Measuring and testing – Gas analysis – Gas chromatography
Reexamination Certificate
2001-10-29
2003-07-29
Raevis, Robert R (Department: 2856)
Measuring and testing
Gas analysis
Gas chromatography
C073S023420, C073S061550, C073S863120, C347S019000
Reexamination Certificate
active
06598461
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to the field of testing fired ink from inkjet pens for purposes of analyzing the components of the ink to determine whether an inkjet pen is performing properly.
2. Description of the Related Art
Inkjet pens are widely utilized in printing systems, and are increasingly finding uses in other applications to provide controlled delivery of a wide range of substances. For many reasons, it is advantageous to analyze the actual output from an inkjet pen. However, many quantifiable parameters such as solvent concentrations and thermal degradation products of the ink/printhead interaction are difficult to analyze with traditional gas chromatography injection and mass spectrometry methods due to their volatility and the necessity of producing large quantities of analyte; large analyte quantities are needed due to the inefficiency of traditional sample introduction (i.e., liquid injection).
The current method for analysis of fired ink requires that the pen be fired onto a reasonably clean glass fiber pad; the pad is usually held under the printhead in a Drop Break-off Observation System (“DBOS”) (i.e., an optical system having a camera pointed at an inkjet pen which allows an analyst to see the way in which ink drops are formed on a substrate upon being fired by the inkjet pen). Following the firing of the ink onto the glass fiber pad, the current method uses a thermal desorption inlet system coupled to a standard gas chromatograph/mass spectrometer; the gas chromatograph/mass spectrometer analyzes the volatile components of the ink which are released from the glass fiber pads.
After the ink is fired onto the glass fiber pad: (a) the pad is cut to an appropriate size and placed inside a thermal desorption tube which, in turn, is placed within a thermal desorption inlet coupled to a gas chromatograph/mass spectrometer; (b) the inlet to the gas chromatograph/mass spectrometer is closed (i.e., sealed); (c) the carrier gas flow in the gas chromatograph/mass spectrometer is restored; and (d) the inlet zone is heated to an appropriate temperature to achieve thermal desorption. The analyte (i.e., the ink to be analyzed) is mixed with the carrier gas and is swept onto the analytical column where it is cryo-focussed by cooling the gas chromatograph/mass spectrometer oven with a jet of liquid nitrogen. When the analyst determines that the sample has been sufficiently desorbed, the oven temperature is brought to an operating temperature (usually approximately 50° C.) and the analysis begins.
Unfortunately, the traditional analytical method has a plurality of inherent drawbacks which: (a) reduce the integrity of the ink to be analyzed (either by loss of volatile components or by contamination); (b) create an undesirably long analysis duration; (c) require great precision and care when managing the glass pads and depositing the ink thereon; and (d) cause chromatographic peak broadening due to analyte trickling into the column while the analysis is being completed (thereby reducing the benefit cryo-focusing would otherwise generate). These drawbacks are discussed in more detail hereafter.
First, although glass fiber pads are a better substrate than most available materials for thermal desorption, they are not ideal in several respects. For instance, the current method contemplates depositing the ink onto the glass fiber pads at ambient temperatures at which loss of volatile ink components can occur. Moreover, critical amounts of volatile ink components may further be lost when: (a) the glass fiber pads are transferred into the thermal desorption tube associated the gas chromatograph/mass spectrometer; and (b) when the thermal desorption tube is transferred into the gas chromatograph/mass spectrometer. The lost of volatile ink components when the ink is deposited on the glass fiber pads (due to the ambient temperatures at which such transfer occurs) and when the pads are subsequently moved into the desorption tube and then into the gas chromatograph/mass spectrometer can greatly reduce the integrity of the chromatography. In addition, although glass fiber pads are the most suitable substrate for the performance of this traditional method, the pads are known to contribute contaminants to the ink deposited thereon thereby further degrading the integrity of the chromatography.
Glass fiber pads are also problematic for a host of additional reasons. First, by way of example, glass fiber pads must be handled with great care to avoid sample contamination with finger oil, etc. Second, as the analyte ink is only fired onto a portion of the pad, an analyst must choose the area to be analyzed very carefully. Third, the system by which the ink is deposited is particularly inconvenient as the analyst must place the pad precisely, by hand, in the DBOS machine. Fourth, in terms of obtaining accurate analysis results, the analyst must assume that the glass fiber pads (which are not chemically deactivated) do not change the chemical composition of the analyte ink when heated in the inlet liner.
The traditional process itself also suffers from inherent drawbacks. For example, constantly opening and closing the gas chromatograph/mass spectrometer is cumbersome and very time consuming. If one waits until the heated zone in the inlet has cooled to room temperature, each complete analysis can easily take more than an hour and half, thereby severely limiting sample throughput. Unfortunately, it is prudent to cool the inlet in this way to avoid sample oxidation when the inlet liner and sample (and an unavoidable amount of outside air) are introduced into a hot inlet.
Cryo-focusing is traditionally used to avoid introducing the sample into the column over a long period of time, which would broaden analyte chromatographic peaks unacceptably (as the principal advantage of modern capillary column gas chromatography is the superior resolution of sample components in sharp peaks); this advantage is destroyed if the sample mixture is allowed to seep into the instrument over time. By concentrating all of the components of interest in a single, short section of column (which can be easily heated by the gas chromatograph oven), cryo-focusing allows the analyst to start the analysis of the entire sample at once. Unfortunately, in practice, it is possible that the entire sample to be analyzed will not be transferred to the cryogenically cooled analyte column before the analysis is started. As a result, small amounts of less volatile components will continue to trickle into the system during the run and will, thereby, contribute to high background response (i.e., chromatographic peak broadening) and generally poor chromatography. Although this peak broadening is a problem with standard gas chromatographs, it is particularly noticeable in gas chromatograph/mass spectrometers. In addition, such poor chromatography is difficult to avoid using the traditional method as the sample can not be removed from the heated zone until the analysis is complete.
Accordingly, there is a need for an improved method for determining the volatile components of inkjet ink from a complete and functional inkjet pen. In determining the components, the purity and quantity of the sample to be analyzed may be improved by eliminating, or at least reducing one or more of: (a) the amount of contaminants that are added to a sample of inkjet ink to be analyzed; and (b) the amount of volatile ink components lost prior to analysis. In addition, there is a need for an apparatus capable of performing a method having one or more of the aforementioned benefits which is both easy to use and which shortens the duration required for traditional analysis.
SUMMARY OF THE INVENTION
A first embodiment of the invention herein described addresses a gas chromatography inlet system. The inlet system includes a block having a chamber therein accessible through an opening in a side of said block. In addition, the system includes a stage, located in the chamber, which is adapted to receive an analyte sample. The
French Alan L.
Hering Trenton M.
Lofton Calvin B.
Cygan Michael
Raevis Robert R
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