Rapid Field and 

Laboratory Method for 

the Determination of 

Copper in Soil and Rocks

GEOLOGICAL SURVEY BULLETIN 1036-A

Rapid Field and 

Laboratory Method for 

the Determination of 

Copper in Soil and Rocks

By HY ALMOND

A CONTRIBUTION TO GEOCHEMISTRY

GEOLOGICAL SURVEY BULLETIN 1036-A

UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON : 1955
UNITED STATES DEPARTMENT OF THE INTERIOR 

Douglas McKay, Secretary

GEOLOGICAL SURVEY 

W. E. Wrather, Director

For sale by the Superintendent of Documents, U. S. Government Printing Office 

Washington 25, D. C. - Price 10 cents
CONTENTS

Page

Abstract- _________________________________________________________ 1

Introduction. _____________________________________________________ 1

Experimental data.__________________________-_^-_----_-_-_-------- 3

Reagents and apparatus.__________________--_-_-__------_----_-_-_- 3

Field method procedure____________________________________________ 4

Rapid laboratory procedure_________________________________________ 6

Results ___________________________________________________________ 6

Literature cited_ __________________________________________________ 8

ILLUSTKATION

FIGURE 1. Digestion and fusion rack shown with a gasoline stove and

covers--__ ___________________________________________ 5

344573 55

A CONTRIBUTION TO GEOCHEMISTRY

RAPID FIELD AND LABORATORY METHOD FOR THE 

DETERMINATION OF COPPER IN SOIL AND ROCKS

By HY ALMOND

ABSTRACT

A rapid method for the determination of traces of copper in soils and rocks 

under field conditions and in the laboratory involves fusion of the sample with 

potassium bisulfate and estimation of copper with biquinoline in an isoamyl 

alcohol extract. The method is useful for prospecting and for gathering basic 

geochemical data. Only simple equipmnt is needed in the field. Because the 

reagent and copper complex are stable, the standard series for visual colorimetric estimation are prepared about once a month. The method is simple 

and about 60 to 80 determinations can be made per man-day under field conditions.

INTRODUCTION

Colorimelric reagents are used by the IT. S. Geological Survey to 

estimate the trace-element content of various soils, rocks, and other 

natural materials. The data collected aid in formulating basic geochemical principles and in prospecting. Until recently the reagents 

commonly used for the determination of copper have been diphenylthiocarbazone (dithizone), sodium diethyldithiocarbamate, and 

rubeanic acid, but each of these reagents has undesirable properties. 

Estimation of copper with dithizone, as described by Lovering, Huff, 

and Almond (1950), requires careful adjustment of the acidity of the 

solution to a pH of about 3. A lower pH requires shaking for more 

than 2 minutes to extract the copper; a higher pH results in interference from zinc. Oxidation of dithizone by sunlight or by ferric 

iron also causes difficulties (Sandell, 1950). Sodium diethyldithiocarbamate also has properties that are undersirable. Iron interferes 

unless properly complexed and even in the presence of large amounts 

of citrate, bismuth will invariably react with sodium diethyldithiocarbamate. This reagent must be freshly prepared because it may 

decompose to impart yellow products in the organic solvent that are
2 CONTRIBUTIONS TO GEOCHEMISTRY

reported as copper. Rubeanic acid has been used in. the Geological 

Survey's laboratory in Denver, Colo. as a confined spot test reagent 

for the determination of copper with the chromograph (Stevens and 

Lakin, 1949). This equipment must be kept in good working order 

to give accurate results, but proper maintenance of the chromograph 

is difficult under field conditions. The determination of copper with 

rubeanic acid by solution colorimetry is underisable because the complex is insuluble and, as far as known, nonextractable with organic 

solvents.

Breckenridge, Lewis, and Quick (1939) report that the reaction 

of copper (I) with biquinoline is specific for copper. Hoste (1950) 

states that biquinoline is superior to dithizone as a reagent for the 

determination of copper. A spectrophotometric method for the determination of coper with cuproine (biquinoline) is described by Hoste, 

Eeckhout and Gillis (1953). The determination was made on many 

kinds of material. Cheng and Bray (1953) used the reagent to determine copper in soils. They found that the copper complex is extractable into isoamyl alcohol with a maximum absorption at 540 mju,. 

Studies carried out by Cheng and Bray indicate interference from the 

following: citrate, concentrated ammonium hydroxide, ethylenediaminetetraacetate, oxalate, cyanide, thiosulfate, soluble silicate, 

bromate, iodate, ferricyanide, and cyanate.

By modifying the technique for sample decomposition and by using 

the standard-series method of estimation, biquinoline reagent was 

found to be suitable for the determination of traces of copper in soils 

and rocks under field conditions. The biquinoline method, as a field 

method for the determination of copper, has five distinct advantages 

over the dithizone method: (1) the pH of the aliquot taken is more 

easily adjusted, (2) the time that the buffered solution needs to be 

shaken with reagent is less, (3) the reagent is specific for copper, (4) 

the reagent and complex are more stable, and (5) the standard series 

has a greater range.

The rapid laboratory method and its field adaptation, both using 

biquinoline, are described below. A pyrosulfate fusion of a powdered 

soil or rock sample, followed by extraction into hydrochloric acid, 

dissolves essentially all of the copper. Neither sulfate nor chloride 

interfere with the biquinoline method, so this treatment is suitable 

for dissolving copper from soil or rock. Hydroxylamine is added to 

an aliquot to reduce copper (II) to copper (I), tartrate to complex 

iron and aluminum, and acetate to buffer the solution. The copper 

biquinoline complex is then extracted into isoamyl alcohol. Field 

and laboratory techniques differ only in that, in the former field 

stoves are used rather than Bunsen or Fischer burners, measurement of
RAPID METHOD FOR DETERMINATION OF COPPER 6

volumes is approximate rather than exact, and estimations are made 

by comparison with a standard series rather than instrumentally.

EXPERIMENTAL DATA

The fusion with potassium bisulfate followed by extraction with 

hydrochloric acid dissolves copper in soils and rocks. The final 

acidity of the hydrochloric acid solution has* to be such that on standing overnight the copper content of the solution will be the same as 

the copper content of the freshly prepared solution, because frequently 

the copper in samples is decomposed in the late afternoon of one work 

day and aliquots for estimation are not taken until the next morning. 

Replicates of a sample in 0.3 N hydrochloric acid analyzed within 

one hour after dissolving the copper and replicates of a sample 

analyzed after standing overnight show the result of too low an acidity 

as follows:

Copper content, in parts per million

1 Hour Standing overnight 

40 8

36 6

37 16

37 8

7

As can be seen, a significant loss takes place on standing overnight in 

this weakly acid solution. For this reason the extraction of the bisulfate melt is done with 3 ml of 6 N hydrochloric acid, which is then 

diluted to 10 ml with water. No losses of copper were detected when 

using this more acid solution in repeating the above experiment.

The use of a fixed volume of buffer to eliminate titration to a given 

pH is a timesaving step especially important for field analyses. An 

experiment was made to determine the amount of buffer needed per 

aliquot of test solution. One gram of potassium bisulfate was fused 

to a clear melt, cooled, dissolved in 4 ml of (1 +1) hydrochloric acid, 

and then diluted to 10 ml with water. Five milliliters of this solution 

with 10 ml of the buffer solution, described later, resulted in a solution 

of pH 4.4, a proper pH for the test. In the procedure, 10 ml of buffer 

is recommended to 2.5 ml of sample solution, allowing a considerable 

safety factor for variation of the acidity of the solution before the 

addition of the buffer.

REAGENTS AND APPARATUS

All reagents listed are analytical grade. Items needed for field use 

only are preceded by an asterisk (*), those needed for laboratory use 

only are preceded by two asterisks (**).
4 CONTRIBUTIONS TO GEOCHEMISTRY

Biquinoline (0.02 percent, W/V). Dissolve 0.2 gram of 2,2'-biquinoline in 

900 ml isoaniyl alcohol by warming in a beaker on a hot plate. Cool, make 

up to 1 liter with isoamyl alcohol in a 1-liter volumetric flask. The reagent 

in isoamyl alcohol should be colorless. If the solution is yellow, the reagent 

is impure and should not be used.

Buffer solution. Dissolve 400 grams of sodium acetate and 100 grams of 

sodium potassium tartrate in 1 liter of water. To 10 ml of the solution 

in a screw-cap culture tube add about 50 mg hydroxylamine hydrochloride, 

mix to dissolve, then add 1 ml of 2,2'-biquinoline reagent. Screw the cap 

in place and shake 2 minutes. If no pink appears in the organic phase, the 

buffer is free of copper contamination and is satisfactory for use in the 

procedure described.

Hydroxylamine hydrochloride.

Potassium pyrosulfate.

Hydrochloric acid (1+1). Add 500 ml of concentrated hydrochloric acid to 

500 ml of metal-free water.

Standard copper solution 0.01 percent. Dissolve 0.2 gram of clear uneffloresced 

crystals of CuSCv5H2O in water, add 70 ml of concentrated hydrochloric 

acid, then dilute to 500 ml with water. One milliliter contains 100 micrograms of copper. Prepare more dilute solutions from this solution.

Culture tubes, 16X150 mm, borosilicate, marked at 3 and 10 ml.

Resin demineralizer. Pass stream water or tap water through a resin demineralizer to free it of heavy metals.

Sieve, 100-mesh sieve made of noncontaminating material.

Mortar and pestle, to grind rock samples.

Torsion balance. Sensitivity to 2 mg is satisfactory.

Pipets, serological; capacities 1.0 ml and 5.0 ml, both graduated at 0.1 ml.

Pipet, volumetric, 10-nil capacity.

Test tube rack, to hold 30-50 culture tubes.

*Automatic pipet, 2-nil capacity. Any simple, commercially available one is 

satisfactory.

* Screw-cap culture tubes, 25X100 mm.

*Digestion and fusion rack. This piece of apparatus, shown in figure 1, is 

used to support culture tubes over a gasoline stove. The rack consists of 

three disks of sheet steel 115 mm in diameter, welded to a central supporting 

rod 200 mm long. The upper and central disks have holes large enough 

for the culture tube to pass through. The lower disk has holes which are 

just small enough to prevent the culture tube from slipping through, but 

large enough to permit the ready flow of heat.

**Volumetric flask, glass stoppered, 25 ml.

**Automatic buret, 25-ml capacity.

* "'Cotton, absorbent.

**Filter paper, Whatman no. 42, 1-cm diameter.

**Funnels, 50 mm diameter, 50 mm stem.

**Colorimeter or spectrophotometer. The Beckman, model B was used with 

Corex absorption cells at 10 mm light path. Any such instrument is 

satisfactory.

FIELD METHOD PROCEDURE

Place 0.1 g of minus-100-mesli soil or rock sample in a culture tube, 

add about 0.5 g potassium pyrosulfate, place in the fusion and digestion rack, and fuse over the gasoline stove (fig. 1) for several minutes.
RAPID METHOD FOR DETERMINATION OF COPPER

I

FIGURE 1. Digestion and fusion rack shown with a gasoline stove and covers. The covers

serve as hot-water baths.

Remove from heat, rotate the tube so that the melt solidifies in a 

thin layer on the walls of the tube, then cool and add 3 ml 6 1ST hydrochloric acid. Add water to the smaller cover of the stove, and warm 

over the gasoline stove. Place the culture tube in the digestion and 

fusion rack, then place the entire rack in the water bath so that the 

culture tube is immersed in the hot-water bath. Allow to remain in 

the hot-water bath until the melt is broken up. Then remove and 

dilute to 10 ml. Mix the solution.

Transfer a 2.5-ml aliquot to a screw-cap culture tube, add about 50 

mg of hydroxylamine hydrochloride, and allow to stand but shake 

occasionally until the hydroxylamine hydrochloride is dissolved. Add 

10 ml of buffer solution, then, using a plunger-type automatic pipet, 

add 2 ml of isoamyl alcohol containing biquinoline. (Avoid getting
6 CONTRIBUTIONS TO GEOCHEMISTRY

reagent in the rubber bulb of the pipet as this may contain copper.) 

Screw a polyethylene cap on the culture tube, and shake the tube 30 

seconds. Allow to stand about a minute or until the isoamyl alcohol 

phase separates, then compare with a copper biquinoline standard 

series.

Prepare copper standard series as follows: To a series of screw-cap 

culture tubes add standard copper solution equivalent to 0, 0.2, 0.4, 

0.7, 1.0, 1.5, 2.5, 4.0, 7.0, and 10 micrograms of copper. Dilute to 

about 5 ml with water, add about 50 mg of hydroxylamine hydrochloride, and proceed as in the previous paragraph. Loosen the 

polyethylene screw caps so that they do not freeze in place. New 

standards need be prepared not oftener than once a month.

RAPID LABORATORY PROCEDURE

Place 0.2 g mimis-100-mesh soil or rock sample in a culture tube, 

add 1.0 g of potassium pyrosulfate, and fuse. Remove from the flame 

and rotate the tube so that the melt solidifies in a thin layer on the 

tube. Add 4 ml N hydrochloric acid, place in a water bath, and digest 

until the melt is broken up. Filter into a 25-ml volumetric flask. 

Wash with hot water. Dilute to volume with water. Mix. Carry out 

the estimation within an hour after dilution.

Transfer a 5-ml aliquot to a separatory funnel. Add about 50 mg 

of hydroxylamine hydrochloricle, then 10 ml buffer solution. Add 

exactly 3 ml of isoamyl alcohol containing biquinoline from an automatic buret. Stopper and shake for 1 minute. Allow the solution to 

stand for about 5 minutes. Drain and discard the inorganic phase. 

Add about 0.5 ml water, shake, allow the layers to separate, and drain 

and discard the water. Insert a plug of absorbent cotton in the stem 

of the funnel. Drain the organic solvent into absorption cell, and 

determine the absorbance at 546 niju,.

RESULTS

The precision and accuracy of the field method were determined 

by analyzing 30 soil and rock samples by the carbamate laboratory 

method described by Holmes (1945). These samples were then 

analyzed by the field method in duplicate. The first 27 samples ranged 

from the highly silicic rocks to the basic rocks. With each fresh 

rock, the corresponding weathered rocks and overlying soils were 

analyzed. The results of the analyses are givren below.
RAPID METHOD FOR DETERMINATION OF COPPER 7

Comparison of results by laboratory and field methods of analysis

Sample

Copper content, in parts 

million

Laboratory

method 

(carbamate)

Field

method 

duplicates

(biquinoline)

Castle Rock rhyolite, fresh__ ____________________

Weathered-_____ _________________ ______ Soii_____-________________________________

Silver Plume granite, fresh_____________________

Weathered._______________________________

Soil___________________________

Pikes Peak granite, fresh._________ ____________

Weathered._______________________________

Soil_____.________________________________

Boulder Creek granite, fresh ____________________

Weathered _______________________________

Soil.____. _______________________________

Intermediate quartz monzonite (St. Vrain Canyon), 

fresh_______________________ __________ . Weathered._______________________________

Soil_____________________________ . Monzonite porphyry (Gold Hill), fresh_ _________

Weathered._____________________________

Soil______________________________________

Diorite (Jamestown), fresh____________ _______

Weathered_________________ ___ _________

Soil__________________ _______________

Basalt (Table Mountain), fresh_ __ _____

Weathered________________ _____ _______

Soil_____________ _________ ... . ________

Basalt (Ralston Dike), fresh. _ _ _. ...___________

Weathered._______________________________

Soil___________--______--_._______________

Eastern soil, composite A________ ______________

Composite B_______________________________

Boulder clay ___________________________________

3

1

17

13

19

17

8

10

11

38

9

29

35

21

10

9

11

32

82

83

65

58

45

57

42

56

360

60

30

8 9 

> *

6, 2

18, 16

9, 12

12, 12

20,24

10, 12

8, 13

8, 8

40,36

36,20

20,24

4, 24

60,70

24,24

6, 3

8, 4

14, 12

40, 70

60, 60

70,80

60,60

80, 60

40,50

60,46

60,36

65,50

350

50

20

Youdeii (1951) expresses the confidence limits at the 95 percent 

levels as follows :

r

Confidence limit =JU,±-T= 

Yn

where

fji= arithmetical average

f= factor of 2.78 for 5 replicates and 3.18 for 4 replicates

0 = standard deviation

n= number of replicates
8 CONTRIBUTIONS TO GEOCHEMISTRY

The 95 percent confidence level of the field method was examined 

by analyzing three samples by the field method 5 times and applying 

the results to the equation. The 95 percent confidence level of the 

rapid laboratory method was examined by analyzing the same three 

samples 4 times by the rapid laboratory method and again applying 

the results to the equation. The results are given below. The laboratory value is that value obtained by the analyses of the sample by the 

Holmes method where, after suitable separation, copper is estimated 

with sodium diethyldithiocarbamate.

Confidence limits at the 95 percent level for the field and the rapid laboratory methods 

compared with results obtained by an accepted laboratory procedure.

Sample number

1 .

2 _ _

3 _

Copper content, in parts per million

Field 

(biquinoline)

332 ±80 

39 ±12 

31 ±8. 3

Rapid 

laboratory 

(biquinoline)

325 ±33 

61 ±4. 8 

38±3

Laboratory

(carbamate)

360 

60 

38

LITERATURE CITED

Breckenridge, J. G., Lewis, E. W. J., and Quick, L. A., 1939, 2,2'-biquinoline, a

reagent for copper: Canadian Jour. Research, v. 17, p. 258-265. 

Cheng, Kuang Lu, and Bray, Roger II., 1953, Two specific methods of determining

copper in soil and plant material: Anal. Chemistry, v. 25, p. 655-658. 

Holmes, R. S., 1945, Determination of total copper, zinc, cobalt, and lead in

soils and soil solutions: Soil Science, v. 59, p. 77-84.

Hoste, J., 1950, A new copper-specific group: Acta Anal. China., v. 4, p. 23-37. 

Hoste, J., Eeckhout, J., and Gillis, J., 1953. Spectrophotometric determination

of copper with cuproine: Acta Anal. China., v. 9, p. 263-274. 

Levering, T. S., Huff, L. C., and Almond, Hy, 1950, Dispersion of copper from

the San Manuel copper deposit, Final County, Ariz.: Econ. Geology, v. 45,

p. 493-514. 

Sandell, E. B., 1950, Colorimetric determination of traces of metals, 2d ed.,

New York, Interscience Publishers, Inc., 673 p. 

Stevens, R. E., and Lakin, H. W., 1949, The chromograph, a new analytical tool

for laboratory and field use: U. S. Geol. Survey Circ. 63, p. 1-11. 

Youden, W. J., 1951, Statistical methods for chemists, New York, John Wiley &

Sons, Inc., 126 p.

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