The solvent venting injection technique in capillary supercritical fluid chromatography

Berg, B. E.; Greibrokk, Tyge

doi:10.1002/jhrc.1240120516

Cited by 38 publications

(22 citation statements)

References 2 publications

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“…Due to the enhanced spreading of the sample in the precolumn, poor column efficiencies have been obtained with 100-pm i.d. precolumns [17,41]. One reason for this can be due to the large surface area on which the sample is spread.…”

Section: Solvent Ventmentioning

confidence: 99%

“…In SFC, there have been several different methods that have been used to focus the solutes. Focusing of nonvolatile compounds occurs (a) when the solvating power of the supercritical fluid suddenly decreases either by decreasing the pressure [l-71 or by increasing the temperature [8-121, (b) when a mixing chamber is used in front of the analytical column [13-151, (c) when samples are introduced with solvent vent injection [16,17], (d) when a small volume of solvent is introduced as a "chaser" to refocus the sample after solvent venting [16], and (e) when an uncoated precolumn (retention gap) is used in front of the analytical column [18].…”

Section: Introductionmentioning

confidence: 99%

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Solute focusing in supercritical fluid chromatography

Koski

Lee

1991

J Microcolumn Separations

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Abstract. Solute focusing is an important topic in chromatography, but it has not been discussed extensively in the recent supercritical fluid chromatography literature. The purpose of this paper is to review the different methods that have been used to focus solutes in supercritical fluid chromatography. The theoretical basis for phase ratio and partition coefficient focusing is described. Different solute focusing devices that are used in on-line supercritical fluid extraction and chromatography are shown. The methods and principles of removing the solvent from the solutes prior to the analytical column, and hence reducing band broadening in the column due to the solvent, are discussed in context with the use of a retention gap or a mixing chamber, and in solvent vent injection.

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Section: Solvent Ventmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Solute focusing in supercritical fluid chromatography

Koski

Lee

1991

J Microcolumn Separations

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“…The major part of the solvent is vented through a restrictor at a rapid (10-15 cm/s) but controlled flow rate. With a 2-m precolumn the venting time was 15-20 s. Discrimination losses occur for early eluting peaks if venting times are too long, while peak shapes are degraded when the starting pressures are too high [23]. Sample recovery can be quite acceptable with this technique.…”

Section: Solvent Venting Under Supercritical Conditionsmentioning

confidence: 99%

Injection techniques in SFC

Greibrokk¹,

Chester²

1999

Analusis

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The objective of the injector is to transfer the whole sample or a predetermined fraction of the sample quantitatively to the column in the narrowest possible band. The first part of this objective, a quantitative transfer of all components, is not always obtained since sample discrimination occurs in some injection techniques in SFC as well as in GC. The second part of the objective, transfer in a narrow band, is a process which is affected by numerous factors, such as diffusion, linear velocity, temperature, solvents, loading and mixing efficiency, as well as phase transitions. Some of these factors also influence the first part of the objective, the yield of the transfer process. Injector temperatures exceeding room temperature are only used with solutes which need higher temperature to stay in solution, such as some polymers. Injection at high temperature should be performed with caution, since a solvent which starts to evaporate from a hot injector, before the valve is actuated, may result in sample loss and poor reproducibility.In most applications the sample is introduced as a relatively large (depending on the analyte concentration) liquid plug into the stream of mobile phase. Due to limited mixing, the major part of the sample often arrives at the column inlet dissolved in a liquid composed of the solvent partially mixed with the mobile phase. Thus, the transient elution strength of the sample may often be considerably higher than the elution strength of the mobile phase, and can adversely affect the peak shapes by flooding and dispersing the sample over the column inlet.It is well known that an exponential decay injection profile is obtained because of the laminar flow of the displacing mobile phase [1]. By moving the valve back to the load position from the inject position after a predetermined time, the solvent tail can be removed. The injection syringe should be removed first, since the pressure in the sample loop is released through the injection and waste ports when the valve is returned to the load position. With large sample loops the syringe might be pushed out of the port, or the plunger pushed out of the barrel, if the syringe is left in the injection port.By injecting very small volumes, using splitting or small sample loops, a more thorough mixing with the mobile phase can be achieved prior to the column. Currently the nominal volume of the smallest commercially available sample loop is 60 nl. However, small volume (< 100 nl) internal sample loops are difficult to manufacture with high accuracy, and the small volumes are difficult to maintain without changes, particularly with loops made from polymeric materials.Column overload is rarely caused by the mass of the solutes, but almost always by the amount of solvent. With a retention factor k = 1, the injected volume that produces 10 % peak broadening has been calculated to be 24 nl on a 50-µm-ID open-tubular column, and with a retention factor of 10, the volume was calculated to be 130 nl [2]. With an actual injection of 223 nl, 10 % loss of...

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“…This system suffers some problems associated with delivering the sample to a narrow bore capillary tube and satisfactorily refocusing the analyte band for optimum capillary column analysis. Greibrokkk group have used a precolumn maintained at supercritical or near supercritical conditions, such that the analytes are selectively retained before reaching the solvent vent [13,14]. This method of solvent removal can suffer analyte discrimination if the sample and solvent are not separatedin the precolumn…”

Section: Solventless Injection Systemmentioning

confidence: 99%

Solventless injecction for packed column supercritical fluid chromatography

Dean

POOLE

1989

J. High Resol. Chromatogr.

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SummaryThe adverse effects of injection solvent strength on microbore packed column SFC band broadening are demonstrated and a solventless injection system that eliminates these effects is introduced. The injection system removes solvent in a GC-like manner using a retention gap and an on-column capillary GC syringe. The analyte is delivered to the analytical column in a solvent-free plug of supercritical fluid mobile phase.

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The solvent venting injection technique in capillary supercritical fluid chromatography

Cited by 38 publications

References 2 publications

Solute focusing in supercritical fluid chromatography

Solute focusing in supercritical fluid chromatography

Injection techniques in SFC

Solventless injecction for packed column supercritical fluid chromatography

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