US3036215A - Spectrometric cell structure - Google Patents

Description

y 1962 R. N. JONES ET AL 3,036,215

SPECTROMETRIC CELL STRUCTURE Filed April 30, 1959 3 Sheecs$heet 1 l/ L T W m HI I 24 "f T? am; z/mind Jones Jose/ah Mn /Va deez May 22, 1962 R. N. JONES ET AL SFECTROMETRIC CELL STRUCTURE Filed April 30, 1959 3 Sheets-Sheet 2 3,036,215 SPECTRGMETRIC CELL STRUCTURE Richard N. Jones, Ottawa, Ontario, and Joseph M. A.

Nadeau, Hail, Quebec, Canada, assignors to National Research Council, ()ttawa, Ontario, Canada, a body corporate of Canada Filed Apr. 30, 195'9, Ser. No. 810,141 Claims priority, application Canada June 3, 1958 4 Claims. (Cl. 25043.5)

This invention relates to the construction of cells of the type employed for mounting specimens for spectrometric examination. The use of spectral analysis, particularly infra-red spectral analysis, is now a well-established laboratory technique for the identification. of organic compounds, and infra-red spectrometers have become standard equipment in most laboratories concerned with organic chemical analysis.

The preferred method at present in use for mounting a sample in a spectrometer is to dissolve the sample in a suitable solvent, and then introduce resulting specimen into a cell-containing device which is mounted in the spectrometer. The term sample is used herein to denote the material for analysis; the term specimen is used to denote the combination of sample and vehicle that is placed in the cell for examination in the spectrometer. The basic requirements for the solvent that is used as the vehicle are that it should be chemically inert both towards the sample and towards the material of which the cell-containing device is constructed. Also, of course, the sample must be sufiiciently soluble in the solvent. Moreover, it is necessary that the solvent have satisfactory optical properties, that is, it must be optically transparent to the radiation being employed in the spectrometer. To be optically transparent the solvent must not only transmit the radiation employed in the spectrometer, but it must not modify such radiation to any appreciable extent, since any such modification would swamp the characteristic spectral modifications imparted to the radiation by the sample in solution.

The present invention is concerned with improvements in the construction of devices which contain a cell in which such a specimen can be mounted in a spectrometer for spectral analysis. Cell-containing devices in use at the present time are of comparatively complex structure usual ly involving many separate pieces of different materials, often including precision made metal parts fabricated into a complex assembly. As a result, these devices are expensive, and it is only economical for a laboratory to keep on hand a comparatively small number of them. They must be thoroughly washed out after each use and carefully stored for further use. This economic need for the frequent reuse of known cell-containing devices is also disadvantageous in that it reduces the utilization of the spectrometer, since this instrument will normally have to remain idle while each cell-containing device or a group of such devices is washed out and recharged with a new specimen.

A principal object of the presentinvention is to provide an improved cell-containing device that will be considera-bly simpler than existing devices, and consequently cheaper to manufacture, while still performing satisfactorily in the spectrometer. By cheapening the manufacture of such devices, it becomes practicable for a laboratory to have on hand sufiicient of the devices for a large number of them to be charged in advance and fed into the spectrometer without delay, thus obtaining maximum utilization of this expensive instrument and of the time of the skilled technician who operates it. i

If an infra-red examination is to be made, the cellcontaining device will be made of a material optically transparent to infra-red radiation. Numerous suitable 3,93 6,2 l 5 Patented May 22, 1962 materials are known. These are normally chosen from the alkali metal halides, although a silver halide is sometimes used. Other materials that may be used are barium, calcium and lead halides; also arsenic trisulphide. Sodium chloride in the form of natural or synthetic rock salt is the most readily available material commercially. When rock salt is used, there is a requirement that it must be in the form of a single crystal, but there is no diliiculty in obtaining crystals of rock salt of suflicient size, since they can be readily synthesized. Typical dimensions for a cell-containing device of this type would be about two centimeters long, one centimeter wide and 0.5 centimeter thick. Pieces of rock salt crystal of this comparatively small size are readily available as scrap left over from the manufacture of larger optical bodies.

If ultra-violet or visible radiation is to be employed in the spectrometer, the material of the carrier body may be quartz crystal, or in some cases one of the optical glasses available and having suitable optical transparency.

It will be assumed, however, for the purposes of the subsequent specific description, that infra-red spectrometry is concerned and that the cell-containing device is formed from rock salt, since, although the invention is essentially sufiiciently broad in scope to include the other forms of trum.

radiation and other materials indicated above, infra-red spectrometry is by far the most common form of spectrometry employed and rock salt is the most convenient material to employ.

In our previous United States Patent 2,927,209, issued March 1, 1960, there is disclosed a device containing a cell which may be of a size suitable for containing a macroscopic sample (about 1 milligram); a microscopic sample (about micrograms) or an ultramicroscopic sample (50 micrograms or below).

The present invention is concerned with cell structures designed for use with specimens containing samples in the macroscopic and microscopic ranges, but not in the ultramicroscopic range. In the ultra-microscopic range, the specimen is so small that the shape of the cell is of little or no importance. With the larger specimens involved with microscopic and macroscopic samples, however, the shape of the cell becomes important. In particular, it becomes necessary for satisfactory optical performance 'to provide-the cell with a pair of planar side walls, parallel to one another, through which the radiation enters and leaves the cell. It is principally this requirement that has led to the comparatively complex construction previously employed in most cell-containing devices. With few exceptions, devices in current use consist essentially of a pair of flat plates of optically transparent material separated by a spacer. Access to the cell cavity is' provided by holes drilled through the edge of the spacer, or through the face of one of the windows. Unless carefully constructed and maintained, such devices are subject to leakage. If the windows and spacers are sealed with a chemical adhesive, leaks may develop through attack on the adhesive by the solvent, and products extracted from the adhesive may contaminate the sample and invalidate the spec- In cell-containing devices of more recent design, these difficulties have been overcome by careful polishing and machining of the component parts so that a leak re- "sistant seal between cell window and spacer can be l to as the nec 'to solvent and to the rock salt.

tangular cross-section or other cross-section having a pair of flat and parallel opposite faces. This can be done by the impact grinding technique described below.

Forfurther details, reference is directed to the accompanying drawings which illustrate-three forms of cell-containing device constructed in accordance with the present invention.

FIGURE 1 is aneXploded perspective view of a first form of cell-containing device; I

FIGURE 2 is a central vertical section of the main portion of the device seen in FGURE 1 taken on line IIII in FIGURE 3; 1 7

FIGURE 3 is a transverse section takenv on the line III-IIl in FIGURE 2;

FIGURE 4 is an exploded perspective view of a second cell-containing device according to the invention;

FIGURE 5 is a central vertical section of the main portion of the device seen in FIGURE 4 taken on line V-V in FIGURE 6;

V the present'invention;

FIGURE 8 is a transverse section taken on the line VII'L-VIII in FIGURE 7; and

FIGURE 9 is a vertical central section taken 011th line IX-IX in FIGURE 7.

The device seen in FIGURES 1-3 consists of an elon gated body 10 of a single crystal of rock salt drilled centrally to provide afirst cavity 11, which will be referred This neck 11 is of circular cross-section and serves to receive a stopper 12 (shown only in FIGURE 1) formed of a resilient material inert both to A suitable material is the synthetic resin known under the trademark Teflon. Inwardly of the neck 11 and communicating therewith is a second cavity which constitutes the cell itself. This cell 13 is rectangular in cross-section so as to provide a pair of parallel planar faces Hand 15' (FIGURE 3).

Whereas the neck 11 is formed by conventional drilling,

the cell 13 is formed by ultrasonic impact grinding. The general technique for producing small cavities in brittle materials by ultrasonic impact grinding has been described by M. S. Hartley in Electronics, I anuary 1956,

pages 132-135. A bit of approximately the cross-section of the cavity to be made is pressed down against the maachieved. by flushing out the cell rapidly with 50% aquejous ethanol followed immediately by absolute ethanol.

For best optical properties, the outer faces 24 and 25 of the body 10 will be ground and polished parallel to one another 'and'the faces 24 and 25 will be parallel to faces '14 and 15. Some deviation in the planarity and parallelism of faces 14 and 15 can be tolerated. In a spec trometer' the radiation will pass through the device as I demonstrated by the arrows R.

A modified form of cell is illustrated in FIGURES 4-6. In this case the body of the cell-containing device is formed in two parts, a lower main, specimen-mounting part, 10a and an upper part',10b.; Before parts 10a and 10b are joined together, a rectangular cell cavity13 is I formed in the lower body part 10a by impact grinding in the same manner as just described. Parallel planar faces 14 and 15 are thus provided as before.- Indepention of dumb-bell shape.

larger cross-sectional dimension) of the rectangular cell 13. When these two cavities have been made,the two parts 10a and 10b of the body are brought together and bonded; To eifect this bonding the contact surfaces of the two parts of the body are smoothed, moistened with saturated aqueous sodium chloride solution, placed together and then clamped under pressure with heating to 110 C. for twelve hours. Strong bonds between two bodies of rock salt can be obtained in this manner and the bond will resist'cleavage at temperatures up to 200 C. The bonded surface is not optically clear, but this is no disadvantage, since this surface is not placed in the optical beam in the spectrometer. Stopper 17 is provided to close neck 16. This second construction has the advantage over the construction shown in FIGURES l-3 that the neck 16 is of smaller diameter than the neck 11 and can thus be more effectively sealed. With the wider neck of the first embodimentit is more difficult to avoid solvent evaporation and greater care must be exercised to ensure a tightly fitting stopper while the cell is in use. On the other hand, the first embodiment is cheaper to manufacture as not involving the two-part construction and bonding step. V

In both types of cell-containing device so far described the thickness of the cell (i.e. the smaller of the two dimensions in cross-section, the distance between faces 14 and 15) is approximately one millimeter. This is a substantial distance for the radiation to traverse through the specimens and as a result these cells are satisfactory with comparatively dilute solutions. With solutions of greater opacity, it is desirable to have a shorter optical path through the specimen if good results are to be obtained in the spectrometer. It is possible to form cavities narrower than 1 millimeter in rock salt by the ultrasonic drilling technique, but the bits employed become very thin and delicate and tend to deform during the grinding process producing curved cavities that are no longer parallel with the outside faces of the body. This isundesirable for optical reasons.

This ditficulty can be overcome by adopting the shape of cavity illustrated in the third embodiment shown in FIGURES 7-9, where a cavity is formed with a cross-sec- A dumb-bell bit is employed comprising a pair of rounded side members of approximately 0.75 millimeter diameter connected by a cross-bar of approximately 0.1 millimeter thickness to form the actual functional slot portion of the cell cavity. Such a bit forms a cell cavity of complex shape having a pair of cylindrical chambers 17 and 18 joined by a slot porslot portion 19, of the cell cavity, this slot having parallel planar faces 14 and 15 as before. As in the case of the structure shown in FIGURES 4-6, the body of the device shown in FIGURES 7-9 is made in two parts a lower part 10a and an upper closure parts 10b. The upper part 10b'is formed with a pair of circular holes 20 each to receive a- Teflon stopper 21. In manufacture thetwo parts 10a and 10b are bonded together in a manner similar to that alreadydescribed, the holes 20 being in register wtih chambers 17 'and 18 to enable the cell cavity flow of sodium chloride solution. down the slot 19 during the bonding process, the upper end of such slot is enlarged into semi-circular cross-section as shown at 22.

dently of this operation a neck hole 16.is formed in the upper body part 10b; This has to'be done separately as 1 a the diameter of the neck 16 is smaller than the (the When this device is filled with a specimen, the two cylindticalehambers 17 and 18 represent an appreciable parasitic volume, but the capillary action of the very narrow slot 19 is such that it will remain filled with liquid even when the cylindrical chambers are themselves only partly filled or even empty. In this way the parasitic volume, if it should be disadvantageous, can be almost wholly eliminated by placing only enough specimen in the device to fill the slot 19.

We claim:

1. A device for mounting a liquid specimen for spectrometric examination, at least the specimen-mounting portion of said device comprising a unitary body formed from a single piece of a material chemically inert to the specimen and optically transparent to the radiation of the spectrometer, said body being provided with a cell cavity for containing said specimen, said cell cavity having an elongated chamber and a narrow slot portion, one edge of said slot portion opening into and communicating with said elongated chamber along the length thereof, said slot portion being defined by a pair of planar, mutually parallel faces disposed so close together that liquid specimen will be retained for spectrometric examination in said slot portion by capillary action even when the total volume of said specimen is insufiicient to fill said chamber to the same level as said slot, said chamber being too wide to retain liquid specimen therein by capillary action, the dimensions of said slot portion as determined by the extent of said faces in their own planes being substantially greater than capillary size.

2. A device for mounting a liquid specimen for spectrometric examination, at least the specimen-mounting portion of said device comprising a unitary body formed from a single piece of a material chemically inert to the specimen and optically transparent to the radiation of the spectrometer, said body being provided with a cell cavity for containing said specimen, said cell cavity being of dumbbell shape in cross-section, the central portion of such dumb-bell shape being defined by a pair of planar faces parallel to each other and disposed so close to each other as to define a narrow slot portion in which said liquid specimen will be retained by capillary action.

3. A device for mounting a liquid specimen for spectrometric examination, at least the specimen-mounting portion of said device comprising a unitary body formed from a single piece of a material chemically inert to the specimen and optically transparent to the radiation of the spectrometer, said body being provided with a cell cavity for containing said specimen, said cavity having a pair of planar faces extending parallel to each other to define a slot portion therebetween, the width of said slot portion as determined by the spacing apart of said faces being of capillary dimension While the length and breadth of said slot portion as determined by the extent of said faces in their own planes both being substantially greater than capillary dimension whereby a sheet of said liquid specimen having only one dimension of capillary size will be retained by capillary action in said slot portion.

4. A device as claimed in claim 3, wherein said slot portion communicates with at least one other portion of said cell cavity, 211- the dimensions of said other portion being greater than capillary in size whereby such other portion provides a substantial space non-competitive with said slot portion for the volume of liquid specimen required to charge said slot portion but available to contain liquid specimen in excess of said volume.

References Cited in the file of this patent UNITED STATES PATENTS 2,857,524 Talbern et al Oct. 21, 1958 2,927,209 Jones et a1. Mar. 1, 1960 FOREIGN PATENTS 679,711 Great Britain Sept. 24, 1952

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