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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

1226 ANALYTICAL CHEMISTRY

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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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