NATIONAL BUREAU OF STANDARDS REPORT

3064

OPTICAL SPECTROSCOPIC DETERMINATION OF HYDROGEN

ISOTOPES IN AQUEOUS MIXTURES

by

H.P.Broida^ II. J.Moroidtz and M.Selgin

Progress Report

to

T\£feterans Administration

and

Atomic Energy Commission

U. $. DEPARTMENT OF COMMERCE

NATIONAL BUREAU OF STANDARDS
NATIONAL BUREAU OF STANDARDS

A. V. Astin, Director

U. S. DEPARTMENT OF COMMERCE

Sinclair Weeks, Secretary

ized research, development, and engineering in the field indicated by its title. A brief description

of the activities, and of the resultant reports and publications, appears on the inside of the back

cover of this report.

Electricity. Resistance Measurements. Inductance and Capacitance. Electrical Instruments. Magnetic Measurements. Applied Electricity. Electrochemistry.

Optics and Metrology. Photometry and Colorimetry. Optical Instruments. Photographic

Technology. Length. Gage.

Heat and Power. Temperature Measurements. Thermodynamics. Cryogenics. Engines and

Lubrication. Engine Fuels. Cryogenic Engineering.

Atomic and Radiation Physics. Spectroscopy. Radiometry. Mass Spectrometry. Solid State

Physics. Electron Physics. Atomic Physics. Neutron Measurements. Infrared Spectroscopy.

Nuclear Physics. Radioactivity. X-Rays. Betatron. Nucleonic Instrumentation. Radiological Equipment. Atomic Energy Commission Instruments Branch.

Chemistry. Organic Coatings. Surface Chemistry. Organic Chemistry. Analytical Chemistry.

Inorganic Chemistry. Electrodeposition. Gas Chemistry. Physical Chemistry. Thermochemistry. Spectrochemistry. Pure Substances.

Mechanics. Sound. Mechanical Instruments. Aerodynamics. Engineering Mechanics. Hydraulics. Mass. Capacity, Density, and Fluid Meters. Organic and Fibrous Materials. Rubber. Textiles. Paper. Leather. Testing and Specifications. Polymer Structure. Organic Plastics. Dental Research.

Metallurgy. Thermal Metallurgy. Chemical Metallurgy. Mechanical Metallurgy. Corrosion.

Mineral Products. Porcelain and Pottery. Glass. Refractories. Enameled Metals. Concreting Materials. Constitution and Microstructure. Chemistry of Mineral Products.

Building Technology. Structural Engineering. Fire Protection. Heating and Air Conditioning. Floor, Roof, and Wall Coverings. Codes and Specifications.

Applied Mathematics. Numerical Analysis. Computation. Statistical Engineering. Machine

Development.

Electronics. Engineering Electronics. Electron Tubes. Electronic Computers. Electronic

Instrumentation.

Radio Propagation. Upper Atmosphere Research. Ionospheric Research. Regular Propagation Services. Frequency Utilization Research. Tropospheric Propagation Research. High

Frequency Standards. Microwave Standards.

Ordnance Development. These three divisions are engaged in a broad program of research

Electromechanical Ordnance, and development in advanced ordnance. Activities include

Ordnance Electronics. basic and applied research, engineering, pilot production, field testing, and evaluation of a wide variety of ordnance materiel. Special skills and facilities of other

NBS divisions also contribute to this program. The activity is sponsored by the Department of

Defense.

Missile Development. Missile research and development: engineering, dynamics, intelligence,

instnimentation, evaluation. Combustion in jet engines. These activities are sponsored by the

Department of Defense. • Office of Basic Instrumentation • Office of Weights and Measures.
NATIONAL BUREAU OF STANDARDS REPORT

NBS PROJECT NBS

0301-20-2682

0301-20-2691 December 31* '2-953

OPTICAL SPECTROSCOPIC DETERMINATION OF HYDROGEN

ISOTOPES IN AQUEOUS MIXTURES

by

H„P, Brolda, H.J. Horowitz and M. Selgin

Temperature Measurements Section

Division of Heat and Power

Progress Report

to

Veterans Administration

Washington 25, D.C.

and

Atomic Energy Commission

Washington 25,<-D*C*

<NBS>

U. S. DEPARTMENT OF COMMERCE

NATIONAL BUREAU OF STANDARDS

The publication, reprin Approved for public release by the

unless permission isobt Director of the National Institute of

25 , d.c. Such permiss Standards and Technology (NIST)

cally prepared If that; on October 9, 2015

ait, Is prohibited

irds, Washington

has been speclflI for Its own use.

REPORT

3O6A

FOREWORD

The present report covers the completion of phases of the

projects involving studies of the accuracy and limitations of

the general optical spectroscopic method of determining hydrogen

isotope ratios in aqueous solutions. It also contains a summary

of some of the results of the use of this method for measurements

with blood. Although part of this work was supported by the

Veterans Administration and part by The Atomic Energy Commission,

the results are interrelated and thus a joint report has been

issued. later, it is intended to publish this report in the

Journal of Research, National Bureau of Standards.

F, G. Brickwedde, Chief

Heat and Power Division

A. V. Astin

Director

OPTICAL SPECTROSCOPIC DETERMINATION OF HYDROGEN

ISOTOPES IN AQUEOUS MIXTURES

by

H. P* Broida, H. J.Morowitz'* and M.Selgin

ABSTRACT

Extension of the optical spectroscopic method for

isotope analysis of gaseous mixtures of hydrogen and

deuterium to mixtures of water and heavy water provides

a direct method for determining total water content of

materials, A determination can be made on a sample of

less than Q*1 ml in less than 10 minutes to an accuracy

of a few percent. Using a sample of at least 1 ml, an accuracy of the order of 0,1 percent is obtained in an hour or less. This paper describes the system and the

investigation of optimum operating conditions and effect

of variations in operating conditions on precision and

accuracy of measurement as well as limitations of the

technique, A sample of blood or serum can be measured

directly almost as easily as one of distilled water.

The optical spectroscopic method can be used to determine water content of most materials whether in the

solid, liquid or gas phase.

1, INTRODUCTION

Following initial work on an optical spectroscopic analysis

of gaseous mixtures of hydrogen and deuterium [1,2]^ a similar

technique was tried with mixtures of water and heavy water. A

preliminary study [ 3 ] indicated that it was possible to carry out

such analyses to an accuracy of better than 3 percent. The work

discussed in this paper represents a detailed extension of the

preliminary study in an effort to extend both the precision and

the range and to determine present limitations of the analysis,

A detailed study was made to determine the influence of operating

variables on precision and accuracy of measurement in order to

find the optimum operating conditions. In these studies the

-^-Figures in brackets indicate the literature references at the end

of this report.

'^'Present address - National Heart Institute, National Institutes of

Health, Bethesda, Maryland.
-2-

following accuracy was obtained: (a) .1 percent of the intensity

ratio, in the isotope ratio range .01 to 1.0$ (b) 1 percent, in

the range .00015 to .01 (see table 5 )•

In addition the rather practical problems of developing the

method into a routine analytical technique werp taken into conTM

sideration. For this reason efforts were made to achieve a rapid

analysis, and operating conditions were viewed with the possibility

of constructing a simple flow system and optical system for routine

use. Several types of routine measurements were made concurrently

with the study of the technique.

‘The technique used is as follows. The vapor from an aqueous

sample containing a mixture of IIpO and DpO is pumped through a tube

where a high frequency electrodeless discharge is maintained. The

light emitted from the discharge tube contains lines of the Balmer

series of hydrogen and deuterium with a very small amount of background radiation. The emitted light is dispersed by a monochromator

and the relative intensities of the g lines of the Balmer series of

hydrogen and deuterium are recorded and measured. The ratio of the

intensities of the two lines is a monotonic function of the relative

concentration of the isotopes and to a high degree of accuracy is

equal to the ratio of the isotope concentrations. For precise work

the measurement is a relative rather than an absolute one in that

the relationship between intensity ratio and concentration ratio is

obtained from calibration curves taken on standard samples whose

compositions are determined by independent measurements.

The statistical terms [ 4 t ^

1 used in this report are defined

as follows. Precision refers to the variation encountered during

readings taken in close succession under identical conditions.

Reproducibility refers to the variation among readings when they

are spread over a considerable time period. It is not a fixed

quantity but depends somewhat on the time interval and the history

of the apparatus in that interval. Accuracy refers to the variation of the measured concentration from the true value and is determined from the precision and reproducibility of the measurements

and from the accuracy of the calibrated samples. The relationship

between reproducibility and time determines how frequently it is

necessary to take calibration points. These factors arc all

dependent on the stability of operating conditions.

The above variations are expressed either as standard deviation or as the coefficient of variation. These terms apply either

for single measurements or for averages • Since the standard deviation of the average is dependent on the number of readings taken.
this value is most useful when compared to other sets of the same number of readings, for the purposes of this study, ail standard

deviations of the average refer to sets of 10 readings.

Stability of this system may be viewed in the following

manner* Consider the measured ratio of intensities of the Calmer

.line to the ILBalmer line at 4360,0 A and 4361,3 A, respectively

,

and represent this ratio by Dp/llg . This ratio is a function of a large number of variables such as the actual concentration ratio d/h

in the sample t the temperature, the pressure, the flovr rate,

etc,, and may be represented in the following fashion:

Vi - D/H Od/h, xlt ;c2 ... %,)

where X-j_ are independent variables. In practice, operating con- ditions are found such that f is very nearly unity,

A completely stable set of operating conditions is one in which

Di/Hi is a function of D/H only and unaffected by small changes of

Xt, Xp ,,,, At*, From a practical point of view the conditions of

stability are what changes of Dg/llp due to variations of the Xp are small compared with changes due to variations of D/H, Many of the

experimental curves shown in the following sections are graphs of

the ratio Dp/fh as a function of one of the independent variables

with all other variables kept as constant as possible.

The samples employed in these e;qoeriments are in all cases aqueous solutions or suspensions in which the solvent is a mixture

of hydrogen oxide HpO and deuterium oxide DpO. The number used to

describe concentrations is, unless otherwise specified, the atom

ratio of deuterium to hydrogen, D/lI, This figure depends only

upon the number of atoms of hydrogen and deuterium in the sample

and is independent of the equilibrium between HpO, HDO and DpO.

In taking measurements of isotope ratios the vapor is pumped

from the liquid through the discharge tube. This procedure raises

two questions ; what is the relationship between D/H in the liquid

and the vapor and what fractionation (isotope separation) occurs in the flow process? The first question is purely academic with

respect to the analysis of water, A given ratio of D to H in the

liquid mil always give rise to a reproducible ratio in the vapor

and since all measurements are taken relative to calibration samples

the measurement taken is in all cases referred back to the liquid.
-4

-

Owing to the difference in vapor pressure between I12O, HDO

and D2O the process of evaporating liquid from samples involves

some degree of fractional distillation. This has been investigated experimentally to study the overall effect and will be

discussed in a later section.

The processes occurring in the breakdown of water vapor in

the radio frequency field are imperfectly understood and will be

discussed only briefly. The discharge through the water vapor in

the tube causes excitation, ionization and dissociation giving

rise to the following atoms and molecules from a mixture of normal

and heavy water:

H, D, HD, H2 , D2 , QE> 0D j h2°2> °2°2» h2°> mo> D

2°> im2

as well as other groupings, most of which may exist as normal,

excited, or ionised molecules. The emission spectrum from the discharge contains lines and bands from many of these components. The

Balmer lines of hydrogen and deuterium are prominent in this spectrum.

The p

line of the Balmer series was chosen because the largest

output signal was obtained for this line. This is a result of the

product of the actual intensity and the phototube sensitivity being

a maximum in the region of the p Balmer line of the hydrogen spectrum.

The o< lines at S56I.O A and 6562 .B A for D and H, respectively,

also can be used; this pair has the advantage of a somewhat larger

separation than the p

pair ( 1.3 A compared to 1.3 A).

2. EQUIPMENT

2.1 Glass Plow System

A glass flow system was employed to. provide a steady flow of

sample vapor through the discharge tube. A flow system decreases

problems of contamination by previous samples and simplifies the

preparation of the sample for analysis. The s3'

- stem, shovm photographically in figure 1 and schematically in figure 2, consists

of the following components

(l) Sample bottles.- The sample bottles are equipped with an

inverted standard taper ground glass joint so that rapid change of

samples can be made.
(2) Sample connectors.- The connectors are standard taper

ground glass joints corresponding to those on the bottles. A

special vacuum line (figure 2) provides a means of evacuating

the air from the sample chamber before admitting sample into the

main flow system.

(3) Pressure regulator.- In order to vary and control

pressure in the discharge tube a parallel network is provided con- sisting of a capillary and a continuously variable metal leak valve.

In most of the studies described in this paper, the variable metal

leak valve was used because fine pressure control and frequent

adjustments were necessary. However, for routine measurements a fixed non-metallic orifice is preferable.

(4) Pressure gauge.- To measure pressure in the system, a pressure line connects through stopcocks to various critical

locations. Pressure measurement is made by means of a commercial

ionization gauge, which utilizes alpha particles from a radium source

to provide ionization. The gauge can be used from pressures of 1

micron to 1 centimeter.

(5) Discharge tube.- The discharge tube consists of a glass

inner cylinder surrounded by a glass water jacket. Water flows

through the jacket at a constant rate controlled by a regulator

at the tap. Air bubbles in the water, which might affect intensity

measurements, are eliminated by an extractor shown at point G in

figure 1.

(6) Pumps.- The two main vacuum lines shown in figure 2

connect with independent pumping systems. The left hand line goes

to a trap, single stage oil diffusion pump and forepump while the

right hand line goes only to a trap and mechanical pump. The

diffusion pump was used in these investigations because a wide

variation in conditions was to be studied.

2.2 High Frequency Source

The energy necessary to excite the spectrum of the sample was

provided by a commercial I5O megacycle 156 watt oscillator. The

energy is carried through a radio frequency cable which terminates

in a tunable quart er-wavelength tank circuit with antennae

held near the discharge tube. This terminal circuit is shown

diagramatically in figure 2. A radio frequency shield (point J in

figure l) cuts down stray radiation which might affect other

electronic equipment.
2.3 I5ono chronator

The apparatus used to analyse the spectrum consists of a high

resolution grating monochromator with a photomultiplier detector

and associated amplifier and recorder . A detailed discussion of

the original monochromator is given by Fastie [6 •

The plane diffraction grating used in the monochromator is 3

by 3 inches and is ruled with lines per inch; the instrument

has a practical resolving power ( X/Al) of 55jOOO. This resolution

is sufficient to observe some of the fine structure splitting of

H<x and lines, Mie choice of optimum resolving power is governed

by two considerations: it must be sufficient to resolve the lines

to be analyzed and at the same time be low enough to allows for the

integrated intensity of a line to be approximated by the peak height

of that line. The resolving power was varied by varying the width

of the entrance and e:d.t slits until the p line of deuterium could

be resolved in a normal water discharge (D/H = .00015) [7i. Figure

3 shows the H, D, and H ghost lines resolved and indicates, on the

basis of the half width of the line, a resolving power of 20,000.

This resolving power proved suitable for subsequent studies.

The first Rowland ghost of the /3 line of hydrogen was spaced

about 2.0 A from the line and was approximately I/5OO as intense.

The ^

line of deuterium appears between the H line and its first

ghost. The ratio of ghost intensity to line intensity is a function

of the optics of the system only, and under conditions of fixed

optics may be taken as a constant. For low deuterium concentrations

the ratio between the deuterium line and the H ghost is a fixed

multiple of the ratio between the D and II lines. This fact proves

useful in allowing comparison to be made between signals taken at

the same scale of amplification, the calibration in this range being

independent of the ratio of amplification for different scales.

2.4 Power Supply, Amplifier and pLecorder

A chopper before the entrance slit of the monochromator converts the input signal to 60 cps. This signal is fed into a narrow

band-pass synchronous amplifier, the output of which is recorded by

'“This equipment was on field trial loan to the National Bureau of

Standards from the Research Division of the Leeds and Northrup

Company.
-7-

a pen on ten-inch chart paper* The recorder has a response time of one second. The power supply for the photomultiplier is continuously

variable from 500 to I3OO volts. By using the photomultiplier with

a sensitive linear a-c amplifier which has an accurate amplification

factor ranging from 2 to COO, very small signals can be observed.

3 . EXPERIMENTAL fiEs O LTS,

The primary purpose of this study was to determine the effects

of numerous interrelated variables on the speed, accuracy and sensitivity of the method. The variables include pressure in the flow

system, flow rate, sample size, solute composition of the sample,

temperature, and oscillator characteristics. These variables will

be considered in detail. The percent change in ratio per unit change

in variable was computed for each operating curve and can be used to

determine how closely each variable must be controlled to achieve a desired precision (see table 7 )*

The methods of measuring intensity ratios for the 0-1 percent

D

2O range and the 1-99 percent DoO range are shown in figure 3 . As previously discussed the deuterium to ghost ratio is used instead

of the deuterium to hydrogen ratio in the 0-1 percent range. In the

1-99 percent range the D and H lines were measured directly at a lower amplification. In both concentration ranges the baseline, or background, is somewhat arbitrary and is taken at a fixed distance

from the deuterium peak. This causes no error in the final measurement since the calibration is made in the same manner as the measurement.

3.1 Memory

The speed with which a measurement can be taken is largely

dependent on the memory of the system: i.e. the time required to

clean the system of one sample and saturate it with another so that

a constant ratio is obtained. Metal parts are troublesome, but the

metal leak valve usually was employed to gain fine pressure control

in spite of its memory effect.

Figure 4 shows a series of experiments under extreme conditions

in which a pure water sample was run and then switched to commercial

heavy water. Curve a shows the effect, under the slowest conditions,

of using the metal leak valve with no intermediate pumping or flushing. Curve b shows the effect of using a glass capillary tube and a glass stopcock for pressure control with no intermediate pumping or

flushing. For routine measurement the capillary tube and stopcock

were used under the following
conditions. The system was pumped with and without sample between

extreme pressures in the ratio of at least 15 to 1. hese changes

were made rapidly for approximately 2 minutes and then the pressure

was stabilized to 400 microns. The memory effect was thereby re- duced to that shown in curve c.

These curves show that an all glass system with intermediate

flushing produces the greatest reduction of the memory effect. Even

with an extreme change in concentration, equilibrium is reached to

within 1 percent in less than 3 minutes and complete equilibrium in

approximately 1 hour. The flow system shown in figure 2 was designed

for maximum variability, but for routine use a much simpler system

is advantageous. Also the elimination of side projections should

reduce the memory time.

3.2 Pressure

The operating pressure in the discharge tube has an effect on

the intensity ratio, especially in the 0-1 percent DpO range (see

figure 5)* Flow rate was not held constant so actually the traces

show ratio vs a combination of pressure and flow rate at constant

pumping speed as determined by settings of the metal leak valve and

the speed of the pump. The flow rate in milligrams per minute

decreased from 0.011 at a pressure of 900 microns to 0.0023 at 400

microns and 0.001 at 200 microns. The pressure gauge used had the

disadvantage of large metal surfaces and considerable memory effect.

Such memory is undesirable for measurements where the concentration

is being changed frequently. Therefore the gauge was isolated from

the system after initial pressure setting and during the course of

most intensity ratio measurements. The disadvantage of not taking

continuous pressure readings was overcome by utilising the fact

that the length of the discharge is a sensitive function of the

pressure, it provided a good check on the constancy and reproducibility of pressure and flow conditions.

Intensity as a function of pressure was investigated at various concentrations and the results are shown in figure 6. The curves are quite similar at all concentrations. An operating

pressure of approximately 400 microns was chosen for routine use

because it makes use of maximum intensity and the flattest portion

of the intensity vs pressure curve. It also occurs at regions of

the ratio vs pressure curves that are reasonably flat. The percent

change of ratio per unit change in pressure at 400 microns as com-

- puted from figure 5 is .020 percent per micron. This means that

the pressure must be held to ±5 microns to achieve a precision of

±.l percent.
-9-

3.3 Fractionation

At 20°G there is a difference of 2,3 rani of mercury between the

vapor pressure of HpO and DpO with HDO having an intermediate pressure [7J. Thus a sample which is being evaporated will begin to

concentrate deuterium.. To check on the error to be expected from

this effect, a 0,5 ml sample was run continuously to dryness with

frequent checks made on the D/H ratio. The results at an operating

pressure of 200 microns are shown in figure 7. From this curve the

minimum sample size can be computed for a given flow rate and

allowable error. This is shown in detail in Section 5* Discussion,

3.4 Temperature

The ratio of the vapor pressure of ITpO, DpO and HDO changes

with temperature so that some error might be expected from variation of sample temperature. To study this effect sample bottles

were immersed in a constant temperature bath during these determinations, Table 1 shows the results taken at temperatures ranging

from 0,4° to 25.8°C. From this table the percent change in ratio

per unit change in sample temperature was computed to be .15 percent per degree Centigrade,

TABLE 1, Intensity Ratio vs Sample Temperature

Sample

Ho.

Temperature

~ OP

Ratio

Di/Hi

3-4 4.0 0.3895

25.8 .0965

3-9 0.4 0.0454

3.0 ,0452

17.0 .0466

22.0 .0470

Pressure = $00 microns
-10-

3.5 Flow-Rate

Flow rate affects the D/H ratio, the rate of fractionation,

and the size of the smallest sample measurable. It is a function of

pressure, the geometry of the flow system, and the speed of the

pump. Table 2 gives data obtained for Dj /Hj_ ratio as a function of

the flow rate at constant pressure. This table shows that Dp/Hp

decreases with decreased flox'f-rate and indicates that at least part

of the effect of change of pressure (figure 5 ) is caused by the

reduced flow rate at lower pressures. The percent change of ratio

per unit change of flowrate computed from table 2 is 0.5 percent

per g/min»

TABLE 2. Intensity Ratio vs Flow-Rate

Flow

(grams/min)

Ratio

Di/Hi

0.01125 0.899

.00983 .894

.OO33I .857

Pressure = 40C microns

Flow-rate obtained by weighing sample

before and after flow.

3.6 Oscillator and Discharge Characteristics

The discharge characteristics can be varied by changes in

oscillator plate current, anenna tuning, position of electrodes

with respect to the tube, and the temperature of the cooling

stream in the jacket of the discharge tube. Plate current is

variable betx\reen 100 ma and 200 ma and the tuning is adjusted

by the tuning capacitor in figure 2 as veil as by the position

of the radio frequency shield and electrodes. The radio frequency
-11-

shield and electrodes were placed to obtain maximum intensity and

the tuning capacitor varied to give a range of discharge lengths.

Ratio of %/% as a function of discharge length is shorn in table

3. The effect on Di/% of changing the oscillator plate current

is shown in table 4. It is seen that there is no appreciable effect

of the discharge length or plate current on the measured ratio. The

temperature of the cooling stream was varied by changing the water

flow rate through the discharge tube jacket. %/% varied less than

1 percent over the extreme range of temperature from a stream, of the

coldest water available from the tap (approximately 13° C) to no cooling (greater than 200°C).

TABLE 3. Intensity Ratio vs Percent Maximum Discharge Length

Sample

No.

Percent of Maximum

Discharge Length

Ratio

Di/Ili

S-9 100 4.71

38.6 4.73

73.8 4.35

49.4 4.48

S-12 100 49.74

93 49.5

91.3 49.71

32.7 49.79

75.1 49.97

64.7 50.17

52.0 '50.04

49.0 49.79

Pressure = 500 microns
-12-

TABLE 4. Intensity Ratio vs Oscillator Plate Current

Sample

No.

Plate

Current

(rna)

Ratio

Di/Hi

3-9 100 0.0503

122 .0499

140 . .0491

175 .0491

190 .0490

S—12 100 1.015

125 1.016

130 I.013

150 I.015

185 1.012

200 1.012

210 1.012

Pressure = 500 microns

3.7 Solute Composition

Since this method of analysis may be extended for use with

many aqueous solutions, preliminary investigation was made of the

variation of ratio with the amount of solids dissolved in

the sample. This test was made with NaCl. With concentrations

of 0 percent, 1 percent, 10 percent and a saturated solution, no variation of was found within the experimental error,

4. CALIBRATION CURVES, PRECISION AND REPRODUCIBILITY

Calibration curves were necessary to achieve the highest

accuracy. Figure 8 shows the 0-1 percent D9O range and figure 9

the 1-30 percent DpO^ range. Samples were made by mixing portions

of distilled water and commercial DoO (99 •&%) which had been weighed

to an accuracy of 0,1 mg.

Q

^Calibration curves were taken on samples up to 99*3 percent DpO

(commercially available), but no extensive measurements were made

in the high concentration range. The analysis in this range differs

from that in the low range only in the method of preparing standard

samples.
-13-

Table 5 gives examples of the isotope content expressed., for

comparison, in ratio and in percent, and shows precisions obtained

under optimum conditions.

TABLE 5. Comparison of

Method

Ratio Method and Percent Conceir

of Expressing Isotope Content

bration

Ratio

(D/II)

Standard

Deviation

of

Average

of

Ratio^

Coefficient

of

Variation

of

Average^

Deuterium

Concentration

Expressed in

Percent

(D/D+H x 100)

Standard

Deviation

of

Average

of

Concentration-1'

Coefficient

of

Variation

of

Average^

500 5.0 1.0 99.8 0.002 0.002

100 0.1 0.1 99.0 .001 .001

10 .01 .1 90.9

i • o1— 1 O1— •

1 .001 .1 50.0 .25 .05

.1 .0001 .1 9.09

I • o1— .01

• OH .00001 .1 0.99 .001 .1

.001 .000007 .7 .100 .0007 n

• i

.0001 .000002 2.0 .01 .0002 2.0

1-M3ased on a set of 10 readings,

oStandard deviation of average expressed in percent

Reproducibility was measured on a 21 percent D90 sample and

a 0.2 percent D£0 sample. Measurements were taken at varying time

intervals and in some cases with major changes taking place during

the interval, both in the apparatus and in the concentration ratios.

Results are shown in figure 10 for four portions of the 21 percent

sample. Each point shows the average of 10 readings with the precision depicted as vertical spread. The grand average is a solid
-14-

horizontal line and the standard deviation computed directly from

all 21 averages is shown by dotted lines on either side of the grand

average. Thus the relation between precision and reproducibility

at this stage of development can be seen at a glance. The results

obtained for the 0,2 percent sample were similar. Data for it are

listed in table 6,

TABLE 6, Reproducibility of Intensity Ratio for a 0 , 2%

D2O Sample Over One Month, Each Ratio is the

Average of 10 Readings,

Date D-^/Gj*.

April 28, 1953 O.76O

May 1 .737

May 2 .736

May 4 .733

May 7 .729

May 7 .724

May 7 .744

May 8 .751

May 8 .743

May 11 .753

May 15 .740

May 18 .769

May 18 .754

May 19 .765

May 20 >753

Average 0.746

Pressure =: 200 microns * Gj_ is the measured intensity of the ghost of the H line
-15-

5. DISCUSSION

The great number of variables which influence the measurement of D/H ratios makes it impossible to be certain that the final

operating conditions are in fact the optimum ones. Indeed, it is

not necessary to assume that there is a unique set of optimum con- ditions for this analysis. The operating conditions chosen therefore are the "best set" based upon data available and the nature

of the measurements to be performed. Some of the final data used

to evaluate operating conditions are shown in table 7* This table

illustrates that there is no extreme problem in keeping the

operating conditions constant enough so that the measurement can

be made within the desired accuracy.

TABLE 7. Operating Variables

Condition

Varied

Percent change

of ratio per

unit change of

variable

Routine

Operating

Conditions

Sample temperature .15# per °C room temperature

Pressure . 020fa per micron 400 microns

Salt concentration 0% per mole/liter any

Flow-rate 0.5 per g/min depending on sample

size and desired

speed of measurement

Tuning 0# per % change

in discharge

length

maximum discharge

length

Osc. Plate Current 0% per mA 175 mA

Discharge Tube Temp. .005# per °C room temperature
Accessory factors enter into the choice of best conditions.

The fractionation curve (figure 7) can be represented as RS^ = K

where R is the isotope ratio, S is the sample size and k and K

are experimental constants. In differential form the fractionation

curve can be represented as

dR = -k dS

R S

where the left hand side represents the percent change of ratio

due to fractionation. Setting dR/R equal to e the maximum,

tolerable fractionation error and realizing that dS = - f&t, the

flow-rate times the time increment, we arrive at the following

expression for minimum sample size:

S =

e

The value of k, 0.068, was obtained from the data shown in

figure 7® As has been mentioned previously, flow-rate depends on operating pressure, flow-geometry and pumping speed, while time

of measurement depends on memory and time necessary for pressure

equilibrium, so that sample size is some complex function of the

major operating variables. Under normal conditions at 400 microns

operating pressure the flow-rate was ,0023 ml/min and the time

per determination was 20 minutes. The minimum sample size is

therefore ,00313/e or ,3 ml for a 1 percent error. The absolute

minimum sample size under present conditions involves an operating

pressure of 200 microns and a maximum error of 3 percent. Under

these conditions, a seven-minute measurement is possible and the

minimum sample size is ,02 ml.

The operating conditions which were found to be most suitable

with the equipment described in this paper are shorn in table 6,

This study is not exhaustive inasmuch as there are many

combinations of variables \vhich were not tried. In addition no attempt was made to vary systematically such things as the

oscillator frequency or discharge tube geometry. A few preliminary

experiments with a 2240 me oscillator indicate that a stable set

of operating conditions can be set up at that frequency.
17-

As pointed out in the beginning of this paper, the chief object

of these studies was to determine how to minimize error, sample size,

and time of determination. Of course it is impossible to minimize

all three factors at once. Highest precision requires many determinations per sample, hence a long time and large sample size. The

minimum values attainable at the present stage of development and

the maximum values obtained while minimizing the others are given as follows

I'-Hnimum Maximum

Precision (coefficient

of variation of the

average) .1 - 2% yf0

Sample Size .02 ml 1 ml

Time per Sample 7 minutes 60 minutes

With respect to precision and time per determination the optical spectroscopic case compares favorably with other methods. It

finds particular application where the water samples contain impurities. Whereas other methods require one or two stages of purification, the sample vapor can be analj^zed directly by this method.

This method appears to be considerably more rapid and, for similar

accuracy, less expensive than other methods.

While it is not the function of this paper to discuss, in detail,

applications of hydrogen-deuterium analysis, we shall review briefly

in the following paragraphs some of the most important uses to which

the optical spectroscopic method has been placed. The dilution

technique for determining the total water content of materials involved

in these uses is described in reference [ 3 ]. Essentially it consists

of dissolving or suspending a known amount of the material to be

analyzed in a mixture of DqO and HqO and then determining spectroscopically the resulting change in the ratio of DqO to HqO.

(1) Determination of DqO content of blood. In this application

the blood, serum or plasma is placed in the sample bottle and the

vapor analyzed in the usual manner. No prior preparation of the blood

is necessary and high precision is obtainable. This technique finds

application in the determination of total body water by DqO dilution

and in the study of water exchange in capillarj7- beds. Over I5O blood

samples have been run and no difficulty has been encountered in adapting the techniques to routine analysis.
-13-

(2) Determination of water of hydration or water of crystallization. The crystal to be analyzed is dissolved in DpO, and the

final intensity ratic gives a measure of the HpO originally present

in the crystal. Several hydrates have been tried and results agree

with other methods.

(3) Determination of labile hydrogen. A weighed quantity of

dry material containing labile hydrogens is dissolved in DpO and

the resultant ratio measured. From the number of exchangeable

hydrogen atoms per molecule, information about structure of the

molecule is obtained.

The most extensive work has been done with blood for which a brief description of the routine application follows.

Army Medical Service gave injections of 100 gms of commercially

pure DpO to several hemorrhagic fever patients and sampled blood at

various time intervals. The serum samples were analyzed at the

National Bureau of Standards to determine the total body water content of the patients. 73 samples in the concentration range .029

percent to .425 percent gave precisions of the order of 0.7 percent

coefficient of variation of the average. Ten readings were taken

per sample using the metal leak valve for pressure control. Time

per sample ranged between 25 and 55 minutes depending on stability

of operating conditions.

Reference Of] gives details of a study of transcapillary exchange

rates of D2O ariu thiocyanate in the forearm of man. A study has

since been made of the exchange rates from the artery of one arm to

the vein of the other. In this case only 5 readings were taken per

sample and metal parts were eliminated, thus cutting the total time

per sample down to 15 minutes plus data calculation time. The

precision of measurement was of the order of 1.5 percent coefficient

of variation of the average for 17 samples in the concentration

range .015 percent to 2.000 percent DpO.
19-

6. REFERENCES

[ 1 ]

[ 2 ]

C3l

[43

[ 5 ]

[ 6 ]

[7]

C83

H.P.Broida and J.W.Moyer, Spectroscopic analysis of deuterium

in hydrogen-deuterium mixtures, JOSA £2, 37(1952).

H.P.Broida and G.H.Morgan, Optical spectrophotometric analysis

of hydrogen-deuterium mixtures in presence of air, Anal. Chem.

24, 799(1952).

H. J.Morovdtz and H.P.Broida, Rapid spectroscopic determination

of total water content. Anal. Chem. Si, 1657 (1952).

Statistical method for chemists, (John Wiley and

A.S.T.M. Manual on Quality Control of Materials, A.S.T.M.

,

Phila., Pa., Jan. 1951*

William G. Fastie. A small plane grating monochromator,

JOSA 2, 641(1952).

I. Kirshenbaum, Physical properties and analysis of heavy

water, p. 396 (McGraw-Hill 1951) •

Edward D. Freis, Thomas F. Higgins and Harold J. Morowitz,

Transcapillary exchange rates of deuterium oxide and thiocyanate

in the forearm of man, J. Applied Physiology £, 526 (1953)
-20-

7. LEGS:IDS FOR FIGURES'

Fig. 1. Flow System for H-D Analysis, Points indicated are:

A, Sample bottles. B. Sample connectors. C, Metal leak

valve. D ? Glass capillary. E, Pressure gauge.

F, Discharge tube. G, e:ctractor. H, Trap.

J, Shield for high frequency source. K, Lens. L, Chopper.

M, Photomultiplier tube.

Fig. 2. Schematic Diagram of Flow System.

Fig. 3. Method of Measuring Intensities (Hy, Dy, Gy). Height of IT line (Hy) is approximately 500 times that of H ghost line

(Gy). The zero line is arbitrarily taken 6.6 A from the

H line and intensities are measured as distances above the

zero line. From left to right, traces are of O.Zj. percent

and 10 percent DgO samples ? respectively.

Fig. 4* Memory Effect. Pressure = 400 microns.

a. Metal leak valve with no intermediate pumping or flushing

between samples.

b, Glass stopcock with no intermediate pumping or flushing.

£, Glass stopcock with intermediate pumping and flushing.

Fig. 5. Intensity Ratio vs Pressure. Seven samples at various concen- trations. The calibrated concentration of each sample by

weighing is given at end of each trace.

Fig. 6. Total + D*s Intensity vs Pressure at various concentrations.

Fig. 7. Fractionation Effect. Flow x-ra,s continuous at .063 ml/hr.

Dy/Gy scale is greatly expanded.

Fig. 8. Calibration Curve for 0-1^ D

2

O Concentration Range. Samples

were made up by weighing.

Fig. 9. Calibration Curve for l-SO^o D

2

O Concentration Range. 80-99

percent portion of the curve is omitted because of the

extended scale. Samples were made up by weighing.

Fig. 10. Precision and Reporducibility for 21/o D2O samples. Readings

were taken on 4 identical samples over 3 months. Times of

taking data are^ from left to right, as follows
-21-

Sample Number

3-2S .

S-29

S-30

S-31

Date

Dec. 9, 1952

Dec. 9, 1952

Dec. 23, 1952

Dec. 1, 1952

Dec. 1, 1952

Dec. 2, 1952

Dec. 2, 1952

Dec. 3, 1952

Dec. 3, 1952

Dec. 4, 1952

Dec. 5, 1952

Dec. 5, 1952

Dec. 5, 1952

Dec. 5, 1952

Dec. 22, 1952

Feb. 25, 1953

Dec. 4, 1952

Dec. 4, 1952

Dec. 23, 1952

Dec. 19, 1952

Dec. 19, 1952

FIGURE I.
-

'
ALPHATRON

PRESSURE

GAGE 3 0= O 3 £ ^

FIGURE

2.

FLOW

SYSTEM

FOR

ISOTOPE

ANALYSIS

c

o

•O

c

3

ow.

CT» o

o

©<

K)

G

K.o

Q.

<U

(/)

0-1% D 2 0 RANGE 1-99% D 2 0 RANGE

<NBS>

FIGURE 3.

amplification

scale

- 10

FIGURE 4.

FIGURE 5.

D

2

0

CONCENTRATION

(percent)

($*!un Ajojjjqjo) A1ISN31NI 1V101

o

O

O

CVJ

o

o

o

o

o

CO

o

o

CD

o

o

o

o

CM

o

CD

yj

a:3

CD

iZ

PRESSURE

(microns)

REMAINING

VOLUME

(ml)

o

o

o

CO

LlJ

o 1

I—

o

CM

o

! 9/'a

FIGURE

o

ro c\j

o\

Q

FIGURE
I
D 2 0 CONCENTRATION (percent)

33 50 67 75

FIGURE 9.

roi CO0

ro1 C

<T> CMI CO

cr

Id

CD

yj

_i

CL1<

CO

CD

CMI CO o in O Is- co CD

OJ CM CM

FIGURE

10.

THE NATIONAL BUREAU OF STANDARDS

Functions and Activities

The functions of the National Bureau of Standards are set forth in the Act of Congress, March

3, 1901, as amended by Congress in Public Law 619, 1950. These include the development and

maintenance of the national standards of measurement and the provision of means and methods

for making measurements consistent with these standards; the determination of physics! constants and properties of materials; the development of methods and instruments for testing materials,

devices, and structures; advisory services to Government Agencies on scientific arid technical

problems; invention and development of devices to serve special needs of the Government; and the

development of standard practices, codes, and specifications. The work includes basic and applied

research, development, engineering, instrumentation, testing, evaluation, calibration services, and

various consultation and information services. A major portion of the Bureau’s work is performed

for other Government Agencies, particularly the Department of Defense and the Atomic Energy

Commission. The scope of activities is suggested by the listing of divisions and sections on the

inside of the front cover.

Reports and Publications

The results of the Bureau’s work take the form of either actual equipment and devices or published papers and reports. Reports are issued to the sponsoring agency of a particular project

or program. Published papers appear either in the Bureau’s own series of publications or in the

journals of professional and scientific societies. The Bureau itself publishes three monthly periodicals, available from the Government Printing Office: The Journal of Research, which presents

complete papers reporting technical investigations; the Technical News Bulletin, which presents

summary and preliminary reports on work in progress; and Basic Radio Propagation Predictions,

which provides data for determining the best frequencies to U3e for radio communications throughout

the world. There are also five series of nonperiodical publications: The Applied Mathematics

Series, Circulars, Handbooks, Building Materials and Structures Reports, and Miscellaneous

Publications.

Information on the Bureau’s publications can be found in NBS Circular 460, Publications of

the National Bureau of Standards ($1.00). Information on calibration services and fees can he

found in NBS Circular 483, Testing by the National Bureau of Standards (25 cents). Both are

available from the Government Printing Office. Inquiries regarding the Bureau’s reports and

publications should be addressed to the Office of Scientific Publications, National Bureau of Standards, Washington 25, D. C.