Numerous spectroscopic techniques (e. g., Ut-vis spectroscopy, IR spectrophotometry, X-ray fluorescence) are used to analyze, identify, and quantitate samples. These samples are often placed in a sample holder to facilitate spectroscopic analysis.

A sample holder or cell typically is used to hold a sample in the path of the incident radiation beam. The material used for the sample holder is generally transparent to the incident radiation in the spectral region of interest and are not soluble in or reactive with the sample or any solvent that is used in preparing the sample. Examples of materials commonly used in sample holders include inorganic salts, glasses, quartz, metals and polymeric materials (e. g., polyethylene).

Summary of the Invention In one aspect, the invention provides a sample holder including a support, an opening extending through the support and having a side wall formed by the support, a membrane disposed on the support and extending across the opening, and an insert open at first and second opposing ends and positioned within the opening. The insert compresses a first portion of the membrane against the side wall to form a liquid impervious seal and leaves a second portion of the membrane extending across the first open end of the insert. In preferred embodiments, the insert defines, in combination with the membrane, a sample-receiving volume. The insert may be substantially liquid pervious or liquid impervious. Preferably, the support is substantially planar or substantially cylindrical.

The membrane is preferably microporous and has micropores that are collapsed in portions of the membrane that are compressed.

In one preferred embodiment, the opening is generally circular and the insert (e. g., in the form of a truncated cone or a cylinder) protrudes beyond a plane defined by a major surface of the support. In another preferred embodiment, the insert protrudes beyond both a first plane defined by a first major surface of the support and a second plane defined by a second major surface of the support. In other embodiments, the insert extends through only a portion of a thickness of the support.

Optionally, the sample holder further includes a second membrane extending across the opening.

In another aspect, the sample holder according to the present invention, optionally further includes at least two openings extending through the support.

The openings each have a side wall formed by the support, a membrane disposed on the support and extending across the opening, and an insert positioned within the opening. The insert compresses the membrane against the side wall to form a liquid impervious seal.

In another aspect, the invention features a sample holder that includes a support, an insert, and a membrane. The support has an inner wall surface defining a support orifice with a first end and an opposite, second end. The inner wall surface further defines a shoulder within the orifice. The insert includes a body having an inner wall surface defining an insert orifice with a first end and an opposite second end, and an outer wall surface. The insert is shaped and sized to be received through the second end of the support orifice and into engagement upon the shoulder. The insert orifice and the support orifice are in overlapping relationship. The membrane has a first region spanning the insert orifice and the support orifice and a second region disposed in compressive, liquid impervious sealing engagement between the shoulder and the insert.

In preferred embodiments, the sample holder further includes a third region disposed in compressive sealing engagement between the inner wall and the outer wall. Preferably, the third region generally surrounds the second region. The

orifices can be cylindrical bores. In preferred sample holders, the diameter of the support orifice is greater than the diameter of the insert orifice. The orifices are preferably coaxial. The shoulder is preferably relatively closer to the second support end.

In another aspect, the present invention provides a method of confining a sample, the method includes introducing the sample into the sample-receiving volume of a sample holder according to the present invention. The sample can then be analyzed by transmitting radiation through it. Optionally, a vacuum is applied to the membrane before analysis.

The sample holder according to the present invention allows introduction of a relatively large volume of, for example, a dilute solution or dispersion of a sample into the sample-receiving volume of the sample holder and prevents the sample from migrating beyond the sample-receiving volume. Certain embodiments of the sample holder according to the present invention provide good analytical results, yet are sufficiently inexpensive to be disposable after use.

Microporous sheets can have a plurality of interconnecting microscopic pores, some of which form a tortuous pathway extending through the thickness of the sheet.

Other features and advantages of the invention will be apparent from the following description of preferred embodiments thereof, taken together with the drawings, and from the claims.

Brief Description of the Drawings FIG. 1 is a perspective view of a sample holder according to one embodiment of the invention.

FIG. 2 is a partial cross-sectional view taken along line A-A'of the sample holder shown in FIG. 1.

FIG. 3 is a detail view of a portion of the sample holder shown in FIG.

2.

FIG. 4a is a perspective view of a sample holder according to a second embodiment of the invention.

FIG. 4b is a partial cross-sectional view taken along line B-B'of the sample holder shown in FIG. 4a.

FIG. 5 is a cross-sectional view taken along line A-A'of a third embodiment of the sample holder shown in FIG. 1.

FIG. 6 is a perspective view of a sample holder according to a fourth embodiment of the invention.

FIG. 7 is a partial cross-sectional view taken along line C-C'of the sample holder shown in Fig 6.

FIG. 8a is a perspective view of a sample holder according to a fifth embodiment of the invention.

FIG. 8b is a cross-sectional view taken along line D-D'of the sample holder shown in FIG. 8a.

FIG. 9 is a perspective view of a sample holder according to a sixth embodiment of the invention.

FIG. 10 is a cross-sectional view taken along line E-E'of the sample holder shown in FIG. 9.

FIG. 11 is a cross-sectional view taken along line E-E'of a seventh embodiment of the sample holder shown in FIG. 9.

Description of the Preferred Embodiments Referring to FIGS. 1-3, sample holder 10 comprises membrane 12 extending across opening 14 in support 16. Frustoconical shaped insert 18 is positioned within opening 14 against membrane 12 and sidewalls 20 so as to compress membrane 12 against side walls 20 and form sealed sample-receiving volume 22.

Liquid impervious seal 24 located between insert 18 and sidewall 20, extending continuously along the perimeter of sidewall 20, is a region of

compressed membrane that is impermeable to a liquid sample. Liquid impervious seal 24 prevents migration of the sample into the portion of membrane 12 that extends beyond sample-receiving volume 22. Liquid impervious seal 24 also prevents migration of the sample into support 16. The liquid impervious seal preferably extends along the entire interface between membrane 12 and its interface with sidewall 20 defined by the perimeter of opening 14 and the thickness of support 16.

Support 16, which preferably is substantially flat and rigid, acts as a device for mounting sample holder 10 in a spectrophotometer and provides support for membrane 12. Support 16 can consist of two substantially identically shaped pieces 25,26 having opening 14 extending from the top surfaces to the bottom surfaces of pieces 25,26. Pieces 25,26 are joined such that membrane 12 is fixed between the two pieces and extends across opening 14 in support 16.

Alternatively, as shown in FIGS. 4a and 4b, sample holder 40 may include insert 48 extending through opening 44 in single piece support 46.

The support can be constructed from a variety of materials. Examples of suitable materials include cardboard, paperboard, polished stock calendared chipboard, plastic (e. g., polypropylene) sheet stock, metals, metal alloys, ceramics (including glass), composites, and elastomers. Preferred materials include paperboard, polished stock calendared chipboard, and plastic sheet stock.

For those embodiments in which the support includes two or more pieces, the pieces can be joined together by any of a number of means appropriate to the material from which they are made, including adhesive (e. g., hot melt and pressure sensitive adhesives), double-sided pressure sensitive adhesive tape, welding (e. g., sonic, spot, solder, arc, and thermal welding), radio frequency (RF) sealing, and mechanical fastening (e. g., crimping).

In some instances, a user of the sample holder may wish to archive or store a sample for future reference. Accordingly, the support is preferably constructed of a material that can be written on or otherwise labeled so that

pertinent information relating to the sample (e. g., sample or index number) can be recorded. Alternatively, a label or other additional information bearing media (e. g., microfilm, magnetic media, or bar code), may be included on the support.

The size and shape of the support is dependent, for example, upon the sample cell receptacle of the particular spectroscopic instrument (s) to be used with the sample holder. Users of spectroscopic instruments typically use sample holders that are about 5 cm (two inches) wide.

Referring to FIGS. 1-3, insert 18 is sized to fit tightly against sidewalls 20 of opening 14 so as to compress membrane 12 therebetween and to form liquid impervious seal 24. Insert 18 thus assists in confining the sample to sample- receiving volume 22. Insert 18 also provides additional sample capacity to the sample holder.

The insert is preferably either a hollow frustoconical cup or a hollow cylinder that protrudes above a major surface of the support. The insert may, however, extend both above and below the support. For example, in FIGS. 4a and 4b, sample holder according to the present invention 41 has membrane 42, insert 48, and support 46, wherein insert 48 is shown extends through opening 44 such that it protrudes above and below two major surfaces of support 46. In FIG. 5, sample holder according to the present invention 51 has membrane 52, insert 58, and support 56, wherein insert 58 protrudes above a major surface of support 56 and extends only partially into opening 54 to a distance that is less than the entire thickness of support 56.

The walls of the insert are preferably thin so as to minimize the amount of membrane that is beneath the insert, (i. e., the amount of membrane that is in contact with the perimeter of the insert but that is not compressed between the insert and the support). Such an arrangement tends to minimize the potential for a liquid sample to migrate into the area of the membrane beneath the insert, which may affect the use and accuracy of the sample holder for quantitative analysis.

The insert can be constructed from a variety of materials that are compatible with the sample applied to the sample holder (e. g., materials that do not significantly react with, dissolve or cause the swelling of the sample holder).

Suitable insert materials include both liquid pervious and liquid impervious materials. Liquid impervious materials are preferred for quantitative applications.

Examples of suitable liquid impervious materials include polyethylene, polypropylene, polytetrafluoroethylene (PTFE) (available, for example, under the trade designation"TEFLON"from E. I. DuPont de Nemours of Wilmington, DE), metal, and glass.

The membrane is preferably inert with respect to the sample material, including the solvents that such samples might contain. Further, the membrane is preferably made from a material selected to minimize spectral interference and to exhibit relatively low absorbance (i. e., is highly transmissive) in the spectral region (s) of interest.

Particularly preferred membrane materials are thin (e. g., having a thickness of not greater than about 200 micrometers (preferably not greater than about 150 micrometers); preferably, in the range from about 15 to about 200 micrometers, more preferably, in the range from about 15 to about 150 micrometers, more preferably in the range from about 15 to about 125 micrometers) microporous sheets having a basis weight in the range from about 1 to about 90 glu2.

Typically, the pore density of preferred microporous sheets is such that the void volume, as measured by ASTM D4197-82 (the disclosure of which is incorporated herein by reference), is greater than about 20%, preferably in the range of about 50 to about 98%, more preferably between about 75 and 90%. In general, the greater the void volume, the greater the amount of sample in the beam path (which improves spectroscopic accuracy), the less likely inherent absorbances and light scattering of the sheet are to interfere with analysis of the response of the sample, and the more readily solvent evaporates from a sample applied to the sheet.

Many useful microporous polymer sheets are open structures, wherein only a fraction of the total volume is occupied by the polymer material; thus, a greater portion of the matter in the beam path is the sample itself.

Examples of suitable microporous sheets are described, for example, in U. S. Pat. Nos. 4,539,256 (Shipman), 3,953,566 (Gore), 3,962,153 (Gore), 4,096,227 (Gore), 4,110,392 (Yamazaki), 4,187,390 (Gore) and 4,194,041 (Gore et al.), the disclosures of which are incorporated herein by reference. Further examples of microporous sheet materials include microporous sheets of polyolefins (e. g., polyethylene, polypropylene, and copoly (ethylene-propylene)), poly (vinylidene fluoride), polyvinyl alcohol, polyester, polycarbonate, cellulose acetate, cellulose nitrate, poly (vinyl chloride), and nylon (e. g., nylon-6 and nylon- 66). Particularly preferred microporous sheet materials are polyethylene and PTFE.

A preferred microporous sheet material is (microporous) polyethylene.

Polyethylene is inert toward many chemicals, is insensitive to moisture, and provides strong (e. g., tear and puncture resistant) films at low thicknesses (e. g., 15 micrometers). Except for the region of about 3000 to about 2800 cm-1 where polyethylene's aliphatic carbon-hydrogen (C-H) bond stretching is evident as strong absorbances (i. e., 2918 and 2849 cm-1), polyethylene can be used across the IR range of about 4000 to about 200 cm-1. Polyethylene exhibits a limited number of other signals in other portions of the IR range (e. g., 1465 and 721 cm-1), but these are typically narrow, well-defined, low intensity absorbances that are easily taken into account. (Polyethylene having a substantial crystallinity has two additional absorbances caused by the splitting of the latter two absorbances into pairs of peaks.) A preferred microporous polyethylene used to make microporous sheets is prepared according to the teaching of U. S. Pat. No. 4,539,256 (Shipman), Example 8, the disclosure of which is incorporated herein by reference.

Another useful polymer, particularly where the aliphatic C-H bond stretching region is of significant interest, is microporous PTFE. This material has no absorbances above about 1500 cm-1, so the aliphatic C-H stretching region

(about 3000 to about 2800 cm-1) is free of interfering absorbances. Sheets made from PTFE (as well as polymers and copolymers of chlorotrifluoroethylene) can be useful, for example, in the range of about 4000 to about 200 cm-1.

Commercially available microporous materials include hydrophobic or hydrophilic microporous polyethylene or polypropylene films (available, for example, under the trade designation"CELGARD"from Hoechst Celanese of Charlotte, NC), microporous PTFE films (available, for example, under the trade designation"GORE-TEX"from W. L. Gore of Newark, Del), microporous PTFE films (available, for example, under the trade designation"ZITEX"from Norton Performance Plastics of Wayne, NJ), and microporous hydrophilic films (available, for example, under the trade designation"DURAPORE"from Millipore Products Division of Bedford, MA).

In the case of a microporous membrane, the liquid impervious seal is formed by collapsing the micropores of the membrane in the region of the seal.

Once the structure of a micropore has been collapsed, the micropore no longer has capacity for holding a liquid therein, which in turn inhibits liquid migration through the micropore and, in turn through the liquid impervious seal.

Regardless of the particular size and shape of the sample holder according to the present invention, samples are preferably easily introduced into the sample-receiving volume. Although neat liquid samples can be applied directly to a sample holder, if desired and if the sample is a material that is soluble, it may be dissolved in a suitable solvent (e. g., water, toluene, methylene chloride, and methyl ethyl ketone) prior to applying the sample to the sample holder. Samples that have been dissolved in an organic liquid typically readily wet the surface of the membrane (with little or no swelling of the membrane), and the solvent quickly evaporates from the surface thereof.

The large volume of a sample capacity of the sample holder allows a relatively dilute sample solution dispersion to be accommodated by the sample holder. This is particularly beneficial, for example, when analyzing very dilute

solutions. The larger volume of sample, however, increases the time it takes to evaporate the solvent. To accelerate solvent evaporation, the sample may be exposed to a vacuum. For example, a sample can be applied to the sample- receiving volume of the sample holder and the sample holder is subsequently placed in a vacuum chamber. Alternatively, the sample may be applied to the sample- receiving volume while the sample holder is in the vacuum chamber. Another suitable method involves applying a low level vacuum (e. g., a vacuum no greater than 11.4 cm (4.5 inches) of water), to the surface of the membrane opposite the membrane surface forming the sample-receiving volume. Solvent evaporation can also be accelerated, for example, by exposing the sample to an external heat source (e. g., a heat lamp) for a short time after the sample is applied to the holder (see, e. g., European Patent No. 478,596B1 published Nov. 3,1993, the disclosure of which is incorporated herein by reference). The effectiveness of these methods may be increased, for example, by using sample holders that include membranes having pores that open through both surfaces and extend all the way through the sheet.

Such a pore structure may have a tortuous path through the sheet. After the solvent is evaporated, the sample holder can be mounted in a spectrophotometer.

One method for using the sample holder for spectroscopic analysis involves applying a sample to the sample holder, transmitting infrared radiation through the sample and the sample-receiving volume, and analyzing the transmitted radiation to obtain both qualitative and/or quantitative information about the sample. Such methods are generally discussed, for example, in U. S. Pat. No.

5,470,757 (Gagnon et al.) and pending U. S. Pat. Application Serial No.

08/587,316, filed Jan. 11,1996, the disclosures of which are incorporated herein by reference.

Sample holders according to the present invention can also be used for tandem filtration/IR analysis, (see, e. g., U. S. Pat. No. 5,470,757 (Gagnon et al.) and Prasad et al.,"Non-Dispersive Solvent Extraction Using Microporous Membranes, New Membrane Materials and Processes for Separation,"AIChE Symposium Series

No. 261, vol. 84, pp. 42-53 (1988) and Baker et al.,"Membrane Separation Systems-A Research and Development Needs Assessment,"Final Report, vol. II, U. S. Dept. of Energy, Office of Program Analysis (March 1990), the disclosures of which are incorporated herein by reference.

Further, for example, sample holders according to the present invention may include multiple sample receiving volumes. Such sample holders are thus capable of holding multiple samples. It is also within the scope of the present invention to have multiple openings one or more of which utilize a different membrane material.

It is also within the scope of the present invention to have a second membrane extend across an opening in the support. The second membrane may be the same or a different membrane material than of the first material.

In another aspect, the insert may be in the form of a variety of shapes, provided the shape does not interfere, or at least significantly interfere, with the analysis of the sample. For example, in FIGS. 6 and 7, sample holder according to the present invention 70 has insert 68 provided in the form of a hollow ring disposed entirely within opening 64 of support 66.

Another embodiment of a sample holder according to the present invention is shown in FIGS. 8a and 8b. Sample holder 80 having second insert 89 positioned within opening 84 in support 86 so as to compress membrane 82 between second insert 89 and first insert 88 and to form second liquid impervious seal 92 at the interface between first insert 88 and membrane 82. Liquid impervious seal 92 thus extends from the interface between membrane 82 and sidewalls 90 to the interface between membrane 82 and first insert 88. The second liquid impervious seal provides an additional barrier to the migration of a liquid sample beyond the sample-receiving volume and into the support.

Referring to FIGS. 9 and 10, sample holder according to the present invention 100 includes cylindrical support 116 having an inner wall surface 122.

Inner wall surface 122 defines an orifice having a first end and an opposite second

end, and shoulder 121 within the orifice. Insert 118, which has an inner wall surface 128 defining an insert orifice, has a first end and an opposite second end.

The insert is shaped and sized to be received through the second end of the support orifice and into engagement upon shoulder 121. The insert orifice and the support orifice are in overlapping relationship with each other. Fig. 10 also depicts membrane 112 having a first region that spans the insert orifice and the support orifice. A second region of membrane 112 is disposed in compressive liquid impervious sealing engagement between shoulder 121 and the insert 118. A third region 120 of membrane 112 is disposed in compressive liquid impervious sealing engagement between inner wall surface 122 of cylindrical support 116 and insert 118 such that third region 120 is adjacent and generally surrounds the second region of membrane 112. Inner wall surface 122 of cylinder 116, in combination with membrane 112, defines sample receiving volume 123.

Referring to FIG. 11, sample holder 100 of FIGS. 9 and 10 is positioned within opening 124 of second support 126. The second support is capable of maintaining sample receiving volume 122 of sample holder 100 in the beam path of a spectroscopic instrument.

Further, some embodiments of the sample holder according to the present invention, include a protective cover or flap (not shown), which covers the opening during storage but is removed or moved clear of the beam path for the spectroscopic analysis. Alternatively, the protective cover may be transparent to the wavelength of the radiation of interest (e. g., is transparent to IR radiation), and therefore need not be removed or moved away from the beam path for the analysis.

Although the above description of the sample holder of the present invention has been primarily discussed with regard to IR spectroscopy, sample holders within the scope of the present invention can also be for use in a variety of spectrophotometers including, e. g., IR (about 5000 to about 200 cl-'), X-ray fluorescence, X-ray diffraction, fluorescence, and Raman.

Objects and advantages of this invention are further illustrated by the following examples, but the particular materials and amounts thereof recited in these examples, as well as other conditions and details, should not be construed to limit this invention.

EXAMPLES Example 1 A support for a sample holder was prepared using two, 5 cm x 10 cm x 0.1 cm pieces of flat paper card stock (polycoated paper, 0.5 mil poly, available from Flower City, Inc., Minneapolis, MN), which were glued together using a light coating of adhesive (available under the trade designation"3M SUPER 77 SPRAY ADHESIVE"from the 3M Company, St. Paul, MN), to create a support having a thickness of 0.2 cm. A circular opening (2.5 cm in diameter) centered on the card face provided a side wall against which the microporous membrane could be sealed.

A polyethylene microporous membrane (approximately 3.5-4.0 cm in diameter and 0.025 cm thick, prepared according to Example 8 of U. S. Pat. No. 4,539,256, previously incorporated by reference) was placed over the opening and an injection molded, high density polypropylene ring insert having a 2.5 cm outside diameter (OD), a tapered inside diameter (nid) of 2.3 cm on one end and 2.0 cm on the opposite end, and a height of about 0.3 cm, was placed over the membrane, with the 2.0 cm ID end of the ring contacting the membrane. The insert ring was forced into the opening with finger pressure, causing the membrane to stretch and forming a liquid impervious seal between the paper card stock and the polypropylene ring insert. Excess membrane was trimmed away between the insert and the paper card stock. Approximately 2 ml of water was introduced into the sample receiving volume and allowed to evaporate. No evidence of fluid leakage was observed.

Example 2 A sample holder was prepared utilizing a"dual ring"assembly and a paper card stock support. The dual ring assembly consisted of a polypropylene support cylinder which had been machined from polypropylene rod stock. The cylinder had an outer diameter of about 2.85 cm, an inner diameter of about 2.50 cm, a height of about 0.60 cm, and a circumferential lip (approximately 0.15 cm wide) on one end (see FIG. 9), and an insert ring. The support ring was machined from 3.2 cm diameter high density polypropylene rod stock (part number R80-11 from Minnesota Plastic of Eden Prairie, MN). The insert ring had a 2.5 cm outer diameter, a 2.3 cm to 2.0 cm tapered inner diameter by approximately 0.3 cm high polypropylene ring (as described in Example 1). The support cylinder was heated to approximately 60°C in a circulating air oven to expand the cylinder and facilitate insertion of the membrane and insert ring. A piece of microporous polyethylene membrane (as described in Example 1 but 0.50 cm thick) was placed over the "circumferential lip end"of the expanded support cylinder and the insert ring forced into the support ring as described in Example 1. Excess membrane was trimmed away outside of the seal area. The"dual ring"assembly was inserted into a single layer paper card support as described in Example 1, except that the opening was 2.85 cm in diameter, to form the sample holder.

Various modifications and alterations of this invention will become apparent to those skilled in the art without departing from the scope and spirit of this invention, and it should be understood that this invention is not to be limited to the illustrative embodiments set forth herein.