Radioactive waste disposal cartridge

This invention relates to the use of a unique apparatus and method for extracting radioactive components from liquids, such as electrophoresis buffers. In the present invention, the radioactive liquid is pumped or transported by other suitable means and is passed through a cartridge having an elongated chamber that contains an exchange medium. The exchange medium, i.e. exchange resin, is contained within the elongated chamber between an upper frit and a lower frit. Further, the cartridge has a means within the elongated chamber for retaining pressure between the upper frit and the lower frit. The nucleotides, being charged molecules, bind to the exchange medium and are removed from the liquid. The liquid then exits the cartridge and has such a low amount of radioactivity that it can be disposed of to a conventional drain.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention relates to an apparatus and method for treating radioactive 
waste. More particularly, this invention relates to an apparatus and 
method for treating radioactive waste generated from gel electrophoresis. 
Gel electrophoresis is a common technique widely used for separating DNA 
fragments and determining the "sequence" of DNA. Many gel electrophoresis 
procedures use DNA that has been rendered radioactive through the 
incorporation of radionucleotides. During gel electrophoresis the 
electrophoresis buffer generally becomes contaminated with both free and 
incorporated nucleotides necessitating its disposal as radioactive waste. 
The handling and disposal of liquid waste is both hazardous and costly. 
Until the present invention, there was no convenient and practical way to 
extract radioactive components from electrophoresis buffer. 
Another application of the present invention is to treat radioactive waste 
generated in the use of radioactive labelled molecular probes. Those of 
skill in the art will recognize the different applications of the present 
invention for treating radioactive waste. 
2. Description of the Prior Art 
Gel electrophoresis is a fundamental biochemical separation technique that 
forms the basis for distinguishing a variety of biologically important 
molecules on the basis of size, charge or a combination thereof. Specific 
examples of biological molecules advantageously separated by gel 
electrophoresis include proteins and nucleic aids. Electrophoresis is 
usually performed in a gelled (e.g., agarose) or polymerized (e.g., 
polyacrylamide) media (generically termed a "gel") that contains an 
electrically conducting buffer. Electrophoresis is performed wherein a 
voltage is applied via chemically inert metal electrodes across the 
cross-sectional area of the gel. The biological sample of interest is 
placed into pre-formed sample wells in the gel, usually at one end of the 
gel, and the polarity of the applied voltage is arranged so that the 
biological sample migrates through the gel towards one of the electrodes 
(usually positioned at the opposite end of the gel from the samples). 
Where appropriate, the inverse linear relationship between migration 
distance and molecular size is maintained by the addition of chemical 
denaturants (such as urea, formamide, or sodium dodecyl sulfate) to the 
gel and electrophoresis buffer. 
A particular application of gel electrophoresis is the separation of 
single-stranded DNA fragments in the determination of the nucleotide 
sequence of a nucleic acid of interest. To this end, a collection of 
single-stranded DNA fragments is generated either by chemical degradation 
of the nucleic acid (using the Gilbert method, see e.g., Maxam and Gilbert 
(1980), Methods Enyme, 65, p499-500) or by replacement DNA synthesis using 
a polymerase (using the Sanger method, see e.g., Sanger, F., Niklen, S., 
and Coulson, A. R. (1977) Proc. Nat. Acad. Sci. USA 74, p5463-5467). This 
collection of single stranded DNA fragments includes a fragment 
corresponding to each position in the sequence to be determined; in the 
most frequently-used sequencing method, this correspondence is directly 
related to the distance from a fixed site of initiation of polymerization 
at a primer that is annealed to the nucleic acid to be sequenced. Thus, 
determination of the desired sequence depends on the separation of each of 
the fragments, which differ in length by only a single nucleotide. 
Traditionally, the identity of each of the possible nucleotides at each 
position (adenine, guanine, cytosine or thymidine) is distinguished by 
performing a sequencing reaction specific for each ending nucleotide in 
separate chemical reaction mixtures. Thus, each sequencing experiment is 
typically performed in 4 separate tubes, wherein are generated a 
collection of fragments each ending at a position corresponding to the 
terminating nucleotide used in that reaction. A nucleotide sequence is 
thereafter determined by performing denaturing gel electrophoresis on each 
of a set of 4 reactions, each reaction electrophoresed individually in 
adjacent lanes of a single sequencing gel. The presence of a band at a 
position in a nucleotide-specific lane of such a gel indicates the 
identity of that nucleotide at that position in the sequence. Using 
conventional techniques, each of the fragments is radiolabeled, and the 
bands are visualized after electrophoresis by autoradiography. 
The radiolabelling is accomplished by using radionucleotides that attach to 
the fragments. As previously noted above, during gel electrophoresis, the 
electrophoresis buffer generally becomes contaminated with both free and 
incorporated nucleotides necessitating its disposal as radioactive waste. 
Moreover, the radioactive electrophoresis buffer is dangerous and must be 
handled with caution. Prior to the present invention, available 
electrophoresis units have no provision for disposal of the buffer 
solutions and require manual emptying of the lower buffer chamber (DNA 
sequencing instruments have an upper and a lower buffer chamber, both 
containing similar buffers). Radioactive components are collected in the 
lower buffer chamber. This is because excess radioactive nucleotides and 
DNA strands elute off the bottom of the electrophoresis gel and into the 
lower buffer chamber during the run. Typically the lower buffer chamber is 
shaped like a rectangular tray without special provisions for emptying. 
The tray is simply tipped at an angle and the liquid is poured through a 
funnel and into a waste disposal container. The procedure is awkward and 
it is very common for practitioners to splash and spill small amounts of 
the radioactive liquid onto themselves and their surroundings. 
Attempts by others to address this problem include using an exchange resin 
to remove the radioactivity from the liquid to the level where the treated 
liquid can then be disposed of according to the specific Nuclear 
Regulatory Commission rules and regulations (Title 10, Chapter 1, Code of 
Federal Regulations--Energy, 1992, Part 20, Standards for protection 
against radiation). However, these attempts have given rise to operational 
problems. See e.g., "A Method for Removal of Radioactive Nucleotides from 
Electrophoretic Buffers", T. Kaczorowski et al., University of Wisconsin 
et al., BioTechniques, Vol. 16, No. 6, 1994). This reference teaches that 
it is very important not to allow the resin to dry out during 
decontamination. It is believed that this reference requires a wet resin 
because otherwise, the resin matrix would cease to be uniform because it 
would shrink and develop cracks as it dried out. Keeping the resin wet as 
required in this reference would lead to operational problems such as 
always keeping the resin wet during decontamination by running a 
non-contaminated solution through the resin both before and after 
decontamination of the liquid to be treated, and always keeping the resin 
wet thereafter if the resin is to be used again for treatment of 
additional radioactive waste. This in turn would require additional 
operator attention. 
In addition, this reference requires that the resin bed be prepared prior 
to decontamination by suspending the resin in distilled water, apparently 
to create a wet, uniform bed without cracks. Further, this reference 
requires the operator to form a sufficient liquid head above the resin 
before the contaminated liquid is allowed to pass through the resin. 
Moreover, this reference fails to teach that non-ionic species of S-35 are 
created during cycle sequencing, and fails to teach how such species would 
be removed. 
SUMMARY OF THE INVENTION 
This invention relates to the use of a unique apparatus and method for 
extracting radioactive components from the electrophoresis buffer. In the 
present invention, the radioactive liquid generated by gel electrophoresis 
(for example) is passed through a cartridge that contains an anion 
exchange medium. The nucleotides, being negatively charged molecules, bind 
to the anion exchange medium and are removed from the liquid. The liquid 
then exits the cartridge and can be disposed of to a conventional drain 
because the level of radioactivity of the treated liquid is low enough to 
do so under U.S. Nuclear Regulatory Commission Rules and Regulations. 
Alternatively, the treated liquid can be deposited into a storage vessel, 
and can be disposed of as desired or recycled for further use. 
In addition, the preferred embodiment has a unique, compacted matrix of 
exchange resin between a porous upper frit and a porous lower frit. In the 
preferred embodiment, this matrix is made using a spring loaded upper frit 
to maintain the upper frit in contact with the matrix. The preferred 
embodiment has a porous upper frit with a thickness and porosity that has 
been chosen in order to provide sufficient back-pressure so that a "liquid 
head" is formed by allowing the contaminated liquid to simply drip onto 
the top of the upper frit. This liquid head reaches a certain height that 
is then maintained until the end of the decontamination process, wherein 
the last remaining contaminated liquid is drawn through the cartridge. It 
is surprising that a liquid head can be properly maintained even as the 
contaminated liquid is drawn through the cartridge. This liquid head 
provides additional operational benefits. Specifically, this preferred 
construction helps to reduce channeling of the radioactive liquid as it 
moves through the cartridge, and thus helps improve the extraction of 
radioactive particles from the liquid. 
Those skilled in the art of column chromatography will recognize that there 
are a number of factors that are critical to successful extraction 
chromatography. 
One such factor is "bed uniformity". Chromatography is typically carried 
out using fine particles or beads, capable of selectively binding or 
adsorbing the solute of interest. These particles are tightly packed into 
the column (or cartridge) and great care is taken to exclude air bubbles 
and other artifacts which might cause non-uniformities in the column bed. 
It is critical that the bed is uniform throughout the column so that 
liquid passing through any given portion of the bed will encounter the 
same density of matrix particles and will thus be subject to identical 
extraction potentials. The porous beads swell upon hydration and contract 
upon drying. As a result, chromatographers are careful to never allow the 
column bed to dry out once it has been packed for fear that cracks and 
void spaces should form. 
As noted above, the present invention includes a spring loaded frit placed 
on top of the column bed to maintain an evenly packed bed throughout 
cycles of drying and rehydration. This innovation allows a column to be 
used for many applications, such as the daily extraction of DNA sequencing 
electrophoresis buffer, where the column will dry out between uses. 
Another critical factor familiar to the chromatographer is that of "flow 
uniformity." For maximum extraction efficiency, the liquid flow should be 
substantially uniform through the column. The liquid typically enters the 
column through a small orifice in the top of the column and then must be 
distributed across the surface of the bed in a manner so that uniform flow 
downward through the column is achieved. One method by which this can be 
achieved is through the use of a "liquid head". A liquid head is simply a 
liquid layer that sits atop the column bed, into which the liquid just 
entering the column can disperse. If the column is appropriately designed, 
then the action of the fresh liquid entering into the liquid layer will be 
sufficient to mix the liquids. When properly done, the chemical 
composition of the liquid entering into the column bed should be very 
nearly identical at all points. This uniformity of chemical flow through 
the column allows one to realize the full extraction potential of the 
matrix contained within. 
There are two methods by which a liquid head is typically generated on a 
column. The first is a manual technique where a fluid layer is gently 
layered atop the bed and the feed tubing for the column is filled, taking 
care to remove all air bubbles. The disadvantage of this procedure is that 
the column must be "primed" by hand before each use. 
The second method is to simply pump liquid onto the top of the column bed 
until the space above the column is filled. As long as there is some 
resistance to flow through the column, a liquid head will be maintained. 
The disadvantage of this method is that if the column should become 
clogged for any reason creating a rise in pressure, then the tubing that 
feeds the column can leak or burst. While in some cases this may be an 
acceptable outcome of system failure, in an application such as the 
treatment of radioactive waste, this is entirely unacceptable. In cases 
where safety is a concern, liquid is always drawn through the bottom of 
the column using either gravity or suction generated by a pump. This 
prevents the buildup of pressure within the column should it become 
clogged. One disadvantage, however, is that the column must be hand primed 
in order to generate the liquid head. 
This invention teaches that through the judicious selection and arrangement 
of porous frits, it is possible to create a column that will automatically 
generate its own liquid head when the liquid is drawn from the bottom 
using a pump. 
The combination of both the spring loaded upper frit with the ability to 
automatically create a liquid head allows one, for the first time, to 
repeatedly use an extraction column in applications where it will run dry 
in between uses. 
In addition, the preferred embodiment has an activated carbon (i.e., 
charcoal) layer within the cartridge that adsorbs non-ionic forms of the 
radiolabeled particles that may be present either as contaminants or that 
have been created during the synthesis or electrophoresis of the DNA. For 
example, when the isotope sulfur-35 is used, a non-ionic form of the 
radioisotope that cannot be captured using ion exchange is created (see 
Table 1). This compound(s), which is believed to include hydrogen sulfide, 
is removed from the effluent stream by adsorption to carbon. The hydrogen 
sulfide is believed to contain radioactive sulfur and/or sulfur compounds. 
TABLE 1 
______________________________________ 
Adsorption of the non-ionic species present in electrophoresis buffer 
from sulfur-35 containing DNA. One milliliter portions of buffer that 
had been treated with Dowex .TM. 1 .times. 8/Acetate resin were 
treated with various adsorbents and chromatographic media. 
Background = 19 counts per minute (cpm) (+/- 4.4). 
Treatment cpm 
______________________________________ 
no treatment 89 
alumina 77 
anion exchange resin 
74 
cation exchange resin 
65 
Amberlite .TM. XAD4 
68 
carbon 21 
______________________________________ 
In the preferred embodiment, the cartridge is also made of shielding layer 
that is of suitable material and thickness to protect the operators from 
radiation from the concentrated radioactive material retained in the 
cartridge. 
Further, in the preferred embodiment, the radioactive liquid generated by 
gel electrophoresis is pumped or transported by other suitable means from 
the electrophoresis device and through the cartridge. 
The means by which the liquid is pumped or transported by other means can 
be any practical and commonly known pumping or transportation means. For 
example, hydrostatic pressure can be used to transport, i.e., drive, the 
liquid. 
In a preferred embodiment of the invention, a pump is used and can be 
placed in the same housing as the cartridge. In the preferred embodiment, 
the pump is located on the effluent side of the cartridge and pulls the 
radioactive liquid from the lower buffer chamber or reservoir of a manual 
or automated electrophoresis device to the cartridge where the radioactive 
particles are retained by ion-exchange resin in the cartridge. The pump 
then draws the treated liquid out of the cartridge and to a storage vessel 
and/or disposal drain. 
Notably, a mixed bead ion-exchange resin within the cartridge could be used 
to extract either negatively or positively charged radioactive particles. 
Other types of chromatography media, such as, hydrophobic, 
hydrophobic-interaction, affinity, adsorption, permeation, or perfusion, 
could be employed as required by the application. For example, one could 
use such a cartridge to extract radiolabeled DNA probes, RNA, proteins, 
carbohydrates and other biomolecules of interest. 
The ion-exchange resin of the cartridge eventually is spent with continuous 
use, and can be disposed of according to the rules and regulations of the 
Nuclear Regulatory Commission. However, the volume of solid waste of the 
cartridge is much less than the volume of radioactive liquid waste that 
otherwise would have then been disposed of according to the same rules and 
regulations. In fact, the volume of radioactive waste is reduced by the 
present invention by about forty (40) fold. Unlike liquid radioactive 
waste, solid radioactive waste need not be absorbed onto a solid 
absorbent, such as vermiculite, before it can be transported according to 
the rules and regulations of the Nuclear Regulatory Commission. 
The advantages over prior art apparatus include the ability to run the gel 
electrophoresis experiments that utilize DNA which has been generated 
using other sequencing methodologies without having the onerous, wasteful, 
expensive, time-consuming, and dangerous task of disposing radioactive 
liquid waste generated by gel electrophoresis, and further, protecting 
operators from radioactivity. The present invention teaches a radioactive 
waste treatment cartridge that need not be kept wet during decontamination 
and that can be easily used for treatment of waste from different 
experiments. 
Moreover, a majority of DNA sequencing reactions are done using cycle 
sequencing methods and this is rapidly becoming the predominant method of 
choice. The inventors of the present invention have discovered that cycle 
sequencing, which involves higher temperatures than non-cycle sequencing, 
generates radioactive non-ionic species of S-35, such as radioactive 
hydrogen sulfide, and that such radioactive species are not removed from 
the liquid being treated using only an ion exchange resin. Thus, the 
inventors have discovered the source of a problem previously unknown, and 
have provided a solution to that problem. Specifically, the present 
invention teaches how to remove radioactive non-ionic species of S-35 
using activated carbon.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Electrophoresis buffer solution that has become radioactive during the 
course of an experiment is pumped through a cartridge that extracts the 
radioactive components out of the liquid. FIG. 1 is a sketch of a 
preferred embodiment of the invention. The figure shows a tubing 1 leading 
from opening 4 of bottom 5 of lower buffer chamber 2 of gel 
electrophoresis device 3 to cartridge 6. Alternatively, opening 4 can be 
located at a wall 26 of the lower buffer chamber 2. As shown in FIG. 1, 
radioactive liquid 28 can be drawn by pump 9 from lower buffer chamber 2 
and through tubing 1 to cartridge 6. 
The cartridge 6 comprises an elongated chamber 21 and an anion exchange 
resin 7 contained within elongated chamber 21 that binds radioactive DNA 
in radioactive liquid 28. The elongated chamber 21 is preferably 
cylindrical in shape. Cartridge 6 also has an entry port 33 at a first end 
of cartridge 6 through which radioactive liquid 28 can enter elongated 
chamber 21. Cartridge 6 also has an exit port 33' at a second end of 
cartridge 6. Effluent 8 from the cartridge 6 is then drawn by pump 9 
through exit port 33' and sent through tubing 10 into a container 11 
(carboy). The effluent 8 is not radioactive and can be disposed of by 
sending it to a conventional drain 12. Fluid flow of liquid 28 from lower 
buffer chamber 2 to cartridge 6 and fluid flow of treated effluent 8 from 
cartridge 6 to container 11 is shown with arrows. This invention provides 
the user with a number of advantages previously unavailable. 
In the preferred embodiment, the cartridge 6 has an upper frit 14 that is 
loaded by retaining spring 15 between the entry port 33 and upper frit 14 
to maintain the upper frit 14 in contact with resin 7. First end 20 of 
cartridge 6 has an extended tip 24 that points down inside chamber 21 and 
which allows the entering liquid to be deposited on top and center of 
upper frit 14. The pressure of retaining spring 15 helps to provide a 
uniform bed of resin 7 so that the liquid 28 will pass uniformly through 
the resin 7 thereby providing for more uniform and effective adsorption of 
the radioactive material onto resin 7. 
In a preferred embodiment, the cartridge 6 also has a layer of activated 
carbon 16. Activated carbon layer 16 is about 50% to 30% of the volume of 
resin 7 in cartridge 6 and is positioned between resin 7 and lower frit 
17. As shown in FIG. 1, a middle frit 30 is used to separate resin 7 from 
activated carbon 16. Alternatively, middle frit 30 can be eliminated. 
Activated carbon 16 acts to remove radioactive hydrogen sulfide and/or 
sulfides from the liquid. Cartridge 6 also has a lower frit 17 that acts 
with the upper frit 14 to hold resin 7 in a compacted matrix. The upper 
frit 14, middle frit 30, and the lower frit 17 of cartridge 6 are porous 
screens that retain the chromatographic resin 7 and the activated carbon 
16 in their respective positions in cartridge 6 and prevent the resin 7 
and the activated carbon 16 from passing through the entry port 33 and the 
exit port 33' at the respective first end 20 and second end 22 of 
cartridge 6. 
FIG. 2 shows the inside bottom view of support 25 of lower frit 17. As 
shown in FIG. 2, support 25 has raised bars 23 and channels 34 and hole 
35, which, result in uniform removal of effluent 8 from lower frit 17 
through hole 35, thereby permitting the effluent 8 to move in a uniform 
manner through cartridge 6. 
Upper frit 14, middle frit 30, and lower frit 17 are preferably made of 
powder molded polyethylene frits commonly known to those of skill in the 
art. 
The cartridge 6 is a canister that contains a chromatographic resin 7. The 
resin 7 can be one of many types depending upon the specific application. 
The first end 20 has an upper fitting 18 that allows the connection of 
tubing 1 to the cartridge 6, and second end 22 has a lower fitting 29 that 
allows for the connection of tubing 10 from cartridge 6, so that liquid 
can be pumped through the tubing 1 and 10 and through cartridge 6. An air 
tight seal 19 is formed between the first end 20 and cartridge body 34 by 
ultrasonically welding them together or sealing them together with a 
suitable adhesive. 
The above-described construction results in a head 27 of liquid 28 forming 
on top of upper frit 14. A continuous vacuum is created by pump 9, which 
draws liquid 28 from lower buffer chamber 2, through tubing 1, through 
cartridge 6, and out of lower fitting 29 as treated effluent 8. Treated 
effluent 8 specifically flows through opening 34 of support 25, and down 
through lower fitting 29. Because of the head 27 created by this 
construction, there is a continuous flow of liquid 28 through tubing 1 and 
cartridge 6, and a continuous flow of treated effluent 8 out of cartridge 
6 and through pump 9. This construction reduces pump cavitation and 
results in a uniform and an effective system for treating radioactive 
liquid 28 so that it becomes treated effluent 8 which has a such a low 
amount of radioactivity (i.e., about 20 counts/minute) that it can be 
disposed, after confirming the low radioactivity of treated effluent 8 
collected in container 11, by sending it to a conventional drain 12. 
Moreover, this construction does not require that the resin be kept wet 
during decontamination of the liquid being treated. 
The expected results of the present invention include the ability to create 
a vacuum and draw radioactive liquid 28 through cartridge 6 so that it 
exits cartridge 6 as treated effluent 8, and to do so with a pump 9 that 
only comes in contact with treated effluent 8. 
In the preferred embodiment of the invention, the cartridge 6 is filled 
with the anion exchange resin from Dow Chemical Co. (Midland Mich.): 
Dowex.TM. 1x8. This resin binds DNA efficiently and is appropriate for 
this application. To improve resin binding of DNA, the resin is treated 
with acetate or formate, which then allows the resin to bind DNA with more 
efficiency than if the resin was treated with chloride alone. 
A similar resin could be used for the binding of radioactively labeled 
proteins, including but not limited to, TMAE, DEAE, DMAE, hydroxylapatite, 
and carboxymethylcellulose. A mixed bed ion exchange could be used to bind 
both positively and negatively charged particles and could be used for 
generic applications. Those of skill in the art will recognize suitable 
resins for use in the present invention. 
Any suitable strongly basic anion exchange resin having high capacity can 
be used in the present invention for the treatment of electrophoresis 
waste containing radiolabeled nucleotides, including, but not limited to, 
the Dowex.TM. 1x, 2x, 21K, XUS, I9680, or I0131 resins, or the 
Amberlite.TM. IRA or I6766 or Duolite.TM. AP-143/1083 Cholestryamine Resin 
USP resins made by Rohm and Haas Co. (Philadelphia, Pa.). All of these 
resins have quaternary amine functional groups. 
In the preferred embodiment, the cartridge 6 is made of clear plexiglass 
having a thickness of about 1 cm. This plexiglass material and thickness 
is sufficient to shield the emission of radiation from radioactive waste 
particles retained by the exchange resin. Specifically, this material and 
thickness is sufficient to shield isotopes S-35, P-33, and P-32. 
Any suitable material can be used in the present invention as cartridge 
material that functionally prevents transmission of radiation from 
radioactive waste particles retained by the exchange resin in the 
cartridge. Examples of suitable cartridge material include, but are not 
limited to, any plastic, such as plexiglass, acrylic, polycarbonate, 
polystyrene, polyethylene, polysulphone, ABS 
(acrylonitrile-butadiene-styrene), PVC (polyvinyl chloride), polyurethane, 
and polypropylene. Those of skill in the art will recognize suitable 
materials for the cartridge in the present invention. 
Another preferred embodiment is shown in FIG. 3, wherein there is no middle 
frit 30, and elongated chamber 21 of cartridge 6 contains a substantially 
homogeneous matrix 32, which is a mixture of resin 7 and activated carbon 
layer 16. Again, a head 27 forms on top of upper frit 14 when cartridge 6 
is used as shown in FIG. 1. 
Alternatively, as shown in FIG. 4, activated carbon layer 16 can be 
contained in a second cartridge 31 having substantially the same 
construction as cartridge 6, this second cartridge 31 being positioned in 
series and between cartridge 6 containing resin 7 and pump 9. A second 
head 27' of liquid forms on top of upper frit 14 of second cartridge 31 
when the embodiment shown in FIG. 4 is used. 
Extraction of the radioactive waste from the radioactive liquid 28 
concentrates the waste into a small, conveniently sized cartridge 6. The 
cartridge 6 of the preferred embodiment is sufficient to bind the waste 
from ten (10) different electrophoresis experiments. The cartridge 6 
concentrates the waste twenty (20) fold and eliminates the need to dispose 
of radioactive liquids. The disposal of radioactive liquid is more costly 
than the disposal of radioactive solids. Radioactive liquids must be 
absorbed onto a solid adsorbent such as vermiculite before it can be 
transported and this effectively doubles the volume of the waste. Thus, 
the cartridge reduces the volume of radioactive waste by about forty (40) 
fold. 
The cartridge 6 also makes disposal of radioactive waste safer. Instead of 
handling liters of radioactive liquid, an operator need only handle a 
relatively easy to handle cartridge (the cartridge is a cylinder that is 
about 5-10 inches long and about 2 inches in diameter). The radioactive 
decay particles being emitted from the DNA that is trapped inside of the 
cartridge 6 is of a low energy variety that cannot penetrate the walls 13 
of the cartridge 6. Thus, when it is time to dispose of the cartridge 6 it 
can be handled without fear of exposure to harmful radioactive particles. 
In order to test the performance of the cartridge 6, fluid containing a 
known quantity of radioactivity was pumped through the cartridge and the 
radioactivity of the effluent that emerged was measured. A properly 
designed cartridge will extract all of the radioactivity from the waste 
stream. FIG. 5 demonstrates the performance of the cartridge 6 during two 
separate experiments. The radioactivity was measured using a Liquid 
Scintillation Counter and is expressed in units of "counts per minute." 
Column 1 shows the activity of a buffer (1/4.times.TTE) before it was 
pumped through the cartridge, column 2 is 1/4.times.TTE that contains no 
radioactivity (the negative control), and column 3 is the effluent from 
the cartridge. Column 4 is a different radioactive buffer (1.times.TBE) 
before passage through the cartridge, column 5 is that same buffer without 
radioactivity (the negative control), and column 6 is the effluent from 
the cartridge. Radionucleotides were extracted from both 1/4.times.TTE and 
1.times.TBE using BioRad.TM. AG 1-X8 anion exchange resin. Electrophoresis 
buffers containing radionucleotides from DNA sequencing were collected 
from the lower buffer chambers. The radioactive buffers (designated LB in 
FIG. 5) were then passed through chromatography columns containing AG 1-X8 
resin and the elute was collected (designated+1-X8 in FIG. 5). It is noted 
that the 1.times.TBE LB was extracted with equal efficiency in spite of 
the fact that both its salt and nucleotide contents were higher than that 
of 1/4.times.TTE LB. In both cases the cartridge removed substantially all 
of the radioactivity from the buffers. In fact, the radioactivity has been 
reduced to a level where it can be disposed of to a conventional drain. 
Electrophoresis waste generated in a typical DNA sequence run, and which is 
comprised of a buffer solution (1.times.TTE or 1.times.TBE) containing 
radiolabeled nucleotides, typically has a radioactivity of about 10,000 
counts per minute (cpm) per 100 microliters. The present invention is 
suitable for treating such waste and reducing the radioactivity of the 
buffer solution to the level of about 20 cpm per 100 microliters. 
Those of skill in the art will recognize that the present invention can be 
used to treat other buffer solutions having the same or similar salt 
content. Those of skill in the art will also recognize that the present 
invention can be used to treat any electrophoresis solution generated from 
electrophoresis of both vertical or horizontal agarose or acrylamide gels. 
FIG. 6 shows the performance of the cartridge 6 when a large amount of 
electrophoresis buffer is passed through it. In this experiment 2650 mls 
of radioactive buffer was passed through the cartridge 6 and the effluent 
8 was still devoid of radioactivity. This experiment demonstrates that the 
cartridge 6 has sufficient binding capacity to remove all of the 
radioactive nucleotides and DNA fragments from ten (10) consecutive 
experiments or "runs" or "long reads" (taking about 16 hours to conduct). 
The following Table 2 lists the data points shown in FIG. 6. 
TABLE 2 
______________________________________ 
Point Counts/Minute 
Volume (mls) 
______________________________________ 
0 25 70 
1 20 140 
2 20 230 
3 24 310 
4 24 380 
5 18 470 
6 28 870 
7 18 1000 
8 26 1500 
9 24 2000 
10 18 2500 
11 21 2650 
______________________________________ 
FIG. 7 is another example showing the performance of the cartridge 6 when 
4000 mls of electrophoresis buffer is passed through it. In this 
experiment 4000 mls of radioactive buffer was passed through the cartridge 
6 and the effluent 8 was still devoid of radioactivity. The 4000 mls of 
electrophoresis buffer solution contained Sulfur-35 radioactive 
nucleotides and DNA was passed through a cartridge 6 containing both Dowex 
1-X8 and 14-60 mesh charcoal. The specific activity of the buffer solution 
was 6731 counts per minute before passage through the cartridge 6. This 
experiment also demonstrates that the cartridge 6 has sufficient binding 
capacity to remove all of the radioactive nucleotides and DNA fragments. 
FIG. 8 is yet another example of the performance of cartridge 6 in the 
present invention. In this example, the cartridge was successful in 
substantially reducing the radioactivity of a solution containing isotope 
P-33 having an initial level of 160,417 counts per minute down to the 
background level of about 25 counts per minute. 
The foregoing detailed description of the invention has been made in 
general terms and with respect to several preferred embodiments. Many of 
the preferred apparatuses and methods stated herein may be varied by 
persons skilled in the art without departing from the spirit and scope of 
the present invention as set forth in the following claims and 
equivalents.