Fluid handling – Processes – With control of flow by a condition or characteristic of a...
Reexamination Certificate
2002-08-08
2004-03-30
Krishnamurthy, Ramesh (Department: 3753)
Fluid handling
Processes
With control of flow by a condition or characteristic of a...
C137S014000, C137S487500, C137S557000, C210S198200, C210S741000, C210S659000, C422S070000, C073S061560
Reexamination Certificate
active
06712085
ABSTRACT:
FIELD OF THE INVENTION
The invention concerns a method for the supply of fluid volume streams in channels or capillaries with small stream cross sections, more particularly in chromatographic separation columns for analytical fluid metrology, more particularly for analytical liquid chromatography, wherein a delivery device for the delivery of a volume stream of the fluid through an operating channel and a pressure measuring device for measuring the pressure in the operating channel are provided, wherein a measurement of the volume stream is possible.
DISCUSSION OF THE BACKGROUND ART
Such a method is presently used, for example, in liquid chromatography, more particularly high pressure liquid chromatography (HPLC). Depending on the inner diameter of the separating columns used, HPLC is divided into so-called “normal bore chromatography”, in the case of separating columns with an inner diameter between approximately 3 and 5 mm, “micro bore chromatography”, using separating columns with an inner diameter between approximately 1 and 2 mm, “capillary-LC-chromatography” using separating columns with an inner diameter between approximately 180 and 320 &mgr;m, and “nano-LC chromatography”, using separating columns with an inner diameter equal to or smaller than 100 &mgr;m.
The supplied flow rates must be adapted to the inner diameter of the column according to the application. While flow rates in the range of ml/min and &mgr;m/min are common in normal bore technology and micro bore technology, flow rates in the range of as low as several 100 nl/min must be realized in nano-LC technology. The flow rates are commonly adjusted so that in the separating column a linear stream velocity of approximately 1 to 2 mm/s is achieved. This is important because the efficiency of a separating column depends on the flow rate.
The application of separating columns with an inner diameter of less than 180 &mgr;m is gaining interest not only in high pressure liquid chromatography but also in the area of other microfluid systems. While in high pressure liquid chromatography the volume stream is commonly generated using a hydraulic pump, electric osmosis is often used to create the volume streams in microfluid systems. Evidently, it is also possible to combine hydraulically pumps with microfluid systems. A particular example of such a microfluid system is a microfluid chip.
Another important point in the connection with an optimum flow rate is the detection of the substances to be analyzed. Mass-selective detectors are increasingly being used. The use of such detectors requires suitable preparation and supply of the substances to be analyzed. For this purpose, the operating stream can be atomized, ionized and partially or completely dried after passing through the separating column. The individual ions stream into the opening of the detector while the solvent excess that might still exist is waste. Various methods are known for the creation of the ions. Some methods only work in a certain range of flow rates or volume flow rates. For lower or higher flow rates, the method does not work or works with significant restrictions, i.e. the detection is less sensitive or impossible.
The lower the flow rates, the more important the effects of system volumes, in particular the dead volume or the delay volume. In the case that is of interest here, the case with extremely low flow rates, these volumes must also be flushed with a very low flow rate. Otherwise, thermodynamic effects could disturb the equilibrium of the separating column and of the detector so that undesired effects may occur. Also, high flow rates are impossible simply because of the connection capillaries with very small internal diameters and the consequent pressure drop. To ensure a high efficiency of the analysis, the volumes mentioned above should be kept as small as possible. Ideally, a flush period of one minute should be sufficient to flush the delay volume with the desired low flow rate.
In a chromatographic system, the parameter stream and pressure are always interdependent via the hydraulic resistance of the separating column and the system. However, it has become common practice to determine or define the flow. The linear stream velocity through the column must be kept constant regardless of the transported solvents and the restrictions. This does not pose a problem as long as the flow rates are high enough to either directly supply the desired flow rate or to measure the flow rate. However, if extremely low flow rates in the range of nl/min are to be supplied, the two above-mentioned methods can normally not be applied.
For the above-mentioned applications, pump systems are required that can create or transport extremely low flow rates or volume streams. The delivery must be highly reliable at the high existing pressures in the range of approx. 400 bar.
For the delivery and provision of such small flow rates in separating columns for liquid chromatography, in particular for “capillary LC chromatography” and for “nano-LC chromatography”, the only methods currently known are as follows:
A first method is based on the application of so-called syringe pumps. Syringe pumps are special one-piston pumps. Unlike in common piston pumps, the pistons do not move back and forth during the analysis. Instead only one piston stroke is performed. This means that the syringe pumps always work in delivery mode. The pump chamber must therefore be chosen sufficiently large so that a single piston stroke is sufficient for a complete separating analysis. The pump chamber is put under pressure before the analysis by pushing the piston in the pump chamber forward. No further suction is thus performed during the separating analysis. With this method, a volume flow can be achieved that is independent of the elasticities inside the pump chamber. The elasticities of particularly the seals and the drive mechanics as well as the elasticity due to the compressibility of the solvent can be compensated for accordingly.
However, syringe pump technology has little flexibility in the realization of different analysis times and in the use of different column diameters. This is because the possible analysis time and the choice of the separating column diameter is dependent of, and limited by, the respective available maximum displacement volume of the syringe pumps. In addition, only one high pressure gradient can be realized with a syringe pump. This means that a separate high-pressure syringe pump is necessary for every solvent used in the analysis.
Further more, the leak rate inside the delivery system plays an important role for the delivery amounts of only several nl/min. The seals and valves used for high-pressure syringe pumps typically have relatively low leak rates. Nevertheless, these leak rates can have a dramatic effect for the small flow rates used in nano-LC chromatography. Even temperature influences can cause undesired flow shifts due to thermal extension. For this reason, special thermostat arrangements and controls are often necessary.
Another possibility for the creation and provision of liquid volume streams in channels or capillaries with small diameters is the use of traditional piston pumps suitable for “normal bore chromatography”. This method uses the so-called passive splitter technology, which is very common in practice. It means that suitable flow divider are used to divide the total stream created and supplied by the pump into at least two partial streams, a surplus stream in a surplus path and an operating stream in an operating path.
The regulation and provision of the respective operating stream is done by so-called restrictors, i.e. by hydraulic resistances located in the surplus path. The flow dividers, and in particular the hydraulic resistors, are usually made of so-called “fused silica capillaries” with small inner diameter. The length and the inner diameter of these elements determine the stream resistance. The total flow rate is split according to the resistance ratios. Typically, the smaller part flows through the separating column.
The
Glatz Bernd
Weissgerber Hans-Georg
Agilent Technologie,s Inc.
Krishnamurthy Ramesh
LandOfFree
Method for the provision of fluid volume streams does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Method for the provision of fluid volume streams, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Method for the provision of fluid volume streams will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3213492