WO1993003911A1

WO1993003911A1 - Static free coated sample vials for scintillation spectrometry

Info

Publication number: WO1993003911A1
Application number: PCT/US1992/004465
Authority: WO
Inventors: Leslie Alan Daniels; Robert Elmer Olson; Stanley Andrew Zielinski
Original assignee: Packard Instrument Co Inc
Current assignee: Revvity Health Sciences Inc
Priority date: 1991-08-19
Filing date: 1992-05-27
Publication date: 1993-03-04
Anticipated expiration: 1994-02-19

Abstract

A vial (10) for holding a radioactive sample for radiometric analysis which has an outer surface (14) on which a coating comprising a transparent antistatic agent (18) is deposited to prevent the accumulation of electrostatic charges on the vial. The vial (10) is treated to make the vial free of electrostatic charges by immersing the vial (10) and cap (12) with a solution containing the antistatic agent, spraying the vial (10) and cap (12) with a solution containing the antistatic agent or by contacting the vial (10) and cap (12) in a heated air stream with a flexible substrate carrying the antistatic agent.

Description

STATIC FREE COATED SAMPLE VIALS FOR SCINTILLATION SPECTROMETRY

Background Of The Invention

Field of the Invention

The present invention relates generally to vials for the containment of a liquid radioactive sample, and more particularly, to sample vials that are free of electrostatic charges for use in an apparatus for detecting and measuring radioactivity by liquid scintillation counting techniques. Background of the Art

The use of sample vials for containing cell cultures and the like has become common place in liquid scintillation spectrometry. In many situations, the cell cultures are labeled with radioactive isotopes such that the radioactivity of the final samples must be measured. The sample vial is provided with a scintillator that converts radiation, such as beta particles, into corresponding light pulses. As an example, a predetermined amount of a radioactive sample and a liquid scintillation cocktail is placed in a sample vial before the vial is loaded into a counting chamber of a scintillation spectrometer. Then, as the radionuclide in the sample decays, emitted beta particles energize the fluor contained within the liquid scintillation cocktail. The fluor converts the energy from the beta particles into optical events which are detected by a photomultiplier tube in the scintillation spectrometer. The scintillation spectrometer includes at least one photomultiplier tube which senses scintillation from each sample vial and converts the sensed scintillation into corresponding electrical pulses.

Sample vials used in liquid scintillation counting tend to accumulate substantial electrostatic charges from a variety of sources during packaging and handling. When the sample vials are subsequently placed within the scintillation counting device, the electrostatic charges are discharged in the form of a visible flash which presents a false light signal to the scintillation counter. This light is indistinguishable from the sample scintillations, and gives a false value of radioactivity of the sample.

Furthermore, these electrostatic charges on the sample vial attract random dirt which accumulates on the vial. When a sample vial is placed within the counting device, the static charge is dissipated and the dirt remains and accumulates within the counting device. This accumulation of dirt causes a loss of optical counting efficiency. Over time this interferes with the ability of the scintillation counter to measure accurate and reproducible scintillation counts. Sample vials which are currently available for scintillation counting typically are made of a plastic such as polyethylene, and have electrostatic charges of about 3,000 volts as a result of the process used in packaging the vials. Electrostatic charges also result because technicians generally wear gloves formed from latex, vinyl or other materials while handling vials for scintillation counting. A method for removing these electrostatic charges that is currently used in the industry involves ionizing radiation. As the sample vial enters the detector of the scintillation counting device for analysis, the vial passes in close proximity to an alpha particle emitting source such as Polonium-210. This method is disadvantageous because long exposure times are required to adequately remove electrostatic charges from the sample vial, reducing the throughput of the counting device. Additionally, the alpha particle emitting source must be periodically replaced due to its short decay half life.

Another known method for removing static charges from sample vials involves the use of electrical current to generate an ionized atmosphere of both positive and negative ions in close proximity to the vial. This method is often ineffective in removing very high electrostatic charges from sample vials. Neither of the known methods remove static from areas of a vial that are not visible to the device, such as the bottom.

There has been a need for an improved sample vial for use in transporting test samples including a liquid scintillator and a radioactive isotope to and from a scintillation counting device without imparting an electrostatic charge to the sample vial. The sample vial of the present invention has improved counting efficiency because it eliminates the accumulation of electrostatic charges and random dirt on the vial. Summary Of The Invention

It is a primary object of the present invention to provide an improved sample container which is coated with a transparent fabric softening agent to avoid the formation of electrostatic charges on the container. In this connection, a related object of this invention is to provide such an improved sample container by tumbling the vial with a material conta ing a fabric softening agent in the presence of a heated air stream.

It is another object of this invention to provide such an improved coated sample container which does not interfere with the normal operation of a liquid scintillation counting device or reduce the rate at which the samples may be analyzed, and which has an improved counting efficiency.

Another important object of this invention is to provide a coated sample container which is resistant to electrostatic charges which result from handling the containers with gloves when preparing the sample and transporting the container to the scintillation counting device.

Other objects and advantages of the invention will be apparent from the following detailed description and the accompanying drawings.

In accordance with the present invention the foregoing objectives are realized by providing a vial for holding a radioactive sample for radiometric analysis which has an outer surface on which a coating comprising a transparent antistatic agent is deposited to prevent the accumulation of electrostatic charges on the vial. The vial is treated to make the vial free of electrostatic charges by immersing the vial and cap in a solution containing the antistatic agent, spraying the vial and cap with a solution containing the antistatic agent or by contacting the vial and cap in a heated air stream with a flexible substrate carrying the antistatic agent.

In another embodiment of the present invention, a vial for holding a radioactive sample is integrally formed from a plastic material including an amount of a tansparent antistatic agent for neutralizing electrostatic charges on the vial. A cap integrally formed from the plastic material is removably attached to the vial. The vial and cap may also be treated with an antistatic coating. Brief Description Of The Drawings

FIG. 1 is an enlarged elevational view, partly in section, of a sample vial embodying the present invention.

While the invention is susceptible to various modifications and alternative forms, specific embodiments thereof have been shown by way of example in the drawings and will herein be described in detail. It should be understood, however, that it is not intended to limit the invention to the particular forms disclosed, but on the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the invention as defined by the appended claims.

Detailed Description Of The Preferred Embodiment

Turning now to FIG. 1, there is shown a sample vial 10 having a snap or screw cap 12 to prevent spillage of the liquid radioactive sample within the vial. Liquid scintillation sample vials are generally formed from glass or plastic, such as high density polyethylene. The sample vial 10 and cap 12 have respective outer surfaces 14 and 16 on which a transparent coating 18 is deposited. The coating 18 includes an antistatic agent to prevent the accumulation of electrostatic charge that would be present on an uncoated sample vial.

The antistatic agent may be any compound or composition that effectively prevents the accumulation of static without inhibiting the transmission of light, such as fabric softening agents that are available for reducing static on clothing. Suitable antistatic agents are selected from group consisting of cationic surfactants, nonionic surfactants and mixtures thereof. Examples of such agents include quaternary ammonium compounds, glycerol stearates and ethoxylated synthetic amines. Impregnation or coating of liquid scintillation sample vials with antistatic agents which inhibit the transmission of light is ineffective. Such unacceptable antistatic agents include carbon, metal fibers such as stainless steel, nickel or brass, and agents that are yellow or tinted in color.

A further aspect of the present invention is directed toward a method of making an antistatic sample vial. One method of treating antistatic vials involves tumbling the vials and caps in the presence of a heated air stream and a substrate carrying the antistatic agent. Each cap may be placed on a vial or the caps may be tumbled along with the vials. The vials may be tumbled in a conventional laundry dryer so that the antistatic agent is transferred from the substrate to the vials upon contact. Typically, the substrate is a flexible cloth material which is embedded or surface coated with the antistatic agent Such substrates include commercially available fabric softening sheets.

A second method of treating a vial so that it prevents the accumulation of static charge involves immersing the vials with caps in place in a solution containing an antistatic agent as discussed above. A third method involves spraying the vials with caps in place with a solution of an antistatic agent so as to form an antistatic coating on each vial.

When the vials are properly coated with the antistatic agent, a zero static charge is measured by an electrostatic meter such as the Chapman ESM 5000, Portland, ME. Moreover, the vials will not accept a static charge even while handling with latex gloves. Typical vials as packaged in shipping containers have charges of about 3000 volts. At low relative humidity conditions, touching the vials with latex gloves will produce voltages of 10,000 to 20,000 volts. The vials of the present invention which are coated with an antistatic agent remain at zero charge during handling. A fourth method of making a static-free vial involves integrally forming the vial and cap from a plastic material including an antistatic agent as discussed above. A suitable plastic material is one in which the transparent antistatic agent migrates to the surface of the vial and cap during molding so that electrostatic charges on the vial and cap are prevented. The vial and cap may also treated with a transparent antistatic coating such as those discussed in the above methods.

The following examples set forth transparent coating compositions and method incorporating the same for coating sample vials. Standard commercially available materials were used whenever possible. It will be understood that the formulations and the procedures which follow are provided for purpose of illustration only and that other ingredients, proportions and procedures can be employed in accordance with the disclosures of this invention. .-gflm tf .- Comparison of Coated and Uncoated Vials

The static charge of each vial was measured by a refrigerated Packard Tri- Carb^® 1900CA liquid scintillation analyzer having the static controller disconnected. Polyethylene vials (20 ml) as manufactured by Packard Instrument Company, Inc. were immersed with their caps in place in a coating consisting of 1 percent by volume of Ethoquad C/12 solution (Aπnak Quaternary Ammonium Compound) as manufactured by Akzo Chemicals Inc. The vials were dried and filled with 5 πύlliliters of Optifluor scintillation cocktail as manufactured by Packard Instrument Company, Inc. New Latex gloves were worn during cocktail dispensing. Four cassettes which each contained 12 vials were loaded into the refrigerated 1900. Static measured was less than (-) 100 volts.

A second group of the polyethylene vials were prepared according to the protocol as discussed above. However, the vials were immersed in deionized water with a small amount of "Liqui-Nox" detergent. Static measurements were (-) 100 to 200 volts.

A third group of polyethylene vials were filled straight from the packaging carton using new latex gloves. Voltage measured was (+) 1000 to 2000 volts.

A fourth set of polyethylene vials were prepared as discussed above for the first set of vials except the vials were sprayed with the Ethoquad solution instead of being immersed in it. Voltage measured was (-) 100-200 volts.

Using a criteria of 40 cpm as the maximum for a one-half minute "static- free count", the following was observed in 96 counts:

Ryqmple 2; Effect of Coating on Tritium Counting Performance

Twelve polyethylene vials were coated with the Ethoquad composition as discussed in Example 1. Twelve vials remained uncoated. Each vial was filled with ten milliliters of Optifluor and 10,000 DPM of ³H radionuclide. Two cassettes of samples were alternately counted for one minute, and each count was repeated. The results indicated that the coating caused a minimal loss of 0.64 percent ±..14% 3H counts.

The foregoing description is not limited to the specific embodiment herein described, but rather by the scope of the claims which are appended hereto. For example, although the invention has been described with reference to cylindrical sample vials, any conventional sample vials may be coated or formed by the methods of the present invention.

Claims

CLAIMS:

1. A vial for holding a radioactive sample for radiometric analysis, wherein a coating comprising a transparent antistatic agent is deposited on an outer surface of the vial to prevent the accumulation of electrostatic charges on the vial.

2. The vial of claim 1 wherein the antistatic agent is selected from the group consisting of cationic surfactants, nonionic surfactants and mixtures thereof.

3. The vial of claim 2 wherein the antistatic agent is selected from the group consisting of glycerol stearates, ethoxylated amines and quaternary ammonium compounds.

4. The vial of claim 1 wherein a cap is removably attached to the outer surface of the vial and the cap has a transparent coating comprising an amount of an antistatic agent to prevent the accumulation of an electrostatic charge on the cap.

5. The vial of claim 1 wherein the coating is deposited by contacting the vial with a substrate carrying the antistatic agent.

6. A vial arrangement for storing radioactive samples, wherein the arrangement comprises: an integrally formed plastic vial comprised of a base having an upwardly open sample well for receiving a sample; and a cap which is removably attached to the upwardly open sample well to prevent the contamination of the sample, wherein a transparent antistatic coating is deposited on the vial and the cap to prevent the accumulation of electrostatic charges on the vial and the cap.

7. The vial arrangement of claim 6 wherein the coating is deposited by contacting the vial with a flexible substrate carrying the antistatic agent in the presence of a flow of heated air.

8. The vial arrangement of claim 7 wherein the antistatic agent is nonionic or cationic is selected from the group consisting of cationic surfactants, nonionic surfactants and mixtures thereof.

9. The vial arrangement of claim 8 wherein the antistatic agent is selected from the group consisting of glycerol stearates, ethoxylated amines and quaternary ammonium compounds.

10. The vial arrangement of claim 6 wherein the vial is integrally formed from a plastic material including an amount of an antistatic agent for preventing the accumulation of electrostatic charges on the vial.

11. A method of treating a vial for holding radioactive samples for radiometric analysis to make the vial free of electrostatic charges, wherein the method comprises the steps of: a) providing a vial having a cap which is removably attached to the vial; and b) coating the vial and cap with an antistatic agent that does not inhibit light transmission.

12. The method of claim 11 wherein the coating step b) includes the step of immersing the vial and cap in a solution containing the antistatic agent.

13. The method of claim 11 wherein the coating step b) includes the step of spraying the vial and cap with a solution containing the antistatic agent.

14. The method of claim 11 wherein the coating step b) includes the step of contacting the vial and cap in a heated air stream with a flexible substrate carrying the antistatic agent.

15. The method of claim 11 wherein the vial as described in step a) is comprised of a plastic material including an amount of a transparent antistatic agent for preventing the accumulation of electrostatic charges on the vial.