Spectrophotometric Determination of Gold, Copper, and Cobalt M. H. HASHMI, ABDUR RASHID, MOHAMMAD UMAR, and FAROOQ AZAM West Regional Laboratories, Pakistan Council o f Scientific and Industrial Research, Lahore, West Pakistan
b Formic acid hydrazide reacts with gold, copper, cobalt, and nickel in acid medium to give violet, pink, blue, and violet colors having a visual limit of identification at 2, 30, 60, and 100 pg. per ml., respectively. This color reaction provides the basis of a new method for colorimetric determination of gold and spectrophotometric determination of copper and cobalt. Nickel cannot be determined with this color reaction because of low sensitivity. The maximum tolerable limit of various ions i s reported. The mechanism of the color reaction i s not clear.
0.15 t
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400
500
600
700
Wave Length
D
mfi
Figure 1. Absorption spectra of formic acid hydrazide complexes with copper and cobalt
a systematic study of the action of organic reagents on inorganic compounds, it was found that acid hydrazides forin rolored complexes with gold, copper, and cobalt in acid medium. The color thus produced is morc senqitive with formic acid hydrazide than any other acid hydrazide. Reference to the literature indicates that this color reaction has not been reported previously ( 1 , 2 ) . This color reaction of forinic acid hydrazide provides the baeis of a new iiiethod for the colorimetric determination of gold and the spectrophotometric determination of copper and cobalt. S o doubt, the colored complex is also formed with nickel, but the reaction is not very sensitive. Hence this color reaction cannot be used for the determination of nickel. Organic compounds (except aldehydes) do not interfere with the determination. The maximum tolerable limit of various URIXG
metal ions which do not interfere is reported. The mechanism of the color reaction is not clear. EXPERIMENTAL
Materials. -ill reagents were of analytical grade or comparable purity. All acid hydrazides except isonicotinic acid hydrazide mere prepared (4) and purified by recrystallization from alcohol. Apparatus. A11 absorbance ineasurements for the determination of gold were made with a n S P 1300 Unicam colorimeter, using filter No. 1 and 1-cm. cells. Copper and cobalt mere measured with S P 600 Unicain spectrophotometer using 1-cm. cells. The p H meter was a Pye Dynacap, and graduated pipets, accurate to &0.005 nil. w r e used. I
Procedure. COBALT. To a solution containing 300 to 1500 p g . of cobalt, 0.1 ml. of 0.25N sulfuric acid is added and the volume is made to 8 ml. with distilled water. To it 2 ml. of 10% formic acid hydrazide solution is added.
Table II. Quantitative Assessment of Tolerable Amounts of Different Ions
Ion
Na + K+ Ag Fe Hg:2 Ca + * +
Color Reaction of Metal Ions with Different Acid Hydrazides"
Metal ion
Color
Gold Cobalt
Violet
2
2 80 _.
Bluk Violet
30 ~. 60 100
Copper
Sickel
Pink
Formic
Visual limit of identification, ___-- pg./ml. Oxalyldihydra- IsonicoAcetic Propionic Xalonic zide tinic SO 200
3 8n _.
SO 200
Benzoic and salicylic acid hydrazides give no color.
4
4
2
120
120 __.
60 200
120
...
150
200
- ~ .
40 ~-
Maximum amount not interfering,&70 Gold Copper Cobalt 200.0
200.0 0.5 0.5 0.5
200.0
300.0 300.0 5.0 300.0 300.0 300.0 300.0 300.0 300.0
200.0 200.0 0.2 0.5 0.5 10.0
10.0 200.0 10.0 Sr -L2 200.0 0.5 0.5 Hg +? 250.0 250.0 5.0 Pb +2 Cd + 2 100.0 100.0 10.0 Zn +2 500.0 300.0 5.0 ?.In+? 5.0 150.0 10.0 Sn T2 1.0 5.0 2.0 A1+ 3 300.0 10.0 500.0 Bi+3 2,i.O 300.0 5.0 Sn-'A 1 .o 5.0 2.0 a Three solutions containing 200, 2000, and 2000 pg. of gold, copper, and cobalt taken and different amounts of various com ounds added under experimental conchions of temperature and pH. Percentage of various ions is with respect to amount of gold, copper, and cobalt. Ba + 2
Table I.
I 800 900
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The solution, which has a final volume of 10 ml. and a p H of 3.0 to 4.5, instantly becomes pink. The color intensity remains constant for more than 6 hours a t room temperature. Absorbance is measured a t 480 mp. COPPER. The procedure for the determination of copper is the same as for cobalt, except that 1 ml. of 0.25,V sulfuric acid is added. The solution, which has a final volume of 10 ml. and a p H of 2.4 to 3.7, instantly develops a blue color. The color intensity remains constant for more than 6 hours a t room temperature. Absorbance is measured at 630 mp. GOLD. The procedure for the determination of gold is the same as for cobalt, except that 0.1 ml. of 0.025N sulfuric acid is added, so that the p H of the final solution lies between 5.4 and 5.9. The color intensity remains constant for about 1 hour. Since no maximum is obtained with the violet color produced with gold, the absorbance measurements were made by a n SP 1300 L-nicam colorimeter using filter KO.1. The experiment was repeated with different volumes of gold solution, and a calibration curve was prepared. The color reaction obeys Beer’s law. When determining the maximum tolerable amount of different metal ions (cf. Table 11), the p H of the solution is adjusted with dilute nitric acid in the case of those metal ions where addition of sulfuric acid might result in precipitation.
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Figure 3.
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ANALYTICAL CHEMISTRY
6
Effect of pH on color intensity 0 Copper 0 Gold
h Cobalt
Table 111.
Determination of Gold, Copper, and Cobalt from Pure Solution and in Presence of Other Ions
Metal ion to be determined Gold
Compounds present in addition to metal ion to be determined ...
Other metal ions present, with respect to metal ions to be determined, Metal io11 determined, W/nll. W /C Present Found 2.0 ... 2.0 ...
. . I
Silver nitrate
Cobalt
, . .
200.0 300.0
Stannous chloride
1.0
... ...
fiIangaileke sulfate
150:o
Aluminum nitrate Mercurous nitrate
150.0 150.0
Calcium nitrate ...
150.0
...
... Mercurous nitrate
5.0 10.0
5.0 10.0
10.0
10.0
20.0
20.0
30.0 50.0 80.0
30.0 50.0 80.0
100.0
100.0
40.0
40.0
80.0 95.0 120.0
50.0 95.0 120.0
100,o
100.0
200.0
200.0
0.5
Strontium nitrate Zinc nitrate Copper
RESULTS AND DISCUSSION
The visual limit of identification of gold, cobalt, copper, and nickel with different acid hydrazides is given in Table I. The reaction is most sensitive with formic acid hydrazide, which is therefore used in all determinations. The color reaction is more sensitive with gold than with copper and cobalt. The limit of identification of gold, co-
4 PH
... ...
... 0.5
Barium nitrate Cadmium nitrate
10.0 10.0
Bismuth nitrate
5.0
balt, and copper is not affected by the addition of other metal ions, provided they are not present in more than the maximum tolerable amount (cf. Table 11)* The color reaction between cobalt and copper has maxima at 480 and 630 mp, respectively (Figure 1); hence, all absorbance measurements were carried out a t these wavelengths. The effect of temperature and pH on color intensity is given in Figures 2 and 3. The interference due to various inorganic and organic compounds was qtudied and it was found that aromatic or aliphatic aldehydes which give a yellow color with formic acid hydrazide interfere with the determination of gold. The interference caused by various cations and anions under the
experimental conditions was studied, and a quantitative assessment of the tolerable amounts of different ions is given in Table 11. The results for the determination of gold, copper, and cobalt with formic acid hydrazide in pure compounds as well as synthetic mixtures are given in Table 111, which indicates that these metals can be determined accurately. I n analyzing synthetic mixtures, the amount of other metal ions present must not exceed the maximum tolerable amount (cf. Table 11); otherwise the accuracy of the procedure will be affected. The reaction between formic acid hyrazide and gold consists in the formation of colloidal gold, while with copper, cobalt, and nickel, colored complexes are probably formed (the mechanism
is not very clear). However, the present reaction has no similarity to the color reaction between copper and oxalyldihydrazide in the presence of aldehyde and ammonia (3). The color produced by formic acid hydrazide with gold, copper, cobalt, or nickel disappears on addition of a small amount of aliphatic or aromatic aldehyde. LITERATURE CITED
(1) Beamish, F. E., As.4~. CHEM. 33,
1059 (1961).
(2) Beamish, F. E., Talanta 8 , 8 5 (1961). (3) ~, Stark. G. R.. Dawson. C. R., ANAL. CHEM.30, 191‘(1958). ‘ (4)Vogel, A. I., “Practical Organic Chemistry,” p. 395, Longmans Green,
London, 1956.
RECEIVEDfor review August 5, 1965. Accepted December 30, 1965.
Determination of Coal in Formalin-Fixed Pneumoconiotic Lungs N e w Method of Tissue Digestion Using Glacial Acetic Acid IMANUEL BERGMAN Safety in Mines Research Establishmenf, Ministry o f Power, Sheffield 3, England
b Treatment with hot glacial acetic acid containing ammonium acetate is a convenient method of digesting formalin-fixed lung tissue. A short treatment with formic acid completes the digestion. This procedure forms the basis of a new method for the quantitative isolation of coal from pneumoconiotic lungs. Even the reactive bituminous coals are recovered in good yield. The method compares favorably with a number of other procedures. Minerals such as kaolin and mica are recovered in good crystallographic state, while calcifications and iron deposits are removed.
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United Kingdom pneumoconiosis is a condition found mainly in coal miners. The dusts to which the miners are exposed consist mainly of various types of coal, as well as of clay minerals such as kaolin, mica, and quartz. The post-mortem analysis of lungs of pneumoconiotic coal miners has been carried out for over two decades, with the aim of correlating the observations of radiologists and pathologists with the types and amounts of minerals involved. The quantitative determination of coal in formalin-fixed lung tissue preN THE
sents some difficulties, as the resistance of coal to various digestion procedures can vary considerably with the region and the seam from which it comes. I n general, the “low rank” bituminous coals, with a high content of volatile matter, are more reactive than the “high rank” anthracites, which have a low volatiles content. The greatest incidence of pneumoconiosis in Great Britain is in South Wales, where the coal mined is predominantly of high rank, and nearly all the lungs studied initially were from this area. A method developed in the late E, J. King’s laboratory, for the digestion of dried ground lungs in hot alkali, gave complete recoveries of anthracite ( 5 ) . A comparatively high rank bituminous coal from South Wales lost about 5% in the digestion, though the loss might have been higher had the sample been as fine as respirable dust. I n recent years formalin-fixed lungs of miners exposed to low rank coals have become available. I n the present investigation various digestion procedures have been tested on these lungs, on low rank coal powders of respirable size and on dust-free formalin-fixed lung tissues. One of the most common methods for the hydrolysis of tissue is heating in 6N hydrochloric acid ( 1 ) . This solution
was tested a t temperatures ranging from 105’ to 140’ C., in the presence of various amounts of stannous chloride, and before and after the treatment of the tissue with lipid solvents. A procedure, developed a t the Pneumoconiosis Research Unit of the Medical Research Council, for the hydrolysis of defatted rat lungs in 12N hydrochloric acid a t 60’ C. (6) was also tested. Enzymatic methods were discarded after a few preliminary tests, for although a number of commercially available crude mixtures of proteolytic enzymes were effective in dissolving alcohol-fixed lung tissue, they were not effective in dissolving formalin-fixed tissue. Thomas and Stegemann (8)developed a method for the digestion of lung tissues in formamide a t 135’ C. They also noted that formic acid and hydrofluoric acid can be used to digest tissue. Einbrodt (3) used a formamide digestion, followed by a formic acid treatment to remove the remaining traces of tissue. Formamide, formic acid, and hydrofluoric arid digestion procedures have been tested in the present work. As part of the development of an analytical method for blood in formalinfixed lungs, it was discovered that the lung tissue would dissolve if heated in VOL. 38,
NO. 3,
MARCH 1966
441
