US3496777A

US3496777A - Sampling device

Info

Publication number: US3496777A
Application number: US709432A
Authority: US
Inventors: Herbert Packer; William S Foulks Jr
Original assignee: Arthur D Little Inc
Current assignee: Arthur D Little Inc
Priority date: 1968-02-29
Filing date: 1968-02-29
Publication date: 1970-02-24
Anticipated expiration: 1987-02-24

Description

FIG.

INVENTORS HERBERT PACKER S. FOULKSuJR.

WILLIAM BY FIG. 5.

ATTORNEYS United States Patent M 3,496,777 SAMPLING DEVICE Herbert Packer, Cleveland Heights, and William S.

Foulks, Jr., Cleveland, Ohio, assignors to Arthur D. Little, Inc., Cambridge, Mass., a corporation of Massachusetts Filed Feb. 29, 1968, Ser. No. 709,432 Int. Cl. G01n 1/34 US. Cl. 73422 6 Claims ABSTRACT OF THE DISCLOSURE A device for preparing analytical samples for infrared spectroscopy, and formed of an elongated, porous wick coated on its sides to prevent evaporation but open at the ends, and having a pointed tip which is removably emplaced against one end of the wick. The tip is of a porous, spectroscopic-grade matrix material such as potassium bromide.

This invention relates to spectroscopy and more particularly to means for preparing analytical samples particularly in infrared spectroscopy.

Spectral absorption examination of solids has been accomplished by a number of techniques such as the use of solutions, mulls, dry powder films and pressure-fused discs. Solution techniques involve the use of a suitable solvent with wide band pass characteristics in the pertinent infrared region and with relatively high solubility for the solid to be examined. Mull techniques are useful if the absorption bands of the mulling agent do not interfere with the absorption bands of the solid, and if reflection losses can be tolerated. Very small particle sizes are required for dry powder films to avoid scattering, particularly of infrared radiation.

Fused disc techniques have been widely used for both qualitative and quantitative work because they present fewer problems. Typically, the solid material, frequently as a tiny quantity, is diluted by admixture with purely ground matrix powder of, for example KBr, and pressing the mixture to a fused disc which can be introduced into the light beam of a spectrophotometer. A number of different matrix materials have been used, all of which are capable of being compressed from a finely powdered state into homogeneous plates or discs substantially transparent to the radiation region of interest. Typically, alkali halides such as KBr, KI, KC], NaBr, NaI, NaCl, and CsBr have been used. Other materials as diverse as AgBf and polyethylene have also been used as matrices. Since KBr of high purity is transparent in the ultraviolet as well as the infrared (as far in the latter as 28 microns for KBr) it is the most widely used material.

Heretofore, the matrix material is usually finely ground and intimately mixed with the sample as by grinding the first mixture in a mill, the concentration of sample in the matrix material usually being below 0.5%. The final mix is pressed, for example at 25,000 p.s.i., in a die to form an imporous, transparently clear disc,

This latter technique possesses a number of other shortcomings. For example, homogeneity of sample and matrix is frequently obtained by prolonged grinding of the mix, but this can produce polymorphic changes in the sample structure, and sometimes cause the sample to become hydrated or changed into a salt, giving rise to undesired spectral anomalies.

3,496,777 Patented F eb. 24, 1970 The above technique pre-supposes the availability of sufficient sample to permit ready admixture with matrix material, and thereby to obtain a disc with suitable sample concentration. However, when only a dilute solution of a minute quantity of a sample is available, as is often the case when the samples are obtained as the result of chromatographic, or electrophoretic or other microanalytical separation and purification processes, conventional transfer operations employed to obtain a sufficiently high level of concentration without either recontaminating or losing the sample are often very difiicult or ineffective. For example, silica gel is typically employed as a selective adsorbent in chromatographic separations. However, silica gel displays undesirable infrared properties and has to be removed from the sample in order to al ow the infrared spectrum of the latter to be determined without interference. The removal of all of the silica gel by conventional filtration techniques is an extremely difiicult process because some of the silica is possibly present as a colloidal suspension rather than as a conventionally filterable solid.

The prior art techniques are useful with batch samples. In processes involving periodic analysis of a flow stream, it is therefore necessary to remove samples as in a pipette, beaker or the like and process these samples on an absorbent. This may involve interference with the process undergoing analysis.

In copending application Ser. No. 553,208, now US. Patent 3,452,601, assigned to the common assignee of the present application, there has been disclosed a novel structure for use in transferring microsamples into a matrix subsequently suitable for absorption spectroscopy, which structure comprises an elongated element of matrix material formed as a porous stratum capable of transporting by capillarity from one end to the other of the element, a solvent containing the sample as a solute. While such structures are quite useful, they require severance of a tip portion of the structure for use in forming a pellet. These portions are indeterminate in size and therefore the pellets formed are often different in weight and thickness, even when the same pelletizing die is employed. After the tip portion is removed, the remainder of the structure is comparatively useless and is uneconomically discarded. Lastly, although the entire structure is formed of a particular material, only the tip portion is actually used to provide pelletizing material.

The present invention involves an improvement in such structures useful in solid phase absorption spectroscopy which considerably simplify the preparation of uniform pellets or discs including microsamples, and which overcome a number of the foregoing problems. A principal object of the present invention is to provide a novel structure for use in transferring microsamples into a matrix subsequently suitable for absorption spectroscopy, which structure comprises an elongated element of matrix material formed as a porous stratum capable of transporting by capillary from one end to the other of the element of a solvent containing the sample as a solute, a sheath surrounding the elongated surfaces of the structure, and a separate removable tip element of a matrix material which tip comprises means for concentrating the solute in a limited amount of matrix material without any loss of solute.

These and other objects of the invention will in part be obvious and will in part appear hereinafter. The invention accordingly comprises the apparatus possessing the construction, combination of elements, and arrangement of parts and the several steps and the relation of one or more of such steps with respect to each of others all of which are exemplified in the following detailed disclosure and the scope of the application of which will be indicated in the claims.

For a fuller understanding of the nature and objects of the present invention, reference should be had to the following detailed description taken in connection with the accompanying drawings wherein:

FIG. 1 is a sectional view of an embodiment of the invention in packaged form and taken across its axis of elongation;

FIG. 2 is another sectional view of the embodiment of FIG. 1 ready for use;

FIG. 3 is yet another sectional view of the embodiment of FIG. 1 following usage;

FIG. 4 is a sectional view taken along the line 44 of the embodiment of FIG. 1, i.e., across the axis of elongation; and

FIG. 5 is a sectional view of another embodiment of the invention taken across its axis of elongation.

As shown in FIGS. 1 through 4, a preferred embodiment of the invention comprises three elements, an elongated, porous element 20, sheath 22 around element 20, and a separate tip 24. Element 20 is formed of a material meeting a number of criteria: it must form a porous mass wherein the pores are interconnected to provide channels of size appropriate to allow capillary flow through element 20 of a solvent and a solute sample; it should be relatively highly insoluble with respect to that solvent; and it should be substantially non-reactive chemically with either the solvent or the solute.

The criteria are readily met by the usual solid state matrix materials previously noted above, if one is judicious in the selection of solvents and solutes with which element 20 is employed. However, unlike the sampling device described in copending application Ser. No. 553,208, element 20 can also be formed of a number of open materials that may, when compressed into an imporous disc or pellet, exhibit substantial absorption in the band of radiation intended for use in identifying material to be analyzed. Thus, element 20 serves primarily as a capillary conduit. Element 20 is typically a rod having two

ends

28 and 30, the shapes of which will be described later.

Sheath 22 at least surrounds all but ends 32 and 34 of element 20, preferably tightly, and in the embodiment of FIG. I initially extends well beyond both ends of element 20. The ends of sheath 22 are sealed, as by crimping, thus forming a container or bag in which element 20* is protected from atmospheric and other contaminants. Preferably, sheath 22 in this embodiment is lightly scored or grooved peripherally adjacent the juncture of

ends

26 and 30 as at 34, and similarly scored adjacent but

intermediate ends

32 and 28 as at 36.

Sheath 22 is an imporous material, i.e. impermeable to and non-reactive with the solvent with which element 20 is to be used. Typically, sheath 22 is a metal (e.g. aluminum), glass, or synthetic polymer such as polytetrafiuorethylene, polyvinylchloride or the like, of sufficient flexibility to be sealed and thin enough to be readily torn by manual stress.

Lastly, the device includes tip 24 which is of a matrix material capable of being formed into a porous mass wherein the pores are interconnected and of a size to allow capillary into the tip. The matrix material must also be capable of being compressed, as from a powdered state, into an imporous mass or pellet that is substantially transparent to (i.e. substantially non-absorbent) the radiation intended for use in identifying the sample material to be mixed with the matrix material. Additionally, the matrix material should be relatively highly insoluble and substantially non-reactive chemically with either the solvent or solute with which it is used. Typical matrix materials useful in the invention are those hereinbefore noted.

Tip 24 preferably is shaped so as to have one end 38 thereof of substantially the same cross-section configuration as end 28 of element 20 and shaped to conform to or rest in contact with the surface of end 28. Most simply then both

surfaces

28 and 38 are flat, but of course can be mating surfaces of other shapes such as conical or the like. End 40 of tip 24 on the other hand preferably is tapered or considerably reduced in cross-section compared to end 38, conveniently to a point or line. In such case, tip 24 is then substantially either conical or chisel shaped. Tip 24 is disposed inside the envelope formed by sheath 36 with

surfaces

28 and 38 nested.

Ordinarily, the section configuration of element 20 (as shown in FIG. 4) can be rectangular, but the particular shape is not very important and can be circular, oval, polygonal or the like. Similarly, surface 26 need have no particular shape, but conveniently is flat.

In use, the end portions of sheath 22 are torn or cut away along the scoring at 34 and 36 to provide a structure as shown in FIG. 2. Because of the location of scoring at 36, a portion of sheath 22 extends beyond the juncture of

surfaces

28 and 38 to provide a sleeve 42 which serves to releasably hold tip 24 in contact with element 20.

The structure of FIG. 1 could be manufactured in a number of ways. For example, sheath 22 could be a polyvinylchloride tube. The latter is then filled, for example with KBr powder (such as a spectroscopic grade available from Harshaw Chemical Co., Cleveland, Ohio) and the tube placed into a die. The powder is compressed by a hydraulic plunger for 1 second at, for example, 8000 p.s.i., to form a flat-ended KBr mass having dimensional rigidity and the requisite porosity. The tube, if necessary, can be trimmed flush with one end of the KBr mass, and so as to leave sleeve 42 at the other end. However, this method may result in non-uniform porosity of the KBr mass.

Thus, in a preferred method where uniform porosity is desired, an elongated rectangular female die is filled with KBr powder and a male flat placed thereon. This is then compressed at a pressure suflicient to form a substantially rigid but porous element 20 of KBr. The KBr element is removed from the die and an imporous polyethylene or other appropriate plastic sheet wrapped around the element and then sealed along an edge to form a sheath leaving the ends of the element exposed. A tip 24 is similarly formed in a die and appropriately emplaced within one open end of the sheath. The ends of the sheath are then sealed. It should be remembered that while tip 24 must be formed of a spectroscopically suitable material, element 20 need not be so made, but can be of less expensive materials such as non-spectrographic grade polyethylene or the like.

In the preferred usage, after removal of

ends

30 and 32, only end 26 of element 20 is placed in contact with a solution containing the dissolved sample of material, the absorption spectrum of which is to be determined. If the solution is aqueous, the materials of element 20 and tip 24 are preferably water-insoluble and typically can be AgBr, polyethylene or the like. For use with non-aqueous solvents, KBr is preferred as the tip material. Porous element 20 acts as a wick and therefore capillary action transfers the solutions to the surface 28 of the element 20. Sheath 22 serves to prevent solvent evaporation from the surface of element 20 except at surface 28. *Because

surfaces

28 and 38 are in contact, the solution transfers to tip 24. As solvent evaporates from the narrower end of tip 24, the concentration of the solute sample in the tip increases. Of course, the length of time one continues to wick solution through element 20 depends on a number of factors such as solvent volatility in the ambient atmosphere, temperature, the original concentration of solute in the solvent and the like. If desired, particularly where only a minute quantity of the solute is available, additional solvent can be added from time to time to the original solute container to aid transport of all of the solute to the exposed end of the element. When it is determined that an appropriate solute concentration has been achieved at tip 24, the latter is simply lifted out of sleeve 42 away from the body of element 20 as by tweezers, as shown in FIG. 3. The tip is then preferably allowed to dry.

Tip 24 with its dried sample can then be pressed sufficiently to render the matrix material transparent. However, where it is desired to achieve homogeneity of matrix and sample material, tip 24 need only be crushed and the resulting debris mixed. Because of its porous structure, the tip tends to return to powder form readily with a minimum of undesirably-prolonged grinding. The crushed tip need only be compressed in the usual manner in a die, for example at 15,000 lbs. pressure for 20 minutes, to form the desired transparent pellet ready for spectroscopic examination. The actual time of compression depends, inter alia, on pellet dimensions, moisture content and the like.

The foregoing device is particularly useful with samples requiring saparation of solute from insoluble materials, such as in samples prepared by silica-gel chromatography. When the solute is wicked through element 20, the latter apparently serves not only to filter out large silica particles completely, but by some mechanism prevents the remainder of the silica (e.g. colloidal particles), from appearing in interfering quantities at end 24, even with wick structures of as short as one inch. Using conventional techniques to transfer the solute to the matrix material often contaminates the latter with silica regardless of how careful the operator may be.

Thus, it will be apparent that the invention provides material in a form directly suitable for use in the pellet ing process of the prior art. By doing so, one minimizes transfer losses of sample, avoids the accumulation of contaminants and permits more rapid and convenient preparation of pellets of uniform size, whereby greater sensitivity in the ultimate absorption spectrum and a spectrum representing a purer sample is obtained. Further, additional tips may be inserted in sleeve 42 to obtain additional samples without removing element 20 from contact with the solution and without the necessity of discarding element 20 for each usage.

The basic principles of the present invention can be advantageously embodied in other forms. For example, as shown in FIG. 5, the device (wherein like numerals de note like parts) can be used to monitor a body of solution 50 in conduit or container 52. Element 20, encased in sheath 22 is preferably mounted veritcally in a semipermanent or permanent manner as by O-ring 54 sealing one end of the sheath within an opening 56 through a wall of the conduit so that surface 26 is in contact with solu tion '50. An apertured cap 58 can be used to compress the O-ring and prevent leakage around the outside of sheath 22. The other end of the sheath defining sleeve 42 is directed upwardly and holds tip 24. With this device,

a series of analytical samples can readily be obtained, each in a predetermined uniform matrix of spectroscopic material without periodically opening container 52 and without replacement of the entire wick (formed by element 20) at each sampling.

Since certain changes may be made in the above apparatus without departing from the scope of the invention herein involved it is intended that all matter contained in the above description or shown in the accompanying drawing shall be interpreted in an illustrative and not in a limiting sense.

What is claimed is:

1. A device for preparing samples from a liquid solution for analysis by selective absorption of radiation, and comprising in combination:

an elongated, substantially rigid mass of material, substantially insoluble in said solution; said mass being sufiiciently porous to allow transfer of said solution between the ends thereof by capillarity;

a separate tip adapted to contact one end of said mass and being formed of a porous mass of material convertible into a substantially imporous mass transparent to said radiation, and;

a sheath enclosing at least said mass so as to reduce evaporation of said solution, said sheath being substantially impervious to and insoluble in said solution.

2. A device as defined in claim 1 wherein said tip has two ends one of which is shaped to conform to and has substantially the same cross-section configuration of said one end of said mass, and the other end of which is tapered to a substantially smaller cross-section.

3. A device as defined by claim 1 wherein said tip is convertible by compression.

4. A device as defined in claim 1 wherein said tip is in contact with said one end, said sheath extends beyond said tip and the other end of said mass, said sheath being sealed so as to provide a container wholly enclosing said mass and tip.

5. A device as defined in claim 1 wherein said sheath terminates adjacent the other end of said mass but extends beyond said one end of said mass to form a sleeve, and said tip is dimensioned so as to be realeasably held in contact with said one end by said sleeve.

6. A device as defined in claim -5 including means for mounting said other end of said sheath Within a container for said solution.

References Cited UNITED STATES PATENTS 2,863,319 12/1958 Melin 73-4254 3,191,813 6/1965 Dufi 73425.4

S. CLEMENT SWISHER, Primary Examiner US. Cl. X.R.