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TECHNICAL

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Separation and Purification

Section:

Summary of Activities

July 1967 to June 1968

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U.S DEPARTMENT OF COMMERCE

National Bureau of Standards

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NATIONAL BUREAU OF STANDARDS

The National Bureau of Standards1 was established by an act of Congress March 3,

1901. Today, in addition to serving as the Nation's central measurement laboratory,

the Bureau is a principal focal point in the Federal Government for assuring maximum application of the physical and engineering sciences to the advancement of technology in industry and commerce. To this end the Bureau conducts research and

provides central national services in three broad program areas and provides central national services in a fourth. These are: (1) basic measurements and standards,

(2) materials measurements and standards, (3) technological measurements and

standards, and (4) transfer of technology.

The Bureau comprises the Institute for Basic Standards, the Institute for Materials

Research, the Institute for Applied Technology, and the Center for Radiation Research.

THE INSTITUTE FOR BASIC STANDARDS provides the central basis within the

United States of a complete and consistent system of physical measurement, coor- dinates that system with the measurement systems of other nations, and furnishes

essential services leading to accurate and uniform physical measurements throughout

the Nation's scientific community, industry, and commerce. The Institute consists

of an Office of Standard Reference Data and a group of divisions organized by the

following areas of science and engineering

Applied Mathematics—Electricity—Metrology—Mechanics—Heat—Atomic Physics—Cryogenics2—Radio Physics2—Radio Engineering2—Astrophysics2—Time

and Frequency.2 THE INSTITUTE FOR MATERIALS RESEARCH conducts materials research leading to methods, standards of measurement, and data needed by industry, commerce,

educational institutions, and government. The Institute also provides advisory and

research services to other government agencies. The Institute consists of an Office of

Standard Reference Materials and a group of divisions organized by the following areas of materials research:

Analytical Chemistry—Polymers—Metallurgy — Inorganic Materials — Physical

Chemistry.

THE INSTITUTE FOR APPLIED TECHNOLOGY provides for the creation of appropriate opportunities for the use and application of technology within the Federal Government and within the civilian sector of American industry. The primary functions

of the Institute may be broadly classified as programs relating to technological meas- urements and standards and techniques for the transfer of technology. The Institute

consists of a Clearinghouse for Scientific and Technical Information,3 a Center for

Computer Sciences and Technology, and a group of technical divisions and offices organized by the following fields of technology:

Building Research—Electronic Instrumentation — Technical Analysis — Product

Evaluation—Invention and Innovation— Weights and Measures —Engineering

Standards—Vehicle Systems Research.

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and application of radiation to the solution of Bureau mission problems and the

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Reactor Radiation—Linac Radiation—Applied Radiation—Nuclear Radiation.

1 Headquarters and Laboratories at Gaithersburg, Maryland, unless otherwise noted ; mailing address Washington, D. C. 20234.

2 Located at Boulder, Colorado 80302.

3 Located at 5285 Port Royal Road, Springfield, Virginia 22151.
UNITED STATES DEPARTMENT OF COMMERCE

C. R. Smith, Secretary

NATIONAL BUREAU OF STANDARDS • A. V. Astin, Director

NBS TECHNICAL NOTE 459

ISSUED DECEMBER 1968

Separation and Purification

Section:

Summary of Activities

July 1967 to June 1968

Edited by David H. Freeman

Separation and Purification Section

Analytical Chemistry Division

Institute for Materials Research

NBS Technical Notes are designed to supplement the Bureau's regular publications program. They provide a means for making available scientific data that are of transient or limited interest. Technical Notes may be

listed or referred to in the open literature.

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

Washington, D.C., 20402 - Price 60 cents
FOREWORD

The Analytical Chemistry Division was established as

a separate division at the National Bureau of Standards on

September 1, 1963, and became part of the Institute for

Materials Research in the February 1, 1964 reorganization.

It consists at present of nine sections and about 100 technical personnel encompassing some 57 different analytical

competences from activation analysis and atomic absorption

to vacuum fusion and x-ray spectroscopy. These competences,

and in turn the sections which they comprise, are charged

with research at the forefront of analysis as well as awareness of the practical sample, be it standard reference

material or service analysis. In addition it is their

responsibility to inform others of their efforts

.

Formal publication in scientific periodicals is a highly

important output of our laboratories. In addition, however,

it has been our experience that informal, annual summaries

of progress describing efforts of the past year can be very

valuable in disseminating information about our programs.

A word is perhaps in order about the philosophy of these

yearly progress reports. In any research program a large

amount of information is obtained and techniques developed

which never find their way into the literature. This

includes the "negative results" which are so disappointing

and unspectacular but which can often save others considerable work. Of importance also are the numerous small items

which are often explored in a few days and which are not

important enough to warrant publication—yet can be of great

interest and use to specialists in a given area. Finally

there are the experimental techniques and procedures, the

designs and modifications of equipment, etc., which often

must be covered in only a line or two of a journal article.

li
Thus our progress reports endeavor to present this

information which we have struggled to obtain and which we

feel might be of some help to others. Certain areas which

it appears will not be treated fully in regular publications

are considered in some detail here. Other results which are

being written up for publication in the journal literature

are covered in a much abbreviated form.

At the National Bureau of Standards publications such

as these fit logically into the category of a Technical Note

In 1968 we plan to issue these summaries for all of our

sections. The following is the second annual report on

progress of the Separation and Purification Section.

W. Wayne Meinke, Chief

Analytical Chemistry Division

111
PREFACE

The Separation and Purification Section has completed

its second year of formal existence. The lines of development have been partly in sequel to those started the first

year, and partly the product of the unpredictable. The most

dramatic, and possibly the most simple, of the undertakings

demonstrated that laser light scattering is elegant in its

ability to provide a highly sensitive measurement of trace

particle contamination. The most extensive activity has

pivoted around the fundamental development of understanding of ion exchange resin structure. The output of practical or technological usefulness has been ample.

An important shaping factor of the Section's enthusiasms and responsibilities has been the needs of the Office

of Standard Reference Materials. The needs of materials

science, which are documented by asserted requirements and

proposals for standards, have grown more complicated and

more difficult. An outstanding example is the development

of meaningfully characterized samples of highly purified

organic chemical substances that are useful as clinical

measurement standards . Nowhere is there a satisfactory

wholeness of approach to this sort of task. The trace

characterization of labile organic compounds needs fundamental and developmental work. In a different area, it is

apparent that organic matrices may have an extremely important role to play as carriers for precisely known and very

small quantities of matter. The first efforts in this direction involve single ion exchange resin beads as microstandards , and the results are promising.

The Section's facilities include a growing array of

various types of gas chromatographs , an extensive assortment

of analytical distillation apparatus, a low temperature laboratory, plus various measuring instruments, and hardware

for electronic computation. The microscopy laboratory has

iv
reached a state of advanced versatility for particle examination under a wide variety of available optical conditions.

An electron microscope has been added very recently. While

such units may appear as disconnected bits and pieces, the

individual cooperative effect can be impressive. To illustrate, the low temperature laboratory has proved to be far

more helpful than when we first decided to prepare the facility.

Similarly, our infrared spectrophotometer surged from routine

role into one of focal importance to everything that we are

doing with ion exchange materials

The formal structure of the Section activities has

developed with recognizable program lines. The largest

efforts are given to the characterization of ion exchange

resin, which is one important example of materials used as a

discriminating phase for chemical separations. The result is

that the control of resin composition and network characterization are seen to be moving on improved and valuable paths

of dependability. Our capabilities for gas chromatography

have evolved from a first stage of cumbers omeness into the

middle ranks of efficient and flexible competence. The impact of analytical gas chromatography upon several purification efforts was encouraging. The interest in evolving

competence in ultrapure reagents, stimulated by the laser

study, has also attained routine dependability to those

trace analysts who use this facility. Several castings

about have been made in the attempt to find an area where

container problems can be attacked fruitfully.

In sum, the second year of operation of the Section

has been productive. There is a basis for even more

optimism as new avenues of attack are made in the separation

and purification fields. The organizational structure of

the work is embodied in the subject outlines used in the

presentation made in the following pages.

In order to specify adequately the procedures, it has

been necessary occasionally to identify commercial materials
and equipment in this report. In no case does such identification imply recommendation or endorsement by the National

Bureau of Standards, nor does it imply that the material or

equipment identified is necessarily the best available for

the purpose.

The assistance of Mrs. Rosemary Maddock in the preparation of this report is gratefully acknowledged.

David H. Freeman, Chief

Separation and Purification Section

vi
TABLE OP CONTENTS

PAGE

1. ION EXCHANGE 1

Introduction 1

Ion Exchange Resin Homogeneity 2

Molecular Structure of Ion Exchange Resin ... 3

Introduction 3

Stoichiometry 4

Chemical Derivatives of the Copolymer ... 5

Infrared Spectrophotometry 7

Peroxide Scission of Ion Exchange Resin . . 10

Chemical Microstandards 12

Introduction 12

Preparation 14

Range of Usefulness 16

2. GAS CHROMATOGRAPHY 18

Introduction 18

Dimethylsylfoxide (DMSO) 18

Divinylbenzene 19

GLC Study of Trimethylsilyl Derivatives of

Organic Compounds 23

Introduction 23

Experimental Methods 24

Ethylenediaminetetraacetic Acid 27

Clinical Standard Reference Materials ... 28

3. CRYSTALLIZATION 31

4. DISTILLATION 33

5. REAGENTS 36

Introduction 36

Facilities 36

Particle Detection 37

Containers 40

Purified Reagents 4l

vii
TABLE OP CONTENTS (Con't)

PAGE

6. PERSONNEL AND ACTIVITIES 43

A. Personnel Listing 43

B. Talks and Publications 43

7. REFERENCES 45

LIST OF TABLES

TABLE NO.

1. Band assignments (cm" ) of sulphonated

copolymer 10

2. Description of laboratory stills 35

3- Measurements of water insoluble particles

in solid chemical reagents 40

4. List of highly purified chemical reagents . . 42

LIST OF FIGURES

FIGURE NO.

1. Spherical copolymer beads suspended in

density gradient column 2

2. Activation analysis of single ion exchange

beads plotted to show bead capacity

departures from a constant value 3

3. Solvent stressed ion exchange bead 6

4. Infrared spectrum of styrene monomer liquid . 8

5. Infrared spectrum of meta-divinylbenzene

showing vinylic character at 905 and

980 cm-1 p

6. Infrared spectrum of commercial copolymer

of styrene and divinylbenzene (nominal 8%) . . 8

7- Infrared spectrum of cesium form of sulfonated

Q% DVB, nominal, copolymer (Halocarbonoil) . . 9

8. Infrared spectrum of cesium form of sulfonated

Q% DVB, nominal, copolymer (Nujol) 9

9. Scission of ion exchange resin by dilute

hydrogen peroxide 11

10. Electron micrograph of 1.5 micrometer copolymer

bead indicates high degree of sphericity of

very small resin particles 13

viii
LIST OP FIGURES (Con't)

FIGURE NO. PAGE

11. A two-dimensional dispersion technique is

used to isolate single microstandard ion

exchange beads 14

12. Microscope and micromanipulator are used

in the processes of measurement of individual

microstandard beads 15

13. A periodic table shows the broad range of

possibilities for loading elements onto

anion or cation exchange resin beads 16

14. Nomogram for determining mass of counterion

as a function of particle size and of specific

counterion density 17

15. Gas chromatographic calibration of trace water

in dimethylsulfoxide 20

16. Gas chromatogram of crude divinylbenzene

mixture 21

17. Gas chromatogram of 98+$ pure para

divinylbenzene 22

18. Gas chromatogram of 90$ pure meta

divinylbenzene 22

19. Photograph of rubber septum vials that

have been used to assist silylation gas

chromatography 25

20. Gas chromatogram of C,/-\to C,ppvnormal

hydrocarbons as they appear from temperature

programming procedure followed in silylation

gas chromatography 26

21. Reagent blank as obtained during silylation

gas chromatography 26

22. Nitrilotriacetic acid is obtained as a

well formed peak after silylating and use of

gas chromatography 27

23. Silylation chromatogram of EDTA containing

a small quantity of NTA contaminant 28

24. Gas chromatogram of silylated high purity

urea 29

25. Gas chromatogram of silylated high purity uric

acid, a material being characterized prior to

issuance as a clinical Standard Reference

Material 29

IX
LIST OF FIGURES (Con't)

FIGURE NO. PAGE

26. Gas chromatogram of silylated allantoin shows

evidence for poor feasibility of detecting this

substance as a contaminant of uric acid .... 30

27. Three tube zone crystallization apparatus

equipped with three heaters per tube 32

28. Heavy duty gear drive apparatus used for

normal freezing 32

29. Photograph of recently constructed Hazards

Laboratory 33

30. New High Ceiling laboratory for planned use

as distillation facility in Hazards

Laboratory 34

31. Low temperature (to -30°C) laboratory 37

32. Quartz distillation apparatus 38

33- Photograph of laser light scattering

apparatus 38

3^. Apparatus for scrubbing dust from measured

volumes of laboratory air 39

35- Photomicrograph of solid particle embedded

in a polyethylene container hi
SEPARATION AND PURIFICATION SECTION: SUMMARY OP ACTIVITIES

JULY 1967 to JUNE 1968

Edited by David H. Freeman

ABSTRACT

The research activities of the Separation and Purification

Section are described, including their significance to the

program of the Office of Standard Reference Materials. The

work involves basic developments to characterize ion exchange

resins using infrared spectrophotometry, stoichiometric analysis

of resin structure, and the study of chain scission. The

availability of spherical particles of homogeneous ion exchange

resin has been exploited with the recently developed microstandards. Analytical gas chromatography has been developed

with emphasis given to the specialized needs of measuring trace

contaminants in purified organic compounds including divinylbenzene, EDTA, and clinical standards such as uric acid and

urea. Purification capabilities involving the use of crystallization, analytical distillation, and of the newly installed low

temperature (-30°C) laboratory are described. The activities

of the ultra-pure reagents project, including work on the

laser light scattering measurement of traces of liquid borne

particulate matter, on reagent preparation, and methods of

reagent storage are described.

Key words: analytical distillation, crystallization, clinical

standards, divinylbenzene, EDTA, ion exchange resins, microstandards, particulate matter, reagents, resin structure,

ultra-pure reagents, urea, uric acid.

XI

1. ION EXCHANGE

A. Introduction

Ion exchange resins are among the most versatile and useful materials known to chemistry. Their wide scope of application includes the capability for removing salts from water,

the conversion of a compound into a different salt form by exchanging either a positive or a negative ion, the isolation of

electrolytes, the separation of amino acids, or of various

families of closely related elements, and their major role in

water processing, including water "softening".

In recent years, there has been little work to improve

the state of the art of understanding or controlling resin

structure. Most efforts are aimed at improved applications,

and few are aimed at improved understanding. In this report

we will describe our own interest in improving the means for

characterizing these materials

Scientific research is not always expected to provide

directly useful results. In the past year, however, we were

able to show that there is a new and exciting future role for

ion exchange resins which will be described in this report.

In essence, it has to do with the new capability of single

resin beads to perform as microstandards . While the subject

is still in its infancy, it is already obvious that exciting

new applications of ion exchange materials are just around

the corner.

The ion exchange program at the NBS has three components: synthesis, structure, and metrology. This triad

is focussed upon improved characterization, control and

application of the basic resin structure, with emphasis

given to the microstandards aspect. While the use of ion

exchange has in the past cut across much of chemistry,

engineering, and medicine, it is now clear that the metrological aspects of ion exchange can be expected to develop into

broad new roles that are of basic scientific significance.
B . Ion Exchange Resin Homogeneity

Ion exchange resins in the present discussion are formed as

derivatives of copolymers of styrene and divinylbenzene . The

network structure of the copolymer, or of the resin, is one of

statistical isotropy if the synthesis is properly carried out.

To illustrate what that means, consider the contrast between the

usual liquid and crystalline solid states . In the crystalline

solid there is a high degree of repeated order that tends to be

stationary with time. In the liquid state, there is molecular

motion and a time average of uniform disorder. The resin network structure is closer to the liquid state; it is uniformly

disordered, but it is also stationary with time.

The simpliest criterion for homogeneity is that the copolymer exhibit bead-to-bead constancy. Walton and Suryaraman

[1] have shown that the Linderstrom-Lang technique is suitable

for use with ion exchange resin. The result of using a vertical

density gradient axis of glycerol solution is shown in figure 1;

the narrow stratification of the copolymer beads is a direct indication of the precise constancy of the density of the beads.

Figure 1. Spherical copolymer beads suspended

in density gradient column.
The test for homogeneity with ion exchange beads can be

done with considerable sensitivity. With relatively large beads

having diameters above 300 micrometers (a micrometer equals

10" cm) , we have previously reported procedures for measuring the

ion content after neutron activation [2] where the bead diameter

was measured with the bead immersed in an inert hydrocarbon fluid

These particular results are indicated at the right portion of

figure 2. The rest of the measurements were done while the

+0.2

+ 0.1

_

1 1

wmeas

1

o

1

-

" o

D ^o°o •* ° J* " • ••* o oo

O O o -

1

1 1 1

MEASURED WEIGHT OF SODIUM (GRAMS)

Figure 2. Activation analysis of single ion

exchange beads plotted to show bead

capacity departures from a constant

value. The measurements at the left

are affected by inconsistencies in 3

resin moisture content.

beads were exposed to the laboratory atmosphere, and there is a loss of precision. However, it is obvious that bead-to-bead

exchange site concentration is approximately constant over a much wider range than has previously been recorded, and there

is also considerable likelihood that marked improvement in

measurement precision is possible. These latter measurements

are a part of the recently reported [3] capability of ion

exchange beads to act as microstandards

C . Molecular Structure of Ion Exchange Resin

1 . Introduction

Four approaches to the molecular structure of ion exchange

resin are being made. The first involves the relationship between resin composition and the implied stoichiometry of the

3
resin network. The second is a study of the precisely homogeneous formation of copolymer derivatives, with special attention given to sulfonation. The third involves the use of spectroscopy to observe the structure; here we will discuss our

recent efforts with infrared absorption spectrophotometry. The

fourth is the use of scission reactions which may have a fundamental capability of extracting structural information from a network in which the information may not otherwise be observed.

2 . Stoichiometry

It is common practice to measure the exchange capability

of a resin sample

C = milliequivalents/gram

where the number of equivalents of exchangeable ion are

measured in one way or another by ion exchange displacement

reaction. It is a simple matter to convert this into the ion

exchange equivalent weight

E = 1Q0Q

where the subscripts refer the equivalent weight to that of

the network (N) and the counterion (C), the latter being

simply the formula weight of the ion divided by the electrostatic charge on the ion. The former quantity can be calculated from the first principles of the network synthesis and

is therefore a fundamental guide to the resin composition.

The combination of styrene and divinylbenzene during

copolymerization can be carried out with a known mole fraction

(X) of the latter and (1 - X) of the former. Using brackets

to refer to formula weight, the aromatic equivalent weight

can be defined:

E

c = (l-x)[STY] + x[DVB] (1)

The formation of cation exchange resin is usually followed by

sulfonation in which each aromatic ring can, in the ideal case,

receive exactly one sulfonate group:

4
so. A

1005?

S0~H (2)

It follows for this model that monosulfonated copolymer should

have a network equivalent weight

E SH

= E

C + [S0

3

] (3)

Note that E„ H refers to the hydrogen form resin and, it follows

in this instance that

E

N

= ESH " CH]

This provides the stoichiometric framework for evaluating

the composition of any ion exchange resin. For example the

weight fraction (f) of sulfur in dry sodium form cation exchange

resin has the predicted value:

f [S]

1 ESH -LHJ +LNaJ

(4)

This relationship, and those like it, are readily subject to

experimental test. A report on these measurements is expected

to be forthcoming from work that is already in progress.

3- Chemical Derivatives of the Copolymer

Normally, chemical reactions are conducted in the gas or

in the liquid phase so that there is ample opportunity for

mixing. The chemistry of the copolymer network is complicated

by the requirement that any reactant or diffusible product is

involved in two processes: diffusion and reaction. The

situation can be very complicated.

One test for adequacy of a structural reaction in the network is to search for the possible birefringence of the product.

If marked birefringence is observed, that indicates mechanical

5
strain. While studying the use of nitrobenzene as a solvent for

sulfonation, we recorded a finding of unusually poor conditions

for this reaction. The results of the agony of a single bead

which has been exposed to bad synthetic conditions are depicted

by the photomicrographs shown in figure 3- The results are

1

•'

\m -- **&

Figure 3. Solvent stressed ion exchange bead (a) disgorging

its interior during sulfonation, (b) after disgorgement and (c) a piece of the expelled interior.

explained as follows . The procedure calls for preswelling by

the solvent, but this has been incomplete. As the sulfonating agent penetrates the network, the process of sulfonation

causes network contraction and apparently enormous forces are

exerted at the interface between swollen exterior and unswollen

copolymer core. The result of the contractive shearing action

is the expulsion of the core, as shown in the photomicrograph.

Experiments are now in progress to determine the implications of various possible swelling conditions. The results to

date include the use of methylene chloride as a network expanding solvent, and the addition of nitromethane because of its

ability to swell the resin. In a 1:1 mixture of these two

solvents, the addition of oleum leads to 90$ of complete sulfonation within one hour of exposure for a network with

X = 0.08. These conditions are not as good as we had hoped.

It appears that sulfonation with oleum may tend to be accompanied by sulfone bridging. However, the point remains that

6
the relationship between the solvent and the nature of the

reaction is an important aspect of network chemistry and the

attempts to exert improved solvent control are being continued.

4. Infrared Spectrophotometry

When irradiated with infrared light it is possible for

an organic matrix to absorb some of the radiant energy which

is then converted into increased vibrational energy. The

observation of IR absorption at particular frequencies can

often be interpreted in terms of a particular structure whose

vibrational modes become known.

The present uses of infrared spectrophotometry are illustrated as follows . In figure 4 is shown the absorption spectrum for styrene, and in figure 5 is shown for meta divinylbenzene. Both molecules have vinyl groups. In figure 6 is

shown the spectrum for a copolymer formed with 0.08 mole

fraction of commercial divinylbenzene . It should be noted

that the vinylic character is absent. This is, of course,

expected, since the copolymerization involves the formation of

a hydrocarbon backbone. This occurs with a corresponding loss

of vinylic character of the reactants

In the copolymer, we find that disubstituted benzene

compounds exhibit strong ring C-H out-of-plane vibrations in

the region between 720 cm" and 850 cm" . In figure 6, for

example, the meta isomer vibration for divinylbenzene is

evident at 805 cm" , and the corresponding para vibration is

obscured at 845 cm" . It is apparent that infrared spectroscopy provides a convenient and sensitive approach to determine

isomeric purity for either position isomer. To illustrate,

the polymerization of the vinyl group (to form a substituted

hydrocarbon matrix is detectable using the -CH„- deformation

vibration at 1450 cm . This wavelength is notable because it

tends to be vacant with a sample of pure monomer.

The infrared spectrum of ion exchange resin beads has

been implied in a related study by Zundel [4] on sulfonated

membrane films. With small ion exchange resin beads there

7
4000 3000

100

800 700

WAVELENGTH (MICRONS)

Figure 4. Infrared spectrum of styrene monomer liquid,

Vinyl group absorptions are specifically

indicated at 910 and 990 cm" 1 .

4000 3000

100

1000 900 800

WAVELENGTH (MICRONS)

Figure 5. Infrared spectrum of meta-divinylbenzene showing

vinylic character at 905 and 980 cm-1 .

1000 900 800 700

WAVELENGTH (MICRONS)

Figure 6. Infrared spectrum of commercial copolymer of

styrene and divinylbenzene (nominal 8%).

8
is no difficulty in preparing samples for IR analysis. An

example of the resin spectrum is shown in figures 7 and 8.

The band assignments are shown in table 1.

While this work is being continued, we have been encouraged by the potential of these methods for describing localized molecular structure in a copolymer, or in an ion exchange

resin. One of the problems in improving the synthesis of copolymer is the controlled use of pure divinylbenzene . In this

instance, we were able to find that para divinylbenzene is

readily distinguished from two types of contaminants; meta

divinylbenzene and polymerized meta or para divinylbenzene.

4000 3000 2000 1500 CM-' 1000 900 800 700

0.0

NHl.l.lJ.1 ,1,1,1, I .1.1.1. .1. 1 ,i 1 I.I. 1. ##**# I

i ' j j

-[

1 ' ' I

'

1

' 1' !

i

i rj-T*-

i f nn

Trrrrni i in ii - --UTTT 1 1 1 1 1 1

-T4-

.10 .10

UJ ?n z TiTl 1 IHmT nil i • lit t|H|sffi M |! 1 S.30 s

d± ^bBBS .30 o

£•40 w "" '"" ijjillit±: 8 If

.40 «50

.60 .70 wrrll .50.60 .70

_ 1.0 + Jl- i ii ii ii 1

1 li i

i iii in oo CO WAVELENGTH (MICRONS)

Figure J. Infrared spectrum of cesium form of sulfonated

8% DVB, nominal, copolymer (Halocarbonoil)

4000 3000

WAVELENGTH (MICRONS)

Figure 8. Infrared spectrum of cesium form of sulfonated

Q% DVB, nominal, copolymer (Nujol)
Table 1. Band assignments (cm ) of sulphonated copolymer,

3450 OH - valence vibration of HO in resin phase

3040 C-H - valence vibration of aromatic hydrogen

2930 Symmetric and antisymmetric valence vibration of

the C-H„ group

1640 HpO deformation

1610 Aromatic ring quadrant stretch

1490 Semicircle stretch

1450 C-H deformation

1408 Semicircle stretch

1333 S0„ antisymmetric vibration

1

1175 Antisymmetric valence vibration of S-0 group

1111 In-plane aromatic hydrogen bend

1030 Symmetric valence vibration of S-0 group

1005 In-plane aromatic hydrogen bend

833 Out-of-plane aromatic hydrogen bending for

para substitution

775 Out-of-plane aromatic hydrogen bending for

ortho substitution

671 C-S valence vibration

5 • Peroxide Scission of Ion Exchange Resin

In 1957a Hookway and Shelton [5] described the degradation of cation exchange resin by 3% hydrogen peroxide. We have

established that the peroxide attack depends upon the presence

of a catalyst, and ring opening may or may not occur depending

upon chemical conditions. In 3% hydrogen peroxide with catalyst and with temperature in excess of 65 °C we find:

vAA^v

H2°2

> cat.

C0

2 + HSO^ + H

2 (5)

S0

3

H

10
The reaction is altered by threefold dilution of the hydrogen

peroxide: in that case, no sulfate is formed before complete

dissolution of the resin has taken place, and it may be that

aromatic ring opening is impeded up to, and possibly beyond,

that point

The progress of the scission reaction may be followed

through observation of increased resin swelling. The swollen

volume of a sample of ion exchange resin is a measure of the

limiting steric extendability and if scission occurs, this

limit is necessarily increased. Following an empirical tactic

stated by Boyd and Soldano [6] we have the relationship:

q-1 = k

X

(6)

where q is swelling ratio (q = V( swollen/V(unswollen) )

, and

X is the molar crosslinking. On this basis we have measured

the variation in "X" with time of exposure of resin to 2%

hydrogen peroxide solution. The results are shown in figure 9

^"3 x- >Q

2 X:

|xx

[4% DVB]

X^ [2% DVB]

X^X^

*^

[|%DVB]

x X

^

-X-—X

J L^.J I I Hi I

I I vv I ^ 23456789 10 II time (hours)

Figure 9. Decrease of "X" during exposure of sulphonated

copolymers to 2% of H

2 2

at 65 °C.

11
At the point of dissolution of the resin, network segments may

exist in varying degrees of complexity. When random scission

continues to occur, their molecular weights must decrease.

The scission reaction offers several opportunities for

interest. The controlled chemical dissection of this kind of

network, if properly done, should carry information to reflect

upon the original network structure. To illustrate, the

effective change AX/X =0.2, implying loss of 20$ of the

apparent crosslinking, is evidently just sufficient to cause

total network dissolution. That quantity must be a product

of the mechanism of the scission, and the structure that is

being cut; it is obvious that an understanding of the former

should have an important bearing upon the nature of the latter.

D. C hemical Microstandards

1. Introduction

Ion exchange resin beads have an important capability for

holding an exact quantity of matter [3] as dictated by the law

of electroneutrality . The amount of matter that is calculated

to be present on a single bead depends upon two assumptions,

both of which are subject to precise test. First, the concentration of the exchange sites is taken to be a physical constant

of the material; that depends upon the exact achievement of

homogeneous site distribution during the resin synthesis.

Second, because the beads are extremely spherical, the amount of

matter is related to the bead diameter.

Consider that all of the exchange sites on a single resin

bead are saturated with a single type of chemical element.

Then:

m = pfv (7)

where p is density, f is weight fraction of the particular

element, and v is Trd J /6, the bead volume. Since diameter can

be measured accurately under the microscope, it is possible

to use microscopy as a weighing tool. In this way, extremely

small quantities of matter are fixed into a round container,

and their amount is related to the measured container diameter.

12
The range of single ion exchange bead capacity is indicated

in figure 14 by a nomograph which varies the bead diameter from

one to one thousandth of one millimeter. The fractional loading

is taken as the product pf and this is usually somewhat less

than unity. The range of counterion mass is thus seen to extend

. _Q . to quantities much smaller than a nanogram (10 gram).

One aspect of ion exchange resins that is not widely known

to the casual user is the remarkable sphericity of these beads.

This is a result of the conditions of synthesis in which the

formation of copolymer is carried out as a droplet suspended

in a liquid in which the droplet is immiscible. A surface free

energy minimum is required and the corresponding minimum surface

geometry is that of a sphere. We have recently obtained an

electron microscope to perform a variety of tasks, and one of

the first of these was to show that this sphericity extends

to even the smallest of resin particles that can be made

synthetically. This is shown by the electron micrograph shown

in figure 10, where it is fully evident that this micrometer

resin bead is indistinguishable from a spherical shape and,

hence, can be measured meaningfully for its diameter.

Figure 10. Electron micrograph of 1.3 micrometer

copolymer bead indicates high degree of

sphericity of very small resin particles.

13
2 . Preparation

The usefulness of the foregoing concepts is of direct

significance to the growing needs of science to operate effectively with smaller and smaller quantities of matter. Highly

sensitive analytical instrumentation is dependent upon standards

which can be used effectively to set detection limits, and to

perform calibration. There are vast areas in which the availability of microchemical standards will become useful.

The methods of preparing ion exchange beads saturated with a particular element are well known. Then, for microstandards

,

it should be obvious that ion exchange must be rigorously

prevented. Careful washing, rinsing and drying procedure is

needed, and highly purified solvents are essential. After

drying, bead clusters are broken up and, in the presence of

a pure inert solvent, the beads can be cast onto a slide, as

shown in figure 11. One difficulty is that the larger beads

tend to fall off. For the electron microprobe we have found it

useful to embed the beads in a film of polyisobutylene • in this

Figure 11. A two-dimensional dispersion technique

is used to isolate single microstandard

ion exchange beads: nine such beads

are visible in this photomicrograph.

(125 X)

14
way the beads do not move appreciably, even when they are

extensively irradiated with the electron beam.

The use of a microstandard for calibration depends upon

suitable technique. The measurement of diameter and the transfer of a single bead to a desired location can be done with the

illustrated in figure 12. The results of activation

analysis experiments provide a rest of equation (7) 3 as shown

earlier in figure 2. It is evident that the results exhibit

scatter in the vicinity of ten percent. There is good reason

to expect that the precision can be improved, and efforts are

now underway to provide sharpened control.

Figure 12. Microscope and micromanipulator are used

in the processes of measurement of

individual microstandard beads, and for

transpositioning to the apparatus

requiring calibration.

15
3. Range of Usefulness

Ion exchange resins can be saturated with any ion that is

suitably stable in an appropriate polar solvent. That applies

to most of the periodic table, as shown in figure 13. Positively charged ions (cations) must be placed onto the negatively

charged sites that exist on a cation exchange resin. Conversely,

negatively charged ions (anions) must be placed onto anion exchange beads with their fixed positive charge sites. Counterion

loading is not limited to inorganic chemistry, however. There

are many organic structures that may be placed onto the resin

sites carrying the opposite charge.

FIXED TO

1 FIXED TO

CATION EXCHANGER

ANION EXCHANGER

• OXY-CATION (YXn* )

X COMPLEX ION 00

000

Si*

S88S1 ° ° o

c* r

p*

o o o 00

00

CI

Ti ' Cr» Mn G X 0000

00

Ge* Se* 00

00

00

Zr* Mo*

00

To* Sn Sb*

i.eiiii;

Te*

00

I ooo

Ht*

o o o

Re*

0000

00

05 Po At

30o6o<xx>6£\Sc

Ce

y.-y.-y.

Pr Nd Pm Sm Eii

_ Gd Tb

: : :•::

Dy

'<<:::

Ho _

//.

Er

. .. .

It... Yb

'yy'y

Lu

Th* ?°V. y. y*

Np Am Pu Cm Bk Cf Es Fm Md No Lv

:•,•:•:: Figure 13. A periodic table shows the broad range

of possibilities for loading elements

onto anion or cation exchange resin

beads for subsequent use as microstandards .

The microstandard capability can be carried into broad

usefulness. To illustrate, consider available bead sizes which

may range from about one millimeter down to one micrometer.

The corresponding volumes extend over nine magnitudes

.

Assume saturated ion exchange sites have a value of of as

16
roughly 0.2 (it varies for different counterions ) . Using the

nomograph in figure 14 of equation (7) given on page 12, it

is seen that this corresponds to a counterion content reaching

-4 -1^ from over 10 to less than 10 grams . If the conditions of

mixed elemental leading can be brought under good control, it

should be possible to use these beads to carry just a few atoms

of a required element or isotope.

- - O.OOI

- 001 it ' ,si ..0

(pf*)

PARTICLE DIAMETER

(MCR0NS)

Figure 14. Nomogram for determining mass of counterion as a function of particle size and of

specific counterion density (grams/millimeter).

17
2. GAS CHROMATOGRAPHY

A. Introduction

Gas liquid, chromatography (GLC) is an interesting subject

in its own right, and it is frequently useful for following

chemical purification. Our activities in this area have been

pointed at two objectives. First, we have sought experience

with trace volatile constituents that may be present in widely

different types of sample materials. Second, we have made a

series of efforts to apply these techniques to the characterization of materials that are being tested for certification as

Standard Reference Materials. Notable in this regard are the

relatively recent undertakings to develop biomedical and

clinical Standard Reference Materials

.

B. Dimethylsy Ifoxide (DMSO ) The Section on Molecular Biophysics of the National

Institutes of Health (under the supervision of Dr. Edwin D.

Becker) communicated to us the need for anhydrous hexadeuterated DMSO as a reference standard in NMR studies.

Ordinarily, the drying of a stable organic liquid would be

a minor problem, but this material is not easily dried by

any of the obvious methods. For example, it is believed that

sodium metal is apt to react with it explosively. It is a

costly material so that conventional water determination

by Karl Fischer titration, which wastes relatively large

samples required for trace water analysis. GLC offers

the obvious advantage of requiring very small samples for

analysis (0.001 ml) and the results of our calibration are

reported in the following.

The water measurements involved the use of a 3.5 nim

diameter (i.d.) stainless steel column 40 cm in length packed

with Porapak-Q, a chromatographic material that forms a particularly sharp water peak. With temperature programming from

100 to 250 °C at a rate of 30 °/min, the following relative

retention times for fully resolved peaks were obtained: air,

18
0.024; water, 0.062; and DMSO, 1.000. Under these conditions,

a determination is completed within one minute.

One of the typical problems here is a need to have analytical capability without having a completely dried sample.

This calibration was carried out using the method of standard

addition. Known amounts of water were added to the DMSO which

also contained an unknown amount of water. The resulting peak

heights h(water) and h(DMSO) are assumed to obey the relation:

h(water) _.. Q . ,„ h(DMSO) ^Hf + °W j (b}

where C° = cone, of residual water, and

W

C w

= known cone, of water.

The test of this equation was carried out by adding water

to a constant stock solution of DMSO. The results are shown

in figure 15. From the parameters obtained using linear least

o squares analysis, we have C TT =0.3% and k = 1/4.07. This

w gives the analytical equation for subsequent analysis:

h , = 4.07 /

ater

(9)

'DMSO

On this basis, it was possible to establish a series of

reference solutions of known water content to be used for subsequent calibration purposes . It was eventually determined

that hexadeuterated DMSO, containing approximately 0.04% water,

or less, would not exhibit the exchange reaction that interferes with its use for nuclear magnetic spectroscopy.

C . Divinylbenzene

This material is widely used as a polymer crosslinking

agent. It is used to prepare copolymers with styrene, and

these are among the intermediates described earlier for the

synthesis of ion exchange resins. The crude commercial

material is a mixture of diethylbenzenes , ethylvinylbenzenes

,

19
0.6

'WATER 'dmso

-0.4 0.0 0.4 0.8 WATER ADDED (PERCENT)

C° = 0.30%

Figure 15. Gas chromatographic calibration of trace water in

dimethy Is ufoxide

.

and divinylbenzenes . Generally, these occur as the mixed

meta and para isomers, where the total divinylbenzene content

is about one half of the total. Naphthalene may also be

present since:

CH=CH.

CH=CH,

H,

These materials have been studied extensively by Wiley, Allen,

Chang, Musselman, and Venkatachalam [7]. We have used his

gas chromatographic analytical methods to provide a basis for

measurement of the composition of various samples of

divinylbenzene

.

For the analyses of mixtures of para- and meta- divinylbenzenes, a 305 cm by 3.5 mm stainless steel column packed

with a mixture of 85% by wt. of chromasorb W, 15% Bentone-3^,

and 5$ Ucon oil was used. Small samples of about 0.0002 ml

20
were injected and, for the estimation of constituents other

than the divinylbenzenes , the temperature was programmed from

135°C to 200°C at 6°C/min. Under these conditions the paraisomer elutes before the meta-isomer. It has been found

inadequate resolution if the mixture contains a high concentration of p-dvb (>95%) so that the first peak is relatively large. Columns packed with FFAP (Varian Associates, free

fatty acid analytical p_hase) elute the isomers in the reverse

order and may also be effective for such mixtures

Development quantities of divinylbenzene were procured

from the recently formed Petrochemicals Division of the Shell

Chemical Company of New York, N.Y. The commonly available

crude divinylbenzene has a gas chromatogram shown in figure

16, in which the peaks due to the mixed ethylvinylbenzenes

,

and the mixed DVB isomers are evident along with the least

volatile naphthalene. The corresponding analytical chromatom EVB m DVB

I I I I I I I I 1 I I

I I

I

. J I

I

I

i I I I I II I I I I

I I

I

I !

I

I I I I 1 I I I I I I I I I I I I

I

I I * 1 I I I I I I I I I I I I

I Gas chromatogram of crude divinylbenzene

Figure 16 . Gas chromatogram of crude divinylbenzene mixture

21
grams of concentrated para and meta isomers are shown in

figures 17 and 18. This analytical effort has provided us

with a basis for continuing our purification efforts leading

ect

p DVB

Naphtha ene

Figure 17. Gas chromatogram of 9Q+% pure para divinylbenzene

In ect

Hexane

m DVB

Naphtha ene

Figure 18. Gas chromatogram of 90% pure meta divinylbenzene

22
toward the preparation of hopefully 99+% pure isomers, and

for potential for issuance of samples for investigative use.

That aspect of the work is being coordinated through the

NBS Office of Standard Reference Materials.

D . GLC Study of Trimethylsilyl Derivatives of Organic

Compounds

1. Introduction

Because of its speed, accuracy and sensitivity, gas

chromatography can offer an advantage over conventional

methods of detecting or measuring impurities. In the application of this technique it may be necessary to prepare

volatile derivatives of compounds with otherwise low volatility.

A suitable derivative must provide enhanced volatility and

adequate stability.

Among the derivatives used in gas chromatography, considerable versatility is provided by trimethylsilyl ethers

The silylation of various functional groups has been known for

some time [8-10]. The trimethylsilyl group can be substituted

into many organic compounds containing active hydrogens . This

method may be applicable to a wide variety of organic compounds

which include alcohols, amines, amides, amino acids, carbohydrates, carboxylic acids, phenols, sterols and steroids Among

the commercially available reagents used for preparing trimethylsilyl ether derivatives are trimethyl chlorosilane (TMCS),

hexamethyldisilazane (HMDS) and Bis (trimethylsilyl) acet amide

(BSA) . Representative reactions are indicated by the following equations

(CH

3

) SiCl + ROH—>(CH

3

) 3

SiOR + HC1

(CH ) SiNHSI(CH ) + 2ROH —*2 (CH ) SiOR + NH

3

23
VJ.

Si(CH )

C CH + CH C=N Si(CH

3

) 3

-N 6 CH

3 + CH C NH Si(CH

3

) 3

Si(CH )

2 . Experimental Methods

The ease of formation of the silyl derivative varies widelyFrequent ly, organic compounds will establish reaction saturation after a few minutes at room temperature. With other compounds, several hours of reflux in an appropriate solvent may be

needed. Exact conditions are established by following the

reaction progress as a function of time.

In general, it is important that air be excluded during

reaction. In this regard we have used septum vials as shown

in figure 19. The separated components show the vial, septum,

and aluminum cap. The cap crimper is used to tighten the septum

against the vial. We have seen that the ampoulation technique

is suitable for repeated withdrawal of samples using a hypodermic needle to penetrate the septum. However, punctured

vials do not provide protection for more than an hour or so

against contamination from the atmosphere. By contrast,

unpunctured vials have been stored for several weeks at -20 °C

with no noticeable deterioration. A disadvantage that can

have serious analytical consequences is that organic liquids

may leach impurities from the rubber septa. This is especially

important if the liquid swells the rubber.

The conditions for GLC analysis after silylation were to

improve as a result of quite rapid temperature p. 'to r* m

24
Figure 19. Photograph of rubber septum vials that have

been used to assist silylation gas chromatography .

The chromatographic column was 3-5 (i.d.) by 180 cm in length.

Temperature programming was used from 100 to 300 °C at a rate

of 30°/min. The packing was 10$ (w/w) of silicone gum rubber

(UCW-98) on Chromosorb W (80-100 mesh). Helium carrier gas was

used with a flame ionization detector. It was necessary to

clean the flame chimneys after every 100 hours of use in order

to improve the sensitivity, and to sharpen the peaks which

otherwise tended to become irregular and jagged.

The results of using the foregoing conditions is illustrated with the chromatography of a series of hydrocarbons,

as shown in figure 20. The chromatography of all compounds

studied was found to be subject to contamination peaks that

were identified by running a blank, as shown in figure 21.

Some of the various impurities are in the silylating reagents,

some appear to be formed by reaction of the reagents with

impurities in the rubber septa, and none are attributed to the

solvent

25
:

m , :£ ^ I *

p. I—1—1—1—!—1—1—1—1—1—1—1—1—1—

1

= - * STRAIGHT CHAIN —-—^d j

i i i i i

i i i i

i i i i i i i i 1 1 1 1 1 1

B

i £ HYDI OCARBON STANDA RDS H niunuvniiDun vinnun nil -L-L-L-L-UUL-L-L-L-L-L-L-UL-L-L-^^

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aj

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. 37 :

*

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=4 - F 1~ h

it-

•a r

_ _

n. " t " " 1 1 i v w r _ _

III1 » t t : •:i :j: : "'-a :

jj. l _ 4 1- 4- ''- 3V -

< i , --.1 „_3..__1._« t—Zt

—^ —^- 1^^' 1 1 1 1 1 1

i

1 1 1 1 1 1 1 i

1 1 1 1 ' 1 1 1 1 1

i Figure 20. Gas chromatogram of C5 to C22 normal

hydrocarbons as they appear from temperature programming procedure followed in

silylation gas chromatography.

Figure 21. Reagent blank as obtained during silylation gas chromatography. Impurities in

the reagents, from the septum and from

atmospheric contamination are apparent.

26
In all cases, the formation of a well resolved peak was

followed up to identify the mass of the derivative using mass

spectroscopy. We are happy to acknowledge the cooperative

assistance given to our efforts by Dr. Ray Pittman and

Dr. Robert Milne at the National Institutes of Health.

3. Ethylenediaminetetraacetic Acid

As noted by Farrow and Hill [11] it is common for ethylenediaminetetraacetic acid (EDTA) to be contaminated with

small quantities of nitrilotriacetic acid (NTA) . This has been

useful in screening to find a material of sufficient purity for

issuance as a Standard Reference Material. We have found

commercial samples of EDTA do tend to be contaminated by varying quantities of NTA. As shown in figures 22 and 23, the NTA

peak which corresponds to the trisilyated derivative, and the

EDTA peak which corresponds to the tetrasilylated derivative

are obtained after refluxing with the silylating reagents in

pyridine for a period of approximately twenty hours. Subsequently, it was found that "BSA" reacts much more rapidly.

" N^ "tl C

' itj - ? -it- s tr

Vs tr • j B*' j \i S II _

* 2 "tit NTA t^5 ~W

1 .a E: "iJt ? =n N - [! ^.-^ * it * 5 i- 41

?>-*-.» 4lt

i

' - 1

% + 2 4lt 3 w 41

* S lit

kx " 5 S "4lt C 5 jtr

2. t 4ft

J C\ l|

-

J

'

''

'

jl t

t "it

z-z~:z u\ -*============-=*-=14 1 1 IJm 1 1 1

1 111 1 1 1 1 1 1

1

1 1 1 1 1 1 1 li 1 14

f.

Figure 22. Nitrilotriacetic acid is obtained as a well formed

peak after silylating and use of gas chromatography

27
u I rijL

! j

,; ji j ' ^ ' !|i

_L ill J ) 1 fd i - ^ llll LU ft s llll C

,; ;

1 i

i ill j[ ii C* i l[ II ii rp iil il il ii i

ill 'i ii i

' *o —• 1!l

! " * II i

|| _£ ">, lli 1 l

1 | 5 3s .11 1 1

1

||

|

j V » ^g, II Hi ? \ I ^

* - °

-. s, 1 ^ Iil 1 (il | ^ 2 S! i

! i" J "^

i 1! IP | ^ ^ / Q ' I C» |j

| || J L= il

!

: Si i l> fr- III II j

i i j» ' II l| ll i f ii ji il j T i i I

ii i ! c p iil r ^ Jlj IIT1 5 ill niA v j II

i l||

-i 1 „ i^"" ^--i«_. (L_«-:===3====:2=====23::5~-~~ := ~:i

J=J> Figure 23. Silylation chromatogram of EDTA containing a small

quantity of NTA contaminant.

4 . Clinical Standard Reference Materials

The NBS Office of Standard Reference Materials has

spurred the development of purified and carefully characterized chemicals to serve as standards for biomedical and clinical analysis. Without silylation, the gas chromatography of

some of these materials is practically useless. The silylation reaction has been helpful in the formation of derivatives

of urea (disubstitution) as shown in figure 24, and uric acid

as shown in figure 25.

Although this work is still incomplete, we have formed

several conclusions concerning the use of silylation in the

investigation of these clinical materials. First, volatile

derivatives can be formed in good yield. Second, it is

necessary to unscramble trace contamination from the reagent

blank and from that which may be present in the compound

under investigation. In general, the highly purified materials

show relatively few contaminants compared with the many that

28
>0 II

C~" —— a b," III

-> U- ^ v~ 1

-*». "^ ] -"> rt\ I 5 j _i> •> V 1 ' CN 1 ^I -v :

' llli ~^ -,2-5 <* iiiiii -<C' -t «

: i ._ 1 ^ r ^ II

fc.

1 > 5 ' J

1 **> II 111

i tin ~«5"^ ^ II II DPI P u 1 UHLA i "» s 1

> ' y Hill £ : : . __ _ mo:

F

rt > 5-, *. ii in ~< _, c

1 IIIIII r> 2 5

£ E

' ?

t- '3 II II t

»"-> ~ 1 V ?

5 t lit I 1 s ' ill 1 1

,[—

iit I I i*~ \\\

i i ~"^ *-• ni I t ^

'i iii \ ?s: -Hff --"--^-sji

H = = = = == = = L1 — — — — — — — — — — — _jt,_ -.„_ ___.

<a =E

Figure 24. Gas chromatogram of silylated high purity urea,

?*" a

5,V^ - - ,-

~r3' ^ 2

* * ~^

!!v_jl.ZE>_>4 fr-S ?' : r

_, '' J

< < Ml |p A pin : ^" _ Ul lb flblU _

ft T

&-,=> 2 " O -* i- —

>lJ3 ^ S 4_ *»£>= -• £

»<""" S a- J

S

-1 '1-'? « _ . -• 5' * ' s -I ?

5l £,_ to , _ _ 1 .

!| ;;r

: 1 : t ' - < -t 41

i- *« £ 4 41 t' ii 41 5 a 2 J : :j s

I *~

4J P

ii j ? " r j f" "" *' ' "S^ 2 5- C t

t fcl 5 3 V ' i

^TMS=~!==-= _TM=:==s=====================fe ==== ---------------

= - ==

--

= z"

jjl _ _________

Figure 25. Gas chromatogram of silylated high purity uric

acid 3 a material being characterized prior to

issuance as a clinical Standard Reference Material.

29
may occur in the blank. However, systematic unscrambling is

possible and, especially with the use of mass spectroscopy,

it is clear that silylation does permit identification of

impurities, providing that the impurities actually form a volatile silylate adduct . Third, not all impurities will form

such adducts. As shown in figure 26, allantoin, which is a suspected contaminant in uric acid, does not silylate.

Similarly, with urea, we were able to show that the biuret

peak tends to coincide with the urea peak. Finally, we have

found several preliminary indications that the quantitative

calibration of GLC for measurement of silylated components

in a mixture may be feasible, that precise work may require

the use of an internal standard, and that precise control of

reaction conditions is necessary in order to obtain reproducible

chemical reaction yields.

Figure 26. Gas chromatogram of silyated allantoin shows

evidence for poor feasibility of detecting this

substance as a contaminant of uric acid.

30
3. CRYSTALLIZATION

The purification of chemical compounds is often possible

by using crystallization techniques, including crystallization

from a solvent or from the melt. The first procedure is

practiced in virtually all organic chemistry laboratories.

The latter has achieved considerable importance as a result of

work done in the metallurgical and solid state physics laboratories. Unfortunately, the adaptation of zone melting by

chemists has not been rapid in this country. The principles

and techniques are described in the works of Pfann [12],

Schildknecht [13], and Herington [14]. The first of a two

volume series in the general area has been published under

the editorship of Zief and Wilcox [15]

One of the major advantages of crystallization from the

melt is its potential for repetition that leads to extreme

purification and, indeed, spectacular accomplishments have been

made. The method is not always applicable, however. A major

problem with chemical compounds is the possibility of decomposition. We found, for example, that zone crystallization of urea

was an excellent method for removing sulfate contamination,

but the simultaneous generation of ammonia limited the operation

to just two passes. This gave ample indication that the urea

was undergoing rapid decomposition at its melting point.

Zone refining is a particularly effective purification

technique when it is applicable. Contraindications include

glass formation, instability at the melting point, and breakage

problems caused by volume expansion upon crystallization.

Apparatus capable of accommodating three samples tubes, while

operating at temperatures down to -50°C is shown in figure 27-

In addition to this, we have obtained the heavier duty commercial instrument shown in figure 28. This is suited to larger

scale operation for horizontal or vertical operation. Both

devices are scheduled for future testing, with emphasis upon

their use of temperatures below 0°C.

31
Figure 27. Three tube zone crystallization apparatus equipped

with three heaters per tube.

Figure 28. Heavy duty gear drive apparatus used for normal

freezing.

32
4. DISTILLATION

During the past two years, the use of precision laboratory

distillation in the Analytical Chemistry Division has been held

in abeyance. This is partly because of need for greater

emphasis on other methods of separation, and partly for lack

of facilities at the new NBS location. Specially designed

facilities in the newly constructed Hazards Laboratory have

now become available. The newly constructed Hazards Laboratory

is shown in figure 29. The inside of this laboratory is shown

in figure 30 which displays the facilities which were

especially designed for a variety of tall-column experiments,

including high efficiency distillation.

Figure 29. Photograph of recently constructed Hazards

Laboratory

The Purification Section has in storage a number of types

of stills the more important characteristics Of which are

summarized in table 2. Efforts are being made to return the

distillation laboratory into operation. Originally, the

laboratory was quite active because of the scarcity of other

sources of distillation capability. Today, there are several

sources of purified organic solvents. The present status of

33
distillation has been described [16]. It is essential that

one knows when to use distillation, or when to choose the more

complicated alternative of preparative scale gas chromatography

It is already evident that distillation from quartz apparatus

is appropriate in the purification of mineral acids, and such

apparatus is being readied for use in the areas more fully

described in the next section.

Figure 30. New high ceiling laboratory for planned use as

distillation facility in Hazards Laboratory.

34
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5 . REAGENTS

A. Introduction

The study of chemical reagents impinges upon broad areas

of chemistry. The purity of solvents or reagents is often a direct limitation to the sensitivity that can be reached with

wet chemical methods of analytical chemical measurements.

Past studies of chemical reagents have been relatively rare

and unenlightening. A recent article by Robertson [17] s however, sets a good example. There is a growing interest in

highly purified reagents, and there is indication that some of

the needs for such materials can be satisfied as a result of

recent industrial investments in this area.

Recent advances in chemical reagents have taken directions that could not have been forecast a few years ago. This

can be illustrated. First is the concern for the measurement

of particulate impurities at the trace level; this is indicated

in the following discussion of laser light scattering techniques

Second is the bottleneck problem in which purification is

counteracted by the limiting processes of contamination.

Thus, container methods and materials have a way of eventually

dominating any discussion of the limiting benefit of trying

to improve chemical purity. It is important that the reagent

composition be time independent so that inadvertent contamination, either by exposure to the atmosphere, by degradation,

or by dissolution of the container, is somehow avoided.

B. Facilities

The construction of a low temperature laboratory was

completed during the early part of 1968, and the facility has

been tested since that time. A plan of the facility is shown

in figure 31. The design provides for a core laboratory that

can reach to -30°C and be sustained for long periods. An

anteroom is used to give a temperature buffer, or it can provide a second independently operated laboratory at temperatures

to 0°C. Crystallization apparatus is being developed, as

36
Figure 31. Low temperature (to -30°C) laboratory.

described on page 32, and It will be used in the facility.

The experimental capability includes electrical and liquid

conduits. Finally, there is a large window for viewing of

experiments in progress.

The reagents project maintains quartz distillation

apparatus; two units that are suited to mineral acid distillation are shown in figure 32; this will have an efficiency of

approximately 14 theoretical plates.

C . Particle Detection

The concern for particulate impurities in reagents has

given impetus to the construction of a new type of light scattering apparatus . This is shown in figure 33 . It is used for

detecting traces of fluid-borne contamination by laser beam

scattering. A detailed description of the apparatus and its

applicability in determining suspended particles in solutions

of various reagents, water, and air is to be published [18].

37
Figure 32. Quartz distillation apparatus.

Figure 33. Photograph of laser light scattering apparatus

38
Briefly, the cylindrical cell containing the liquid sample is

placed vertically in the cell holder and the amount of

scattered light is measured with a photomultiplier . With

different concentrations of suspended polystyrene latex spheres

of known diameters a calibration curve is obtained for estimating concentration. Light scattering measurements were made of

water obtained from different sources, organic solvents, organic

compounds dissolved in distilled water. A few of the solutions

were filtered through a 0.01 micrometer (as indicated by

manufacturer) porosity filter to study the effect of filtration.

The results of some of these measurements are shown in Table 3.

The laser detection of particles was also adapted to

monitoring particle contamination in the air. In one test, the

solids in air were estimated at 0.014 ppm when 115 liters of air

were scrubbed by slowly bubbling through distilled water. The

apparatus is shown in figure 3^.

Figure 3^. Apparatus for scrubbing dust from measured volumes

of laboratory air.

39
Table 3. Measurements of water insoluble particles in

solid chemical reagents.

Estimated Estimated

particle

ltereda

particle

concentra- Pi concentraSolute Wt. (:%)

tion (ppm) (I "V^W tion (ppm)

in solute

cadmium nitrate 10 10. 8.4 0.40

silver nitrate 10 0.74 2.9 0.030

sodium nitrate 10 0.76

sodium chloride 10 0.63

sodium sulfate 10 0.72

potassium iodide 10 1.6

glycine 10 5.0

sodium benzoate 10 0.45

agar ,i 132. 2.0 1.0

sulfonated .1 160. 4.7b

13

polystyrene

disodium ethylene- 2

diaminetetraacetate

6.6 1.4 20

Through 0.01 micron millipore filter, except for polystyrene sulfonated sample.

Filtered through 0.22 micron millipore filter.

D. Containers

The purification of reagents can be hindered by improper

containment. A program of monitoring container materials is

being carried out with attention given to purity, durability,

solubility, permeability and other aspects of container use.

Microscopic examination has shown the presence of many fine

particles embedded in polyfluorocarbon materials. Figure 35

illustrates this. Laser probe spectroscopic analysis of

these particles in one instance showed Fe , Mg, Si, Zn, Al,

Ni, Cu and Mn among the constituents. Methods of cleaning

and removing these particles are being investigated.

40
Figure 35. Photomicrograph of solid particle embedded in

a polyethylene container.

E . Purified Reagents

The present project was designed with the idea of anticipating the future needs at NBS for high purity reagents in

trace chemical analysis. In order to anticipate these needs,

a materials bank has been made of the purest reagents that

can be obtained commercially. These are kept refrigerated

and ready for prompt use. (Cold storage has the important

benefit of drastically retarding the various deterioration

processes.) The response to these efforts has been favorable.

During the past year 56 of the reagents were issued to various

chemists at the Bureau. All but three of the approximately

28 different types of reagents, listed in Table 4, have been

dispensed within the past year. The completion of a low

temperature (-30 °C) laboratory, shown in figure 31, has

permitted refinements in the practice of storage and dispensing of the reagents.

41
Table 4. List of high

Acids

CH3COOH («)

HBr (**)

HC1 ( #«##*#*#**

)

Hf (**)

HI

HNO3 (***###*«#)

HCIO^ ( ***)

H 2 S0 lt (*)

Salts

CaCl 2 (:«:«)

LIBr (•'**.) KC1 ( **)

NaCl ( **)

BaCl ( **)

BaP (*)

Mg (*)

NaF ( **)

Bases

NfUOH

NaOH

Redox

Br

I2

LIP

KI

Na 2 S 2 3 Csl

Nal

(*)

(*)

(*)

(*)

Buffer Salts

NHuCl (*)

CH 3 COONa

NazSOt,

(*.)

(*)

* Indicates request for one or more units for a specific

application during FY 1968.

Micro filters

material type

Cellulose

tt

11n

it Solvinert

it

Nylon

Poly tetrafluoroe thy lene

Polycarbanate

Pore sizes Diameter size

(micro meters) millimeters ) 0.45 47, + 142

.22 13, 25, 47, + 142

0.10 47, + 142

0.05 47

0.01 13, 25, 47, + 142

1.5 47

0.5 25, + 47

0.25 25, + 47

1.0 47

5.0 25, + 47

8.0 25, + 47

5.0 25

2.0 25, + 47

1.0 25, + 47

0.8 25, 47

0.5 25, 47

42
6. PERSONNEL AND ACTIVITIES

A. Personnel Listing

Separation and Purification Section

David H. Freeman, Section Chief

Ellen L. Matthews, Secretary

Ion Exchange

William C. McCauley - Summer student, 1967, 1968

Walter P. Rittner

Gabriella Schmuckler - On Sabbatical leave from the

Technion - Israel Institute

of Technology, Haifa, Israel

Ultra Pure Reagents

Delmo P. Enagonio

Edwin C. Kuehner

Pure Materials

Robert T. Leslie

Charles B. Romain

Crystallization

Herbert D. Dixon

B. Talks and Publications

D. H. Freeman , W. F. Rittner, "Structure and Its Relation

to Selectivity," Gordon Research Conference, New London, New

Hampshire. August 22, 1967

D. H. Freeman, "Chemical Microstandards , " Massachusetts

Institute of Technology, Cambridge, Massachusetts.

November 30, 1967-

D. H. Freeman, "Chemistry of Ion Exchange," Science Club,

Winston Churchill High School, Potomac, Maryland.

January 11, 1968.

D. H. Freeman, "Laser Detection of Small Particles in

Liquids," New York Academy of Sciences, New York, New York.

February 2, 1968. (Same as ref [18], p. 45)

D. H. Freeman, "Chemical Microstandards," Division

Colloquium, National Bureau of Standards. February 13, 1968.

43
D. H. Freeman, "Modern Reagents for Future Chemical

Standards," 19th Pittsburgh Conference on Analytical Chemistry

and Applied Spectroscopy, Cleveland, Ohio. March 6, 1968.

D. H. Freeman, "Microstandards for Analytical Chemistry,"

155th National Meeting of the American Chemical Society,

San Francisco, California. April 3, 1968.

44
7. REFERENCES

[I] Suryaraman, M. G. and Walton, H. P., Science, 131 , 829

(I960).

[2] Freeman, D. H., Patel, V. C, and Hood, M., J. Poly. Sci:

Part A 3, 2893-2902 (1965).

[3] Freeman, D. H. , and Paulson, R. A., Nature 218 , 563

(1968).

[4] Zundel, G., Noller, H., Schwab, A. M., Naturforschg . 16b , 716 (1961).

[5] Hookway, H. T., and Selton, B., J. Phys. Chem. 62, 493

(1968).

[6] Boyd, G. E. and Soldano, B. A., J. Am. Chem. Soc . 75.,

6091 (1953).

[7] Wiley, R. H. , Allen, J. K., Chang, S. P., Musselman, K. E.,

and Venkatachalam, T. K., J. Phys. Chem. 68, 1776

(1964).

"

[8] Sauer, R. 0., J. Am. Chem. Soc. 6^ 3 1707 (1944).

[9] Sweeley, C. C, et al . ibid 85, 2497 (1963).

[10] Langer, S. H. , Cornell, S., and Wender, I., J. Org. Chem.

23, 50 (1958).

[II] Farrow, R. N. P., and Hill, A. G., Analyst _9°_> 210 (1965).

[12] Pfann, W. G., "Zone Melting," John Wiley & Sons, New York

(1966).

[13] Schildknecht , H. , "Zonenschmelzen, " Verlag Chemie,

Weinheim/Bergstr (1964).

[14] Herington, E. F. G., "Zone Melting of Organic Compounds,"

Blackwell Scientific Publications, London (1963).

[15] Zief, M., and Wilcox, W. R., "Fractional Solidification,"

Marcel Dekker, New York, Vol. 1 (1967).

[16] Leslie, R. T., Ann. N. Y. Acad, of Sci. 137, 19 (1966).

[17] Robertson, D. E., Anal. Chem. 4JD, 1067 (1968).

[18] Freeman, D. H. and Kuehner, E. C, "Liquid Borne Particle

Metrology," Ann. N. Y. Acad, of Sci. (to be published).

45

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