COLORIMETRIC TESTING AND MEASURING DEVICE FOR GASES

DISPOSITIF D'ESSAI ET DE MESURE COLORIMETRIQUE POUR L'ANALYSE DE GAZ

English Abstract

An improved measuring apparatus for the colorimetric
indication of gases is disclosed. The apparatus comprises a
carrier that is impregnated with a solution of a moisture
retainer and a detection indicator. A mixture of sulfolane and
diethylphthalate is used as the moisture retainer. To measure
hydride gases, such as arsine or phosphine, the indicator con-
sists of palladium tetramine chloride. The impregnating solution
may be applied to a paper carrier or to a granular silica gel
carrier. Due to the presence of the moisture retainer, the
moisture required for the indicating reaction remains on the
indicator carrier for a longer period of time, both during stor-
age of the device and during measurements, when the carrier is
exposed to the gaseous substance that is to be indicated.

Claims

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. A testing and measuring device for colorimetrically
detecting gaseous substances, the device comprising:
a carrier on which gaseous substances are detected, said
carrier being impregnated with a detecting indicator and a
moisture store, said moisture store being a mixture of sulfolane
and diethylphthalate.
2. The device of claim 1, wherein said mixture of sulfolane
and diethylphthalate is 10:1 based on the percent by weight of the
sulfolane to diethylphthalate.
3. The device of claim 1, wherein a substance to be
detected is a hydride gas and said detecting indicator is a
palladium (II) chloride.
4. The device of claim 1, wherein a substance to be
detected is a hydride gas and said detecting indicator is a
palladium tetramine chloride.
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Description

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The present invention relates to a testing and measur-
ing device for the colorimetric detection of gaseous substances.
The device has a carrier for a detection indicator which indicator,
together with an additive that serves as a moisture retainer,
impregnates the carrier.
A similar testing and measuring device is already
known from DE-A-40 20 753.
The known measuring device is used for the reliable
detection of, for example, hydride gases, such as arsine or phos-
phine, which are highly toxic components generated during pro-
cessing, for example, in the semiconductor industry. An
indicating apparatus that is both reliable and easy to use is
required for the detection of such gases. For many indicator
materials, such as, for example, the palladium salt that is used
in known dosimeters to detect hydride gases, it is essential that
the indicator has a specific degree of moisture available to it,
both during storage in the unused state and also during more
protracted measuring periods. This is necessary in order that
during a period of storage the indicator does not dry out and that
during the measurement process there is sufficient moisture
available for the colour reaction. Glycols, in particular ethylene
glycol, are used as readily available moisture retainers. However,
since to an increasing degree ever longer measuring periods are
required for continuous monitoring of air, glycols have proved to
be less than adequate as a moisture retainer. Long-term measure-
ments typically require a period of eight, twelve, or even twenty-
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four hours. Thus, there is a need for a moisture retainer for the
impregnating solution of colorimetric testing and measuring
apparatuses that can satisfy the requirement of the protracted
measurement periods.
Thus, it is an object of the present invention to
improve a testing and measuring device of the kind described above
in such a manner that the moisture required for the detection
reaction remains on the indicator carrier for a longer period of
time, both during storage, when the device is not used, and also
during measurement, when it is acted upon by the gaseous substance
that is to be detected.
This object may be achieved by using a mixture of
sulfolane and diethylphthalate as the moisture retainer.
Thus, according to one aspect, the invention provides a
testing and measuring device for colorimetrically detecting
gaseous substances, the device comprising:-
a carrier on which gaseous substances are detected, said
carrier being impregnated with a detecting indicator and a
moisture store, said moisture store being a mixture of sulfolane
and diethylphthalate.
The advantage of the present invention lies essentially
in the fact that a much longer retention time of the moisture
required for indication purposes is achieved. It means that the
drying of the indicator is prevented during a longer continuous
measurement time, even if the indicator is exposed to a relatively
dry gas. A moisture retainer of this kind is useful not only for
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indicators that are used to detect hydride gases, but can be
generally used where the detection indicator must have a specific
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degree of moisture in order to provide a colour reaction with
the gaseous substance that is to be indicated.
Sulfolane is a common name that is given to tetra-
hydrothiophene-l,l-dioxide. Diethylphthalate is another name used
to designate the substance known as phthalic acid diethylester.
A particularly suitable mixture ratio between sulfo-
lane and diethylphthalate is 10 parts of sulfolane to one part of
diethylphthalate. A mixture of this kind has a melting point of
0C, which means that it can be used in a temperature range from
2C to 40C with detection indicators comprising an impregnating
solution. Because of the lower vapour pressure resulting from
the lower melting point, a detection indicator with an impregnating
solution of this kind does not dry out even in the case of con-
tinuous measurements lasting longer than eight hours.
In order to measure hydride gases, it is useful to
combine the moisture retainer with a palladium (II) chloride as an
indicator, so as to form an impregnating solution. This impregnat-
ing solution has the advantage that it remains colourless during
the mentioned longer periods of time and assumes a clearly visible
coloration when acted upon by hydride gases.
Palladium tetramine chloride is also suitable as an
indicator for measuring hydride gases. Both impregnating solutions
for indicating hydride gases have good storage characteristics
thanks to the long-term retention effect of the sulfolane-
diethylphthalate mixture, and both display outstanding indication
sensitivity since the indicator, colourless in the original state,

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assumes a clearly visible coloration in the presence of a hydride
gas.
An impregnating solution that is suitable, for example,
for indicating phosphine is produced as follows. 5 g of
pulverized palladium (II) chloride are weighed into a measuring
flask and dissolved in 50 ml of ammonia at approximately 100C.
Once the excess ammonia has been driven off, and the solution has
cooled to room temperature, 100 ml of water and 100 ml of methanol
are added to it. After this, approximately 250 g of a sulfolane-
diethylphthalate mixture are weighed out and, when required, made
up with methanol. The impregnating solution produced in this
manner is impregnated onto the indicator carrier. This carrier
can be a paper disk or a porous, granular silica gel carrier. The
impregnated paper disk is, for example, clamped into a housing
and used as a dosimeter by exposing the surface of the disk to the
gas that is to be detected and the resulting coloration is used
as a scale for the quantity of substance that is to be indicated.
The granular silica gel carrier is, for example, filled into a test
tube and serves for the colorimetric determination of the concen-
tration of gaseous toxic substances.
The above example describes as a finished detection
indicator a mixture in solution of palladium tetramine chloride,
sulfolane and diethylphthalate, the palladium tetramine chloride
being extracted from palladium (II) chloride to which ammonia has
been added. If, in contrast thereto, palladium (II) chloride is
to serve as a colour indicator, preparation is carried out in the

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same way, although without adding ammonia to the palladium (II)
chloride.
The invention will be further illustrated by way of a
preferred embodiment and with reference to the accompanying
drawings in which:
Figure 1 shows, in cross-section, a dosimeter for
testing gases according to one preferred embodiment of the
invention.
Figure 1 shows a dosimeter which is used as a testing
device for gases and which is formed from a test disk with a disk
carrier (1) that is of circular cross section, on which is laid
a plate-shaped impregnated indicator paper (2) which is then held
on the disk carrier (1) by means of a clamp ring (3). The annular
clamp ring (3) leaves a disk opening (4) unobstructed and the gas
that is to be indicated has access to the indicator paper through
this space. There, the gas reacts with the indicator solution
that impregnates the paper to bring about a change in colour. The
intensity of the colour, compared with a colour standard, is used
as a measure for the quantity of gas that is to be indicated and
which has been collected during the exposure time. A solution of
palladium tetramine chloride with a sulfolane-phthalic acid diethyl-
ester mixture at a ratio of 10:1 serves as the impregnating agent.