U.S. patent number 3,904,373 [Application Number 05/409,876] was granted by the patent office on 1975-09-09 for indicators covalently bound to insoluble carriers.
Invention is credited to Gerald Bruce Harper.
United States Patent |
3,904,373 |
Harper |
September 9, 1975 |
Indicators covalently bound to insoluble carriers
Abstract
Indicators insolubilized by covalent bonding to inorganic
carriers for indicating the hydrogen ion concentration,
oxidation-reduction state or specific ion concentration in liquid
media. Since the indicators are insoluble they do not contaminate
the solution tested, and they may be used repeatedly in different
media. They replace the well known indicator test papers which
consists of a substrate dyed with an indicator. Methods of making
the indicators are also provided.
Inventors: |
Harper; Gerald Bruce (Toronto,
CA) |
Family
ID: |
23622342 |
Appl.
No.: |
05/409,876 |
Filed: |
October 26, 1973 |
Current U.S.
Class: |
422/425; 436/169;
436/166 |
Current CPC
Class: |
G01N
31/221 (20130101); G01N 31/22 (20130101) |
Current International
Class: |
G01N
31/22 (20060101); G01n 029/02 (); G01n 031/00 ();
G01n 033/00 () |
Field of
Search: |
;252/408 ;23/253TP
;424/7 |
References Cited
[Referenced By]
U.S. Patent Documents
Other References
"New Method Makes Possible Nonbleeding Indicator Paper", Chem. and
Engin. News, Vol. 48, No. 10, p. 38 (Mar. 9, 1970). .
"Surface-Produced Alignment of Liquid Crystals", Kahn, F. J., et
al., Proc. of The IEEE, Vol. 61, No. 7, pp. 823-828 (July
1973)..
|
Primary Examiner: Padgett; Benjamin R.
Assistant Examiner: Gron; T. S.
Attorney, Agent or Firm: Rutherford; F. Campbell
Claims
What is claimed is:
1. An insolubilized bound indicator useful in determining
parameters such as hydrogen ion concentration (p.sup.H),
oxidation-reduction potential or specific ion concentrations in
solutions consisting of an organic indicator covalently coupled by
means of an organo-functional silane coupling agent to an inorganic
carrier having available hydroxyl or oxide groups.
2. A bound indicator as claimed in claim 1 wherein said silane
coupling agent is combined with said indicator by means of an alkyl
linkage.
3. A bound indicator as claimed in claim 1 wherein said silane
coupling agent is combined with said indicator by means of an azo
linkage.
4. A bound indicator as claimed in claim 1 wherein said silane
coupling agent is combined with said indicator by means of a
sulfonamide linkage.
5. A bound indicator as claimed in claim 1 wherein said silane
coupling agent is represented by the general formula
X.sub.n SiR.sub.(4.sub.-n)
in which X represents a substituted or unsubstituted aryl, alkyl or
alkyl-aryl group, the substituent(s) being selected from groups
which include hydroxy, lower alkoxy, amino, lower alkylamino, lower
dialkylamino, alkyl, nitro, nitroso, diazo, cyano, isocyano,
isothiocyano, carboxy, carbonyl, keto, halocarbonyl, sulfoxy and
halosulfonyl; R represents a group which may be lower alkoxy,
aryloxy or halogen; and n is one of the integers, 1, 2 and 3.
6. A bound indicator as claimed in claim 1 wherein said carrier is
a glass.
7. A bound indicator as claimed in claim 1 wherein said carrier is
zirconia coated glass.
8. A bound indicator as claimed in claim 1 wherein said carrier is
a metal oxide.
9. A bound indicator as claimed in claim 1 wherein said carrier is
nickel oxide.
10. A bound indicator as claimed in claim 1 wherein said organic
indicator is an N,N-dialkylaniline.
11. A bound indicator as claimed in claim 1 wherein said organic
indicator is selected from the group consisting of diazo, amino,
carboxy and alkylsilane derivatives of N,N-dimethylaniline.
12. A bound indicator as claimed in claim 1 wherein said organic
indicator is selected from the group consisting of B-naphthol and
derivatives thereof.
13. A bound indicator as claimed in claim 1 wherein said organic
indicator is selected from the group consisting of triarylmethyl
compounds.
14. A bound indicator as claimed in claim 1 wherein said organic
indicator is phenolphthalein.
15. A bound indicator as claimed in claim 1 wherein said indicator
is methylene blue.
16. A bound indicator as claimed in claim 1 wherein said organic
indicator is Eriochrome Black T.
17. A process for the preparation of the bound indicator of claim 1
which includes the steps of providing a silane which has an
organofunctional group, causing the silane to react with a carrier
which has available hydroxyl or oxide groups, and causing the
organofunctional group of the silane to react with an indicator.
Description
This invention consists of a new type of indicators, which are
hereinafter referred to as bound indicators.
Indicators are organic compounds which absorb visible light, which
absorption(s) change in wave length and/or intensity as the
composition of a solution to which the indicator may be exposed
changes. Indicators are widely used to determine such parameters in
solutions as hydrogen ion concentration (pH), oxidation-reduction
potential or specific ion concentrations.
The term "indicator", as used herein, refers to organic molecules
or ions which absorb visible light and whose absorption(s) change
in wave length and/or intensity as solution conditions are varied,
and includes "precursors", organic species which are not indicators
as free species, but which when bound to inorganic carriers via
silane coupling agents give a bound indicator. The term "bound
indicator", as used herein, refers to any complex comprising an
organic species covalently coupled via a silane coupling agent to a
carrier having available hydroxyl or oxide groups, which absorb
visible light and which absorption(s) change in wave length and/or
intensity as solution conditions are varied.
Conventionally, indicators have been used by dissolving the
indicator chemical entity in the liquid to be tested, or by coating
a carrier, such as paper, with the chemical entity and then
contacting the coated carrier with the liquid to be tested.
In whatever form indicators were previously used, a quantity of the
indicator was required for each test. If a liquid was being
monitored for changes in pH, ion concentration or
oxidation-reduction potential with an indicator, samples of the
liquid to be tested had to be contacted with the appropriate
indicator and the sample then had to be discarded because it has
been contaminated by the indicator or, in the case of a coated
paper indicator, because the paper had absorbed a component of the
test liquid. Thus the amount of previously known indicators
consumed in an active chemical laboratory, or for control purposes
in a plant, could be substantial. Such use could also be costly
since a typical indicator species is expensive to prepare.
My invention consists of insoluble bound indicators which are able
to fulfill the various functions of soluble indicators. Bound
indicators have several advantages over soluble indicators:
1. they can, in most cases, be used repeatedly
2. they are largely unsusceptible to microbial attack
3. they are insoluble and hence do not contaminate systems
4. they may be made in a form which is especially convenient for
laboratory operations, e.g. glass stirring rods
Bound indicators are very useful in analytical procedures in
laboratories and industry and may also be used in the preparation
of many foodstuffs, chemicals and pharmaceuticals. I have observed
continued and apparently constant activity, as indicated by the
intensity of colour changes, over a period of months, upon exposure
to various organic and aqueous assay conditions. Because of their
advantages, bound indicator sintered glass rods and the like are
preferable to pH papers and soluble indicators for many uses. While
bound indicators may be made with either inorganic or organic
carriers, the former are normally preferable for use because they
are more rigid and insoluble and more resistant to microbial
attack.
Bound indicators must be substantially insoluble in a solution to
be useful in it. Most indicators in widespread use change colour
with pH and are, in fact, used to measure the pH of solutions.
Other indicators have different functions, e.g. the measurement of
the oxidation-reduction potential of a system, and the detection
and measurement of various ions in solution.
The silane coupling agents are molecules which are characterized by
two different kinds of reactivity. These are organofunctional, and
silicon-functional, so characterized that the silicon portion of
the molecule has an affinity for inorganic materials, such as glass
and aluminum silicate, while the organic portion of the molecule is
an indicator or precursor or is tailored to combine with indicators
or precursors. One function of the coupling agent then, is to
provide a bond between the indicator and the carrier. The variety
of possible organofunctional silanes useful in this invention is
limited only by the number of organofunctional groups which bind to
silicon to give a stable coupling agent, by the stability of the
bonds to the carrier and to the indicator and by the available
sites in the organic species which yield an active bound
indicator.
Many different silane coupling agents of the general formula
X.sub.n SiR.sub.(4.sub.-n) can be used, wherein X is a substituent,
which may be a substituted (or unsubstituted) aryl, alkyl or lower
alkyl-aryl, nitro, nitroso, diazo, cyano, isocyano, isothiocyano,
carboxy, carbonyl, keto, halocarbonyl, sulfoxy, sulfonyl halide, or
more complex derivatives of any of these; R is a member selected
from a group comprising lower alkoxy, phenoxy and halo; and n is an
integer which is 1, 2 or 3, usually 1. The silane coupling agent
may or may not itself be an indicator. This definition includes
simple silane coupling agents wherein X is simply amino, carboxyl,
carbonyl, sulfhydryl or halocarbonyl.
Coupling agents include gamma-aminopropyltriethoxysilane,
2,4,6-trimethoxybenzyltriethoxysilane,
N-beta-aminoethyl-gamma-aminopropyltrimethoxysilane, and
N-beta-aminoethyl-(alpha-methyl-gamma-aminopropyl)-dimethoxymethylsilane.
While some simple silane coupling agents are commercially
available, many others, including more complex ones, may be made by
known chemical methods. For example, I have added
2,4,6-trimethoxybenzoic acid to trichlorosilane in acetonitrile,
then added tri-n-propylamine to form
2,4,6-trimethoxybenzyltriethoxysilane. Ethanolysis yielded the
useful coupling agent 2,4,6-trimethoxybenzyltriethoxysilane. As
another example, gamma-aminopropyltriethoxysilane couples to
inorganic carriers giving the aminoalkylsilane derivative, which
can be reacted with alkoxybenzoyl chlorides to form another complex
which binds diazotized indicators or precursors. Another reaction
sequence involves reacting the aminoalkylsilane derivative with
p-nitrobenzoyl chloride, reducing the nitro group with sodium
dithionite and diazotizing with sodium nitrite: this diazonium salt
attacks activated aryl rings of indicators or indicator precursors.
Alternatively, an aminoalkylsilane derivative may be reacted with
thiophosgene to give an isothiocyanoalkyl derivative which binds
amino groups. Where the indicator or precursor or derivative
contains a suitable aromatic ketone, aldehyde, acyl chloride or
carboxy group it is possible to prepare silane coupling agents
which are also indicators or precursors.
The carriers used can be organic, but generally, inorganic
materials with available hydroxyl or oxide groups are preferred.
The quantity of indicator or precursor which can be bound, and
hence the colour intensity of the bound indicator, increases with
increasing surface area of the carrier. Hence, a carrier such as
smooth, unetched glass is an unsatisfactory carrier, as it yields a
bound indicator of weak colour. The carriers must have little or no
solubility in various solutions and are either weak acids or weak
bases. They may also be classified in terms of chemical composition
as siliceous materials, as non-siliceous metal oxides, or as
mixtures of the two, such as zirconia-clad glass. Of the siliceous
materials, the preferred carriers are sintered, etched or porous
glass. These may be used in such forms as rods or discs, or as
fragments. Glass has the advantages of being dimensionally stable,
of being transparent or white in colour thus allowing colour
changes to be easily judged, and it can be thoroughly cleaned to
remove contaminants as, for example, by sterilization. The
corrosion rate of glass varies with glass composition and solution
conditions, but corrosion has remained undetectable throughout this
work. Other useful siliceous inorganic carriers are silica gel,
coloidal silica (commercially available under the trade mark
Cab-O-Sil), wollastonite (a naturally-occuring calcium silicate)
and bentonite. Representative non-siliceous metal oxides include
alumina, hydroxy apatite and nickel oxide. These inorganic carriers
may be classified as in Table I.
TABLE I ______________________________________ Inorganic Carriers
Transition Metal Non-siliceous Metal Siliceous Oxides Oxides
______________________________________ Amorphous Crystalline Acid
MeO Base MeO Glasses Silica Bentonite NiO Al.sub.2 O.sub.3 Hydroxy
Gel apatite Coloidal Wollastonite Silica
______________________________________
Bound indicators may be classified under three general
headings:
1. pH indicators
2. redox indicators (i.e. oxidation-reduction indicators)
3. adsorption indicators (i.e. ion detectors) of which examples of
each class are listed below.
Bound pH indicators can be produced using many pH indicators or
functionalized derivatives of those indicators. Suitable organic
species include: phenolphthalein, fluorescein, phenol red, cresol
red, pararosaniline, magenta red, xylenol blue, bromocresol purple,
bromophenol blue, bromothymol blue, metacresol purple, thymol blue,
bromophenol blue, tetrabromophenol blue, brom-chlorphenol blue,
bromocresol green, chlorphenol red, o-cresolphthalein,
thymolphthalein, metanil yellow, diphenylamine,
N,N-dimethylaniline, indigo blue, alizarin, alizarin yellow GG,
alizarin yellow R, congo red, methyl red, methyl orange, orange I,
orange II, nile blue A, ethyl bis(2,4-dinitrophenyl) acetate,
gamma-naphtholbenzein, methyl violet 6B, 2,5-dinitrophenol,
p-nitrophenol, and/or the various functionalized derivatives of the
above species. Even when an indicator cannot be bound unchanged
with retention of indicator activity, one or more of its
derivativates can often be bound with satisfactory results.
Bound redox indicators can be made from organic species which
include methylene blue, diphenylbenzidine, diphenylamine,
ethoxazene, and N-phenylanthranilic acid and/or suitable
derivatives of any of these.
Bound adsorption indicators can be made from organic species which
include fluorescein, diiodofluorescein, dichlorofluorescein,
phenosafranin, rose bengal, eosin I bluish, eosin yellowish,
magneson, tartrazine, eriochrome black T and others.
The following examples illustrate typical methods of preparation of
the new indicators:
EXAMPLE I
Indicators in the form of a stirring rod, and in the form of a
powder, were prepared, starting with a heavily etched silica glass
stirring rod for the former, and 1 gram of fragments of 96% silica
porous glass for the latter. Both carriers were cleaned by soaking
in 0.2M nitric acid at 95.degree. C for 1 hour, rinsing several
times with distilled water and then heating overnight at
650.degree. in air.
The two samples of glass were cooled, placed in flasks and to each
was added 50 millilitres of a 10% solution of
gamma-aminopropytriethoxysilane. Both mixtures were refluxed
overnight, cooled and washed with acetone.
The two glass products, now in the form of aminoalkylsilane
derivatives, were refluxed for one hour in solutions containing 10
ml of chloroform, 100 mg of p-nitrobenzoyl chloride and 50 mg of
triethylamine, washed with chloroform and air-dryed. The nitro
groups were reduced by refluxing in 1% aqueous sodium dithionite,
giving the arylamine derivative. The amino groups were diazotized
by adding 10 ml of glacial acetic acid followed by an excess (0.3
g) of sodium nitrite. The mixtures were placed under vacuum until
all air and gas bubbles were removed from the glass, after which 1
g of phenolphthalein was added to each followed by placing under
vacuum for a further 30 minutes. The resulting products, which in
each case was phenolphthalein coupled to the silane by an azo
linkage with the silane bound to the glass, were washed with water,
acetone and benzene until any phenolphthalein non-covalently
adsorbed on the glass was not detectably eluted. The
phenolphthalein glasses when exposed to liquids of different pH
concentration underwent a colour change which I observed to occur
in the pH range 8.5-9.0; at a pH of 8.5 the glasses were pale
yellow and at a pH of 9.0 were deep red-brown. These indicators
retained their colour and activity indefinitely, despite exposure
to strong organic and aqueous acids and bases, to various solutions
and reagents, and to air.
EXAMPLE II
A 1 g sample of porous zirconia-clad silica glass amino alkylsilane
derivative (e.g. Corning Glass Works product MAO-3930) was refluxed
for 1 hour in a chloroform solution containing 100 mg
p-nitrobenzoyl chloride and 50 mg triethylamine, as in example I.
The nitro groups on this product were again reduced with
dithionite. This was followed by diazotization by 0.3 g sodium
nitrite in 10 ml glacial acetic acid, under a vacuum at 0.degree..
Excess (0.5 g) N,N-dimethylaniline was added. The product was a
deep-burgundy colour in solutions of pH below 4.5, turning to a
pale orange-red colour at pH 4.5 to 5.5 The bound indicator
retained colour and activity, despite exposure to various
conditions. Presumably, the bound indicator is of the following
structure: ##EQU1##
EXAMPLE III
A 15 g sample of 2,4,6-trimethoxybenzoic acid and 49 g
trichlorosilane were dissolved in 200 ml acetonitrile and refluxed
for 1 hour. Two equivalents of tripropylamine were added at this
point and the resulting mixture was refluxed at
80.degree.-90.degree. for 8 hours. Treatment with dry ether caused
the precipitation of tripropylamine hydrochloride (95%).
Distillation of the filtrate gave 11 g of
2,4,6-trimethoxybenxyltrichlorosilane boiling at
80.degree.-84.degree. (6mm). This product was dissolved in 100 ml
ethanol. Five equivalents of tripropylamine were added and the
mixture refluxed for 1.5 hours at 70.degree.-75.degree.. The
mixture was distilled yielding 2.1 g of
2,4,6-trimethoxybenzyltriethoxysilane. 1 g of porous glass and 20
ml of toluene were added to this and the mixture was refluxed
overnight giving a trimethoxyarylsilane glass derivative.
Fifteen g of 3-nitro-N,N-dimethylaniline was mixed with 17 g of
sodium thiosulphate in 200 ml water and refluxed for 1 hour to give
3-amino-N,N-dimethylaniline. This mixture was cooled to 10.degree.
and sodium nitrite (20 g) was added slowly.
3-diazo-N,N-dimethylanilinium chloride was collected as a filtrate
and added to the trimethoxyarylsilane glass derivative and 10 ml
glacial acetic acid, in an ice bath. The mixture was evacuated for
30 minutes to remove air and gas bubbles from the glass. The
reaction product, which was again N,N-dimethylaniline bound to
glass by azo linkage to the silane, was washed extensively until
molecules non-covalently adsorbed on the glass were not detectably
eluted. The product was a bound indicator of the structure:
##SPC1##
In acidic solutions of a pH below 4.0 it was burgundy in colour and
underwent a colour change to pale orange-red between pH 4.0-5.5.
The bound indicator retained colour and activity despite exposure
to various organic and aqueous solvents and to strong acids and
bases. Exposure to a sodium hypochlorite solution caused
irreversible colour change to pale yellow and hence its destruction
as a useful bound indicator.
EXAMPLE IV
The procedure of Example II was used to produce, from the reduced
form of methylene blue, methylene blue bound by azo linkage to
zirconia-clad glass. The glass is bright blue under most solution
conditions, but turns reversibly pale yellow when exposed to strong
reducing conditions such as zinc dust in dilute sulfuric acid.
EXAMPLE V
2,4,6-trimethoxybenzoic acid was dissolved in sulfonyl chloride and
refluxed over a steam bath for 1 hour to give
2,4,6-trimethoxybenzoyl chloride. To 250 mg of this was added 10 ml
of pyridine and 1 g of aminoalkylsilane porous glass (Corning
GAO-3940). This mixture was stirred at room temperature, and then
refluxed 30 minutes to give a glass complex with highly activated
phenyl rings, presumably of the following structure: ##EQU2##
This glass was decanted, washed in acetone and air-dryed. The nitro
group of Eriochrome Black T was reduced to an amino group, the
product was recrystallized from ethanol, and: 1 g of this indicator
derivative was added to 10 ml of glacial acetic acid over an
ice-bath and diazotized with 0.5 g sodium nitrite. Then 1 g of the
glass complex was added to this mixture. The resulting orange bound
indicator was washed thoroughly with water, acetone and benzene
until colour was no longer eluted. This orange bound indicator
turned reversibly violet in the range pH 10.0 to 12.00.
EXAMPLE VI
Nickel screen, of 150 mesh and 0.1 mm thickness, was heated
overnight in a furnace at 700.degree. in an oxygen atmosphere to
oxidize the surface, thus forming a NiO coating on the screen. The
screen was then cut into strips 1 inch by 4 inches, which were
rolled into cylinders of approximately 0.5 inch diameter and the
ends soldered to prevent ravelling.
One of these NiO coated cylinders was refluxed overnight in a 10%
solution of gamma-aminopropyltriethoxysilane in toluene. This
aminoalkylsilane derivative was washed in toluene and air-dryed.
The screen was refluxed in 10% thiophosgene in chloroform. The
isothiocyanoalkylsilane derivative was washed with chloroform and
coupled to ethoxazene. The bound indicator thus created underwent a
colour change from red below pH 5 to yellow above pH 5.
EXAMPLE VII
4-carboxy-alpha-hydroxy-alpha, alpha-bis (p-hydroxyphenol)-
1-toluenesulfonic acid was prepared by condensing phenol with
3-carboxy-1-sulfobenzoic anhydride in the presence of zinc
chloride. Equimolar quantities of this phenol red derivative and
tri-n-propylamine were combined with 3 molar equivalents of
trichlorosilane in a vigorously exothermic reaction. After
refluxing for 1 hour at 55.degree.-75.degree. and treating the
mixture with tri-n-propylamine hydrochloride in pentane, and
ethanolysis, the product, an indicator silane, was isolated by low
pressure distillation.
This silane coupling agent, 3-carboxyphenol red triethoxysilane was
then bound to 1 g of porous 96% silica glass as in Example I, to
give methylenephenol red glass which was red at pH 7.0 and below
and changed to orange-yellow at pH 8.5.
EXAMPLE VIII
A bound indicator on a glass carrier was prepared by the procedure
of Example I from fluorescein instead of phenolphthalein.
EXAMPLE IX
A bound indicator on a glass carrier was prepared by the procedure
of Example I from xylenol blue instead of phenolphthalein.
EXAMPLE X
A bound indicator on a glass carrier was prepared by the procedure
of Example I from cresol red instead of phenolphthalein.
While a number of examples of the bound indicators of this
invention and methods of preparing them have been given, such
disclosure is intended for illustration only and to impose no
limitation on the scope of the invention beyond those included in
the appended claims.
* * * * *