a 4.6×250mm, 5μm R,R- Whelk-O1 column, the optimum flow was >4mL/min for 5% methanol in CO2, decreasing to <2mL/min for 40% methanol (more than a factor of 2). For a 4.6×50mm column packed with 1.8μm particles the optimum appeared to be near, or >5mL/min with 2.5%, 5%, and 10% methanol, decreasing to between 3 and 3.5mL/min at 40% methanol. This is the first time such shifts have been characterized. Since the solutes were the same in all cases, the differences are likely due to changes in solute diffusion coefficients caused by changes in modifier concentration, and pressure.Pump pressure requirements sometimes exceeded 500. bar. It is shown that a 5. mL/min flow rate is inadequate for use with 1.8. μm particles in a 4.6. mm ID column format. Instead, it is suggested to decrease the ID of the column to 3. mm, where the optimum flow rates are on the order of 2. mL/min with decreased tubing variance. Nevertheless, a number of sub-1. min chromatograms are presented. © 2016 Elsevier B.V.


Patent
SFC Inc | Date: 2012-06-22

An apparatus, system, and process of converting a standard, high performance liquid chromatography (HPLC) flow path to a flow path suitable for supercritical fluid chromatography (SFC) are described. This reversible technique is applied to a variety of flow configurations including binary, high pressure solvent mixing systems and quaternary, low pressure solvent mixing systems than can be conventionally operated or automated. The technique is generally applied to the fields of supercritical fluid chromatography and high pressure liquid chromatography, but users skilled in the art will find utility for any flow system where pressurization components must be periodically applied to and removed from both ends of a flow stream in an automated manner.


Patent
SFC Inc | Date: 2016-04-08

A microwave packaging material including a plurality of susceptors is disclosed. Each susceptor includes a plastic film or polymer with a metal layer on one surface of the plastic film and a paper adhered to the plastic film opposite the metal layer. A patterned adhesive is bonded between a first susceptor layer and a second susceptor layer in a pattern bond creating sealed air pockets. A paper board substrate is adhered using an adhesive in a bond pattern to one of the susceptor layers facing the metal of the respective susceptor layer to provide the microwave packing material rigidity. Upon exposure to microwave energy in a microwave oven, moisture is trapped between the paper board substrate and the susceptor layer creating a vapor pressure that causes the sealed air pockets to form expanded air pockets.


An automated assay platform for determining the presence and/or amount of analytes of interest in a sample at point of care integrates microfluidic enhanced assay sites, disposable cartridge designs, a sensitive low-volume detection module, together with selected pumping and valving modules, customized control board and user friendly graphical user interface (GUI). Comparing to traditional assay platform like 96-well ELISA, the platform is capable of reducing reagent consumption, increasing assay speed, and enhancing assay performance with a sample-in-answer-out automated process. This platform also features flexibility of adapting different assay schemes for different analytes.


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