Chemistry of Strontium 

in Natural Water

GEOLOGICAL SURVEY WATER-SUPPLY PAPER 1496

This water-supply paper was printed 

as separate chapters A-D

UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON : 1963
UNITED STATES DEPARTMENT OF THE INTERIOR 

STEWART L. UDALL, Secretary

GEOLOGICAL SURVEY 

Thomas B. Nolan, Director

The U.S. Geological Survey Library has cataloged this publication as follows:

U.S. Geological Survey.

Chemistry of strontium in natural water. Washington, 

U.S. Govt. Print. Off., 1962.

iii, 97 p. illus., diagrs., tables. 24 cm. (Its Water-supply paper 

1496)

Issued as separate chapters A-D.

Includes bibliographies.

1. Strontium. 2. Water-Analysis. I. Title. (Series)
CONTENTS

[The letters in parentheses preceding the titles are those used to designate the separate chapters]

Page

(A) A survey of analytical methods for the determination of strontium in

natural water, by C. Albert Horr____________________________ 1

(B) Copper-spark method for spectrochemical determination of strontirm

in water, by Marvin W. Skougstad-______-_-_-_--_~__-___-_- 19

(C) Flame photometric determination of strontium in natural water,

by C. Albert Horr_____._____._______________... 33

(D) Occurrence and distribution of strontium in natural water, by Margin

W. Skougstad and C. Albert Horr____________.___-._-___-. 55

iii

A Survey of 

Analytical Methods fc r 

The Determination of 

Strontium in 

Natural Water

By C. ALBERT HORR

CHEMISTRY OF STRONTIUM IN NATURAL rVATER

GEOLOGICAL SURVEY WATER-SUPPLY PAPER 1496-A

This report concerns work done on behalf 

of the U.S. Atomic Energy Commission 

and is published with the permission of 

the Commission

UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON : 1959
UNITED STATES DEPARTMENT OF THE INTERIOR 

FRED A. SEATON, Secretary

GEOLOGICAL SURVEY 

Thomas B. Nolan, Director

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

Washington 35, D.C. - Price 15 cents (paper cover)
CONTENTS

Page

Abstract_______________________________________________________ 1

Introduction______________________________________________ 2

Chemical behavior of strontium__________________________________ 2

Analytical methods for strontium__________________________________ 3

Gravimetric methods___________________"_______________ 3

Volumetric methods_____________________________________ 6

Spectrochemical methods_______________________________ 7

Emission spectroscopy___________________ 7

Flame spectrophotometry________________________________ 9

Absorptiometry___________________________________... 11

X-ray spectroscopy________________________________ 11

Polarographic methods._______________________________... 11

Chromatographic methods_________________________ 12

Methods for radioisotopes__________________ _____ 13

References cited..._________________________________________ 14

m

CHEMISTRY OF STRONTIUM IN NATURAL WATER

A SURVEY OF ANALYTICAL METHODS FOR TFE 

DETERMINATION OF STRONTIUM IN NATURAL WATER

BY C. ALBERT HOUR

ABSTRACT

Strontium, an alkaline earth metal, is one of the more abundant trace elements in the lithosphere and is universally associated with calcium in igneous, 

sedimentary, and metamorphic rocks. During the weathering cycle, strontium 

is brought into solution and is transported principally as the bicarbonate.

The biological cycle of strontium parallels that of calcium. Natural strontium 

is not toxic to human life, but the artificially produced radioactive isotopes, especially strontium-89 and strontium-90, are highly toxic.

Chemical methods for determining strontium require separation of the element 

from other alkaline earth elements. The most reliable method for separating 

calcium from strontium is extraction with fuming nitric acid. Many methods 

have been reported in which organic solvents are used to extract anhydrous 

calcium nitrate from mixtures of calcium and strontium nitrate. Sepi rations 

based on homogeneous precipitation or precipitate exchange and compler formation are also reported. In all these methods, reliable results can be attained 

only when corrections are applied to compensate for incomplete separations. 

Strontium is usually determined gravimetrically, or volumetrically br oxidimetric titration of equivalent oxalate. Other volumetric methods are rarely 

used.

Emission spectrochemical methods have been applied to water analysis. These 

methods have the advantage that preliminary separations or other treatment 

of the water sample are usually unnecessary. Instrumentation and operational 

techniques for spectrographic analysis are well standardized. Among methods 

of introducing the sample into the excitation source are direct atomization, use 

of rotating-disk or porous-cup electrodes, evaporation of the sample on the electrodes, and packing a cupped electrode with the evaporation residue. The lower 

limit of detection is reported to be approximately 0.001 ppm.

Flame photometry is used extensively in analysis of solutions. Lov-energy 

excitation produces simple spectra relatively free of interferences an advantage 

in the analysis of complex solutions. Differences among methods are mainly 

in the choice of fuel and spectral line. The effects of some cations an(* anions 

on the emission of strontium have been studied. Strontium may be det"«ted in 

amounts as small as about 0.2 ppm.

1
2 CHEMISTRY OF STRONTIUM IN NATURAL WATER

There are no satisfactory direct eolorimetric methods for strorttum. Indirect 

colorimetric methods are generally unsatisfactory and nonspecific. X-ray 

spectroscopy may be applied to evaporated water residues.

Column and paper chromatographic methods are convenient for concentrating 

and separating small amounts of strontium in water samples. Adsorption and 

elution techniques for both column and paper chromatographic methods have 

been described by several authors.

Sensitive radiochemical methods of analysis for the radioactive isotopes of 

strontium, particularly strontium-90, have been developed.

INTRODUCTION

A comprehensive search of the chemical literature of the last 60 

years was made for methods pertaining to the quantitative determination of strontium. From the several hundred references compiled, 

only the comparatively few that describe methods for tH determination of strontium in natural waters and methods that are adaptable 

to natural waters are summarized in this report.

This report is part of a study of the occurrence of strontium in the 

ground waters and surface waters of the United States. Many helpful suggestions were received from John D. Hem, under whose direction this report was written.

This work was done on behalf of the U.S. Atomic Energy 

Commission.

CHEMICAL BEHAVIOR OF STRONTIUM

Strontium, an alkaline-earth metal, resembles calciuir and barium 

in its chemical properties. Strontium is not abundant but is widely 

distributed in nature, and traces of it are contained in all calcium 

compounds (Meunier, 1926). The strontium content of igneous 

rocks varies from about 9 g per ton in ultrabasic rocks to 1,200 g per 

ton in nepheline syenites (Rankama and Sahama, 1950, p. 476). The 

crystal ionic radius of strontium (1.13A) is intermediate between that 

of calcium (0.99A) and that of potassium (1.33A) (Fouling, 1948, 

p. 346). Strontium thus may replace these metals in some minerals, 

especially in the feldspars, micas, pyroxenes, amphiboles, and 

apatites.

Strontium minerals are nearly everywhere present in limestones, 

dolomites, gypsum-bearing rocks, and salt deposits. T" e most common strontium mineral is celestite (SrSO*).

Vinogradov and Borovik-Romanova (1945) have suggested the 

following deposition mechanism for celestite in conjunction with 

dolomite, limestone, and gypsum. The strontium content'and the 

relative solubilities of strontium and calcium in sea winter are such 

that celestite will not be deposited so long as limestone or dolomite
SURVEY OF ANALYTICAL METHODS OF DETEEMINATIOF 3

is being deposited. When the concentration of the solution rises to 

the point where deposition of gypsum begins, however, celesHte will 

also be deposited. The result is a celestite enrichment of the upper 

zones of carbonate rocks in contact with gypsum. Celestite also is 

present in the shells of certain marine organisms.

Eankama and Sahama (1950, p. 295) give the average strontium 

content of sea water as 13 ppm. Odum (1951) in a statistical study 

of his own data and of data from several others found that 8.1 ppm 

is more nearly correct. Alexander and others (1954) in a stud^ of the 

municipal water supplies of 50 cities in the United States found that 

the strontium content averaged 0.21 ppm in untreated surface water 

and 0.49 ppm in ground water.

During weathering, strontium is dissolved and transported principally as the bicarbonate, with lesser amounts as the sulfpte and 

chloride (Eankama and Sahama, 1950, p. 480). Gallo (1935) reports 

that at 20° C in pure water, the solubility of strontium sulfate is 

equivalent to 63 ppm of strontium. The presence of other anions and 

cations increases the solubility of strontium sulfate.

Strontium is accumulated with calcium in the bones and milk of 

animals and in the leaves of plants. Naturally occurring strontium 

has no physiological importance and seems to be nontoxic to human 

beings. It is not listed as an industrial poison by Jacobs (1944), nor 

is a maximum permissible concentration for strontium in dunking 

water given by the U.S. Public Health Service (1946). Tl^ California State Water Pollution Control Board (1952, p. 376; 1954, p. 

114) has found that strontium chloride and strontium nitrate are toxic 

to some aquatic animals and lists threshold concentrations for immobilization and lethal dosages for a few fresh-water fish.

The toxicity of radioactive isotopes of strontium, in particular 

those with long half-lives, is important because of the similar Hhavior 

of strontium and calcium in the life cycle. Strontium accumulates 

in bone tissue, to which radio-strontium causes radiation damage. 

The National Bureau of Standards (1953) lists 800 micromic'"ocuries 

per liter as the maximum permissible concentration of strontium90 -f yttrium-90 in water for continuous ingestion. The Britirh. Journal of Eadiology (1955) also lists 800 micromicrocuries p^r liter 

as the maximum permissible concentration of SE90 +Y90.

ANALYTICAL METHODS FOR STRONTIUM

GBAVIMETBIC METHOIMS

The determination of strontium by gravimetric methods is generally complicated by the presence of much larger amounts of calcium 

and magnesium than the amount of strontium. These elements to-
4 CHEMISTRY OF STRONTIUM IN NATURAL WATER

gether with barium, if present, must be removed prior to the determination of strontium.

In the general scheme of analysis, the alkaline earth metals are 

precipitated as carbonates or oxalates prior to separating strontium 

from the other alkaline earths. Pochinok (1932) recommended that 

the precipitation be made by slowly adding ammonium oxalate or 

sodium carbonate to the boiling solution and then allow the solution to cool before filtering.

The separation of strontium from the other alkaline earth elements 

requires the utmost care and attention to detail to obtain satisfactory 

results. From solubility data, Davis (1942) concluded that selective 

precipitation of strontium as the chromate from aq'ieous ethanol 

should give a satisfactory separation. Fresenius and Ruppert (1891) 

had shown earlier that this procedure gave unreliable insults. Kawson (1897) described a method in which the alkaline earth carbonates 

or oxalates were converted to nitrates and dried. Concentrated nitric 

acid was then used to extract soluble calcium nitrate from the mixture. Willard and Goodspeed (1936) found, in their studies of Kawson's method, that nitric acid of density 1.46 was the mo^t satisfactory 

for the separation. Leliaert and Eeckhaut (1957), using isotope 

tracer techniques to study chemical methods of separation, found that 

for the most reliable results a double extraction with nitric acid should 

be made.

Fresenius (1893) described a method of separation in which a mixture of ethanol and ethyl ether is used to extract calcium nitrate from 

a mixture of anhydrous nitrates. This method was preferred by Noll 

(1931); however, he cautioned that to obtain good results, the separation must be made under completely anhydrous conditions, preferably in a dry box or in an atmosphere saturated with nitric acid 

(d. 1.46). Browning (1893) proposed the use of isoamyl alcohol, in 

which calcium nitrate is more soluble than in an ethanol-ether mixture, for separating strontium nitrate from calcium nitrate. Later 

study by Leliaert and Eeckhaut (1957) showed that 1 to 2 percent 

of the strontium is extracted with the calcium in a single extraction. 

After a second extraction, 0.2 to 1 percent of the calcium remained 

with the strontium in the residue. Szebelledy (1929a) described a 

method of separation by extraction of the soluble calcium nitrate with 

a mixture of absolute ethyl and isobutyl alcohols.

The methods by Browning (1893) and Szebelledy (1929a) have 

been shown (NoU, 1931) to be unsuited for the separation of large 

amounts of calcium from small amounts of strontium. The use of 

anhydrous acetone as an extraction reagent was reported by Shreve 

and others (1939), who recovered 99.7 percent of the strontium.
SURVEY OF ANALYTICAL METHODS OF DETERMINATION 5

A method of separation by selective precipitation of strontium with 

a boiling 23 percent solution of ammonium sulf ate has been described 

by Ukai (1931). However, he found that the method gave erratic 

results because of coprecipitation of calcium sulf ate. Study of the 

homogeneous precipitation of strontium with dimethyl sulf ate (Elving and van Atta, 1950) showed that calcium sulfate was coorecipitated at the concentration of reagent required to precipitate completely the strontium.

Leliaert and Eeckhaut (1957), using radioactive isotopes, made a 

critical study of most of the previously described methods for separating strontium and calcium. Their conclusions were tlmt Rawson's method (1897) of separation with concentrated nitric a "id and 

Fresenius' method (1893) of extraction of the nitrates with a mixture of ethanol and ethyl ether gave the most reliable results, They 

showed that results of highest accuracy can be obtained only when 

errors are evaluated and corrections are applied.

Szebelledy (1929b, 1932) reported a method for separating 

strontium and barium by conversion of the nitrate salts to bromides 

with hydrobromic acid followed by extraction of the more soluble 

strontium bromide with isobutyl alcohol. A correction factor must 

be applied to give accurate results. The separation may also H made 

by the precipitation of barium chromate in an alkaline solution 

(Macchia, 1928). Ballczo and Doppler (1956a) have recently reported a method of separating barium, calcium, and strontium by 

using precipitate exchange and complex formation. Barium is precipitated as the chromate in a solution containing sodium ethylenediaminetetraacetate in which strontium and calcium are soluWo. The 

strontium is then separated from calcium by extraction of the anhydrous nitrate salts. The method was applied to mineral waters.

These same authors (1956b) described another method ir which 

ammonium sulfate is added to a boiling solution of the mixed oxalates; 7 the barium salt is thus converted i

to the insoluble barium

sulfate. The precipitate is filtered after treatment with hydrochloric acid to dissolve the calcium and strontium oxalate?. The 

calcium and strontium are reprecipitated as the oxalates, f,nd the 

strontium oxalate is converted to the carbonate by treatment with 

potassium carbonate. The precipitate is filtered, washed, dried, and 

weighed, and then dissolved in dilute sulfuric acid. The calcium 

and strontium concentrations are then determined indirectly by 

titration of the equivalent oxalate.

Final determination of strontium may be made by several different 

methods. Pochinok (1932) and Haslam (1935) recommended that

503279 59 2
6 CHEMISTRY OF STRONTIUM IN NATURAL WAITER

the strontium be precipitated by the addition of a knc-*m excess of 

ammonium, oxalate to the boiling solution and the ercess titrated 

with standard permanganate. Ignition of strontium oxalate to 

strontium carbonate was found to give a positive error of about one 

part in a thousand. Strebinger and Mandl (1926) recommended 

precipitating strontium as the sulfate from an ethanolic solution and 

drying the precipitate at 170° to 180° C. A modification of the 

Dworzak and Reich-Rohrwig method (1931) for calcium was described by Penchev and Nonova (1955) for the macro-, semimicro-, 

and micro-determination of strontium. They precipitated strontium 

in a warm (50° to 55° C) solution with picrolonic add. The precipitate was washed with carbon disulfide and driei in an air 

stream. Advantages were claimed over other methods. Determination of strontium as the secondary phosphate has been described by 

Denk and others (1956). The precipitation is carried out in a boiling, 

alkaline solution, and the final precipitate is dried at 1£0° to 130° C. 

Sodium and ammonium must be absent.

VOLTTMETBIC METHODS

Titrimetric methods for the determination of strontium are few 

in number and generally are applied to the final determination of 

the element after separation from calcium, barium, and magnesium. 

The most widely used method has been described by Go-xiale (1936). 

The strontium is determined by titrating the equivalent oxalate 

from the acidified strontium oxalate precipitate with standard permanganate. Strontium is sometimes determined indirectly by precipitating it with a known amount of oxalate and then titrating the 

excess oxalate. Ballczo and Muthenthaller (1932) have reported a 

method for determining strontium in mineral water. The strontium 

from a large volume of water was concentrated on an alumina column 

pretreated with sodium hydroxide. The strontium was then eluted 

with dilute nitric acid. The eluate was filtered, evaporated to dryness, and fused with boric acid to convert the strontium to the borate 

salt. The residue was dissolved in a known volume of dilute hydrochloric acid, methyl alcohol was added, and the excers borate was 

evolved as methyl borate. The excess hydrochloric acid was determined by double titration with sodium borate in the presence of 

methyl-red and methylene-blue indicators. In the potentiometric 

method reported by Mayr and Burger (1930), strontium is precipitated by a measured excess of sodium oxalate. The excess oxalate 

used in the precipitation is then titrated potentiom(>trically with 

mercurous nitrate.
SURVEY OF ANALYTICAL METHODS OF DETERMINATION 7 

SPECTROCHEMICAL METHODS

Instrumental methods, including spectrochemical techniques in 

recent years, have been used extensively in analytical chemistry. Development of more precise methods of measurement of spectral intensity of excited samples has lead to a high degree of sensitrdty and 

accuracy in analysis. Spectrochemical analysis has a distinct advantage in that a large number of samples may be analyzed ir a short 

time and generally without preliminary chemical treatment or isolation of the particular element of interest. Emission spectrochemical 

methods permit the simultaneous determination of many elements 

in a single sample. Spectrochemical analysis has widespread application in studies of the geochemistry of trace or minor elements in 

a great variety of geologic material.

For facility of review, this field of analytical endeavor is divided 

into four parts: (1) Emission spectroscopy, in which the spectrum 

of an excited sample is recorded by means of photosensitive plates or 

films for subsequent measurement of the intensity of spectral lines; 

(2) flame spectrophotometry, in which a desired segment of the 

spectrum is isolated by means of filters or a monochromator and the 

spectral intensity measured by photoelectric methods; (3) absorptiometry; and (4) X-ray spectroscopy.

Instrumentation is beyond the scope of this review; but for excellent discussions of this subject, the reader is referred to Sawyer 

(1951), Brode (1943), Harrison and others (1948), and Willard and 

others (1948). A good introduction to spectrochemical analysis is 

given by Meegers (1946). Burriel-Marti and Ramirez-MuiioF (1957) 

have provided a comprehensive review of flame photometry in their 

recent outstanding work.

EMISSION SPECTROSCOPY

Spectrographic methods using direct solution excitation are well 

suited to the analysis of natural waters. Uzumasa and Okino (1933, 

1934) sprayed the sample into a spark gap of 10,000 volts. They 

reported that the calcium and strontium lines were the most sensitive, 

and they were able to detect as little as 10"6 mole of these elements. 

Also, they showed that free hydrochloric acid interfered vith the 

analysis. Bo'rovik-Romanova and others (1954), in their study of 

natural waters, made use of a "fulgerator" which introduced the 

solution to be tested into a 120-v, 2-amp, a-c arc by capillary action 

through a predrilled electrode. Using the sensitive strontium line at 

4607A, they were able to detect as little as 10r5 percent (0.01 ppm) 

of strontium.
8 CHEMISTRY OF STRONTIUM IN NATURAL WAT^R

The porous-cup electrode technique, first described by Feldman 

(1949), was applied by Wilska (1951) to the analysis of natural 

waters. The sample is introduced into a hollow, upper electrode 

and fed into the spark by diffusion through the floor of the electrode. 

A minimum concentration of 0.07 ppm of strontium was determined 

with a precision of ±4.95 percent standard deviation from the mean 

strontium content of the analysis line to the internal standard line. 

Hitchcock and Starr (1954), using the same technique, reported erratic results that were due to nonuniform porosity of the electrode 

material, selective diffusion, and dependency of feed rates on ion 

concentration. These authors claimed improved results with a rotating-disk electrode, which fed the sample continuously to a high 

voltage spark.

Rainwater (written communication, 1958) reports a procedure, 

using rotating carbon-disk electrodes, sensitive to ±0.05 ppm of 

strontium in water samples. A detection limit of 0.001 percent, in 

dry residues, was also reported; the 0.001 percent corresponds to 

0.001 ppm of strontium in water containing 100 ppm of dissolved 

solids.

Preferential volatilization of certain components of tlie sample occurs to a much lesser degree in the high voltage spark than in the 

d-c arc. For this reason, and because spattering effects are minimized, spark excitation is usually preferred. Continuous, uniform 

feed of the sample to the spark assures that the composition of the 

radiating vapor is identical with that of the sample solution.

High-temperature flames have also been used as a means of excitation in spectrographic procedures. An acetylene-air or acetyleneoxygen flame is generally used; but other fuels, including natural gas, 

propane, and hydrogen, have been used. Eusanov (1934), with the 

aid of a Lundegardh burner and atomizer, determined the concentration of several alkali and alkaline earth metals by interposing a 

light-absorbing wedge between the flame and collimator slit. Belating the layer thickness of the wedge at the point of disappearance 

of a spectral line or band to the concentration of the element gave 

results accurate to within 10 to 15 percent of the true value. Hitchcock and Starr (1954) also used a flame for excitation of the solution. 

They found that internal standards were not necessary because the 

excitation is reproducible and is not subject to the random variations 

(Kolb and Streed, 1952) observed with the porous-cup and rotatingdisk electrodes.

Excitation of evaporation residues is more widely applied than 

solution excitation. Nagaoka and Machida (1934) described a 

method in which the solution to be tested was evaporated on the 

surface of clean silver electrodes. They were able to detect as little
SURVEY OF ANALYTICAL METHODS OF DETERMINATIC "ST 9

as 10~9 g of strontium. Impregnation of carbon electrodes with the 

sample solution was found by Hitchcock and Starr (1954) to give 

erratic results. They attributed the inconsistencies to nonhomogeneity of the residue caused by preferential absorption of the solution by 

the electrodes. These same authors also evaluated the cupped-electrode technique, wherein the evaorated residue is packed into a shallow cup cut into the end of a graphite electrode. Expulsion of 

sample from the electrode and difficulties in properly sampling the 

residues led to poor results. Briquetting the sample with pure 

graphite powder was claimed to improve the results.

FLAME SPECTROPHOTOMETRY

Flame excitation yields relatively simple line and band spectra of 

the more easily excited elements and compounds. Because the resulting spectrum contains only a few lines or bands, filters or small 

prism mouochromators may be used to isolate the desired spectral 

area with a minimum of radiation interference.

Flame excitation of strontium gives two prominent spectral lines, 

407.8 m/i and 460.T imi, and a spectral band, 681 im*. The 460.7-m/A 

line is the most intense. The choice of using the 460.7-rmt line or the 

681-m/A band for the determination is a matter of controversy. Chow 

and Thompson (1955) used the 460.7-m/* line with excellent results. 

A. detection limit of 0.5 ppm of strontium at 460.7 m/* with a hydrogen flame and 5 ppm at 681 m/* with an ^ acetylene flame ws listed 

by Beckman Instruments, Inc. (1952). The intensity of the continuous or background radiation of the flame and solvents must be 

subtracted from total intensity at these wavelengths in order to obtain 

true element-emission intensity. Taylor and Paige (1955), in an 

evaluation study of flame-photometric methods, showed the 681-niji* 

wavelength and an acetylene flame to be the best. They pointed out 

that emission at this wavelength is less subject to interference by 

anions and cations present in the water. A standard deviation of 

0.5 ppm or less was obtained for concentrations between C and 10 

ppm of strontium.

In order to reduce radiation interferences, a minimum spectral 

width is used. Because this reduces the total amount of radiant 

energy admitted to the detector, the use of a photomultiplier tube, 

which amplifies the current generated by a factor of 100, is recommended.

The effects of cations and anions most common in natural water 

on the intensity of the emission of strontium have been studied by 

Huldt (1944), Ettre and Adam (1957), Taylor and Paige (1955), 

Chow and Thompson (1955), Sugawara and others (1956), Hinsvark 

and others (1953), and Berry and others (1946). Sodium, potassium,
10 CHEMISTRY OF STRONTIUM BST NATURAL WAT^R

and calcium enhance the emission of strontium in the flame. Aluminum, iron magnesium, sulfate, phosphate, and chloride ions cause 

a depression of the emission. Sugawara and others (1956) found 

that the addition of organic acids, particularly tartaric acid at 0.5 

percent concentration, increases the intensity of emission. Ikeda 

(1956) reported that perchloric acid caused enhancement of the 

emission.

Flame-photometric methods for analysis of strontium in waters 

have been described by several authors. Chow and ThoirDSon (1955) 

developed an "internal standard" technique in which a series of 

standards are prepared with a strontium-free synthetic sea water. 

An equal volume of sample is added to several of the standards, and 

the mixture is atomized. A plot is made of concentration versus net 

intensity of the emission at 460.7 m/*, and the strontium content is 

determined by the slope-intercept method. Any ions that cause interference would have equal effects on standards and urknowns. A 

method for determining strontium in rain, lake, and rive^ waters was 

described by Sugawara and others (1956). They evr/porated the 

samples to approximately one-sixteenth of the original volume and 

precipitated calcium and strontium, with ammonium oxalate. Urea 

was added to prevent coprecipitation of magnesium. Th^ precipitate 

was collected and dissolved in 1:1 hydrochloric acid, and tartaric 

acid was added. Strontium emission was read at 460.7 m/*. This 

method was found to have .an average error of +1.5 percent.

Smales (1951) combined flame-photometric and rodiochemical 

methods to determine strontium in sea water. A known amount of 

strontium containing the radioactive isotope, strontium-89, was added 

to a sample of sea water and coprecipitated with barium sulfate. 

The fraction of strontium coprecipitated is proportional to the decrease in activity of the filtrate. The amount of strontium required 

to restore the original flame intensity of the filtrate vas then determined. The data obtained permitted the calculation of the strontium concentration in the original sample.

Skougstad (1957) has described a method in which a radiation 

buffer technique is used for determining strontium in water. Potassium chloride and ammonium citrate, 1.0 g and 0.5 g, respectively, 

are added to the samples and standards, which are made alkaline with 

potassium hydroxide. The final volume is 100 ml. The net intensity 

at 460.7 m/A plotted against strontium concentration yielis a straight 

line.

Hubble (written communication, 1957) described a method similar 

to the method of Chow and Thompson (1955) in which a series of 

aliquots of a sample are diluted with equal volumes of several stand-
SURVEY OF ANALYTICAL METHODS OF DETERMINATION 11

ard strontium solutions. The emission intensities at 460.7 m/* are 

corrected for background intensity at 454 m/* and plotted against concentrations of the standards. The strontium content is determined by 

the slope-intercept method. This method shows an error of 3 percent 

for the higher concentrations and 5 to 10 percent for the lower concentrations.

The procedures of Skougstad and Hubble have a detection limit of 

about 0.2 ppm of strontium.

ABSOBPTIOMETBT

Colorimetric and absorptiometric methods for determining strontium are limited for practical application and are principally of academic interest. Most of the reagents, such as tannic acid, chloranilic 

acid, and ammonium purpurate (murexide), are useful orly with 

pure solutions of strontium salts and give colors that are transient and 

fade rapidly.

Pollard and Marten (1956) have described a method for d^termining strontium with ethanolic murexide. The color was developed at 

a pH of 11.3, and the optical density of the solution was measured at 

515 rn/t. The authors also described a procedure in which o-cresolphthalein is used as a complexing agent. The determination was made 

at a pH of 10.6, and the optical density was measured at 575 m/*. In 

both procedures, the optical density must be determined rarcidly to 

overcome fading caused by decomposition of the color complex. A 

sensitivity of 1.5 y is claimed for the method.

Welcher (1947, 1948) listed several methods for detecting strontium by reagents yielding colored solutions or precipitates. However, 

all are subject to interferences and are not useful analytically.

X-RAY SPECTROSCOPY

X-ray spectroscopic and fluorescence methods have been used for 

determining strontium in rocks and minerals. Noll (1932) ?,nd Lucchesi (1957) have described a procedure in which an analyze^ crystal 

of lithium fluoride is used with yttrium as the internal standard. 

This analytical tool is widely used in the study and analysis of rocks 

and minerals and may be applicable to water analysis.

POLABOGBAPHIC METHODS

Polarographic .methods have been used, though not extensively, for 

determining the alkali metals and alkaline earth metals in water. 

Only a few methods are reported for the polarographic determination 

of the alkaline earth metals. Zlotowski and Kolthoff (1944, 1945) 

have described the polarographic behavior of strontium and barium
12 CHEMISTRY OF STRONTIUM IN NATURAL WATER

and of strontium, barium, and calcium in water or water-alcohol solution with tetraethylammonium iodide as the supporting electrolyte. 

These investigators found that the strontium wave was well defined 

and that strontium could be determined in the presence of calcium 

and barium. They also showed that the best results were obtained 

using a 50 to 80 percent aqueous ethanol solution.

CHBOMATOGBAPHIC METHODS

In recent years, paper and column chromatographio techniques 

have been successfully applied to the concentration, separation, and 

determination of strontium in various materials. Lerr Q,r and Kieman (1954) collected a mixture of calcium, barium, and strontium on 

a column of Dowex-50 previously equilibrated with ammonium lactate. The column was eluted with ammonium lactate, and successive fractions were collected. The second fraction contained the 

strontium, which was then determined gravimetrically a? the sulf ate. 

Schumacher (1956) described a similar procedure in which 2.5 to 3 N 

hydrochloric acid is used as the eluent. Ballczo and Muthenthaller 

(1952) have described a method for strontium in mineral waters. 

Strontium was separated from calcium and magnesium by passing the 

sample through an alumina column pretreated with sodium hydroxide 

and eluting the strontium with nitric acid.

Paper chromatography of the group II-A elements was investigated by Ishibashi and Tsutsui (1956). Using an ethanol-waterhydrochloric acid system, they were able to separate strontium from 

500 times as much calcium. They found no difference in Kf values 

when nitric acid (6N) was substituted for hydrochloric acid. Pollard, McOmie, and Marten (1956) determined gamma quantities of 

strontium and other group II-A metals in dolomites and limestones. 

The metals are separated as formates by downward elation of the 

chromatogram with a solvent consisting of methanol, formic acid, 

isopropyl alcohol, water, and ammonium formate. Af^r isolation, 

strontium was determined colorimetrically as the orthocresolphthalein 

complex. Magee and Headridge (1955) described a methyl alcohol, 

n-butyl alcohol, y-collidine, 6N acetic acid system for tr«s separation 

of group II-A elements by downward elution. Strontium was detected by using sodium rhodizonate to develop the chromatogram. 

The method was applied to dolomites. A study of chromatographic 

separation of calcium and strontium, in which radioactive tracers 

were used, was reported by Burkser and Eliseera (195*>). Separation by means of pyridine containing potassium tMocyanate or hydrochloric acid containing n-butyl alcohol and water v^as made on 

chromatographic paper that was impregnated successive^ with alco-
SUEVEY OF ANALYTICAL METHODS OF DETEKMESTATION 13

holic sodium hydroxide and hydrochloric acid. Good separations of 

the two elements were obtained by this method.

METHODS FOB RADIOISOTOPES

Increased use of radioisotopes in research, nuclear-power installations, and nuclear-weapons testing has resulted in an increase in the 

amount of radioactive materials being discharged into water courses. 

Gross assays of radioactivity of water samples will not adequately 

measure the hazard from nuclides such as strontium-90.

Radiochemical procedures for the assay of strontium-90 h<\ve been 

described in detail by Hahn and Straub (1955), Martell (1956), 

Goldin (1956), and Kahn and Goldin (1957). Because radioactive 

strontium occurs in extremely small concentrations, these investigators added natural strontium to the samples to serve as a carrier for 

the radioactive strontium. Strontium and other alkaline e?,rth elements were then precipitated with sodium carbonate. The precipitate was collected and redissolved in acetic acid. The solution was 

buffered with ammonium acetate, a barium carrier added, and barium 

chromate precipitated by the addition of ammonium or potassium 

chromate. This precipitation removes radioactive barium and any 

lanthanum daughter that would interfere with the determination 

of radiostrontium. The strontium was again precipitated as the carbonate, and the collected precipitate was washed free of excess 

chromate ion. The precipitate was dissolved in hydrochloric acid; 

and ferric, zirconium, and either lanthanum or cerium chlorides were 

added as scavengers. The scavengers were precipitated as the hydroxides and removed by filtration. A final strontium carbonate 

precipitation was made. After the yttrium daughter had grown in, 

the mounted precipitate was subjected to /3-assay (Beed, 195*1). Alternatively, the yttrium daughter product was separated from the 

precipitate by extraction with 2-thionyltrifluoroacetone and the extract subjected to /J-assay.

Isotope-dilution and neutron-activation techniques are the most 

precise and accurate methods for the determination of strontium in 

microgram quantities. In the isotope-dilution technique, an accurately measured amount of a radioactive strontium isotope of known 

activity is added to the sample solution. Strontium is then separated 

from the solution, usually by a gravimetric procedure, and the activity of the separated material is measured. The concentration of 

the original strontium in the sample is calculated from the ratio of 

the activities of the added and recovered isotope. This general technique is useful in determining the efficiency of wet chemical methods
14 CHEMISTRY OF STRONTIUM IN NATURAL WATER

of analysis. Alimarin and Bilimovich (1956) made a comprehensive 

review of chemical analysis by isotope dilution.

_Leddicotte and Eeynolds (1951) have described the use of a 

reactor at Oak Eidge for neutron-activation analysis. In principle 

the samples, together with standards, are placed in an intense flux 

of slow neutrons for a length of time sufficient to produce a measurable amount of a radioisotope of the element to be deterrxined. Neutron bombardment of strontium produces strontium-87. The activity 

is measured, and the weight of element present, W, is found from 

the equation:

AM

w=_________

vv 6.02 X1028 fa*cS 

where

A = activity in disintegrations per second,

M = chemical atomic weight of the element sought.,

f = slow neutron flux in neutrons/cma/sec.,

cr*0= atomic cross section in cm2, and

S = saturation factor, l-e'A*.

Although this method is expensive and time consuming, as little as 

0.6 j«g of strontium may be determined with an error of ±10 percent.

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16 CHEMISTRY OF STRONTIUM IN NATURAL WATER

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SURVEY OP ANALYTICAL METHODS OF DETERMINATION 17

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18 CHEMISTRY OF STRONTIUM IN NATURAL WATER

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o