Flame-photometric Determination 

of Strontium 

in Natural Water

GEOLOGICAL SURVEY WATER-SUPPLY PAPER 1496-C

Prepared on behalf of the U.S. Atomic 

Energy Commission and published with 

the permission of the Commission
^lame-photometric Determination 

of Strontium 

in Natural Water

r*t C. ALBERT HORR

CHEMISTRY OF STRONTIUM IN NATURAL WATER

GEOLOGICAL SURVEY WATER-SUPPLY PAPER 1496-C

Prepared on behalf of the U.S. Atomic 

Energy Commission and published with 

the permission of the Commission

J''ITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON : 1962
UNITED STATES DEPARTMENT OF THE INTERIOR 

STEWART L. UDALL, Secretary

GEOLOGICAL SURVEY 

Thomas B. Nolan, Director

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

Washington 25, D.C.
CONTENTS

Page

Abstract ___ _____________________________________________________ 33

Introduction- _____________________________________________________ 33

Flame photometry _ ______________________________________________ 34

Interferences in flame photometry. _____________________________ _____ 34

Analytical procedure. ______________________________________________ 42

Flame-photometric method _____________________________________ 42

Ion-exchange method _._______-___-_-_-_________-_____._-___-__ 43

Results and discussion_____________________________________________ 51

References cited. _____-___-_--____-__-________-_-___-_-_______,_-__ 52

ILLUSTRATIONS

FIGURE 3. Effect of ions on strontium emission,. ______________________ 38

4. Effect of pH on strontium emission____________-___- _______ 41

5. Typical calibration curve________-_________________-______ 44

6. Elution curve for strontium, group 1 eluates___ ______ _______ 46

7. Elution curve for strontium, group 2 eluates________ ________ 47

8. Elution curve for strontium and calcium. _-_____-_---______ 48

9. Ion-exchange column___________-_________________-______ 50

TABLES

TABLE 1. Band- width interference of various ions ____________________ 37

2. Effect of various elements on the emission of the 460.7 m/z

strontium line_____-__________________-________________ 39

3. Comparison of results obtained by the flame-photometric, ionexchange flame-photometric, and spectrographic methods _ 51

4. Recovery of strontium added to tap water. Analysis by the

flame-photometric procedure_-_-___-_-_-_-__--___---___- 51

5. Recovery of strontium added to a synthetic water. Analysis

by the ion-exchange flame-photometric method _ _________ 52

in
CHEMISTRY OF STRONTIUM IN NATURAL WATER

FLAME-PHOTOMETRIC DETERMINATION OF STRONTIUM 

IN NATURAL WATER

By C. ALBERT HOUR,

ABSTRACT

The strontium content of natural waters is rarely over 10 ppm and most 

natural waters have concentrations of 1.0 ppm or less. Gravimetric and volumetric methods are unsatisfactory for the determination of strontium in this 

concentration range. Flame-photometric methods, however, have the required 

sensitivity to determine strontium in the 0.02 to 10 ppm concentration range.

A study was made of interferences caused by common ions present in natural 

water on the determination of strontium. The flame-photometric method is 

capable of detecting as little as 0.2 ppm strontium with an accuracy of ± 10 percent. The method is applicable to waters containing 0.2 to 10 ppm of strontium. 

Higher concentrations require dilution.

A method for concentrating strontium in waters containing less than 0.2 ppm 

by means of ion-exchange chromatography is presented. With this method a 

tenfold concentration is effected which permits strontium to be determined at 

concentrations as low as 0.02 ppm within an accuracy of ± 10 percent.

INTRODUCTION

This study was undertaken to develop a rapid, sensitive, and 

accurate method for the determination of naturally occurring strontium in water. Strontium is present in all natural water at concentrations, generally ranging from 0.01 to 40 ppm (parts per million).

Although gravimetric and volumetric methods are satisfactory for 

the determination of large amounts of strontium, these methods are 

time consuming and lack the sensitivity required to determine strontium in amounts less than 10 ppm. Flame-photometric methods, 

however, are rapid, require little or no pretreatment of samples, and 

are especially recommended for the determination of strontium in the 

presence of the other alkaline-earth metals.

Two methods for the determination of strontium in natural water 

are presented in this report. The flame-photometric method has been 

modified from the method described by Skougstad (1957). It is 

rapid, requires little pretreatment of the sample, and is capable of

33
34 CHEMISTRY OF STRONTIUM IN NATURAL WATER

detecting as little as 0.2 ppm strontium. An accuracy within ±10 

percent is obtainable over the range of 0.2 to 10 ppm.

Analyses of a representative group of samples of surface and ground 

water from throughout the United States show that the strontium 

content of water in a significant number of samples is less than 0.2 

ppm (Skougstad and Horr, 1960). Because the flame-photometric 

method is not sensitive for less than 0.2 ppm of strontium, it is 

necessary to increase the strontium concentration tenfold to determine 

strontium in the 0.02 to 0.2 ppm concentration range. The use of ionexchange chromatography as an adjunct to the flame-photometric 

method is described. With this method as little as 0.02 ppm of 

strontium may be determined within an accuracy of ±10 percent.

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

FLAME PHOTOMETRY

Although the flame had been used as early as 1848 as a source of 

excitation for the production of emission spectra, Kirchhoff and 

Bunsen (1860) were the first to use it for qualitative analysis. With 

few minor exceptions, the use of the flame as an excitation source in 

spectroscopy was abandoned in favor of electric-arc and spark excitation sources until 1929, when Lundegardh published his classic work 

on flame photometry. This work firmly established flame spectrophotometry as a modem analytical tool. In recent years, the availability of commercially made flame spectrophotometers with improved flame sources, optical systems, and photo detecting systems has 

extended the scope of flame photometry for the determination of 

approximately 50 elements.

In the analysis of water, the flame photometer is indispensable for 

the determination of sodium, potassium, and lithium. It may be 

used for the determination of alkaline-earth and other metals in 

natural water, such as cesium (detection limit 0.1 ppm), rubidium 

(0.01 ppm), copper (0.01 ppm), manganese (0.01 ppni), and others. 

It is especially recommended for the determination of milligram 

amounts of strontium in the presence of calcium and magnesium.

INTERFERENCES IN FLAME PHOTOMETRY

Quantitative flame photometry is subject to interferences caused 

by variation in the instrumental system and variations in composition 

and physical properties of the analysis solution. Instrumental 

interferences may be minimized or eliminated by proper adjustment 

of such variables as wavelength, slit width, sensitivity of spectrometer 

and phototube, and ratio of fuel gas to supporting gas.

Interference caused by variations in the composition of the analysis 

solution can be grouped into three major types. Band-width inter-
FLAME-PHOTOMETRIC DETERMINATION OF STRONTIUM 35

ference occurs when the analysis element and an interferring element 

radiate at nearly the same wavelength and the two are read together. 

Commonly band-width interference is eliminated or reduced by using 

as narrow a slit width as possible. For some analyses it is possible 

to select another wavelength that will be free of band-width interference.

Radiation interferences are the result of interatomic or intermolecular processes between the analysis element and an interfering 

element in the flame. Studies by Huldt (1944), Taylor and Paige 

(1955), Chow and Thompson (1955), and others have shown that 

radiation interference caused by anions will generally depress the 

emission of the analysis element. A notable exception to this is the 

perchlorate ion. Radiation interference caused by cations may either 

enhance or depress the emission of the analysis element.

Radiation interferences commonly will reach a plateau where 

further increase in the concentration of the interfering element has 

little additional effect on the emission of the analysis element. Addition of excess interferant as a radiation buffer to both standard and 

sample solutions will affect each equally and thus mask the effects of 

interference. West and others (1950) and Skougstad (1957) describe 

methods that use radiation buffers to compensate for radiation 

interferences.

Background interference is the result of continuous emission from 

the flame and solvent and is superimposed on the analytical emission 

causing an apparent increase in the concentration of the analysis 

element. Vallee (1957, p. 252) states

* * * the background observed is a consequence of the molecular events when 

a solution is sprayed into a flame. First, there is dehydration and formation of 

crystals which must be vaporized before excitation of the atoms may take place. 

If these crystals have a high boiling point, vaporization does not occur, and a 

proportion of this material will then serve as a source of "black-body" radiation, 

accounting for the observed background.

A correction for background interference may be made by subtracting the emission intensity measured at a wavelength close to the 

wavelength of the analysis element from the emission intensity of this 

element. This correction will apply only if the magnitude of the background emission is the same at both wavelengths. It is also possible 

to use the average value of the background emission, measured at 

wavelengths above and below the analytical wavelength, as a correction factor.

The magnitude of background emission varies with the square of 

the slit width, whereas response to an emission line varies with the 

first power; thus, the background may be reduced by using a narrower 

slit. The use of hydrogen as a fuel also will reduce background emis-
36 CHEMISTRY OF STRONTIUM IN NATURAL WATER

sion (Burriel-Marti and Ramfrez-Muiioz, 1957, p. 42). Ideally, the 

background emission should be no greater than 10 to 20 percent of the 

total emission.

All interference errors can be eliminated by comparing standards 

and samples of identical composition and concentration. Thus, 

standard and sample are subject to the same conditions in the flame. 

Dilution of the sample will eliminate or reduce radiation interference, 

but may decrease the concentration of the analysis element below its 

detection limit.

Because natural waters vary widely in content of dissolved materials, 

a study was made to determine the nature and magnitude of interferences caused by the common cations and anions on the emission intensity of strontium.

Stock solutions containing 1,000 ppm of aluminum, ammonium, 

calcium, iron (ferric), magnesium, potassium, and sodium were prepared from their chloride salts. The sulfate and phosphate stock 

solutions were prepared from their ammonium salts. The silica solution was prepared by the hydrolysis of tetraethyl orthosilicate. A 

series of standards containing 10, 20, 30, 40, 50, 100, 200, and 500 

ppm each of the cations was prepared from the stock solutions, A 

similar series of cation and anion standards containing 10 ppm of 

strontium in each was also prepared.

A Beckman DU quartz spectrophotometer equipped with a photomultiplier and flame-photometer attachment was used for all measurements. The atomizer burner was operated at an oxygen pressure of 

11.0 psi and acetylene pressure of 5.5 psi. The 460.7-m/* atomic 

strontium line was chosen for the measurements, because of its sensitivity. Corrections for background emission were made by subtracting the emission intensity measured at 458 m/* from the intensity at 

460.7 m/t.

For the determination of band-width interferences, the flame 

photometer was adjusted to 100-percent transmission for 10 ppm 

strontium. Solutions containing 10, 20, 30, 40, 50, 100, 200, and 500 

ppm of aluminum, calcium, iron, magnesium, potassium, and sodium 

were then atomized in the flame and the emission intensity readings 

taken at 460.7 m/i and 458 m/i. As indicated in table 1, aluminum, 

iron, magnesium, potassium, and sodium gave no net emission intensity at 460.7 rn/Lt and hence produced no band-width interference. 

Calcium produces band-width interference with concentrations above 

50 ppm and has a net emission intensity at 460.7 m/*.

Radiation interferences were studied by aspirating solutions containing 10.0 ppm of strontium and varying amounts of individual 

cations and anions and measuring the resulting emission intensity at 

460.7 m/i. No attempt was made to study the effect of mixtures of
FLAME-PHOTOMETRIC DETERMINATION OF STRONTIUM 37

TABLE 1. Band-width interference of various ions

ConstituentAluminum _

Iron (ferric) ..

Concentration 

(ppm)

10 

20 

30 

40 

50 

100 

200 

500

10

20 

30 

40 

50 

100 

200 

500

10

20 

30 

40 

50 

100 

200 

500

Emission intensity 

at 460.7 

mju

49 

49 

49 

49 

49 

49 

49 

49

60

60 

60 

60 

60 

62 

66 

66

50

50 

50 

50 

50 

50 

50 

59

Emission intensity 

at 458 

mju

49 

49 

49 

49 

49 

49 

49 

49

60

60 

60 

60 

60 

60 

62 

62

50

50 

50 

50 

50 

50 

50 

59

Net 

emission 

intensity

0 

0 

0 

0 

0 

0 

0 

0

0

0 

0 

0 

0 

2 

4 

4

0

0 

0 

0 

0 

0 

0 

0

Constituent

Magnesium..

Concentration 

(ppm)

10 

20 

30 

40 

50 

100 

200 

500

10

20 

30 

40 

50 

100 

200 

500

10

20 

30 

40 

50 

100 

200 

500

Emission intensity 

at 460.7 

mju

50 

50 

50 

50 

50 

50 

50 

50

49

49 

49 

49 

49 

49 

49 

49

49

49 

49 

49 

49 

49 

49 

53

Emission intensity 

at 458 

mju

50 

50 

50 

50 

50 

50 

50 

50

49

49 

49 

49 

49 

49 

49 

49

49

49 

49 

49 

49 

49 

49 

53

Net emission intensity

0 

0 

0 

0 

0 

0 

0 

0

0

0 

0

0

0 

0 

0 

0

0

0 

0 

0 

0 

0 

0 

0

cations and anions or of ions not commonly found in natural waters. 

The results obtained, shown in table 2 and figure 3, are expressed as 

the ratio :

Emission intensity of Sr-f added ion 

Emission intensity of Sr alone X100

Thus, ratios greater than 100 indicate enhancement of strontium 

emission and ratios less than 100 indicate depression of strontium 

emission.

Sodium and potassium enhance the strontium emission. The enhancement effects are nearly identical for equal amounts of sodium 

or potassium, but are not proportional to the quantity of ion present. 

The enhancement by sodium or potassium may be due in part to the 

suppression of the ionization of strontium (ionization reduces the intensity of the 460.7-mju strontium line) in the flame by the more easily 

ionized alkali metals. Wilson (1931), however, has shown that ions 

are rarely produced at the temperatures attained in the flame. Enhancement of the strontium emission is probably the result of energy 

transfer from excited sodium or potassium atoms present in the flame.

Calcium also enhances strontium emission. However, the effect 

was constant at calcium-to-strontium concentration ratios of 3 to 1 

and greater. Mitchell and Robertson (1936) suggested that the 

enhancement is the result of an energy transfer. Huldt (1944) concluded that a shift in ionization equilibrium causes the increase in the 

emission intensity of strontium with added calcium.

622035 62 2
38 CHEMISTRY OF STRONTIUM IN NATURAL WATER

lN30H3d Nl '3N01V WlllNOHiS JO NOISSIW3 Oi 3AllV"13y A1ISN31NI
FLAME-PHOTOMETRIC DETERMINATION OF STRONTIUM 39

TABLE 2. Effect of various elements on the emission of the 460.7-mn strontium line

[Strontium=10 ppm]

Constituent

Sodium .... .........

Potassium... .........

Iron 

Phosphate.... ....

Silica.................

Concentration

(ppm)

0

10

20

30

40

50

100

200

500

0

10

20

30

40

50

100

200

500

0

10

20

30

40

50

100

200

500

0

10

20

30

40

50

100

200

500

0

10

20

30

40

50

100

200

500

Emission ratio 

Sr+Mion Sr X10°

100.0

100.0

102.8

102.8

104.0

105.8

108.0

110.4

112.0

100.0

102.0

102.0

103.6

104.4

106.0

108.4

111.8

112.0

100.0

83.0

76.0

76.0

70.0

64.4

52.2

44.0

31.8

100.0

87.0

84.0

80.2

80.2

79.0

79.0

79.0

78.4

100.0

44.2

30.3

22.2

18.1

14.4

7.2

2.8

0.8

Constituent

Calcium. - .

Magnesium . ........

Aluminum... ........

Sulfate. -. ........

Ammonium . .... .

Concentration

(ppm)

0

10

20

30

40

50

100

200

500

0

10

20

30

40

50

100

200

500

0

10

20

30

40

50

100

200

500

0

10

20

30

40

50

100

200

500

0

10

20

30

40

50

100

200

500

Emission ratio 

Sr+Mion Sr X1°°

100.0

102.2

103.6

104.0

104.0

104.0

104.0

104.0

104.2

100.0

100.0

95.0

98.0

98.0

98.0

98.0

96.0

89.0

100.0

60.2

50.2

48.8

43.0

42.0

27.2

14.0

8.0

100.0

33.8

30.0

29.6

29.6

29.0

29.0

28.4

28.0

100.0

100.0

100.0

100.0

100.0

100.0

100.0

100.0

106.3

Aluminum, iron, and silica seriously interfere with strontium 

emission. Increasing concentrations of these ions cause a continuous 

decrease in emission intensity. Mitchell and Robertson (1936) state 

that aluminum extracts energy from the flame so that insufficient 

energy is available for excitation of the strontium atom. According 

to Huldt (1946) and Servigne and Montgareuil (1954), aluminate and 

ferrate complexes of strontuim are responsible for the marked decrease 

in the emission intensity. These authors attribute the effect to the 

very high decomposition temperatures of these refractory compounds 

that preclude excitation of the strontium. Although organic solvents 

are known to enhance the emission intensity of some elements, the
40 CHEMISTRY OF STRONTIUM IN NATURAL WATER

ethyl alcohol produced by the hydrolysis of tetraethyl orthosilicate 

gave no interference.

Vallee (1954) presented experimental evidence indicating that 

cationic interferences are caused by the superposition of monochromatic emission of cations upon heterochromatic background emission. 

He found that the heterochromatic background increased directly 

with the concentration of the radiating species.

Sulfate and phosphate sharply decrease the emission intensity of 

strontium to concentration ratios of sulfate-to-strontium and phosphate-to-strontium of as much as 3 to 1 and 1 to 1 respectively. At 

greater concentration ratios, no further decrease of the strontium 

emission was observed. Baker and Johnson (1954) postulate that the 

formation of partially dehydrated pyrosulfate or pyrophosphate in the 

flame reduces the energy of the flame and therefore prevents excitation 

of the strontium. Margoshes and Vallee (1956) report that because of 

the formation of strontium sulfate or phosphate, which have high 

melting and boiling points, the strontium salt is not dissociated in the 

flame and hence is not excited. Fukushima (1959) has shown that 

sulfate and phosphate interference is the result of a shift in equilibrium 

in the flame.

Fortunately, aluminum, iron, and phosphate are normally present 

in natural waters in amounts ranging from less than one to a few parts 

per million (Hem, 1959) and hence at these concentrations do not 

seriously interfere in the flame-photometric determination of strontium. In order to eliminate or reduce the interference of the other 

cations and anions tested, a radiation buffer was added to samples 

and standards. Skougstad (1957), showed that the addition of 1.0 g 

of potassium chloride and 0.5 g of ammonium citrate per 100 ml of 

of solution eliminated the depressive effect of as much as 1,000 ppm of 

sulfate and 460 ppm of sodium. As shown in figure 3, the enhancement from sodium, potassium, and calcium reaches a plateau at about 

200 ppm concentration, thus the addition of 10,000 ppm of radiation 

buffer to each sample and standard compensates for the effect of 

these ions in the water.

The effect of pH on the emission of strontium was also studied. 

Five series of solutions containing 1, 3, 5, 7, and 10 ppm of strontium 

and a radiation buffer (1.0 g of potassium chloride and 0.5 g of ammonium citrate per 100 ml) were prepared. Such a solution has a pH 

of approximately 5. The pH of four of the series was adjusted with 

hydrochloric acid or ammonium hydroxide, to 1.0, 3.0, 7.0, and 9.0 

and the net emission intensity of each series measured. The maximum net intensities were obtained at pH values between 4 and 7 

(%. 4).
FLAME-PHOTOMETRIC DETERMINATION OF STRONTIUM 41

100

90-

80

I 70

in

rr

I

^ 60 

o

50

UJ

o 40

V)

lOppm Sr

7ppm Sr

5ppm Sr

UJ

fc

20

3 ppm Sr

10

I ppm Sr

23456789 10 

PH

FIGTTEE 4. Effect of pH on the emission intensity of strontium.
42 CHEMISTRY OF STRONTIUM IN NATURAL WATER

ANALYTICAL PROCEDURE

FLAME-PHOTOMETRIC METHOD

The flame-photometric method used for the determination of 

strontium in natural water is practically that described by Skougstad 

(1957). The method has been modified by adding the radiation 

buffer as a solution rather than as a solid, thus, eliminating the 

tedious weighing of the potassium chloride and ammonium citrate. 

Also, adjustment of the pH to the phenolphthalein end point has 

been eliminated. The emission intensity measured at the 460.7-mju 

strontium line is corrected for superimposed background radiation by 

subtracting the emission intensity measured at 458 mp,.

This method may be applied to the determination of strontium at 

concentrations of from 0.2 to 10 ppm. Higher concentrations of 

strontium may be determined if the sample is diluted.

The procedure as adopted, is described below:

Reagents used

Use demineralized distilled water for the preparation of all solutions and 

chemicals of reagent (or, if available, spectroscopically pure) grade. 

Strontium stock solution: 1,000 ppm. Dissolve exactly 1.6848 g of strontium carbonate, previously dried at 105 °C for 1 hour, in a minimal amount of dilute 

hydrochloric acid and dilute to 1 1. Store in a polyethylene bottle. 

Radiation buffer: Dissolve 50.0 g of potassium chloride and 25.0 g of ammonium 

citrate (dibasic) in water and dilute to 500 ml. This solution will keep for 

about 2 months.

Preparation of samples

Prepare a series of standard strontium solutions, containing 1.0, 3.0, 5.0, 7.0, 

and 10.0 ppm strontium by adding aliquots of the strontium stock solution to 

100-ml volumetric flasks that contain 10.0 ml of the radiation buffer. Dilute to 

the mark and mix thoroughly. Prepare a blank (0.0 ppm Sr) by diluting 10 ml 

of the radiation buffer to 100 ml.

Transfer a 50-ml aliquot of the unknown to a 100-ml volumetric flask, add 10 

ml of the radiation buffer, and dilute the solution to 100 ml. Filter if the unknown contains any suspended matter prior to preparation for measurement, to 

prevent clogging the capillary of the atomizer burner.

Measurement of strontium

Use a Beckman DU spectrophotometer equipped with a flame attachment and 

a photomultiplier for all measurements and operate as follows: 

Slit width: 0.01 mm

Sensitivity: 1 to 1*4 turns from full counterclockwise 

Selector: 0.1

Photomultiplier tube: full sensitivity, zero suppression off

Oxygen pressure: 11.0 psi 1 Gas pressures vary according to manufacturer's recAcetylene pressure: 0.5 psij ommendation for the atomizer burner used. 

Strontium line wavelength: 460.7 nijii 

Background wavelength: 458 niju

Because of the very narrow slit width used, a critical adjustment of the wavelength is necessary. With the shutter open and the transmission scale set at 

zero, adjust the dark current control to obtain a null point reading with the
FLAME-PHOTOMETRIC DETERMINATION OP STRONTIUM 43

blank (0.0 ppm) strontium standard. Then adjust the sensitivity control for 

100 percent transmission with 10.0 ppm of strontium. Make readings for the 

1.0, 3.0, 5.0, and 7.0 ppm standards and the correct readings for background by 

subtracting the readings taken at 458 mju for each standard. The calibration 

data yield a straight line over the 0 ppm to 10.0 ppm strontium range (fig. 5). 

Measure the net emission intensity of the unknown solutions, prepared as 

described above, and determine the strontium content from the calibration curve.

Calcinations

Determine the strontium concentration in the sample from the calibration 

curve obtained from known amounts of strontium.

Parts per million Sr= ; X parts per million Sr in sample X dilution factor density

Report strontium concentrations of less than 1.0 ppm to the nearest 0.1 ppm, 

more than 1.0 ppm to two significant figures only.

ION-EXCHANGE METHOD

Strontium in water may be detected by the flame-photometric 

method described above in concentrations as low as 0.2 ppm without 

concentration of the samples prior to atomization in the flame. However, recent data (Skougstad and Horr, 1960) from a selected group 

of surface and ground waters show that the strontium content of a 

majority of these samples is below the detection limit for direct flame 

photometry. Because the flame-photometric method is not sensitive 

for less than 0.2 ppm strontium, it is necessary to increase the strontium concentration at least tenfold in a sample containing strontium 

in the range of 0.02 to 0.2 ppm.

Concentration of strontium in water by precipitation reactions is 

cumbersome owing to the large volume of water required to obtain 

sufficient strontium for easy recovery. Concentration by evaporation 

is time consuming and also may cause precipitation of salts that 

would clog the atomizer burner. These methods of concentration 

are unsuited for the analyses of a large number of samples.

In the analysis of natural water, ion-exchange chromatography is 

used primarily for the concentration of trace amounts of elements 

in solution or for the removal of ions that interfere in a particular 

analytical method. Concentration of trace elements in solution by 

ion-exchange chromatography has been described by Cranston and 

Thompson (1956), Riches (1946, 1947), and Egner and others (1949). 

Tom kins and others (1947), Stanley and Kruger (1956), and Milton 

and Grummitt (1957) have described methods for the separation of 

strontium from the alkali metals and the other alkaline-earth metals. 

However, it is difficult to make a precise separation of strontium from 

these cations. Fortunately, a complete separation of strontium from 

other cations is unnecessary as their effect in the flame-photometric 

determination of strontium is compensated by subtraction of the 

background radiation.
44 CHEMISTRY OF STRONTIUM IN NATURAL WATER 

100

90

80

.

I 70

IT)

60

5 50

2 

UJ

40

to 

to

UJ

20

10

0

Calibration dtata:

Oxygen, ll.Opsi

Acetylene, 5.5psi

Photomultiplier, full sensitivity

Selector, O.I; slit, 0.01 mm

Sensitivity control,Itol l/2turns 

from full counterclockwise

Dark current setatnull point with 0 percent 

transmission and shutteropen for blank 

i I i I i I i

2468 

STRONTIUM, IN PARTS PER MILLION 

FIGURE 5. Typical calibration carve.

10
FLAME-PHOTOMETRIC DETERMINATION OF STRONTIUM 45

Strontium and other cations in water are concentrated from a large 

volume of a relatively dilute solution by absorption on a cationexchange resin followed by elution with a small volume of concentrated 

eluate. Satisfactory results were obtained by absorption on a resin 

in the hydrogen form and elution with hydrochloric acid, but this 

procedure was abandoned because of the objection to atomizing 

large quantities of the acid during the measurement of the strontium 

content of the eluate.

Ammonium acetate and ammonium acetate-acetic acid mixtures 

as eluates for strontium were investigated. Strontium was obsorbed 

on a cation-exchange resin in the ammonium form and the following 

solutions tested for their efficiency as eluate for strontium (1) 1M 

ammonium acetate, (2) 1M ammonium acetate-lM acetic acid, and 

(3) 2M ammonium acetate-lM acetic acid. Successive 5-milliliter 

fractions of the eluate were collected and the strontium content of 

each measured by flame photometry.

Of the three eluates tested, the 2M ammonium acetate-lM acetic 

acid gave the best results (fig. 6). Although the 2M ammonium 

acetate-lM acetic acid curve shows some tailing, this causes no 

serious error in the determination of strontium. A solution of 4M 

ammonium acetate-2M acetic acid also was tried as an eluate, but 

proved useless because of the extremely slow aspiration rate in the 

atomizer burner.

Figure 7 shows the results obtained with 2M ammonium acetate 

at a pH of 8.5 and 7.3 as compared to the 2M ammonium acetate-lM 

acetic acid at a pH of 5.4. Better results were obtained with the 

latter. The elution curves for strontium and calcium, using 2M 

ammonium acetate- 1M acetic acid as the eluate are shown in figure 8.

Analytical procedure

Condition Amberlite IR-120 cation-exchange resin to remove impurities and 

grade to 32- to 42-mesh particle size. Place ten milliliters of this resin in a chromatographic column, converted to the ammonium form, and rinse. Pass a 500-ml 

sample through the column and rinse with distilled water. Elute the strontium 

and other absorbed cations with 50 ml of ammonium acetate-acetic acid solution, 

thus making a tenfold concentration of these cations to that of the original sample. 

Determine the strontium content of the eluate by the flame-photometric procedure 

previously described.

Reagents

Eluatent: Dissolve 154.2 g of reagent grade ammonium acetate in water, add 

57.8 ml of glacial acetic acid and dilute to approximately 800 ml. Adjust the 

pH to 5.4 with ammonium hydroxide and dilute to 1 1. Filter the solution 

before use.

Recharge solution: 5-percent ammonium chloride.

Exchange resin: Amberlite IR-120 prepared as described below.
46 CHEMISTRY OF STRONTIUM IN NATURAL WATER

o

(£.

90

80

70

s

CE 

UJ 

Q.

£60-

ir 

£

| 50

<

CE

40

30

20

10

10 20 30 40 50

ELUATE, INMILLILITERS

60 70

FIGURE 6. Elution of strontium with (A) IM NE^OAe'lM HOAc, pH 4.8; (B) IM NHiOAc, pH. 7.0; 

C2MNH4OAc-lMHOAc, pH 5.4.
STRONTIUM IN ELUENT FRACT

01

O

o o

o o

m 

;o 

in
48 CHEMISTKY OF STKONTIUM IN NATURAL WATER

O 40

OL 

LJ 

CL

tn

OL

^ 30'

uy

z 

o

z

UJ

o

z 

o 0 20

O

entuy 

o

z

< 

o

.0

Calcium 

Strontium

10 20 30 40 SO 6O 70

ELUATE.IN MILLILITERS 

FIGTIEE 8. Elution curves for calcium and strontium using 2M NHiOAc-lM HOAc at pH 6.4 as eluate.
FLAME-PHOTOMETBIC DETERMINATION OF STRONTIUM 49

Preparation of resin.

Condition Amberlite IR-120 cation-exchange resin, which was found to be 

satisfactory, before use to remove traces of iron and other impurities. Place 

the resin in a separatory funnel and shake with QN sodium hydroxide for about 

10 minutes. Decant excess sodium hydroxide, and wash the resin thoroughly 

with distilled water by allowing the water to flow slowly upward through the 

stem of the funnel. Repeat the procedure with 6N hydrochloric acid to convert 

the resin to the hydrogen form. Wash the resin with distilled water until the 

pH of the influent and effluent is the same.

Grade the resin for particle size by wet sieving through a nested set of 20- 32- 42- 

(or 20- 35- 45-) mesh sieves in the following manner: Place the conditioned 

resin on the top (20-mesh) sieve and lower the assembly gently into a beaker 

filled with distilled water. Raise the nested sieves quickly allowing the water to 

drain into the beaker. Continue to alternate lowering and raising of the sieves 

until sufficient resin of 32- to 42- (or 35- to 45-) mesh particle size is obtained 

for packing the column.

Preparation of ion-exchange column

The size of the ion-exchange column depends upon the exchange capacity of 

the resin and the maximum cation concentration of the waters being examined. 

Amberlite IR-120 has a cation-exchange capacity of 1.9 milliequivalents per milliliter of wet resin; thus, a column containing 10 ml of resin is sufficient to completely exchange the cations in 500 ml of water containing as much as 38 equivalents 

per million of cations.

Fill a chromatographic tube (fig. 9) with distilled water, add 10 ml of the 

graded resin as a slurry, and allow to settle. Insure uniform packing of the 

column to avoid channeling and air spaces within the column, which greatly 

reduces its efficiency. After a uniformly packed column has been obtained 

drain the water to the top of the resin bed and pass approximately 100 ml of a 

5-percent ammonium chloride solution through the column. Rinse the column 

with 100 ml of distilled water. The resin is now in the ammonium form and ready 

for use. The chromatographic tube, shown in figure 9, was constructed to require 

minimum attention during the adsorption cycle. The resin bed will not become 

completely drained during operation, as may occur if a buret is used for the 

chromatographic column.

Concentration of strontium

Filter samples that contain suspended material to prevent clogging of the 

column. Pass measured volume of the water sample usually 500 ml, whose 

total cation concentration does not exceed the exchange capacity of the resin 

column through the column at a rate of 1 to 1.5 ml per minute. After the 

sample has passed through the column, rinse the column with 50 ml of distilled 

water to remove traces of anions, and discard the effiuent.

Elute the strontium, together with other cations, from the column with a 

solution of 2M ammonium-acetate-lM acetic acid adjusted to a pH of 5.4 with 

ammonium hydroxide.

Collect exactly 50 ml of the eluate in a volumetric flask. Rinse the column 

with 100 ml of distilled water after elution and it is then ready for the next analysis.

Measurement of strontium

Prepare standard solutions by passing 50 ml each of standards containing 0.0, 

1.0, 3.0, 5.0, 7.0, and 10.0 parts per million strontium through the exchange column 

and elute with 50 ml of the 2M ammonium-acetate-lM acetic acid solution. Use 

results from flame-photometric determinations to prepare a calibration curve and
50 CHEMISTRY OF STRONTIUM IN NATURAL WATER

Chromatogrophic 

tube

 50 ml "Pyrex" conical centrifuge 

tube,cut off and sealed to a 

chromatographic tube

Fritted glass support 

-1.0 mm bore 

capillary tubing

13 cm

FIGUBE 9. Ion-exchange column.

to make the quantitative determination of strontium in the eluate from the 

unknown sample.

Calculations

Determine the strontium concentration in the eluate of an unknown sample 

from the calibration curve of standards containing known amounts of strontium.

Part per million Sr=densityX

parts per million Sr in eluate 

concentration factor

Report strontium concentrations of less than 1.0 ppm to nearest 0.01 ppm and 

concentrations greater than 1.0 ppm to two significant figures only.
FLAME-PHOTOMETRIC DETERMINATION OF STRONTIUM 

BESTJI/TS AND DISCUSSION

51

A comparison of results obtained on routine samples by the flamephotometric, the ion-exchange flame-photometric and the spectrograph 

(Skougstad, 1961) methods is shown in table 3. The values obTABLB 3. Comparison of results obtained by the flame-photometric, ion-exchange 

flame-photometric, and spectrographic methods

[Results in parts per million]

Sample

2640-. ...

2723 .

2785 ...

2802... ...

2874..........

2876- ...

Strontium found by indicated 

method:

Flamephotometric

<0.2

:!

.4 

.8 

.8

Ionexchange 

flamephotometric

0.14

.47 

37

.85

Spectrographic

0.14

.74 

.42 

.47 

1.0

Q

Sample

1

i

OQCQ

3558 

Strontium found by indicated 

method:

Flamephotometric

<0.2

:l

loneschange flamephotometric

0.16

.21 

.08

Spectrographic

0.13 

.44 

.19 

.18 

.06

tained by the flame-photometric and ion-exchange flame-photometric 

methods agree within 13 percent of the spectrographic results. The 

variation between the flame-photometric and ion-exchange flamephotometric methods was 10 percent.

Strontium was added to tap water and analyzed by the flamephotometric method. The results, table 4, show an average deviation 

of 0.10 ppm from the amount of strontium added. The recovery 

varied from 80 to 104 percent.

The results of a similar study for the ion-exchange flame-photometric method is shown in table 5. A synthetic water, containing 

one-tenth the average concentration of the major cations and anions 

found in sea water, was used to prepare three 500-milliliter samples 

containing known amounts of strontium. These samples were then 

concentrated by ion-exchange and analyzed by flame photometry.

TABLE 4. Recovery of strontium, in parts per million, added to tap water 

[Analysis by the flame-photometric procedure]

Sample

la. ...

b ........

d. _ ..

e._ .........

Average

Sr 

added

1.00 

1.00 

1.00

1.00 

1.00

Sr 

found

0.8 

.9 

.9

1.0 

.9

Error

-0.2

-.1 

-.1

0 -.1

-.10

Sample

2a ......

b .......

d...... .

e-._ _ ... 

Average

Sr 

added

1.35 

1.35 

1.35

1.35 

1.35

Sr 

found

1.4 

1.4 

1.4

1.4 

1.4

Error

+0.05 

.05 

.05

.05 

.05

+.05

Sample

3a... ........

b...........

d... ... .....

e... ....... 

Average

Sr 

added

4.20 

4.20 

4.20 

4.20 

4.20

Sr 

found

4.1 

4.0 

4.0 

4.1 

4.0

Error

-0.1 -.2 

_ 2

-!i

 2

-.16
52 CHEMISTRY OF STRONTIUM IN NATURAL WATER

TABLE 5. Recovery of strontium added to a synthetic water l 

[Analysis by ion-exchange flame photometry. Results in parts per millionj

Sample

A__ _ ________ _ ______ _ _______

B__ ______________________________

C_ _______________________________

D_ _______________________________

Sr added

0.08

. 14

.18

.00

Sr found

0.09

. 14

.18

2. 03

Error

0.01

.00

.00

.00

i This synthetic water contains, per liter, the following:

Orams 

Cads.. - . -_ 0.220

KCL--- . 146

NaHCOs -038

Orams 

NaCl _...__.._._ __ 4.696

MgCh.6 HjO ............. ____ 2.130

NaaSOUO HjO..__..,____._____._ 1.780

' The synthetic water contained 0.03 ppm Sr from reagents used in preparation. This blank was 

subtracted from results of A, B, and C.

A recovery of from 100 to 112 percent of the added strontium was 

obtained.

The flame-photometric method is useful for determining strontium 

in concentrations as low as 0.2 ppm with an accuracy of 10 percent. 

A tenfold concentration of strontium in water is accomplished by 

the ion-exchange method by passing the sample through the ionexchange column and eluting with ammonium acetate-acetic acid 

solution. Strontium may then be determined at concentrations as 

low as 0.2 ppm in the ammonium acetate-acetic acid eluant giving a 

determination limit of 0.02 ppm of strontium in the original sample. 

The limit of accuracy is 10 percent.

REFERENCES CITED

Baker, G. L., and Johnson, L. H., 1954, Effects of anions on calcium flame emission in flame photometry: Anal. Chemistry, v. 26, p. 465-468.

Burriel-Marti, F., and Ramirez-Munoz, J., 1957, Flame photometry: Amsterdam, 

Elsevier Pub. Co., 531 p.

Chow, T. J., and Thompson, T. G., 1955, Flame photometric determination of 

strontium in sea water: Anal. Chemistry, v. 27, p. 18-21.

Cranston, H. A., and Thompson, J. B., 1946, Use of ion-exchange resin in the 

determination of traces of copper with special references to powdered and 

fluid milk: Indus. Eng. Chemistry, Anal. Ed., v. 18, p. 323-326.

Egner, H., Eriksson, E., and Emanuelsson, A., 1949, Composition of atmospheric 

precipitation. I. Sampling technique. Use of ion-exchange resins: Kgl. 

Lantsbruks-Hogskol. Ann., v. 16, p. 593-602.

Fukushima, S., 1959, Mechanisms and elimination of interferences in flame 

photometry: Mikrochimica Acta, v. 4, p. 596-618.

Hem, J. D., 1959, Study and interpretation of chemical characteristics of natural 

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Huldt, L., 1944, Intensity anomalies in the flame spectrum of strontium on the 

addition of calcium: Arkiv. Mat. Astron. Fysik, v. B31, no. 1, 4 p.

 1946, The influence of foreign elements on the intensity of spectrum lines 

in the flame of acetylene: Arkiv. Mat. Astron. Fysik, v. ASS, no. 5, 22 p.
FLAME-PHOTOMETRIC DETERMINATION OF STRONTIUM 53

Kirchhoff, G., and Bunsen, R., 1860, Chemical analysis through spectral observations: Annalen Physik u. Chemistry, v. 110, p. 161-189.

Lundegardh, H., 1929, The quantitative spectral analysis of the elements: v. J, 

Jena, G. Fischer.

Margoshes, M., and Vallee, B. L., 1956, Instrumentation and principles of flame 

spectrometry. Effect of extraneous ions in simultaneous determination of 

five elements: Anal. Chemistry, v. 28, p. 180-184.

Milton, G. M., and Grummitt, W. E., 1957, Ion-exchange methods for the quantitative separation of the alkaline earths, and their application to the determination of Sr-90 in milk ash: Canadian Jour. Chemistry, v. 35, p. 541-551.

Mitchell, R. L., and Robertson, I. M., 1936, The effect of aluminum on the flame 

spectra of the alkaline earths: Soc. Chem. Indus. (London) Jour., v. 55, p. 

269-272T.

Riches, J. P. R., 1946, Preliminary experiments with the use of synthetic resins in 

the estimation of trace elements: Nature, v. 158, p. 96.

 1947, Use of synthetic resins in the estimation of trace elements: Chemistry and Ind., v. 66, p. 656-658.

Servigne, M., and Montgareuil, P. Guerin de., 1954, Some results in the determination of elements by flame photometry: Chim. anal., v. 36, p. 115-117.

Skougstad, M. W., 1957, Flame-photometric determination of strontium in water: 

U.S. Geol. Survey open-file rept., 18 p.

 1961, Copper-spark method for spectrochemical determination of strontium in water: U.S. Geol. Survey Water-Supply Paper 1496-B.

Skougstad, M. W., and Horr, C. A., I960, Occurrence of strontium in natural 

water: U.S. Geol. Survey Circ. 420, 6 p.

Stanley, C. W., and Kruger, Paul, 1956, Determination of Sr90 activity in water 

by ion-exchange concentration: Nucleonics, v. 14, p. 114-118.

Taylor, A. E., and Paige, H. H., 1955, Determination of microgram quantities of 

strontium in solution. Evaluation of flame photometric methods: Anal. 

Chemistry, v. 27, p. 282-284.

Tompkins, E. R., Khym, J. X., and Conn, W. E., 1947, Ion-exchange as a separation method. I. The separation of fission-produced radioisotopes, including 

rare earths, by complexing elution from amberlite resin: Am. Chem. Soc. 

Jour., v. 69, p. 2769-2777.

Vallee, B. L., 1954, Fundamental considerations in flame photometry: Anal. 

Chemistry, v. 26, p. 432.

 1957, Trace analysis: New York, John Wiley and Sons, 672 p.

West, P. W., Folse, P., and Montgomery, D., 1950, Application of flame photometry to water analysis: Anal. Chemistry, v. 22, p. 667-670.

Wilson, H. A., 1931, Electrical conductivity of flames: Rev. Mod. Physics, v. 3, 

p. 156-189.

o