zone refiner
Ultra-Purification of Organic Chemicals
Concentration of Impurities

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Table of Contents• Zone Refining Historical Note

Applications of Zone Refining
Zone refining can be used to purify virtually any solid thatmelts without decomposition. Thousands of examples arecited in the literature. Crystalline samples as low as 80% purity have been successfully zone refined; however, in orderto obtain extremely high purity samples (>99.9% pure) it isnecessary to start with samples having a purity of 98% or better. For an explanation of this refer to the zone refiner theory
section below.

•

Applications of Zone Refining•

Zone Refiner Operation•

Zone Refiner Theory•

Bibliography•

Preparing to Operate the MiniZone Refiner•

Unpacking the unit•

Setting up the unit

Among the applications to which Zone Refining can be applied include:•

MiniZone Operation•

Crystalline Polymorph Searches•

Tubing Selection•

Purification of analytical standards•

Preparing and Loading the sample••

Placing the loaded tube in the MiniZone Refiner

Separation of stereo (chiral) and geometricisomers•

Instrument Settings; Purification of the Sample••

Removing the purified Sample

Concentration of sample impurities for further analysis or
identification•

Troubleshooting•

Purification of laser dyes•

Purifier 10 Limited Warranty•

Purification of organic semiconductors

Zone Refining Historical Note
For hundreds of years chemists have used the power of crystallization to enhance the purity of chemicals. Crystallization
was the cornerstone technique of the work of Pasteur, Pierre
and Marie Curie, and many of the early pioneers of organic
chemistry.

In 1952, William G. Pfann at Bell Telephone Laboratories,
looking for a method to obtain ultra-pure specimens ofgermanium, developed a powerful new technique that
improved on fractional crystallization. He named the semiautomatic process zone refining or zone melting. With thenew process, extraordinarily pure specimens of germanium
and silicon could be obtained. Other workers successfully
extended the process to the purification of organic chemicals. These early pioneers predicted that the techniquewould become a routine laboratory tool. These predictions
were based on the fact that zone refining can be applied toa significant portion of organic chemicals and because themethod is powerful, semiautomatic, simple and operates
without consuming solvent.
In practice, however, the traditional method of zone refining
is very slow, requiring days or even weeks to purify chemicals. Also, operators were often frustrated by the bursting ofglass tubes used to contain the sample during purification
due to the high thermal expansion of organic chemicals
relative to glass.

A substantial amount of information is available on applications of melt zone refining. The following lists are takenfrom “Zone Melting of Organic Chemicals”, E.F.G.Herrington,
1963, John Wiley & Sons, New York. This book is out of print.
We are reproducing the lists as a service to our customers.
Compounds that have been purified using zone melting(details available) see below:•

Acetanilide•l Amino 2 methylanthraquinone•

Anthracene•

Anthraquinone•

Benzene•Benzoic acid•

Benzophenone•

p Bromoacetanilide•

p Bromotoluene•

Cetyl alcohol (C16H330H)•

p Chloroacetanilide•

4 Chloro o cresol•

4 Chloro 2 nitroaniline•

Chrysene•m Cresol•

3,4 Dimethylphenol•

3,5 Dimethylphenol•

2,6 Dimethylphenol•

2,4 Dinitrotoluene•

Dioxane•Diphenylsulphone•

Diphenyl sulphoxide•

Ethanol•

3 Ethyl 5 methylphenol•

Fatty alcohols•

p Fluorobenzoic acid•

Hallowax•

Azobenzene [1,2,3]•

Hexacosanol•

Azuline [5]•Hexacosyl hexacosanate•

Benzamide [1]•Hippuric acid•I,2 Benzanthracene [1]•Indole•p t Butylphenol [1]•p Iodobenzoic acid•

4 Chloro 1, 3 dinitrobenzene [2]•Lindane•1 Chloro 2 methylanthraquinone [1]•(Y 1,2,3,4,5,6 hexachlorocyclohexane)•

Cholesterol [3]•3 Methoxybenzanthrone•

Cholesteryl stearate [3]•9 Methylcarbazole•

Cinnamic acid [2]•3 Methylindole (Skatole)•

2 Cyanocyclopentylideneimine [1]•1 Methylnaphthalene•

d Cyanovaleramide [1]•3 Methylpyridine•

Cyclohexane [5]•Naphthalene•n Decane [5]•b Naphthol•

Dibenzyl [1]•Neopentane•

Dichloromaleic anhydride [1]•2 Nitro 4 methylaniline•

1,5 Dihydroxyanthraquinone [1]•Pentamethylpyridine•

1,8 Dihydroxyanthraquinone [1]•Phenanthrene•

2,3 Dimethylindole [1]•Phenazine•

N,N Dimethyl p nitrosoaniline [1]•Phenol•2,5 Dimethylphenol [1]•Phenothiazine•

Dimethylterephthalate [1]•Pyrene••Salicylic acid•

Diphenyl [2,5]•Sexiphenyl•

Diphenylacetic acid [1]•Stearic acid•

Fluorenone [1]•Stearyl alcohol•

Hexamethylbenzene [5]•Stilbene•

1 Hydroxyanthraquinone [1]•Succinic acid•l Indanone [4]•Sulphanilamide•

Isoquinoline [5]•Terphenyl•

Maleic anhydride [1]•p Tolyl methylsulphone•

1 Methylaminoanthraquinone [1]•Di p tolylsulphone•

2 Methyl 4 chlorophenol [1]•1,4,5 Trichloroanthraquinone•

2 a Methyl cyclohexyl 4 methyl alcohol [1]•Vanillin•

2 Methyl 4 nitroaniline [1]

•

Wax

•

Naphthylamine [5]•o Xylene•p Nitroaniline [1]•m Xylene•

1,2,3,5,7 Pentamethylindole [1]•p Xylene•

Phenoxy acetic acid [1]•Pyrazolone [1]Compounds that have been purified using zone melting (nodetails are available):•

Resorcinol [1]•Sitosteryl acetate [3]•Acetamide [1,2,3]•Succinic acid [1]•Aldrin [1]•1,3,5,7 Tetramethylindole [1]•1 Amino 2 cyanoanthraquinone [1]•Tolane [2]•4 Aminoquinoline [5]•1 p Tolyl 3 methyl 5 pyrazolone [1]•Aniline [1]•Urea [1]•p Anisidine [1]•Anthranilic acid [1]The references for the above list are as follows:•

Antipyrine [1][1] Beynon & Saunders (1960)

[2] Schildknecht (1961)[3] Schildknecht & Vetter (1961)[4] Chemistry Research (1957)[5] Wolf (1957)
Acetanilide
Wynne (1961) reported that the melting point of a zone
refined sample was 114.8 C, which may be compared withliterature values of 113~114 C.
Amino 2 methylanthraquinone
Beynon & Saunders (1960) showed that after thirty threezone passes the concentration of amino dimethylanthraquinone at the top of the column was 0.5 per cent and that of
diamino methylanthraquinone was 0.20 per cent. Initially theconcentration of both impurities was 0.31 per cent.
Anthracene
Wolf (1957) reported that tetracene can be removed fromanthracene by zone refining.
Joncich & Bailey (1960) found that Eastman White Labelanthracene after zone refining showed a very sharp peak inthe differential thermal analysis curve, indicating a considerable improvement in the specimen.
Light & Co (1959) produce zone refined batches of 1 to 5 lb
weight which are used to grow single crystals for scintillators.
Wynne (1961) reported that the melting point of a zone
refined sample was 219.10C (cf. literature values of 216~2l8C) and that analysis of the refined material gave: C, 94.46;
H, 5.78. CaIc. for C14H10: C, 94.34; H, 5.1 6.
Hoesterey (1962) reported that single crystals were grownunder helium by the Bridgman method from a zone refined
specimen. The starting material was either Eastman Organic
Chemical X 480 or hydrocarbon synthesized by the cyclization of o benzoyl benzoic acid followed by a two stage
reduction.
l Anthraquinone
Wynne (1961) reported that the melting point of a zone refined sample was 288.90 C and compared this with literature
values of 286~288 C.
Beynon & Saunders (1960) reported that anthraquinone canbe purified satisfactorily by zone melting.
BenzeneRock (1956) treated benzene in an apparatus. The puritiesof the original charge and of samples after treatment were
determined by melting point measurements using a Beckmann thermometer. When technical benzene containing
approximately 0.2 mole per cent impurity was refined, afraction containing less then 0.0008 mole per cent impurity
was obtained.
Sue, Pauly & Nouaille (1958) reported that a sample of benzene containing .002 fraction of acetic acid contained .001
fraction of the acid after ten zone passes. The concentrationof thiophene in a sample of benzene was reduced from .001
to less than .0001 by fifteen zone passes.

Schildknecht & Mannl (1957) reported that the zone refiningof a crude benzene produced a fraction at the end of thesample that was liquid when the rest of the specimen was
solid. It was claimed that almost 90 per cent of the benzene
was free from thiophene, but unfortunately the limits of thesensitivity of the test were not given. Removal of the portion
enriched with thiophen during treatment assisted purification. The work of Hudson, Hillig & Strong (1959) illustrates thecare that must be taken in the manipulation of samples of
the highest purity. Phillips Research Grade Benzene, initially
99.93 per cent pure, was further purified by vacuum sublimation and zone refining. Purification of the sample was carriedout in a vacuum system which included two cold traps toallow successive sublimation in a degassing process, a vertical zone refining tube and a manifold with capillaries forcontaining specimens. The zone melting tube was cooledby pumping alcohol at 0 C round a jacket. Four resistanceheaters in series were used to produce molten zones. The
purification apparatus was evacuated before use, flamed
until the residual pressure was less than 0.01 micron and thenfilled with dry nitrogen. The benzene, introduced through asilica gel filter, was then frozen by means of liquid nitrogen.
The opening through which the hydrocarbon had been admitted was sealed off and the system was pumped until theresidual pressure was below 1 micron. Dissolved gases were
removed by four sublimations between the two cold traps;
the first two sublimations were made with the aid of liquid
nitrogen and the other two by the use of a carbon dioxideacetone freezing mixture. After degassing the benzene wasmelted and condensed into the zone melting tube where
it was again frozen. After each zone pass all residual vapor
was frozen into one of the traps by means of liquid nitrogenand the condensed vapor was isolated from the rest of thesystem. The top inch of solid benzene was melted and asample condensed into one of the capillaries. The specimen
was frozen in liquid nitrogen and all the residual benzene
was condensed into the other trap by use of the same coolant. The sample tube was then sealed off. In this manner,
pyrolysis of benzene vapor during the sealing of the glass
was avoided. Benzene samples with a triple point of 5.527+/ 0.001C Were obtained after three or four zone passes;
the degassed starting material had a triple point of 5.523+/ 0.0020 C. Additional zone melting effected no further
improvement.
Beynon & Saunders (1960) also reported successful zone
refining of benzene.
Benzoic acid
Handley & Herington (1956) reported that the melting pointof a specimen after treatment was 121 121.5 0C; before
treatment it was 119.5 121.5 0C.
Joncich & Bailey (1960) studied the removal of carbon 14 labeled naphthalene from benzoic acid. An initial concentration slightly in excess of 0.1 mg of naphthalene per gram ofbenzoic acid was used, and it was found that after eighteenzone passes the concentration was reduced to below thedetectable limit of 0.0001 mg of naphthalene per gram ofbenzoic acid.
Wynne (1961) reported a melting point of 124 C for the zone
refined acid (literature values 122~123 C) and the analysis ofthat zone refined material gave: C, 68.82; H, 4.85. CaIc. for
C7H602: C, 68.84; H, 4.95.

Benzophenone
The zone refining of this material was studied by Schildknecht (1961) who presented a graph showing that after
three zone passes at 3 mm/h through material with melting
point 43.2~45 C, the maximum melting point of a portionof the specimen was 47.5 C. Eighteen zone passes throughsimilar material gave colorless crystals with melting point48.00 C and there was a large flat plateau in the curve of
melting temperature plotted against distance along bar.
Schildknecht & Vetter (1961) reported the satisfactory purification of this compound on the micro scale.
p Bromoacetanilide
Wynn (1961) prepared a sample with a melting point of
167.3 C (cf. literature values 165~167 C) by zone refining.
p Bromotoluene
A specimen of this compound containing a fraction of .02
of o bromotoluene was shown by the use of 82Br labeled obromotoluene to contain .0002 fraction of the ortho compound at the beginning of the sample after the passage ofnine zones (Sue, Pauly & Nouaille, 1958).
Cetyl alcohol (C16H330H)
Hesse & Schildknecht (1956) prepared a sample with a freezing point of 50 C by zone melting a specimen with freezing
point 48.50 C.
Beynon & Saunders (1960) also reported the successful purification of this compound.
p Chloroacetanilide
A sample with melting point 181.20 C (cf. literature values
178~180 C) was prepared by zone refining (Wynne, 1961).
4 Chloro o cresol
Sorenson (1959) found that a rather slow speed of zone
movement and many zone passes were required to purify
this compound. After eighteen passes (2 cm/h) a sample oftechnical 4 chloro o cresol (m.p. 40.90 C) remained rather
impure, the first fraction having a melting point of only 46.20
C. In a further experiment, however, fifty zone passes gavea pure product with melting point 48.70 C in the first 25 percent of the column.
4 Chloro 2 nitroaniline
Beynon & Saunders (1960) found that after two zone passes
the following impurities were concentrated and weredetectable, C6H3NH2CI2, C~H3NO2Cl2, C6H4NH2Cl andC6H2NH2NO2CI2. Further refinement was not attempted
because concentration of explosive polynitrocompounds
might have occurred.
Chrysene
Handley & Herington (1956) found that a sample with amelting point of 250~250.5 C could be produced by zone
melting a commercial sample with melting point 248 249.5
C.
Wolf (1957) reports that an unidentified impurity was removed from this hydrocarbon by zone melting.

m Cresol
A zone melting apparatus erected in a refrigerator has beenused for zone refining this compound (Chemistry Research,1957).
3,4 Dimethylphenol
Schildknecht & Hopf (1961) studied the purification of amaterial that was pale red in color but was well crystallized
and had a melting point of 62.30 C. A specimen 45 cm long
was treated by twenty five passes of a zone 2 to 3 cm long,
moving at the rate of 0.2 cm/h. Specimens taken at points
7.5 and 12.5 cm. from the beginning had the highest melting
points, 62.60C. Specimens at points 25, 50, 150 and 25 cm
from the beginning melted at 62.5 C, whilst at 27.5 cm themelting point was 62.3 0C and a specimen 31.0 cm from the
beginning melted at 62.2 C.
3,5 Dimethylphenol
Colorless crystalline samples of this compound were obtained by zone refining a specimen in nitrogen (Report of
the National Chemical Laboratory, 1958).
Schildknecht & Vetter (1961) have reported the successful
purification of this phenol on the micro scale.
Schildknecht (1961) has studied the zone refining of a mixture containing 88 per cent of 3,5 dimethylphenol and 12
per cent of 3,4 dimethylphenol. A sample of the more abundant phenol was separated in a yield 97 per cent of that
expected from the phase diagram, but the eutectic did notseparate in a pure form.
2,6 Dimethylphenol
This material was successfully purified by zone refining a
specimen in dry nitrogen (National Chemical Laboratory
Report, 1958).
2,4 Dinitrotoluene
Schildknecht (1961) observed pale yellow transparent
crystals 8 cm long at the beginning of a tube after fourteenzone passes. The end of the tube contained a brown massof fine crystals. Infra red analysis showed that these contained o and p nitrotoluene and trinitrotoluene as impurities.
DioxaneAccording to an unsigned report [Chem. Engr (1959), April
20, 66, 80] water and other impurities have been removed
from this heterocyclic compound by zone refining to yielda solvent of spectroscopic purity [see also Chem. Engng(1959) March 9, p.74].
Diphenylsulphone
Mackle & O’Hare (1961 a) purified a sample of B.D.H. Laboratory Reagent Grade material by zone melting several
times. Another sample was recrystallized eight times frompure ether. The melting point of both specimens was 124 C
and the normal boiling point was 378 C, with appreciable
decomposition. Analysis gave: C, 66.3; H, 4.66 comparedwith theoretical: C, 66.0; H, 4.62.

Diphenyl sulphoxide
Mackle & O’Hare (1961 b) prepared this compound by oxidizing Diphenyl sulphide in acetic acid with one equivalentof 30 per cent hydrogen peroxide added slowly under reflux.
The reaction product was evaporated to dryness undervacuum and the solid was purified by zone melting.

IndoleAnalysis of the purified compound (m.p. 70.20 C) gave: C,
71.1; H, 4.92, compared with theoretical C, 7l.3; H, 4.98.

p Iodobenzoic acid

EthanolIzergin (1958) treated ethanol in a boat made of polytetrafluro ethylene. The alcohol was frozen by means of liquid
air and the zone length was controlled by regulation of thepower of the electrical heater. The alcohol initially contained 4 per cent of water, and after four zone treatments
the water content was 1 per cent.
3 Ethyl 5 methylphenol
Purification of this compound in dry nitrogen was achievedby zone melting (National Chemical Laboratory Report,
1958).
Fatty alcohols
Hesse & Schildknecht (1956) separated the alcohols
C16H33OH and C18H37OH in a micro zone refining apparatus having three heaters and interjacent coolers. See also
Hexacosanol.
p Fluorobenzoic acid
Wynne (1961) prepared a sample with m.p. 187 C by zone
melting.
Hallowax
McClelland, Jnr. (Pfann, 1958) showed that after fifteen zone
passes through a hollow cylindrical charge of a capacitor
impregnator known as Hallowax 1001, the material, a chlorinated naphthalene, exhibited variations in melting point,
melting range and dielectric constant along the sample.
Hexacosanol
Schildknecht (1961) reported a study of a mixture of 80 per
cent hexacosanol (C26H53OH) and 20 per cent eicosanol(C20H41OH). These compounds form mixed crystals; separation by zone melting was followed by melting point measurements. Segregation was found to be slow and difficult;but finally a specimen of hexacosanol with melting point
80.30 C was isolated.
Hexacosyl hexacosanate
Schildknecht (1961) reported the separation of a sample ofhexacosyl hexacosanate by the zone refining of an insect
wax. The specimen was identified by infrared spectroscopy.

Hippuric acid
This compound could not be purified by zone melting
because the sample decomposed at a temperature only
slightly higher than the melting point (Hubbard, Frow & Waddington, 1961).

A sample of this material was zone refined by the Bureauof Mines, Laramie, Wyo., U.S.A., to 99.9 per cent purity (Ball,
Helm & Ferrin, 1958, 1959).

Wynne (1961) reported that a zone refined sample melted
at 270.80 C.
Lindane (Y 1,2,3,4,5,6 hexachlorocyclohexane)
A very pure sample of this insecticide, free from musty odor
and of melting point 112.84 C, was prepared by zone refining. This melting point should be compared with the mostacceptable figure (112.86 C) hitherto published (Report of
the National Chemical Laboratory, 1960).
3 Methoxybenzanthrone
The most abundant impurity (chloromethoxybenzanthrone)in a sample of this compound treated in a 24 in column
by Beynon & Saunders (1960), had a partition coefficient
greater than unity. The rate of movement of the impurity
was therefore very slow. Experiments showed that it was
helpful to use a much longer molten zone (e.g. 2 in) thanusual so that the impurity, which could not move more than
one zone length per pass, could move much further eachtime. The zone length was gradually reduced to a normal
value of about 1 in. The original charge contained 2.0 per
cent of chloro methoxybenzanthrone, 0.12 per cent ofdimethoxybenzanthrone and 0.66 per cent of chlorobenzanthrone. After forty eight zone passes the material at the
top of the column contained 3.4, 0.04 and 0.12 per centof these impurities and the material at the bottom of thecolumn contained 0.70, 0.17 and 0.78 per cent of the same
compounds.
9 Methylcarbazole
This compound was zone refined to a purity of 99.9 per centby workers at the Bureau of Mines, Laramie, Wyo., U.S.A.
(Ball, Helm & Ferrin, 1958, 1959).
3 Methylindole (Skatole)
Beynon & Saunders (1960) reported that this compound,which is notorious for its overpowering odor of feces, completely lost all its objectionable smell when zone refined.
Presumably the odor is due to a small amount of intensely
odoriferous contaminant.
l Methylnaphthalene
This hydrocarbon, m.p. 30.80 C, was treated in a zone refining apparatus enclosed in a space cooled with solid carbon
dioxide (Chemistry Research, 1957).
Wolf (1957) reported that anthracene can be removed fromthis compound by zone melting.
3 Methylpyridine
Workers at the Bureau of Mines, Laramie, Wyo., U.S.A., refined samples of this base to a purity of 99.9 per cent (Ball,
Helm and Ferrin, 1958, 1959).

Naphthalene
Wolf and Deutsch (1954) showed that two zone passes at
the rate of 1 cm/h through naphthalene containing 0.1 percent of anthracene reduced the concentration of anthracene to less than one part per million. The fluorescence
spectrum was used to measure the anthracene concentration. It was suggested that in any further attempt at purification the zone refining should be carried out in vacuum or
under nitrogen.
Handley (1955) and Herington, Handley & Cook (1956)
showed, by studying the fluorescence under ultra violet light,that seven zone passes reduced the anthracene concentration in a synthetic mixture of anthracene and naphthalenefrom 0.2 to 0.00002 per cent.
Beynon & Saunders (1960) demonstrated that it is possible
to purify crude naphthalene. After nine zone passes througha sample with a melting point of 73.50 C, they obtained a
specimen with melting point 80.20 C from the top portion of
the sample.
Wynne (1961) reported obtaining by zone refining a specimen of naphthalene with melting point 82 C. Analysis of thepurified material gave: C, 93.44; H, 6.23; CaIc. for C10H8, C,
93.71;H, 6.29.
Schildknecht (1961) reported the successful purification ofthis hydrocarbon.
Fryer (1962) has published a photograph of a zone melting
apparatus used in the laboratories of Hopkins and Williams
Ltd, to prepare ultra pure naphthalene.
b Naphthol
Colourless crystalline samples of this compound wereobtained by the zone refining of a specimen in nitrogen(Report of the National Chemical Laboratory, 1958).
Neopentane
This aliphatic hydrocarbon (melting point approximately
170 C) has been zone melted in an apparatus enclosed in aspace cooled by solid carbon dioxide (Chemistry Research,1957).
2 Nitro 4 methylaniline
The trace impurities C6H4NO2CH3 and C6H2(CH3)3NH2
were detected after two zone passes but further treatment
was not carried out for fear of concentrating explosive poly
nitro impurities (Beynon & Saunders, 1960).
Pentamethylpyridine
Brown & Buck (1961) zone refined a specimen of this compound before measuring the infra red absorption spectrum.
Phenanthrene
Joncich & Bailey (1960) reported that a sample of Eastman
White Label phenanthrene purified by the method of Feldman, Pantages & Orchin (1951) showed an appreciable
increase in purity after zone refining.
Beynon & Saunders (1960) also reported the successful purification of phenanthrene.
Phenazine
Aftergut & Brown (1961) studied the electrical resistance ofa zone refined sample of this compound that had previously
been purified by chromatography on alumina. As the zone
refined material had a higher resistivity and a lower energy
gap than material purified only by chromatography or by
sublimation it was considered to be purer than other specimens.

PhenolSorenson (1959) made an extensive study of the conditions
necessary for the removal of p nitrophenol from phenol byzone refining. With increasing impurity content it became
relatively more difficult to purify the phenol.
Wolf (1957), Schildknecht (1961) and Schildknecht & Vetter(1961) have reported successful purification of this compound.
Phenothiazine
Brown & Aftergut (1962) measured the resistivity of crystals ofphenothiazine that had been chromatographed, sublimed,zone refined and resublimed. Specimens that had been sublimed only did not show ohmic resistivity, and this behaviour
was attributed to the presence of impurities. Zone refinedmaterial exhibited ohmic resistivity with an energy gap of I 6
eV and this was considered to be a good value.
PyreneHandley & Herington (1956) reported a melting point of
152 C for a zone refined specimen, a value which is to becompared with a melting range of 150 152 C for the starting
material.
Wolf (1957), and also Beynon & Saunders (1960), reported
purification of this aromatic hydrocarbon.
Salicylic acid
Wynne (1961) compared his observed value of 161.90 C for
the melting point of a zone refined sample with literature
values of 159 161 C.
Sexiphenyl
Nozaki, Tamura, Harada & Saito (1960) prepared a sample
of sexiphenyl by a four stage synthesis from p terphenyl. The
material obtained by sublimation from the crude productwas yellow and contained copper and iodine. Neutron activation analysis of products obtained in a series of zone refining and vacuum sublimation operations showed that iodine
containing compounds could be removed. It was considered that these compounds were probably decomposed
during zone refining. However, too high a temperaturedecomposed sexiphenyl itself, especially when the purity
was low. Temperatures between 440~ C and 450~ C were
therefore used in the purification. After vacuum sublimation
and recrystallization from tetralin, the carbon and hydrogencontents of the product were correct. Nevertheless the melting points rose with repeated alternate zone refining andvacuum sublimation until it reached a constant value after
four repetitions of the cycle followed by a recrystallizationfrom tetralin and a vacuum sublimation. The final sample
contained less than 0.04 p.p.m. of iodine. The material wasused as a scintillator and the photo multiplier pulse obtained
was higher than that from anthracene.
Stearic acid
Wolf (1957) reported the removal of an unidentified impurity
from this acid by zone refining.
Wynne (1961) reported a melting point of 70.1 0C for a zone
refined specimen and compared it with values of 68~69.50
C from the literature.

Stearyl alcohol
Hesse & Schildknecht (1956) prepared a specimen with amelting point of 58.50 C from material with melting point
57.5 C.

Vanillin
A melting point of 84.0 C for a zone refined specimen wasreported by Wynne (1961); literature values cited were 82
83.50C. Analysis of the sample gave C, 63.16; H, 5.20.

Schildknecht (1957) treated 180 mg of a sample of stearyl
alcohol and found that after twenty four zone passes themelting point of the material at the front of the specimen
was 60.30 C and at the back was 55.90 C. The pure alcohol
was in the middle portion and melted at 58.40 C.

Theoretical: C, 63.15; H, 5.30.

Stilbene
Light & Co (1959) treat batches of 1 to 5 lb of this hydrocarbon by zone refining as a step in the manufacture of single
crystals for scintillators.
Schildknecht & Hopf (1961) zone melted a 39 g sample ofstilbene with a melting point of 119 1240C in a tube 2 cm indiameter and 46 cm long. After a 2 cm long zone had been
passed twelve times at the rate of 0.3 cm/h a specimen 1
cm from the beginning of the tube had a melting point of
125.4 0C. Samples between the third and eighteenth centimeters had a melting point of 125 C and a specimen near
the far end had a melting point of 80 C.
Schildknecht (1961) and Schildknecht & Vetter (1961) also reported successful purification of stilbene by zone treatment.
Succinic acid
Wynne (1961) reported a melting point of 187.8 C for azone refined specimen (literature values 185~187 C). Analysis of the refined material gave: C, 40.98; H, 5.07. CaIc. for
C4H604: C, 40.68; H, 5.2.
Suiphanilamide
Wynne (1961) reported a melting point of 165.2 C for atreated specimen literature values cited 164 165 C).
Terphenyl
Light & Co (1959) zone refined this compound as a step inthe preparation of single crystals.
p Tolyl methylsulphone
Crude p tolyl methylsulphone was zone melted by Mackle& O’Hare (1961 a) to give a product with a melting point of
83.6~84.10 C (literature values 83~87.50 C), and a normal
boiling point of 316 + 10 C. Analysis gave: C, 56.5; H, 5.90
compared with theoretical: C, 56.4; H, 5.92.
Di p tolylsulphone
Mackle & O’Hare (1961 a) reported that a sample from
Eastman Kodak Ltd was zone refined four times and anotherspecimen recrystallized eight times from diethyl ether was
fused several times. Both batches had a melting point of
158~159 C (lit. 158 C); the normal boiling point was 403+ 10C
and analysis gave: C, 68.4; H, 5.71 compared with theoretical C, 68.3; H, 5.73.
1,4,5 Trichloroanthraquinone
Thirty zone passes were found by Beynon & Saunders (1960)
to produce segregation of impurities, one of which, namely
1,4,5,8 tetrachloroanthraquinone, moved in the opposite direction to the zone. The color of the molten zone was foundto give a sensitive indication of the presence of impurities.

Wax
Various types of wax have been treated; it is reported[Chem. Engr (1959), April 20, 66, 80] that on the industrial
scale low melting waxes are improved by alternatively
heating and cooling closely spaced pipes so as to cause anumber of zones to pass through a bed of material over thepipes.
Hesse & Schildknecht (1956) used a micro zone~melting
apparatus to treat a wax obtained from the larva of the butterfly Attacus edwardsii and found that three zone passes
were more effective than recrystallization from solvents.
Schildknecht (1961) zone refined the wax of the insect Etiopeltisfestucae and hence showed the presence of hexacosyl hexacosanate.
o Xylene
This hydrocarbon, the approximate melting point of which
is 29 C, was treated in a zone refining apparatus enclosed
within a space cooled with solid carbon dioxide (Chemistry
Research, 1957).
m Xylene
This hydrocarbon was treated in zone melting equipment
cooled by solid carbon dioxide (Chemistry Research, 1957).
p Xylene
A sample of p xylene containing 10 per cent of o xylene wastreated by nine zone passes. Sije, Pauly & Nouaille (1958)
then found by measurements of the freezing point depression that a portion of the sample contained .005 fraction of
the o isomer.
Zone Refiner Operation
In zone refining, a short molten zone or zones travel slowly
through an elongated sample of a crystalline material. A
molten zone traversing a solid sample has two liquid solidinterfaces; a melting interface and a freezing interface.
At the melting interface the sample is merely melted andmixed with the contents of the molten zone. At the freezing interface, the just-frozen solid is generally higher in purity
than the molten zone. Extraordinarily high purification ofchemicals can be obtained by repeatedly passing themolten zone or zones through the sample. The impurities
are concentrated at the end of the sample, generally in the
direction of the movement of the molten zone.
A conventional zone refiner is operated by sealing a sample
into a glass tube which is then suspended by a cable/hookand inserted into stationary heating modules (3). As theglass tube containing the sample is moved slowly upward by
the mechanism, the heaters melt a zone of sample immediately inside the heater loops. As the sample tube travels
a distance equal to the spacing of one heating module
the mechanism is reversed and the tube is moved rapidly
downward exactly the spacing of one heater module. The
primary reason for conventional zone refining being so slow
is that the transfer of heat into and out of the sample is very
slow. The thermal conductivity of both glass and organic
chemicals is relatively low. This limits the speed with which
the zone can be moved through the specimen to rates of .1
to 1 cm per hour. Another complicating factor that requires
special experimental techniques is that the coefficient ofthermal expansion of organic chemicals is about 50 times
higher than glass. If the heating is too vigorous or too fast,
the glass tube will burst.

Zone Refiner Theory
Pfann discusses the theory of zone refining quite extensively
in his book (1). We have developed a short computer program that allows the rapid calculation of zone refiner operation. In the example displayed, a zone rate of 10 cm/hour
is selected and the purification profile of an impurity having
a distribution coefficient of 0.5 at the 1% level is simulated.
Twenty curves are displayed indicating four hours of operation or the passage of 20 molten zones. Each line represents
one passage of a molten zone through the sample; the migration of the impurities to one end of the sample is readily
apparent. This Zone Refiner Simulator Program helps greatly
in understanding the power and limitations of the zone refining technique. This program gives results that are identicalto the theory described in Pfanns book. The Zone Refiner
Simulator Program runs on Windows operating systems.
The Zone Refiner Simulator Program divides the 10 cm sample length into 1000 increments. As each increment freezes
at the face of the moving frozen zone the impurity will invariably have a lower concentration in the crystalline phasethan in the liquid phase. This ratio is known as the distribution coefficient. The program adds the amount of impurity
frozen out of the solid increment to the total concentrationof the impurity in the entire molten zone (the molten zone
is 100 increments or 1 cm long). This assumes that stirring in
the molten zone is fast relative to the zone movement. As
each molten zone passes through the sample the cumulative effect of the melting/freezing process can be easily
studied. When the molten zone moves to the end of thesample container, the computer program adds the impurity
concentration to the smaller molten zone. This causes theconcentration of the impurity to appear to have a discontinuity at a distance of 1 cm from the edge.
Examination of the concentration curves shows why starting with reasonably pure starting material is important if
extremely high purity materials is desired. As the impurities
accumulate at one end of the sample they tend to limit
the purification level possible for at least the last half of thesample.
Bibliography
1. P fann, William G., Zone Melting, 1958, New York, John
Wiley
2. H
 erington, E.F.G. Zone Melting of Organic Compounds,
1963, London, John Wiley
3. P
 ahler, L.F. et. al. Zone Refining organic compounds: apparatus modification and procedure, Am Lab 1981, 13(6)46-8, 50-1
4. D
 esign Scientific Web Site address: http\::www.designscientific.com

Preparing to Operate the MiniZone
Unpacking the Unit
Each complete unit should include:•

Purifier 10 MiniZone Refiner Instrument•

One (1) power cord.

•

Purifier 10 Instruction Manual•

Package of assorted Teflon sample tubes•

Please report any missing items.

Retain all packing materials until the instrument is connected
and functioning properly. Any unit return, regardless of thereason, must have prior approval by Design Scientific, Inc.
All returns should be shipped to the address listed below. To
ensure the safe arrival of the unit, we suggest shipping theunit in its original box and packaging or a replacement box
and packaging provided by Design Scientific, Inc.
Design Scientific, Inc.
90 Jay-Bob Lane,
Afton Wyoming 83110
Phone: 770/536-6195
E-mail – dsi@silverstar.com
Web Site:
Setting Up the Unit
Choose a location for the unit on a stable bench or tablewith convenient access to required AC power. Insert thepower cord into the receptacle at the rear of the unit andplug into a convenient power outlet. Check for proper operation by turning on the power to the unit using the switch
on the back of the unit
Operating the MiniZone Refiner
Verify that the unit is operating properly by dialing in atemperature of 60 C for the melt temperature and 40 C for
the freeze temperature. When the unit is operating properly, the small lamps located above the Melt Temperature
control and the Freeze Temperature Control will flicker when
the operating temperature is reached. If the temperatureof the sample block is lower than the temperature set on thecontrol the light will light continuously, indicating that theblock is heating up to the operating temperature. If the lightis off continuously the temperature of the block is above theset temperature. Also, if the set temperature of the freezing
block is more than about five degrees lower than the actual
block temperature, a cooling fan will turn on to cool thefreeze temperature block.
The tube transport mechanism is moved by a stepping motor. Each pulse or step of the motor moves the transportmechanism (and Teflon Tubing if the sample is inserted)
0.0254 mm (0.001 inch). Verify that the tube transport isoperating properly by dialing in 10 cm/hr on the Zone Rate
control. You can feel the pulses on the top of the mechanism. At the rate of 10 cm/hr the pulse rate should be a little
faster than one per second (1.09 pulse per second)
NOTE: The spring clips that hold the PEEK sample plugs areintended to be loose. DO NOT TIGHTEN THE SCREWS HOLDING THESE CLIPS. If these screws are tightened and thespring clips are not allowed to “float” the tube movement
mechanism may bind and improper operation will result.
Tubing Selection
The tubing for the MiniZone is available in the two diameterslisted below.
MZLARGE: 4.72 mm ID X 100 mm Long; internal volume =174.9 microliters per 10 millimeters.
MZMEDIUM: 3.38 mm ID X 100 mm Long; internal volume =89.7 microliters per 10 millimeters.
Although the tubes are approximately 100 mm long, themaximum active fill length is approximately 82.5 mm.

The amount of sample being purified will determine which
tubing size is selected and the number of tubes to be used.
A maximum of about 2.89 ml of sample can be refined at
one time by completely filling and loading two of the large
tubes at one time. A minimum of about 0.179 ml of sample
can be purified by filling the smallest tubing about half full (2cm long fill length).

are also an impurity in a crystal and as the crystallization proceeds, the dissolved gases will be forced out of the crystal
lattice. These gases can be removed by gently striking theends of the tubing with a pencil or similar object to dislodge
the gases upward in the molten zone. Eventually the gas
bubbles will collect at the top of the tubing.

We do not recommend mixing tube sizes. Purifying morethan one kind of a sample at a time is only recommended if
the melting points are within 2 or 3 degrees of one another.

When the zones have formed as shown in the photograph,
the MiniZone can be left to operate unattended. The number of recrystallizations (zone passes) desired is a matter of
personal judgment and will depend on the sample being
purified. The number of crystallizations per hour for eachpart of the sample for various zone rates are listed below:

Preparing and Loading the Sample
The first step in preparing a sample is to plug the end of thesample tube with one of the PEEK tubing plugs supplied withthe unit. (NOTE: PEEK is an inert, high temperature polymer
that will not contaminate your sample.) The powderedsample is then poured into the open end of the tube until
it is full. Most powders will contract 30% to 50% when thesample is melted. In order to completely fill the sample tube
the sample must be melted to remove the air. This can beconveniently done by heating the sample tube with a heatgun or by inserting into the heated blocks of the MiniZone
Zone Refiner.
After the sample is melted and the air is removed, allow thesample tube to cool until it is again crystalline. Additional
powdered sample can be added to the tube and the melting process repeated until the sample tube is filled with thesolid sample.
When the proper amount of sample is loaded into the tubing push another PEEK Tubing plug into the upper end of thesample tube.
Placing the loaded tube in the MiniZone Refiner.
When the sample is loaded and fully crystallized in thesample tube, push the bottom end of the PEEK tube plug
into the lower spring clip then push the upper PEEK tube
plug into the upper spring clip.
NOTE: The spring clips that hold the PEEK sample plugs areintended to be loose. DO NOT TIGHTEN THE SCREWS HOLDING THESE CLIPS. If these screws are tightened and thespring clips are not allowed to “float” the tube movement
mechanism may bind and improper operation will result.
Instrument Settings; Purification of the sample
Next, the instrument settings are adjusted for the sample being purified. The Melt Temperature should be set between
10 and 20 degrees above the melting point of the substance being purified and the Freeze Temperature should be
set between 10 and 20 degrees below the melting point of
the substance.

Zone Rate (cm/hr)		
Crystallizations per hour
1				
.5
2				

1

5				

2

10				

420				

8

Thus at 2 cm/hour in 18 hours each part of the sample will
be recrystallized 18 times. This number of recrystallizations
will give a level of purification that is adequate for most
purposes.
Removing the sample from the tubing
While the sample is being refined the lower and upper limitof the molten zones should be marked on the outside of thetubing. This can be done using tape or by slightly cutting
the tube at the limits of the molten zones.
Turn the unit off or turn the temperature controls down until
the sample fully crystallizes in the MiniZone. The two endsof the sample tube are easily confused once the tubes are
removed. You may want to permanently mark the tube insome way to avoid confusion.
After the sample is cooled, remove the tube by pulling up
on the PEEK end plugs. Remove these plugs and save themfor future use.
The sample can be recovered from the tubing by cutting
sections of the tubing with a sharp knife, scalpel or scissors.
The sample may be removed from each section by dissolving in a suitable solvent, melting the sample or by physicallypushing the solid sample from the tubing. The purest sample
will be adjacent to the lower molten zone limit mark. The
sample purity will be slightly less pure as the samples are cut
from the tubing until the final cut just before the upper mark.
This zone will contain most of the impurities.
Troubleshooting
For assistance in troubleshooting your Purifier 10 Zone Refiner,
consult the troubleshooting guide below. However, if you
are unable to resolve the problem, call Design Scientific forassistance.

The Zone Rate should be initially adjusted to 2-3 cm/hr
The molten and crystalline zones should form as shown in
the photograph to the right. The hot zones are formed by
the block on the left and the cold zones are formed by theblock on the right. The tube will move down at the rate seton the Zone Rate control. After moving about 2 centimeters
the mechanism will reverse and the tubes will be moved
rapidly up two centimeters.

Troubleshooting Guide

This operation will make the crystalline zones move up withrespect to the tubing. Bubbles of gas will sometimes form as
the zone refining proceeds. This is because dissolved gases•••

ProblemPossible Cause•

Solution

Purifier 10 does not have power.
• Power switch located on back of unit is turned off, fuseis blown or power cable is loose
Turn unit on, check fuse or push power cable into socket

The entire sample remains molten.
• Freeze and/or Melt Temperature setting is too high.
•Decrease the Freeze or Melt Temperature until sample
begins to crystallize

The entire sample remains crystallized• Freeze and or Melt Temperature setting is too low•

Increase the freeze or melt temperature until the sample
begins to melt

Sample remains molten and the freeze temperature is below
the melting point.
• Seed crystals are not contacting the lower part of thesample.
•Insert seed crystals in the lower part of the sample tubing below the heated zones.

Sample forms bubbles that block the crystallization• Out gassing of the sample when crystallization occurs•

Vibrate the sample tube to dislodge the bubbles to theupper part of the tube

Sample darkens during the zone refining process• Decomposition of the sample is occurring•

Sample is not stable at the melting point–not suitable forzone refining.

Purifier 10 Limited Warranty
In addition to other manufacturers’ warranties, Design
Scientific Inc. (“the Company”) warrants all products delivered to and retained by their original purchasers to be
free from defect in material and workmanship for one year
from the date of the Company’s invoice to the purchaser.
For a period of one year from the date of such invoice,
the Company will correct, either by repair or replacement
at the Company’s sole election, any defect in material orworkmanship without charge for parts and labor. This does
not include defects due to misuse, abuse, abnormal conditions or operation, accidents, or to service or modification
to the unit without prior authorization of the Company. The
determination of whether any product has been subject tomisuse or abuse will be made solely by the Company.
The Company shall not be liable for any special, incidental,
or consequential damages, or any damage to plant, personnel, equipment or products, directly or indirectly resulting
from the use or misuse of any product sold by the Company
except as set forth in and limited by the foregoing warranties. Representations and warranties made by any person,
including dealers and representatives of the Company,
which are inconsistent, in conflict with, or in excess of theterms of this warranty shall not be binding upon the Company unless placed in writing and approved by an officer of
the Company.

(800) 572 - 6653 • Fax: (616) 396 - 7520 • 590 East 32nd Street, Holland, MI 49423 • info@resolutionsys.com

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