Electric heating – Heating devices – With heating unit structure
Reexamination Certificate
2001-07-23
2004-04-27
Pelham, Joseph (Department: 3742)
Electric heating
Heating devices
With heating unit structure
C219S429000, C219S528000, C073S866000
Reexamination Certificate
active
06727480
ABSTRACT:
TECHNICAL FIELD
The present invention relates to the preparation or testing of heated sample media contained in vessels and, more particularly, to the controlled heating of sample media in the vessels without the use of a water bath.
BACKGROUND ART
In the pharmaceutical industry, the controlled heating of sample media in vessels is an important step in sample preparation procedures. Examples of such procedures include those performed for the purpose of testing and analyzing the rate at which dosages release from pharmaceutical products such as tablets, filled capsules or transdermal patches. The dosages are released in solutions under controlled conditions which may or may not be representative of the human digestive process, contact with the skin, or implantation within the body. The procedural steps, test duration, dissolution medium, and apparatus employed in any given dissolution test must comply with United States Pharmacopeia (USP) guidelines in order for the test to be accepted as valid for the specific dosage or delivery system tested.
For instance, the general requirements of Section 711 (Dissolution) of USP 23-NF18, Ninth Supplement, Nov. 15, 1998, specify a particular apparatus, termed “Apparatus
1
,” which includes a covered vessel made of plastic, glass or other inert, transparent material that does not absorb, react, or interfere with the specimen being tested; a motor; a metallic drive shaft; and a cylindrical basket. Other devices may be specified from time to time for stirring, mixing or retaining the delivery system during the test procedure.
The vessel may be cylindrical with a hemispherical or flat bottom and sides which are flanged at the top. The dimensions of the vessel are specified according to the nominal volumetric capacity of the vessel. A fitted cover can be used to retard evaporation from the vessel and, when used, must provide sufficient openings to allow the ready insertion of a thermometer and withdrawal of specimens. Also included are requirements for the dimensions, construction material, position in relation to the vessel, and performance of the shaft and other operative components. Importantly, the vessel must be either partially immersed in a water bath of placed in a heating jacket to hold the temperature inside the vessel at 37±0.5° C. or other specified temperature. When using a water bath, the bath fluid must be kept in constant, smooth motion.
FIG. 1
illustrates a conventional dissolution testing apparatus generally designated
10
. Apparatus
10
includes a main housing or head
12
containing a programmable systems control module. Head
12
is situated above a vessel plate
14
and a water bath container
16
, and is typically motor-driven for vertical movement toward and away from vessel plate
14
. Peripheral elements located on head
12
include an LCD display
18
for providing menus, status and other information; a keypad
21
for providing user-inputted operation and control of spindle speed, temperature, test start time, test duration and the like; and readouts
23
for displaying information such as RPM, temperature, elapsed run time, or the like. Water must be heated and circulated through water bath container
16
by means such as external heater and pump modules (not shown), which may be combined into a single heater/circulator module. Water bath container
16
thus requires a fluid transfer means such as tubing
25
, as well as a drain line
27
and valve
29
.
Vessel plate
14
supports a plurality of vessels
31
extending into the interior of water bath container
16
. Typically, three, four, six or eight vessels
31
can be supported. Each vessel
31
has a standard shape characterized by a lateral cylindrical section
31
A, a bottom hemispherical (or flat) section
31
B, and a flanged section
31
C around the mouth of vessel
31
. Vessels
31
are locked and centered in place on vessel plate
14
by means such as ring lock devices or clamps (not shown). A stirring element including a motor-driven spindle
37
A and paddle
37
B operates in each vessel
31
. Individual clutches
39
can be provided to alternately engage and disengage power to each spindle
37
A. A dosage delivery module
41
is used to preload and drop dosage units (e.g., tablets) into each vessel
31
at prescribed times and bath (or vessel) temperatures. An automated sampling manifold
45
lowers and raises sampling cannulae
47
into and out of each respective vessel
31
. Sampling manifold
45
can also be vertically movable between head
12
and vessel plate
14
. Sampling cannulae
47
operate in conjunction with a bidirectional peristaltic pump (not shown), and are used during the dissolution testing procedure to periodically withdraw samples from the vessel media for analysis. Samples could also be taken manually using pipettes and/or sampling cannula/syringe assemblies. Miniature temperature probes
49
associated with each vessel
31
can also be located on sampling manifold
45
.
In a typical operation, dosage units are dropped into the bottoms of each solution-containing vessel
31
and each paddle
37
B rotates at a predetermined rate and duration within the test solution as the dosage units dissolve. In other types of tests, a cylindrical basket (not shown) loaded with a dosage unit is substituted for each paddle
37
B and rotates within the test solution. For any given vessel
31
, the temperature of the test solution must be maintained at a prescribed temperature (e.g., 37° C.). Solution temperature is maintained by immersion of vessel
31
in the water bath of water bath container
16
. Accordingly, the temperature of the test solution is dependent upon, and thus indirectly controlled by, the temperature of the water bath which in turn is dictated by the external heating means employed. Temperature probe
49
is used to monitor the test solution temperature, and can be any suitable type of transducer such as a thermistor.
As recognized by those skilled in the art, the use of a water bath in connection with an apparatus such as dissolution testing apparatus
10
has some drawbacks. First, water bath container
16
is necessarily large in order to accommodate the immersion of several vessels
31
, and hence requires a significant volume of water to serve as the medium for transferring heat energy to the media or solution contained in vessels
31
. Consequently, an undue amount of time and energy is required to initially dispense the volume of heated water into water bath container
16
and bring each vessel
31
to the desired set point temperature. The volume of water also adds to the overall weight of apparatus
10
. Second, an external heater and water circulation system is required. It might be possible to eliminate the water circulation system by providing an external resistive heating plate or coil to heat the water bath. Such a resistive heating element, however, would necessarily be quite large in order to heat the entire volume of the water bath, require a large amount of electrical energy to operate, and would not appreciably reduce the amount of startup time required to bring vessels
31
to a desired set point temperature. Third, the water bath system does not allow for individualized control of each vessel
31
. The ability to control the heating profile of a given vessel
31
or group of vessels
31
independently and distinct from other vessels
31
of dissolution testing apparatus
10
would be quite useful during many types of procedures. Fourth, biological growth, scaling, and other impurities tend to collect in the water bath, such that the use of the water bath entails cleaning maintenance and the addition of preservatives or additives, all of which adds to the cost of the water bath system.
One approach to eliminating the need for a water bath and controlling the temperatures of individual vessels, while still conforming to USP dissolution requirements, is disclosed in U.S. Pat. No. 5,589,649 to Brinker et al. The embodiments disclosed therein provide individual flexible, resistive heater elements attached
Fernando C. J. Anthony
Haw Michael F.
Swon James E.
Fishman Bella
Gloekler David
Pelham Joseph
Varian Inc.
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