CHAPTER - II

Sl"'ECTROPHOTO~lETRIC DETERI"IINATION Of CYANIDE

USING ANTHRANILIC ACID AND ITS APPLICATION

'rO BIOLOGICAL F'LUIDS

SUi"iMARY

The method describes the determination of

cyanide by conversion of cyanide into cyanogen bromide

followed by the reaction with pyridine. The glutaconic

aldehyde so formed is condensed with anthranilic acid

to give a yellow-orange dye which shows a maximum

absorption at 400 nm. Beer's law is obeyed in the range

of 1 - 7 ppm. The molar absorptivity and Sandell's

sensitivity was found to be 3.12x103 lit.mol-1cm-1 and

0.0083 fg cm-2 respectively. The method has been

successfully applied for the determination of cyanide

in biological samples.

Published in Analyst, 109 (1984) 1619.

SPECTrtuPHU'l.'OJV,E'l'RIC DE.TERl'IINATION OE' CYANIDE

lJSINli A;,THrlA!:!l.LIC ACID AND ITS APPLICATION

TO BIOLOGICAL FLUIDS

Cyanides are among the most toxic of all

industrial chemicals and they are produced in large

quantities and are used in different applications (1).

Hydrogen cyanide, hydrocyanic acid, or as it is often

called 'prussic acid' is a colourless gas, with a

penetrating odour resembling that of bitter almonds,

Cyanides are used in various industries, e.g., in

extraction of noble metals, manufacturing of organic

chemicals, electroplating, hardening of steel, metal

polishing and photography (2) • Hydrogen cyanide is

used extensively as a fumigant, particularly in the

fumigatiou of ships and citrus trees. Apart from its

principal use in the fumigation, hydrogen cyanide is

used as a reagent in industry and is encountered in

concentrations that may be dangerous in certain indus­

trial processes, as for instance in blast furnaces, dye­

stuff works, gas works, coke ovens, tanneries, fertili­

zer plants and gold gilting and gold mining (2),

The main danger of cyanide and the simple

soluble cyanides is the sudden resorption of concentra­

tion doses (a drop of liquid hydrogen cyanide leads to

death in few seconds) but the danger is less acute when

Nevertheless 100-200 mg HCN m-3 inhaled in hal! to one

hour is lethal (3) , Hydrogen cyanide acts by stopping

the oxidation of pro to plasm in the tissue cells, With

high concentrations the symptoms appear rapidly, viz,

giddiness, headache, unconsciousness and convulsions

with cessation of respiration as a result of paralysis

of the respiratory centre in the brain, Repeated .

exposure to small concentration of cyanide over a long

period causes symptoms such as weakness, nausea, muscle

cramps, loss of appetite and psychoses (2). Relatively

little gross or microscopic pathology can be seen

following inhalation of hydrogen cyanide, While there

may be scattered hemorrhages and scattered congestion,

these are probably the result of anoxia, Venous blood

may appear of brighter red colour than normal. Hydrogen

cyanide vapour is absorbed extremely rapidly through the

respiratory tract; the liquid and possibly the concentra­

ted vapour are absorbed directly through intact skin (1).

·As per the C & EN 1 s Dec., 2, 1985 report of

American Chemical Society, the recent Bhopal gas tragedy

appears to have two aspects in the cyanide issue, One

is the direct exposure and the other is the indirect

exposure owing to unusual generation of toxic amounts of

hydrogen cyanide in the body after exposure to methyl

isocyanate (MIC). Below is shown the proposed mechanism

for the generation of cyanide in the body after eXPosure

to rvnc,

33

34

•

Hb-NH ... + O=C=N-CH3

MIC

[

H H · I I +

Hb-N-C-N5CH "VIV

H

l -

.. - ·-·~ . --.. --~-::;:::;-;:::-::-;-~~r:::---:===="'......---'-_.J The recom~ended maximum allowab e concen

of cyanide is 5 mg m-3 in air calculated as CN-. The

world Health Organization recommends that water contain-

ing more than 0.01 ppm of cyanide (as CN-) should be

rejected as unfit for domestic supplies (4).

The detection and determination of cyanide ion

in small amounts become very important because of the

extreme toxicity of cyanide to living matter. Since

many years there has been steady increase in the methods

for determination and detection of cyanide. The methods

available are not only for 11 free cyanides" (from HCN, KCN,

and NaCN) and unstable cyano-complexes, such as

I Zn(CN4) 12- but also !or relatively stable complex

cyanides, such as, ferrocyanides and cobalticyanides,

which although are not showing typical cyanide proper­

ties, are still toxic and classified by most health

author! ties with cyanides. The methods available for

cyanide detection and determination can be classified

into two groups:

(a) Non-colourimetric and

(b) Colourimetric.

The following methods fall under the non­

colourimetric group -

(i) Titrimetric methods using visual end-point

indicators. The earliest reported method for determin­

ing cyanide is Liebig's titrimetric method (5) based on

the formation of turbidity due to silver cyanide. This

titration is subjected to error in alkaline (6) and

ammoniacal medium (7). A similar method proposed by

Deniger (8) is based on the turbidity due to silver

iodide in the presence of ammonium hydroxide. Accurate

results are obtained in carefully regulated ammonium

hydroxide concentrations (9,10). Beerst~ (11)

modified the Deniger method .by introducing photoelectric

colourimeter and turbidimeter for end-point detection.

Ryan and Culshaw (12) reported the use of p-dimethyl­

aminobenzylidene rhodanine as an indicator in Liebig's

method and this modification was recommended by the

American Public Health Association (13) for determination

35

of cyanide concentrations of 1 ppm and more. Other

titrim~tric methods involving the use of different

indicators and titrants have been reported. Diphenyl­

carbazide (14), Calcein (15) and thiofluorescein (16)

36

have been used as indicators for argentimetric titrations.

Cupric diethyl dithiocarbamate (17), Variamine Blue (18)

and Nitrobenzene (with ferricyan1de)(19) are used for

titration involving the formation of mercury cyanide.

In a recently developed method cyanide is oxidised by

N-bromosuccinimide and then titrated argentimetrically

using starch-iodide, methyl blue or bromo-thymol blue

as indicator (20).

(ii) Titrimetric methods involving instrumental end­

point detection make use of potentiometric titration of

cyanide with silver nitrate described by Treadwell et al.

(21) and Clark (22), This method has been applied for

the determination of cyanide in biological samples (23).

Amperometric titration is also equal in accuracy and

precision (24). Direct amperometry with a rotating

silver anode and a platinum cathode has been used by

f'ilcCloskey (25). Amperometric determination of cyanide

using flow through electrode has been made use by

Pihlar et al. (26) • Polarographic methods suggested

by Karchmer and Walker (27) and Hetman (28) are quite

sensitive too,

(iii) Gas chromatographic method have been employed

for cyanide determination by Woolmington (29), Schneider

and Freund (30) and Honma (31).

Colourimetric methods include -

1) Methods involving formation of a metal complex.

Some of these methods although specific for cyanide and

37

of ample sensitivity, produce unstable colours. Formation

of thiocyanate from cyanide (by reaction with polysulphide)

and then ferric ferrithiocyanate producing a blood red

colour, is an excellent test for cyanide (32). Another

extremely sensitive test for cyanide is the Prussian

blue test (33-35). The copper acetate-benzidine test

(36,37) is extremely sensitive and easily applied test

for the detection of cyanide. The Weehuizen method

(38-40) involves the oxidation of phenolphthalein in

alkaline solution

copper II ions in

to the corresponding red phthalein by and

the presence of cyanide,(. is a recommended

method. Indicator tube method for the determination of

cyanide involves indicato~ like bromothymol blue, bromo­

cresol green, etc. (41).

The ability of the cyanide ion to form stable

complexes and cause demasking of inner-complex bonded

transition metals has also been used by various workers

for the detection and determination Of cyanide (42-44).

Methods developed by Brooke {45) and Hanker et al. (46)

are also based on the above mentioned principle.

Sensitivity is enhanced by complex formation with dimethyl

glyoxime (47). Several methods involving demasking

effects of mercury II too have been used for cyanide

determination (48,49). Spectrophotometric determination

of cyanide is also possible through ligand exchange

reaction proposed by Verma et al. (50) and Roman et al.

(51) and formation of ion-association complexes (52,53).

Schilt (54) described the spectrophotometric determinat­

ion of cyanide baaed on the formation and extraction of

neutral dicyanobis (1,10 phenanthroline)-iron II complex,

produced by the exchange reaction between the reagent

ferroin and cyanide.

38

Indirect spectrophotometric determination of

cyanide have come up quite rapidly. It has been reported

by Wronski (55), Yamasaki and Ito (56), Ohlweiler and

l':editsch (57) and Gregorowicz et al. (58).

Of late, many more such methods have been

developed which are very sensitive for cyanide determi­

nation but tedious too. Dagnal et al. (59) made use of

the inhibiting effect of cyanide ion on the formation of

the blue colour in neutral aqueous solution of silver/

1:10 phenanthroline, bromopyragallol red complex.

Wei-Fu Sheng et al's (60) paper reported that the

supression of the reaction of 2-(5-Br-pyridyl azo)-5-

diethyl aminophenol with Ni2+ can be used to determine

cyanide, It was found that Cu(II), chromazurol S(I) and

excess of cetyl pyridinium chloride (II) formed a stable

aquo red complex suitable for determination of cyanide(61).

Other reagents for indirect spectrophotometric determi­

nation are Cadion 2B in presence of Triton X-100 (62,63),

5-phenyl azo-8-amino quinoline (64), (C.I. Mordent Blue 29)

hexadecylpyridinium complex (65) and copper(II)-2, 2'­

bipyridyl ketone-2-pyridyl hydrazone (66). Ultra violet

methods for the determination of cyanide has also been

cited in the literature (67,68),

2) Colourimetric methods based on Konig reaction,

For the detection and determination of amall amounts of

cyanide in trade wastes and effluents and for water

(69,70) are based on the colourimetric procedure developed

by Alridge (71, 72) which is an example of Konig synthe­

sis (73) and Epstein (74). The best known spectrophoto­

metric methods for the determination af cyanide are

based on the formation af cyanogen bromide or cyanogen

chloride, which then reacts with pyridine to yield

glutaconic aldehyde ;, " .. :: which is then subsequently

39

condensed with pyrazolone (74), benzidine (75), p-phenylene-'

diamine (76), barbituric acid (77), o-dinitrobenzene (78),

isonicotinic acid-barbituric acid (79), dicarboxidine(BO),

ethyl acetone or benzoyl acetate (81). Many of these

reagents viz. benzidine, p-phenylenediamine are themselves

carcinogenic and hence their use is not desirable,

Scanning the literature :'. , reveals that still

there is need of more selective, sensitive and simple

methods for the determination of cyanide which can be

carried out with considerable ease, and also without the

use of any carcinogenic reagent. In this search, a new

method has been developed in which the determination of

cyanide is carried out by converting cyanide into cyano-

gen bromide followed by the reaction with pyridine. The

glutaconic aldehyde so formed is condensed with anthra­

nilic acid, a non-toxic and easily available compound,

forming a yellow-orange dye, which is measured at 400 nm.

The Beer's law is obeyed in the range of 1-7 ppm. The

optimum reaction conditions and other analytical para­

meters have been investigated. The method is success­

fully applied to the determination of cyanide in

biological samples.

EXPEaiMENTAL

~paratus:

An ECIL Model GS-865 spectrophotometer and Carl­

Zeiss spekol were used with 1-cm matched silica cells

for all spectral measurements.

Reagents:

Standard cyanide solution - ~5C.mg of potassium cyanide

was dissolved in 100 ml of de-ionised water to give a

solution of concentration 1 mg/ml. Appropriate dilution

of the stock solution was made to give a working standard

of 10 fg/ml.

Pyridine reagent - 3 ml of concentrated hydrochloric

acid was mixed with 18 ml of freshly distilled pyridine

and 12 ml of deionised water was added to prepare the

reagent.

Sodium arsenite solution- A 1.5% (w/v) solution of

sodium arsenite was prepared in deionised water.

Anthranilic acid A 0.1% (w/v) solution of anthranilic

acid was prepared in deionised water.

40

41 Uromine water - A saturated solution of bromine water

was prepared.

All chemicals used were of AnalaR grade and

solutions were prepared in deionised, deareated water.

Procedure:

An aliquot of aqueous sample containing 10-70 pg

(1-7 ppm) of cyanide was taken in a 10 ml volumetric

flask. To it 0.3 ml of saturated bromine water was

added and the mixture was allowed to stand for 1 minute

for complete bromination. The excess of bromine was

decolourised by dropwise addition of sodium arsenite

solution. Then 0.4 ml pyridine reagent followed by 1 ml

of anthranilic acid solution were added. The mixture

was allowed to stand for 10 minutes for full colour deve­

lopment. The volume was then made upto the lllll.rk and the

absorbance was measured at 400 nm using distilled water

as reference. The same procedure was followed for the

blank, which gave no colour under these conditions.

~ULTS M~D DISCUSSIONS

Spectral characteristics:

The absorption spectra of the dye is shown in

I!'ig. 1. The spectra shows a maximum absorption at 400 nm.

The reagent blank has negligible absorption in this range.

Effect of Varying Reaction Conditions:

For bromination the amount of bromine water

needed was checked by adding various amounts of saturated

42

O.B ..-------------------------,

0.7

B 0.6

0.5 w u z <{

~ 0.4 A 0

(f)

m <{

0.3

0.2

0.1

350 3 75 400 425 450 475 500

WAVELENGTH nm

FIG.1. ABSORPTION SPECTRA OF THE DYE A. CONCENTRATION OF CYANIDE= 30J..tg/10ml. B. CONCENTRATION OF CYANIDE= SOJ...tg/1 Om!.

bromine water. i. minimum 0.2 ml of bromine water was

needed for complete bromination of the cyanide to

cyanogen bromide (Fig. 2). An excess of bromine caused

no effect as the excess was decolourised with sodium

arsenite solution.

43

Sodium arsenite solution was added dropwise until

the bromine was decolourised. In the range of 0.2 to 1 ml

of 1.5% sodium arsenite solution, no change in the absor­

bance values were observed (Fig. 3). Decrease in the

absorbance was marked when more than 1 ml of sodium

arsenite was added.

The amount of pyridine reagent needed for the

conversion of cyanogen bromide into glutaconic aldehyde

was also checked. A minimum of 0.2 ml of pyridine

reagent was needed for the reaction. Addition upto 1 ml

of pyridine reagent had no noticeable effect on the

absorbance but above 1 ml there was decrease in absorb-

ance (Fig. 4).

It was found that constant absorbance values

were obtained with the addition of volumes of 0.1%

anthranilic acid solution from 1 to 5 ml (Fig. 5).

The effects of time and temperature on the

colour development were studied, It was observed that

10 minutes were needed for full·colour development

(Fig. 6) and the colour remained stable for 15 minutes 0 in the range of 15-35 c. At higher temperature there was·

a decrease in absorbance (Fig. 7).

,, .

44

0 7 E ., c 06 "" "' C)

0

'"~ 0 5 1-w u z 04 <( m a:: 03 0 (f)

m 0 2 <(

0 1

0 7 E c 0 6

C)

C)

'" 0 5 ~

w u z 0 4 <(

~ 0 3 0 (f)

m 0 2 <(

0 1

' ' ' 0.1 o.2 o.3 o.L. o.5 o.6 o.? o.e

AMOUNT OF SATURATED BROMINE WATER,ml

FIG. 2. EFFECT OF BROMINA TION CONCENTRATION OF CYANIDE= 50,Ltg/10ml.

0.2 0.4 0.6 0.8 1.0 1.4 1.6 AMOUNT OF 1.5% SODIUM ARSENITE SOLUTJON,ml J:·

FIG.3. EFFECT OF SODIUM ARSENITE ON COLOUR REACTION CONCENTRATION OF CYANIDE=50).!g/10ml.

0 7 E c 06

0 0

"· 0 5 w u

0 4 z < CD

03 0:: 0 lfl CD 0 2 <

0 1

0.2 0.4 0.6 o.s 1. 0 1.2 1 . 4 AMOUNT OF PYRIDINE REAGENT, ml

FIG.L.. EFFECT OF PYRIDINE ON COLOUR REACTION CONCENTRATION OF CYANIDE=50}Jg/10.ml.

0 7 ~ E c 0 6 1- "' 0

0 0

"· 0 5 1-w u

041-z < CD

031-0:: 0 lfl CD 021-<

0 1

' '

0.5 1.0 2.0 3.0 4.0 5.0 6.0 AMOUNT OF 0.1% ANTHRANILIC ACID,ml

45

FIG. 5. EFFECT OF ANTHRANILIC ACID ON COLOUR REAC­TION

CONCNTRATION OF CYANIDE= 50J.Igl10ml.

0.7 E c 0 6 C) •

C)

....r, 0.5 w u z 0.4 <(

CD a: 0.3 0 ln

CD 0.2 <(

0. 1

0.7

E c 0.6

C)

C)

....r._ 0 5 w u z 0.4 <(

CD a: 0.3 0 ln CD 0.2 <(

0.1

46

2 4 6 8 10 12 14 16 18 20 22 24 26 28 30

FIG.6. EFFECT OF TIME (minutes) ON COLOUR DEVELOP­MENT

CONCENTRATION OF CYANIDE,50).lg/10ml.

\

5 10 15 20 25 30 35 40

FIG. 7. EFFECT OF TEMPERATURE (C) ON COLOUR DEVELOP­ME NT, CONCENTRATION OF CYANIDE, 50JJ9 /10m!.

Beer's Law, fY,olar Absorptivity, Sandell's Sensitivity

and neproducibility:

The colour system was found to obey Beer's law

4'i

in the range of 10 to 70 fg per 10 ml o! cyanide solution,(Fi~·fi).

The molar absorptivity and Sandell's

found to be 3.12x103 l.mol-1cm-1 and

sensitivity were -2 0 .0083 ,Pg em

respectively. The reproducibility of the method was

checked by seven replicate determinations (Table I).

The standard deviation and relative standard deviations

computed from the results in Table I were found to be

0.01 and 0.15% respectively.

Effect of Foreign Species:

Interferences from organic pollutants viz.

benzene, phenol, ethanol, benzaldehyde, etc. and metal

ions such as zinc, cadmium, lead, mercury and iron were

not observed, Oxidising and reducing agents if present

in small amounts, are removed by sodium arsenite and

bromine water, respectively. The tolerance limits for

diverse species ar8 shown in Table II.

iU?Plication of the Meth2,!!:

The method has been applied to the detection of

cyanide in urine and whole blood, Several samples of

urine and blood were tested and were found to be free of

cyanide. Known amounts of cyanide were therefore added

to these samples and they were analysed by the above

procedure and Alridge's method (71) after deproteini­

sation with trichloroacetic acid (71). The results in

E c

0 0

O.B

0.7

0.6

"' ~ 0.5 w u z ~ CD 0:: 0 .L, 0 {/)

CD <(

0.3

0.2

0.1

10 20 30 40 50 60

CYANIDE CONCE NTRATION,ttg /10 ml

FIG. 8. CALIBRATION CURVE FOR CYANIDE.

48

70

TABLE - I

HEljHOWCIBILITY OF THE METHOD

Concentration of cyanide - 30 pg/10 ml

-------------------------------------------------------Serial

No. Absorbance max - 400 nm

-------------------------------------------------------1 0.36

2 0.35

3 0.35

4 0.36

5 0.37

6 0.35

7 0.37

Mean = 0.36

Standard deviation = 0.01

Relative standard deviation = 0.15 96

-------------------------------------------------------

49

TABLE - II

EFFECT OF FOREIGN IONS

Concentration of cyanide - 40 pg/10 ml

y------------------------------------------------------Foreign Ions (Tolerance limit in ppm)*

-------------------------------------------------------Benzene (2000), Phenol (1000), Benzaldehyde (800),

Ethanol (1200), Aniline (500), Nitrobenzene (100),

Formaldehyde (700), Hydroxylamine (500), Zn2

+ (200),

Cd2+ ( 100) 1 Pb2+ ( 150), Hl+ ( 100), Fe2+ (250) 1

eu2+ (300), K+ (500), Na+ {500), soz- (350),

Thiocyanates - interfere.

-------------------------------------------------------* Amount of foreign species that cause z 2% error.

50

Table III a & b show that the recoveries !rom urine and

whole blood samples were about 95 and 98% respectively,

which is in agreement with the results of Alridge's

method.

CONCLUSIOti

The method is simple, sensitive and rapid, No

use is made'of carcinogenic compounds and it can be

successfully applied for the detection of cyanide in

biological fluids.

I QMIIIIIIJIIIIIIIWI m" 1~1 "~ T 8492

51

TABLE - III

RECOVEJW OF CYANIDE FROf/1 BIOLOGICAL FLUIDS

----------------------------------------------------------Sample Cyanide Cyanide

No. added/fg found by present method*

Recovery Cyanide Recovery % found by %

Alridge' s method *

pg ?g ----------------------------------------------------------

1

2

3

4

1

2

3

4

{a) VOLU!'lE OF URINE SAMPLE

15 14.25 95.0

30 28.45 94.8

45 42.80 95.2

60 56.15 93.6

(b) VOLUME OF BLOOD SAMPLE

15 14.78 97.9

30 29.45 98.2

45 44.10 98.0

60 58.30 97.2

- 1 ml.

14.25 95.0

28.55 95.2

42.75 95.0

56.10 93.5

- 1 ml.

14.70 98.0

29.35 97.8

44.20 98.2

58.50 97.5

---------------------------------------------------------- •'

* Mean of three repetitive analyses.

52

1 •

2.

4.

5.

6.

7.

8.

9.

REFERENCES

F.A. Patty, "Industrial Hygiene and Toxicology", Second Edition( Vol. II, Interscience, New York (1962) 1991-97.

M.B. Jacobs, "The Analytical Toxicology of Industrial Inorganic Poisons", Vol. 22, Interscience, New York (1967) 721.

W. Leithe, "The Analysis of Air Pollutants", Ann Arbor Science Publishers, Ann Arbor, 1971, 226.

World Health Organization, "International Standards for Drinking Water," WHO, Geneva (1958),

J. Liebig, Annalen, 77 (1851), 102; J. Chern. Soc., 4 (18'52) 219.

J .E. Clennel, · "Chemistry of Cyanide solutions", Me Graw Hill Book Co. Inc., New York, 1910.

I.JVJ. Kolthoff, and E.B. Sandell, "Text Book of Quantitative Inorganic Analysis", The Macmillan Co., New York (1943) 497 and 574. ·

I .M. Kolthoff and V .A. Strenger, "Volumetric Analysis11 , Inter science Publishers Inc., New York, Vol. II, (1947) 227.

R.M. Wick, Bur. Stand. J, Res., 7 (1931) 913.

M.R. Thompson, Bur. Stand. J. Res., 6 (1931) 1051.

E. Beeratrecher, Analyst, 12 (1950) 280.

53

10.

11 •

12. J.A. Ryan and G.W. Culshaw, Analyst, £2 (1944) 370.

13. American Public Health Association, "Standard Methods for the Examination of \Vater, Sewage and Industrial 1-lastes", 10th edn., New York ( 1955) •

14. A. Saeka, Metal Finishing, 58 (1960) 59.

15. F .I"i. Vydra and R. Pribil, Coli. Czech. Chern. Commun., 26 (1961) 2449; Anal. Abstr., 2 (1962) 1801.

16. M. Wron'ski, Analyst, 84 (1959) 668.

Y. Tanaka and s. Yamamoto, Japan Analyst, 2 (1960) 6; Anal. Abstr., ~ (1961) 4547.

17.

18, z. Gregorowicz and F. Buhl, z. Anal. Chern., _173, (1960) 115.

19. I. Kraljic, Acta Pharm Jugosl., 10 (1960) 37; Anal. Abstr., 9 (1962) 2253. --

20. A, Besada, Y.A. Gawargious, B.N. Faltaoos and M,l?. El Shanat, Mickrochim, Acta, 2. (1983) III, 197.

21.

22.

23.

24.

25.

26.

27.

28.

29.

30.

31.

32 0

33.

34.

V. .D. Treadwell, E. Muller and H.Z. Lanterbach, z. anorg. Chern., 121 (1922) 178.

W. Clark, J. Chern. Soc., ~ (1925) 749.

J .0. Egekeze and 'li ,F, Oehme, J. Anal. Toxicol., 2 (1979) 119; Anal. Abstr,, 2§ (1980) 401.

H.A. Laitinen, W.P, Jennings and T.D. Parks, Ind. Eng. Chern. Anal. Ed., ~ (1946) 574.

J .A, !llcCloskey, Anal, Chem., 33 ( 1961) 1842.

B. Pihlar, L. Kosta and B. Hristovski, Talanta, 26 (1979) 805.

J .H, Karchrner and Jill, T. vlalker, Anal, Chern,, 27 (1955) 37.

J. Hetman, J, Appl, Chern., 10 (1960) 16.

K.G. Woolmington, J. Appl. C.hem., 11 (1961) 114.

C.R. Schneider and H. Freund, Anal. Chern., 34 (1962) 69.

H. Honma, K. suznki, :IJI. Yoshida and H. Yanashima, Bunseki Kagaku, 28 (1979) 56; Anal. Abstr., 39 ( 1 980) 14 0 --

J .E • .l?asken, J. Amer. Wat. Wks. Assn., 32 (1940) 487.

R.A. Fulton and M. Van Dyke, Anal. Chern., 19 (1947) 922.

A.O. Gettler and I. Goldbaum, Anal. Chern., 19 (1947) 270.

35. E. Rathenasinkam, J. Proc. Chern. India, 18 (1946) 151.

54

36. A. Steverts and A. Hermsdro!, z. Angrew. Chern., 2:t (1921) 3.

37. J:i', Feigl, "Spot Test on Inorganic Analysis", 5th ed., Elsvier Publishing Co., Amsterdam, New York and London (1958) 276.

38. R.I. Nicholson, Analyst, 66 (1941) 189.

39. W.A. Hobbie, Arch. Riceham, 5 (1944) 49.

40. P. Quispe, A. Luis, L. Frisancho, I, Maria and L.E. Juscamayta, Bol. Soc. Quim., ~ (1982) 148; Chern. Abstr., 99 (1983) 145794,

41. H, Heidrich, GerrnanPatentN0 • 1,105 (1961) 199.

42, F. J:i,eigl and H.E. Feigl, Anal. Chim, Acta, 3 (1949) 300.

43. R.c. Voter, c.v. Banks and H. Diehl, Anal. Chern., 20 (1948) 458 & 632.

44. F. Feigl and G.B. Hesig, Anal. Chim. Acta, 3 ( 1949) 561.

45. M. Brooks, Anal, Chern,, 24 (1952) 583.

46.

47.

48.

49.

51.

52.

53.

54.

55.

J.s. Hanker, A. Gelberg and B. Witten, Anal, Chern., 2Q (1958) 93.

K.T. Kokai (Cl. G. 01N31/22), Appl, 81/189 954; Chern. Abstr., 99 (1983) 27779.

( 1981)

s. Hikima and H. Yoshida, Bunseki Kagaku 1Q (1961) 832; Chern. Abstr., 56 (1962) 5659,

Y. Tanaka and s. Yamamoto, Japan Analyst, 9 (1960) 8; Anal. Abstr., ~ (1961) 4546.

Y.s. Verma, I.S. Singh, B.S. Garg and R.P, Singh, Nikrochim. Acta, I, 5-6 (1979) 445.

JI'I.c. Roman, F .J Vinagre and J .A. l~unozlayva, Microchem. J,, 27 (1982) 265.

F. Buhl and K, Kania, Chern. Anal. (Warsaw), 24 (1979) 689.

J.c. Martinez, F.R. Borch and M.C. Garcia, Alvarez Coque, Talanta, 29 (1982) 139.

A.A. Schilf, Anal. Chern., 30 (1958) 1409.

M. Wronski, Chern. Anal. (Warsaw), 5 (1960) 457.

55

56. J, Yamasaki and K. Ito, J Chem. Soc. Japan, Pure Chern. Sect., 80 (1959) 271; Anal, Abstr., 1 (1960) 920, -

57. O.A. Ohlweiler and J,O, Meditsch, Anal, Chem., .2Q (1958) 451.

58. z. Gregorowicz, F. Buhl and E. Shwa, Z. Anal. Chem., 186 (1962) 407.

59. R.M. Dagnall, !'i,T, El-Guamry and T.S. West, Talanta, 15 {1968) 167.

60, F.s. Wei, Y,Q, Liu, F', Yui and N.K. Shen, Talanta, 28 (1981) 694.

61. Y. Zhu and h. Qi, Fenxi Hau.xue, 9 (1981) 692; Chern, Abstr., 97 (1983) 119677. -

62. Wei Fusheng and Yin Fang, Talanta, 2Q ( 1983) 190.

63. Wei Fu Sheng, Han Bai and Shen Naikei, Analyst, 109 (1984) 167.

64. M. Blanco and S. Maspoch, Talanta, 31 (1984) 85.

65. Y. Zhu and W, Qi, Fenxi Hauxue, 9 (1981) 692; Anal, Abstr., 43 (1982) 131. -

66, G.S. Vasilikirtis and J.A. Stratis, Microchem. J,, 29 (1984) 209.

67. E.O. Umeh and o.o. Fadiya, Talanta, ~ (1979) 1155.

68. R.E. Humphrey, ~.G. Ingran and A.D. Waak, Microchem. J., 24 (1979) 92;

69. s.c. Jolly, Editor, "Official Standardised and Recommended Methods of Analysis", Heifers, Cambridge, for Society of Analytical Chemistry, London (1963) 253.

70. American Public Health Association, American Water Works Association and Water Pollution Control Federation, 11 Standard Methods for the Examination of Water and Waste Water11 , Eleventh Edition, American Public Health Association, Washington,D.C., 1960, Parts III & IV.

71. W.N. Alridge, Analyst, 69 (1944) 262,

72. W .N. AFidge, Analyst, 70 ( 1945) 474.

73. ~~.Konig, z. angrew Chern., (1905) 115; J, prakt. Chern., 69 (104) 105.

56

74.

75.

76.

J, Epstein, Anal, Chern., 12 (1947) 272.

H.G, Higson and L.s. Bark, Analyst, 89 (1964) 338.

L.s. Bark and H.G. Higson, Talanta, 11 ( 1964) 621 •

57

77. E. Asirnus and H.Garschagen, Fresenius z. Anal. Chern., .12§ ( 1954) 414.

78, G.G. Guilbault and .Ll,N, Kramer, Anal. Chem., 38 (1966) 834.

79. Xiang Guangming, Fenxi Huaxu~, 12 (1984) 159; Chern. Abstr., 100 (1984), 179854:-

80. K, Groningsson, Analyst, 104 (1979) 367.

81. P, !Vlalatesta and G. Ceccarini, Boll. Chirn. Farm., 120 (1981) 681; Chern. Abstr., 22 (1983) 32.