Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
1~5~8~
This invention relateQ to an improved method of
tcsting for the presence of lead in aqueous solution. It
i8 known that amounts of lead in the range of from 4 to ~
ppm can be determined using dithizone as well as by
various instrumental methods. ~owever, such tests require
special equipment and chemicals and often involve
complicated experimental procedures. They can therefore
not be performed by the average layman at home.
U.S. Patent No. 3,809,53~ (Horine) discloses a
crude testing method for the presence of lead in aqueous
solution, which comprises addin~ a solution of a soluble
sulfide and inspecting the resulting solution visually.
However, this prior teaching does not permit a
quantitative determination of lead concentration allowing
asse~sment of the seriousness of lead contamination in any
~iven instance. Furthermore, the prior method suffers
from the di~advantage of evolution of unpleasant and
potentially hazardous hydrogen sulfide odour, thereby
inhibiting the practicality of the method in the home and
the ease of use thereof, since inadequate ventilation
~hould be assumed with respect to testing in the home.
There is currently a need for a simple and
efficient manner of quantita~ively detecting the presence
of lead which is capable of being leached Prom the glaze
of various pottery and ceramic containers. The lead-
containing glaze is capable of being leached by food acids
and this has given rise to many cases of lead poisoning in
Canada. However, the lead content of pottery glaze, if
~5
~ ~ 5 ~r~
any, i8 also readily leachable by the use of aqueous
acetic acid. When lead is leached from pottery using 4%
acetic acid ~olution, the concentration limit presently
~onsidered unsafe by the United States Food and Drug
Admini~tration i~ ~ ppm for small holloware. Leglslation
specifying lower tolerable limits (less than 1 ppm) is
under consideration.
Slmilarly, the Hazardous Products ~Glazed Ceramics)
Regulations ~CRCc 925, paragraph ~a)) state that products
releasing lead in excess of ~ parts per million may not be
imported into Canada or sold to the public ~if produced
locally). The evaluation i5 determined on the basis of a
test of a product comprising steeping the product with 4%
acetic acld solution for 18 hours at 20C and determinlng
the quantity lead present in the solution by an atomic
absorption technique.
Accordingly, it is an object of the present
invention to provide a simple test method for the
detection quantification Qf lead, partlcularly in the
range of 2 to 50 ppm, enabling members of the public at
home or industrial users to test qulckly and in simple
manner pottery, ceramics and other articles, to ascertain
the saety thereof and to identify and separate
potentially hazardous items o concern.
Accordingly, one aspect of the inventlon
provides a method of quantitatively testing for the
presence of lead in a concentration of from about ~ to 50
ppm in aqueous solution, which comprises ~a) adjustin~ the
pH of the aqueous solution to a value of from about ~.5 to
13, (b) adding to the solution a predetermined amount of
an aqueous test solution containing a soluble sulfide and
a water-soluble glycol, and (c) comparing the resultant
colour of the solution w~th a standardized calibrated
colour chart so as to obtain a quantitative indication of
the concentration of lead, 1f any, in the aqueous
solution.
Another aspect of the invention provicles a test
kit for testing an aqueous solution for the presence of
lead, which comprises (a) an alkali solution for
ad~usting the pH of the aqueous solution to the range of
aoout 7.5 to 13, (b) a test solution containing a water
soluble sulfide and a water soluble glycol in aqueous
solution, and ~c) a standardized calibrated colour chart
for comparison with the colour of the a~ueous solution
after addition of alkali (a) and test solution tb) so as
to provide a quantitative indication of the concentration
of lead, if any, in the aqueous solution. The test kit
may also include a lead-free reaction vessel, such as a
lead-free ~lass test tube, for mixing the aqueous
solution, the alkali and the test solution.
The soluble sulfide employed in the method is
preferably sodium sulfide nonahydrate, but can also be
potassium, lithium, ammonium, calcium, strontium or barium
sulfide or hydrosulfide.
The glycol i5 advantageously glycerol, ~thylene
glycol, diethylene glycol or propylene glycol and is
l~S678~
conveniently employed in an amount of from about 1 to
about 10% by volume, based on the test so~ution. The
aqueous solution to be tested will normally have been
obtained by leaching a suspect article, such as a pottery
contalner, cutlery item, or paint chips from a suspect
painted product. Such aqueous solution is advanta~eously
acetic acid, such as distilled white vinegar (5~ acetic
acid), but may also comprise citric, oxalic, tartaric,
maleic, formic, lactic, benzoic, adipic, succinic or
propionic acid in water. Thus, the aqueous solution is
~enerally obtained by steeping an article suspected ~o
contain leachable lead in the acid solution for an
extended period of time, for example for about 24 hours.
A particular feature of the invention is the
ad~ustment of the pH value of the aqueous solution to the
alkaline range of about ~.5 to 13 prior to contact with
the test solution. This procedure substantially
eliminates the evolution of hydrogen sulfide yas with
accompanyin~ unpleasant odour during the duration of the
test procedure. Adjustment of the pH value can
conveniently be achieved by the addition of an alkali, for
example selected from alkali metal and alkaline earth
metal hydroxides and carbonates, such as sodium, calcium,
potassium, lithium and magnesium hydroxides and
carbonates, sodium metasilicate, trisodium phosphate,
sodium bicarbonate, ammonium hydroxide, borax, ferrous
hydroxide and magnesium oxide, which alkalis can be added
~X~678~
in solid or in solution form. A preferred alkali is about
2.5N aqueous sodium hydroxide solution.
The test solution is preferably an aqueous
solution containlng about 0.64N sodium sulfide nonahydrate
and from lX -to 10%, preferably about 5% by volume of
~lycerol. ~owever, any alkali or alkaline earth metal
sulfide or hydrosulfide, such as lithium, sodium,
potassium, ammonium, calcium, strontium and barium
sul~ides and hydrosulfides, may be employed as the test
solution, generally in concentrations of up to 50% by
weight, based on the weight of the solution. Glycerol is
preferably used as the stabilizer, but any water-soluble
glycol can be employed, for example ethylene glycol,
propylene glycol or diethylene glycol. An amount of
glycol of from about 1 to 10% by volume is preferred.
The leaching solution is preferably acetic acid,
for example in the form of white vineyar (5~ solution)
which is readily avallable in most households.
However, other acids can also be employed to
form the aqueous solution to be tested, such as oxalic,
tartaric, maleic, citric, formic, lactic, benzoic t adipic,
succinic and propionic acids in solutions generally up to
10% by volume.
The test solution is conveniently packaged in
the kit in 25 ml samples, while the alkali neutralizin~
solution may advanta~eously be employed in amounts of 25
ml. The test kit may include a dropper, e.g. an eye
dropper, for transferring measured amounts of the aqueous
~5~7~3~
solution into the reaction vessel. As mentioned above,
the kit advantageously further includes a lead-free, non-
reactive vessel for use as a standard reaction vessel, as
well as a colour comparison chart for determining the
approximate lead release.
The method and kit of the invention are also
useful in determining the presence of other toxic metals,
~uch as copper and blsmuth which produce a similar brown
sulfide insoluble salt~ They are generally detectable at
a level of approximately 10 ppm. The presence of such
other metals can conceivable result in an interfering
reaction in lead detection. However, this interference is
not generally a real problem when detecting lead since the
above metals are seldom used i~ pottery making or found in
cutlery or paint.
The method of the invention enjoys various
advantages over the prior art procedures. In particular,
the process is completely odour-free since the test
~olution is added to an alkaline environment thereby
avQiding evolution of hydrogen sulfide and the
characteristic rotten eg~ smell. As a result, the testing
operation is considerably more pleasurable for the user.
In an acidic environment (prior method), the
reaction proceeds according to the following equation:
Na~ + 2S= ~ 2H+ + Pb++ = 2Na+ -~ H2S~ + PbS~ (1)
In the procedure of the present invention, the
reaction proceeds as follows:
Na+ t S + OH- + Pb++ = Na+ + OH- ~ PbS~ (2)
~25678~
5ince hydrogen sulfide is not evolved durin~ the
test, the procedure i5 much safer, since H2S ~as is a v~ry
toxic gas, even in low concentrations.
In addition, the resulting test solution is
clear, rather than a cloudy preGipitate as produced by the
prior method of U.S. ~atent No. 3,809,537. In consequence
the observation of a colour change, particularly at the
lower concentrations tless than 4 ppm), is very difficult
to detect utilizing the prior method.
The kit accordin~ to the invention includes a
colour comparison chart which can be employed to determine
the approximate lead (and other toxic metals) release, by
comparing the colour of the resulting solution ~preferably
in a standard glass container supplied with the test kit
against a white background) to the colour of the test
strip.
Futhermore, the test solution contains a
stabilizer which increases the shelf-life of the product.
Thls is an important factor in the present field, since
the use of a stale product may well ~ive rise to a
misleading false negative or "safe" result.
The method and kit of the invention can
furthermore be utilized to detect low levels of lead in
potable water. Thus, lead contamination of a household
water supply can be verified, this being an occasional
occurrence either due to contamination from source or due
to the use of lead solder (especially ~n new homes
containin~ fresh solder on joints). In addition, lead
7~32
stearate is used in the production of plastic pipin~ and
can give rise to the pre~ence of lead in drinking water
emanating from plastic pipes.
Furthermore, the method and kit of the invention
can also be employed to determine leachable lead content
in soil collected around the home. Hazardous levels of
lead in soil can be established and quickly acted upon.
Moreover, the method and kit of the invention
can also be employed to determine the presence of
leachable lead in cutlery, older silverware and painted
surfaces or furniture.
The following Examples illustrate the invention.
Exam~les 1 to 10
A variety of different media were tested for the
presence of lead utilizin~ a 0.64N sodium sulfide
nonahydrate aqueous solution containing 5% by volume of
glycerol. Distilled white vine~ar (5~ acetic acid) was
employed as a leachin~ solution and the pH thereof was
ad~usted to within the range of ~.5 to 13 utilizing 2.5N
sodium hydroxide solution. The pottery article was filled
with the vinegar and allowed to stand for 24 hours. 1 ml
of the vine~ar was then placed into a lead-free ~las~
reaction vessel and ~ drops (0.35 ml) of the neutralizer
(sodium hydroxide solution) was added, followed by 7 drops
(0.35 ml) of the test solution. The colour change, if
any, was noted and compared with the calibrated
standardized colors of a colour comparison chart.
g 12S6~82
For comparlson purposes the experiments were
repeated utilizing the procedure described in U.S. Patent
No . 3, 309, 53~, employing a similar vinegar and a similar
amount of sodium sulf ide nonahydrate. The results
obtained are ~ummarized in the following Table 1.
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h ~ t)
h h ~ 1~ rl ~J rl o ~J
n ~ o h ~ O ~ S-l O
Q, O ~ ~ 3
~: ,c h ~i h , ~ a~ E3 h
O ~ ~ ~ O Q~ h(~ r O 1~ h ~ r o
q~ ~ @ ~) - d~ rl ~ r-l ~ r l
~ ~ I Q. O) I I ~I U) I I (.) I (/) I
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4 U) ~ rl , J .a IJ r1 0 ~rl ~a r-l r-l 3 0 .Q ~ ~ O hC~) ~ O O ~rl ~ al 11) h h ~ ~a ~ r
4 ~ X
O ~
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~2S6~78~
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P. O O rl ~ t~) P~ h::J h10 h ~ P. h
O U~ ~ ~ O ~ h ~ 1 C
o r1 h ~ 10 0 ~ ta O I O h ~ O O
h h 111--~ O h u~ ~1 111 0 ~ O ~ 0 0 ~--
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h ~ O ~ J t~ ~ h OC~i 4 a~ ~ O
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U ~ h --Ih ~) ~ (U 4 O) 3 ~ -1 0
(a O hh P~ O ~ tl) U ~ ~ I r~ r~
r~ O IU ~ 111 4 ~ O r~ ~ h ~ ~ ~ Ei td ~
,aa) ~ ~ ~n ~ O ~ h ~ rl O ~rl 0 ~ rl O U~ ~1) U
~ ~ ~ ~ ~ ~X ~3 r1 ~~ Q~ r
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O ~ a) P O,~1 O O ~I h O O t~) h h O t~
I OI 1~ I r~ I h I U) U Ql U)I a~ I Q-I tl~ U~ I aJ I r~
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Examples 11 to 18
The above described test solution and
neutralizer were also employed for analyzing the lead
content of soil samples, potable water, cutlery and metal
samples employing a similar procedure to that described
above. In the soil analysis test, a factor of 100 is
employed to compensate for the dilution of the vine~ar.
The results are given in the following Table 2.
O
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~ U)
3 0
g ~ ~
_ _ ~
_ ~q
O ~ ~_ p,
~ o ~ e
U
~ O ~, O P- p'
U h ~ ~ O u)
~rl 4 C3 U) A .1 ~D
4 Q
~ U~
cl 4 4
-- 4 a~ O h h
4 h h h ~: Id O
1~ 4 U) h .C g ` 0~ U~ h 0 1)
L> I~s ~ o o o a) o h
` ~ ~ ~ h U
S~ J h h O ~ h O t~
o ~:` O O ~ O^
r-l O~ ~rt ~~ O ~ O O ~ ~1 4 ~-I O O ~r1 Il~ r1
.a .~ 3 4 0 ~ U) O O O ~ 1 4 l~
-~ ~o ~ ~u) 4 0 td ~ E3 0 0 ~
O ~ ~: h ~1 ~ U ` P P~ ~ U ` 0 ~ ~1 ~1
O O P O h ~I p~ h 1~ 4 td rl
~ ~ ` O a) ~ ` o ~1'a E!
4 ~a ~ 4 O Q-'a h -1 4 0 ~ O ~ h r~ tl) --I Q.
~1 0~1 .~ O ~ l U 1~ ~ ~ O
~ ~ oo o o ::~ o ~ o o I a~ 1 o o
u~ 4 o ~ o oo ~i --1 4 0a) o O h ~1 ~1 h 1~ ~1 0
0 Q) ~:: ~t ~ O ~ 1 0 O ~ O ~ O :1 ~
E~ ~ I U) ~J I I P. ~ 1 0 ~ I --11
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rl 4
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P.
O C')
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O h 4
~ 1~1 h ~ S~
h g~ 0 0 0 tlhl:: O O P.
h ~ h ~ ~ 0
0.~~Id O 0 0 ~0 h n~
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O E~ o V ~ R ~ O h 13
O rl ~ O ~ ~ ~ O I ~ P O
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--I O OO O O 0 ~1 ~ A .1:
I Ul I U 1 0 ~ I 1 0 1 1 1 1 1
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~25167~3~
16
In summary, it will be appreciated that the method and kit
provide a convenient means of detecting lead in the range
of 2 to 60 parts per million. The method can be employed
for the detection of lead in a variety of domestic areas,
including pottery and china, cutlery, and painted
articles, as well as soil, water and unidentified metallic
items.
