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the cellulose nitrate used t o prepare th e
propellant is available.
There are three semicri tical s teps in
the bas ic procedure . F irs t , there must
be sufficient potassium hydroxide to
react with th e acidic pro duc ts of th e
hydrolysis. Each gra m of propellant
consumes about 1 gram of potassium
hydroxide. Consequently, a t least
60
ml. of the hydrolysis solution should be
used per gram of propellant. Wh ethe r
sufficient alkaline solution n-as taken is
checked when th e solutio n is acidified
after the 15-hour reaction period. Th e
solution should tur n red upon t he addi-
tion of phenolphthalein.
A
large excess
of hydrolysis solution should also be
avoided. Two phases are present a t the
end of the reaction. Th e lower phase,
in contact with t he cellulose, has
a
higher
concentration of base than the upper.
It may be possible, consequently, to
raise the hydroxide concentration in th e
lower phase so as to att ac k the glucoside
chai n of the cellulose
if a
high tota l base
content is present after hydrolysis.
The second semicritical step
is
in the
washing procedure. Washing mus t be
thorough if the solution being filtered
comes in contact w ith the portion of the
walls in contact with the Gooch rubber
tubing. Because this portion is above
the suction line, it is morc difficult to
wash adequately.
Obtaining and keeping dry cellulose
is
the third operat ion requiring care ,
Cel lulose should be t reated about the
same as phosphorus pentoxide in regard
to atmospheric exposure.
Th e bas ic procedure required ab out
1 /4 hours of operator time per sample
when performed in groups of six. Th e
total elapsed time for six samples is
about
26
hours . This procedure mini-
mizes equipment costs, safety hazards.
working space, and operator time.
Safety . C e r t a i n p r e c a u t i o n s
should be taken
as
to safety. Because
diethyl ether forms explosive mixtures
with a ir , a l l operat ions involving i t , or
the solvent containing it should be per-
formed under a hood. Thi s is partic-
ularly t rue when the solvent is acidified,
because the gases evolved
are
reported
to be poisonous 5) . Fifty per cent
acetic acid will cause blisters if it re-
mains on the skin; hence, precaut ions
should be taken when this reagent is
used. Th e alkaline solvent, after filtra-
t ion ma y s t il l contain glyceryl t r ini t ra te
and should be disposed of properly.
LITERATURE CITED
(1) Fletcher, A . N., ANAL. CHEM.29,
1387-8
(1957).
2 ) Garetio, Giuseppi, Ruffoni, Alfredo,
(3) Joint Army-Navv Specification
JAN-
4) Kenyon, W. O., Gray, H. L., J Am .
Ibid.
27, 400-1 (1955).
N-244
(Jul y 31, 1925).
Chem.
SOC
58.
1422-7 11936).
(5) Will,
Ber.
24, 400 (1891).
RECEIVEDor review October 27, 1958.
A4cceptedFebruary 2, 1059. Division
of
Analytical Chemistry, 134th Meeting,
ACS, Chicago, Ill., September 1958.
Pacific South vest Regional M eeting,
XCS,
Redlands, Calif., October 1958.
Photometric
Application to
Determination of Zinc with Zincon
Wa ter Containing Heavy Metals
J. A. PLATTE and V.M. MARCY
Hagan Chemicals
&
Confrols, Inc., Piffsburgh, Pa.
b
The colorimetric test
for
zinc with
Zincon 2 -ca rboxy-2 -hyd roxy-5 -
sulfoformazylbenzene) is rapid and
fairly sensitive, but lacks specificity.
Many heavy metallic ions, par ticula rly
copper, interfere. Zinc can be sepa-
rat ed from some interfering substances
with an anion exchange resin and
hydrochloric acid of various molarities,
but the method i s somewhat cumber-
some and time consuming. In this
method, heavy metals including zinc
are complexed
by
adding cyanide to
the sample. Chloral hyd rate i s added
to free the zinc without destroying the
other metallic complexes. The blue
zinc-Zincon complex, formed on addi -
tion
of
Zincon to the sample buffered
to pH 9
s
measured with a spectro-
photometer.
R A P I D
accurate method
is
needed
A for the determination of minute
amo unt s of zinc in potable and indus-
trial waters. Zinc may be present as a n
impur i ty or added to a water with poly-
phosphate to minimize corrosion by
accelerating the formation of
a
protec-
tive film
on
metal surfaces
2) .
Although other chromogenic agents
have been used, only methods employing
dithizone (diphenylthiocarbazone) and
Zincon
2- carboxy-2 - hydroxy-5 - sul f o-
forniazylbenzene) have been widely
accepted 1, i , and many heavy-metal
ions interfere with both methods.
Th e ai m of this inve stigation TTas to
devclop
a
rapid direct test with Zincon
in which possible interfering substances
would be niinimizcd or eliminated.
Zincon forms a 1 t o 1 blue complex
n i th bo th z inc and copper in the pH
range 8.5 to
925.
A t
a
wave length of
620
mp, th e absorbance of t he zinc
comples follows Beers l a r in the range
of
0.1 t o
2 4
p.p.ni. of zinc (5 to
120 y
of zinc for 50 nil. of final test solution).
According to Rush and Toe T), lumi-
num, beryl l ium, bismuth, cadmium,
cobslt, chroniiuni. iron, ninnganese,
mol:-Ldenuni, titan ium , and nickel inter-
fere in addition to copper. Ton ex-
change resins and complexing agents
have been t r ied to remove or mask
certain interfering metals 4, 7 ) .
PRINCIPLE OF MODlFlCATlON
The complexing
of
metals with
cyanide, follon ed by selective demash-
ing of zinc and cadmium cyanide coni-
plexes, ha s been used for the (ethylene-
dinitri1o)tetraacetic acid (EDTA) titrn-
tion of zinc and cadmium in the pres-
ence of heavy metals 3) . Zinc can be
determined pho tometrically with Zincon
by the selective deniasking of the cya-
nide complex with chloral hyd rate .
Many metals form cyanide com-
plexes. On the addition of chloral
hydra tc (6) or formaldehyde 3 ) to the
solution, however, zinc and cadmium
cyanide complexes are des troyed r i th
the excess cyanide and these metallic
ions are liberated according to the
reaction:
[Zn(CN)d]-- 4 CCll C H ( O H h c
Z n + +
+ 4
CCla C H ( 0 H ) C N + 4 OH-
(3-trichloro-2-hy-
drosypropionitrile)
Although formaldehyde reacts more
rapidly than chloral hydrate with the
zinc complex, it liberates other metals
from cyanide complexes fast enough to
cause interferences.
(chloral hydrate)
APPARATUS AND REAGENTS
-4.11 absorbancc measurements ivere
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I
1
Figure
1 .
Effect
o f
vary
ing volume
of
cyanide
solution on test samples
containing
10 y
of
zinc
All tests run with 3
rnl.
of
chloral
hydrate so lu t ion
5
I O 15
2 0 2 5
30
0.050
CYANIDE
SOLUTION, M l
m ade wi th e i the r
a
Becknian Mode l
D U
spectrophotometer , us ing matched
1.00-cm. cells, or a Bausch - L o m b
Optical
Co.
Spectroiiic
20
colorimeter,
us ing ' /pinch tubes . An y photom eter
having a b a n d
pass
of 20 m p or l es s a t a
wave length of 620 nip m ay be used .
d
Becliman pH meter, Alodel
G ,
was
used for all
pH
measurements .
Reag ent gr ade chemicals were used.
Cyanide Solut ion. Dissolve
1.00
g r a m
of
potassium cyanide in distilled
n-ater and di lute to 100 ml.
Buffer Solution, pH
9.0.
Dilute 213
nil. of
1N
sod ium hydrox ide to about
600
id wit h distilled water. Dissolve
37.3 grams of potassium chloride and
31.0 grams of boric acid in t he solut ion
a n d d i l u te t o
1
iter.
Zincon Solut ion. Prepare by dis -
solving complete ly 0.130 gram
of
polvdered Zincon in
2
ml. of 114 sodium
hydrox ide and d i lu te to 100 m l . T h e
solut ion is deep red in color and is s table
for about
1
week. Zincon ma y be ob-
ta ined f rom The LnMot te Chem ica l
P roduc t s Co., Ches te r town, M d.
Chloral Hyd rate Solut ion. Dissolve
10 gra ms of chloral h yd rat c in distilled
n-ater an d di lute to 100 ni l.
Sodium A scorbate .
S tandard Zinc Solut ion. Dissolve
0.2745 gram
of
zinc sulfa tr mono hydra te
in d i s ti l lrd w a te r and d i lu te to
1
liter.
Di lu te
10
ml. of s tock solut ion to 100
ml. to prepa re a s tandard containing
10 y
of zinc per ml.
Solutions of Diverse Ion,i. Fo r th e
s tud y of interferences, use solut ions that
contain e i ther 10 or I00 y of metallic ion
pcr m i
PRELIMINARY STUDY
Sufficient cyanide solution must be
added to complex a l l the metal l ic ions
th at form cyanide complexes. Also,
sufficient chloral hydrate must be used
to des troy the excess cyanide and to
free the zinc from its cyanide complex.
-4s
seen in Figure
1,
und er conditions of
t h e t e s t 3 ml. of chloral hyd rate solution
is
adequ ate for the react ion with some-
wha t m ore than 1 nil. of c yan ide solu-
tion. It is dcsirahle to use only a
minimum of chloral hydra te so
as
n o t t o
increase the color intensity of the tre ated
blank.
Absorbance measurements were mad e
at
intervals on t reate d samples contain-
ing z inc, with and without copper, to
determine opt imum tes t condit ions and
to ascerta in th e s tab i l i ty of the z inc-
Zincon color complex. The results
(Tab le I ) show tha t t e s t co lo r in the
absence of copper is completely de-
veloped in 12 seconds and
is
s table for
at
least
2
hours whether or not the
cyanide-chloral hyd rate modification
of the Zincon test is employed. Th e
intensity of th e color with th e cyanide-
chloral hydrate modification is slightly
less than that with the usual Zincon
method [Rush and Yoe 's Procedure A
When the sample contains copper,
the usual Zincon method measures a l l
the copper in addi t ion to zinc. Th e
color reaction for both Zincon complexes
is complete mithin 1 m inute . How-
ever, wit h the cyanide-chloral hyd rate
modification the reaction
M
ith zinc is
complete in 1 minute and the copper is
effectively tied up as the nonreact ive
cyanide complex for
2
h o u r s . l f t e r
2
hours a n increas ing am o unt of copper
is l iberated by the chloral hydrate .
A coloi development time of 2 to
5
minutes is suggested in this procedure
to ensure that the z inc color
is
coni-
ple te ly developed and that the other
cyanide complexes are not affected.
The use of formaldehyde in place of
chloral hydrate as
a
demasking agent
was unsatisfactory because it destroyed
cyanide complexes much faster than
chloral hydrate.
7) I
PROCEDURE
Transfer to a 50-ni l . Erlenmeyer
flask a 10-ml. aliquot of the sample
(approximately neutra l) containing
0
t o 5 0
y
of z inc. Add reagents to the
sample in the fol lowing order with
mixing between a ddi tion s: 1.0 nil. of
cyanide solution, 5.0 of buffer, 3.0 of
Zincon, and 3.0 of chloral hydrate.
Measure absorbance 2 t o
5
m inutes
after add ing the las t reagent .
A.s
refer-
ence solution, use
a
blank ob ta ined by
cftrryi i ig dis t i l led water through the
comp lrte procedure . Es t im ate zinc from
Table
1
Change in Intensity
o f
Zincon
Color Comp lex with Time
(Solution contains 10
y zinc)
Absorbance Rending
Cysnide-
Chloral
Usual Zincon Hy drate
Nethod
Rfodificntion
0 . 2 0 . 165 1.80
0 . 1 5 5 0 . 1 4 5
1
0 . 165 1 . 8 0
0 . 1 5 5 0 . 1 5 4
5 0 . 1 6 5
1 . 8 0
0 . 1 5 5 0 . 1 5 5
120 0.165
1.80 0 . 1 5 5 0.156
180 0.165
1 . 8 0
0 . 153
0.360
300
0.164
1 . 8 0
0 . 151 1 . 70
Table
II.
Effect
o f
Diverse Metallic
Ions
(Solutions contain 0 and 10
y of
zinc)
Apparent Zinc
Content ,
y
Cvanide-
ihloral
Zinc
hydrate
Metallic Present, modifi-
Ion,
Y
cu , 10
c o + + , 3 0
20
300
30
300
Ni++,
30
30
200
,
50
50
F e + + + ,
10
20
70
Fe+T, 10
20
90
100
C d + + , 20
10
50
CP+++,
100
0
10
10
0
10
10
0
10
10
0
10
0
10
10
0
10
10
0
10
0
10
10
cation
0 .0
1 0 . 0
1 0 . 0
0 .0
9.9
1 0 . 0
0 .0
10.0
1 0 . 1
0.0
1 0 . 3
0.0
1 0 . 0
10.0
0 . 0
9 . 8
10.3
0 .0
10.0
0 . 9
1 0 . 8
1 4 . 2
Usual
Zincon
method
10.0
30.0
10.0
1 9 . 9
8.4
7 . 0
0 . 0
1 0 . 3
< o o
8 .5
2 . 3
1 1 . 4
0 .0
0 .0
2 . 0
1 4 . 0
2 4 . 2
. . .
. . .
. . .
. . .
. . .
a
cal ibrat ion curve obtained with
known a mou nts of z inc t reated as above.
D u r i n g t h e l a t t e r p a r t of the in -
vestigation, the preferred reference
solut ion for photometric measurements
was one prepared by adding the f i rs t
three reagents to the unknown sample,
follorred by
3
ml. of distilled water in
place of 3 ml. of chloral hydrate solu-
tion.
By
adding
0.5
gram of sodium
ascorbate to both sample and reference
solution, before addition of the other
reagents , interference from manganese
was
great ly decreased.
EFFECT O F METALLIC IONS
T es ts viere ~ u n y us ing the above
procedure and also the
usual
Zincon
method on samples containing diverse
metallic ions and 0 or 10 y of zinc.
Except for manganese (discussed later),
resul ts are l is ted in Table
XI
T h e
values show that of the metals tes ted,
VOL. 31 NO. 7 JULY 1959 1227
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