The present invention relates to a gaschromatography oven endowed
with means for regulating the temperature of the air inside the oven in an accurate
way, through the controlled influx and outflow of external air.
It is known that, during the chromatographic analysis of a mixture
of compounds, it is necessary to maintain accurate control of the temperature
to which the column is subjected during the various phases of the analysis. In
particular, such temperature control must be maintained during heating and cooling
of the column.
Techniques are known in the art for regulating the temperature of
a gaschromatography oven, in some operational phases, by circulating in the oven
a flow of air withdrawn from the outside.
The American Patent N. US 4 181 613 describes, in one of its form
of embodiment, a gaschromatography oven in which there is provision for a shutter
for the influx of external air at ambient temperature and a shutter for the outflow
of hot air to the outside. Both shutters are on the rear of the oven and the influx
shutter conveys the air to a fan. There is a screen in front of the fan which divides
the oven into a portion containing the capillary column(s) for the analysis and
one containing the fan. The said screen, furthermore, supports electric resistances
for the heating of the air in the oven. With the shutters open, the fan provides
for mixing the cold air with the hot air of the oven before it reaches the column.
In this embodiment however the mutual disposition of the blades of the fan, the
shutters and the heating resistances of the air doesn't allow perfect uniformity
of temperature to be reached in all the flow streams of air that arrive at the
The American Patent N. USA 4 286 456 describes a gaschromatography
oven in which the blades of the fan are arranged around a nucleus containing means
for heating the air. Though offering better uniformity of temperature to the air
in the oven, this solution also presents the problem of not being able to regulate
the temperature with precision and uniformity in the cooling phase.
More in general, the solutions of the known art are neither able to
ensure a flow of air at uniform temperature onto the column during the cooling
phase, nor the most constant flow possible, particularly when the cooling must
be at low speed, i.e. when there is a small ratio between variation of temperature
and interval of time in which said variation takes place.
Another problem is that of maintaining the temperature of the capillary
column constant or varying slowly; which is especially difficult when the column
is near ambient temperature, for instance 50-60°C.
In all these situations, in fact, the automatic opening of the outflow
shutter, following a signal received from a suitable thermostat sensor, generally
reduces the temperature much too rapidly to below the desired value, which causes
the influx shutter to close and initiates automatic heating of the oven which then
temporarily exceeds the desired temperature. This phenomenon generates a series
of beats, i.e. much too frequent opening and closing of the shutters which create
irregularity in the desired course of the temperature of the air.
The object of the present invention is to solve the aforementioned
problems by means of a gaschromatography oven that provides means for accurately
controlling the influx of external air at ambient temperature and the outflow of
hot air from the gaschromatograph, giving a flow of air at uniform temperature
onto the capillary column, also during the cooling phase.
Another object of the invention is to avoid irregularity in the flow
of cold air in conditions of low speed cooling or of temperature maintenance,
above all near ambient temperature.
Such objects are achieved through the present invention which relates
to a gaschromatography oven, of the type comprising a thermally insulated cavity,
defined by a front wall, a rear wall and four side walls and divided into a first
portion, containing at least one gaschromatography column and into a second portion
containing means for ventilation and means for heating the air, characterized by
the said rear wall comprising a shutter for the influx of air from the outside
and a pair of shutters for the controlled outflow of air from the oven, said outflow
shutters being located near the corners of said rear wall, particularly near the
According to a preferential aspect of the present invention, the oven
is further characterized by providing means for controlling thermostatically the
partial or complete opening of one alone or both of the pair of outflow shutters.
According to an further aspect of the present invention, the oven
is characterized by at least one injector of the sample to be analyzed and at
least one detector, being lodged in a removable drawer on the outside of the upper
wall of said oven. The drawer is complete with all the necessary connections for
the operation of the injector and the detector and is anchored to the external
structure of the oven.
The gaschromatography oven according to the present invention offers
the advantage in the first place of giving a flow of air at uniform temperature
onto the capillary column in all phases of the gaschomatography analysis.
Furthermore, the oven allows a regulated, substantially constant flow
of external air, even with elevated shutter control of this external air. In fact,
according to requirements, it is possible to open the exit shutters automatically,
or open only one of said shutters, either completely or partially. That is particularly
advantageous when the oven must undergo a cooling or a heating operation to temperatures
near the ambient temperature, or when a controlled low speed cooling must take
Further advantages and characteristics of the invention will become
more evident from the following description, which is of illustrative and not
limitative nature, with reference to the enclosed schematic drawings, in which:
- figure 1 is an exploded view in perspective of some components of a gaschromatography
oven according to the present invention;
- figure 2 is a view in perspective of the rear part of the gaschromatography
- figure 3 is a view in perspective of the front part of the gaschromatography
In figure 1 are shown the components that cooperate to allow the
accurate regulation of the temperature inside the gaschromatography oven according
to the present invention. In particular, it is shown element 8 which forms a thermally
insulated cavity, defined by a front wall, a rear wall and four side walls. Also
shown are a fan 7 and its related motor 2, a support 6 that can house a plurality
of electric resistances, a pair of outflow shutters 9 and 10, an influx shutter
5 and two screening elements 3 and 4.
In figure 2 is shown the rear part 17 of the oven 1 in correspondence
of which are set the two outflow shutters 9 and 10 and the influx shutter 5.
The screening elements 3 and 4 are applied in proximity of the openings
of the shutters 9 and 10.
In figure 3 the oven 1 is shown, endowed with control unit 16, and
provided on the upper side with a removable drawer 15 which houses the injectors
11 and 12 of the sample to be analyzed and the detectors 13 and 14.
The gaschromatography oven 1 is divided by an internal shield (not
shown) into a first portion, containing at least one capillary column for chromatography,
and a second portion containing the fan 7 and the electric resistances fitted onto
the support 6 for the heating of the air.
The shield allows the passage of the flow of air between its edges
and the side walls of the oven. The fan 7 is shaped in such a way that the blades
surround the support 6 and the related resistances, allowing the creation of a
flow of direct air toward the capillary column which is composed of fluid streams
at substantially uniform temperature.
The shutter 5 and the shutters 9 and 10, on the rear part 17 of the
oven 1, are equipped with means of thermostatically controlling their total or
partial opening and closing. In particular, the shutter 5 is opened to allow the
influx of air from the outside, while the pair of shutters 9 and 10 is used for
the controlled outflow of air from the oven 1. In order to create a circulation
of air between the outside and the inside of the oven, the shutter 5 and at least
one of the shutters 9 and 10 are mechanically linked.
Whenever the outflow of the hot air from the oven 1 must be controlled
with precision, the aforesaid means of thermostatically controlled opening and
closing, are able to effect the opening, partial or complete, of only one shutter
of the said pair of outflow shutters 9 and 10. This prevents the setting up of
the aforementioned beats because of continuous rapid sequence of openings and closings
of the shutters.
The outflow shutters 9 and 10 are set in the corners, preferably in
the lower corners of the oven where the speed of the air is lower and therefore
the pressure is higher, which favors the outflow of the air.
The aforesaid system of control of the temperature of the inside air
in the oven 1 is particularly advantageous in the cases in which cold air must
be admitted. That happens particularly when low speed cooling of the capillary
column must take place, or when a constant or slowly varying temperature near the
ambient temperature must be sustained.
Furthermore, to each of the shutters 9 and 10, for the outflow of
the air, a tubular screening element 3 and 4 is applied, whose purpose is to divert
the flow of hot air away from the influx shutter 5 and from the apparatus connected
with the oven in general.
The connections of the tubular screening elements 3 and 4 to the
shutters 9 and 10 are not airtight. In this way a space is created that allows
a layer of cold air to enter the inside of the tubular elements 3 and 4, which
is useful in the cooling of the hot air that comes out of the oven when it works
at higher temperatures.
The removable drawer 15, which houses the injectors of the sample
to be analyzed 11 and 12 and the detectors 13 and 14, is located above the upper
side of the oven and is separated from it by an insulator layer that prevents metal-metal
contact of the drawer 15 with the wall of the oven. This thermal insulation between
injectors, detectors and oven favors the precision of the temperature control.
The removable drawer 15 has the purpose, furthermore, of increasing
the flexibility of employment of the oven, allowing the substitution and use of
different types of injectors 11 and 12 and/or of detectors 13 and 14.