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Modern Methods of Analysis.

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C O N F E R E N C E REPORTS
Modern Methods of Analysis
The section Analytische Chemie of the Gesellschaft Deutscher
Chemiker, the Osterreichische Gesellschaft fur Mikrochemie,
and the Schweizerische Gesellschaft fur Analytische Chemie
und Angewandte Chemie held a symposium from the 13th to
the 16th April 1966 in Lindau (Germany).
F r o m t h e lectures:
The Importance o f Ultramicroanalysis of Streak
Samples for Trace Analysis
H . Bnllczo, Vienna (Austria)
Ultramicroanalysis of streak samples has become possible
by use of the corundum rod, a small sintered rod of pure
alumina 111. I t is now possible t o isolate minute amounts of
inclusions (inhomogeneities) in, e.g., minerals and to subject
them to complete microanalysis. In this method, not only
are the difficulties of sampling (comminution) and of working
up (choice of material for the containing vessel) overcome,
but the concomitant advantages (better distribution, use of
up to 2000 pg) make it possible to subject the sample to
evaporation analysis and thus to determine also traces.
When it is to be heated (for sublimation) the rod is placed in
a small quartz cylinder, inclined so that the streak is at the
top, covered with a small quartz tube that is somewhat
narrowed in the middle, and heated at the lower end.
If, e.g., a molybdenite contains arsenopyrites, wolframite,
and zinc blende as impurities, the volatile oxides are collected
one after the other (e.g., Se02 from 316'C, As203 from
321 "C, Moo3 from 800 "C) and, if the cover tube is changed,
can be investigated separately in turn; the difficultly volatile
impurities such as WO3, BizO3. SbzOj, ZnO, and SnOz
remain behind and they too can be further separated. For
example, evaporation with HCl converts ZnO into the
volatile (from 732OC) ZnClz. Furtter, the quartz test tube
can be. subjected to reducing conditions (e.g., heating with
sodium azide at 275 "C or with sodium formate at 440 "C),
which results in sublimation of the metals Cd (from 260 "C),
Zn (from 360 "C), and simultaneously also Pb, Ag, and Ga;
or by means of the hydrogen chloride evolved from ZnC12
(from 365 "C) SO3 can be driven out of sulfates and HzS out
of sulfides, as shown by F. Feigl. The sulfide formed during
the reduction can be removed by cautious heating with
ammonium chloride (evolution of HCl at 135OC). The
detection of HIS has been improved by more than two
powers of ten (5 ng instead of 2 pg) by a development
process (CdS -+ Ag2S + Ag). The solubilizing medium is
conveniently sprayed on in aqueous or alcoholic solution
(ZnClz). However, very small amounts of water or OH
groups (OH-apatite, etc.) or free sulfur (in sulfides) can also
be determined - for the first time - in a streak (in a melt
with KSCN or benzoin by F. Feigl's method).
An Oscillometric Analytical Procedure with
C o n t i n u o u s Recording
R. Bertram, Clausthal-Zellerfeld (Germany)
In oscillometry chemical processes are followed by measuring
the electrical properties of the reaction mixture. Generally
changes in conductivity and dielectric constant are determined. For the procedure in question the measuring cell
[ I ] Degussit Al 24, from DEGUSSA, F r a n k f u r t / M . (Germany).
Angew. Chem. internat. Edit.
Vol. 5 (1966) 1 No. 7
containing the mixture is placed in a special circuit element
coupled to the rest of the circuit so that the resulting frequency is an unambiguous measure of the changes occurring
in the cell. The resulting frequencies (50 cis to 1 Mc/s), are
measured by a receiver, and a n attached high-speed recorder ensures instantaneous and complete recording. The
process is applicable over the whole ionic conductivity range
for cells with or without direct electrode contact. Among
other reactions, the rapid hydrolysis of phenyl trifluoroacetate and the slow adsorption of sodium hydroxide on
quartz powder has been investigated; finally, a new mode
of dissolution of molten lead in a cadmium chloride melt
has been discovered. Drying processes have been recorded
for solids in platelet form down to water contents of 10-2
wt.- %. Even though recording is instantaneous a relative
accuracy of l O - 3 % is obtained, which is beyond that of
any other conductivity method.
Determination of Traces of Arsine in Inert-Gas Mixtures
in Presence of a L a r g e Excess of Stibine. Influenceof
Precipitation Conditions on the Enrichment of Arsenate
d u r i n g Coprecipitation with Phosphate
W. Gann, Hagen (Germany)
Arsine and stibine are removed from the gas mixture to be
analysed by absorption in a perchloric acid solution of
sodium triiodide. Antimony is determined in an aliquot of
the absorbing solution by reduction with hypophosphite and
photometric determination of the resulting iodoantimonate(111). Traces of arsenate are enriched from the absorbing
solution by addition of sodium phosphate and then of
calcium chloride at pH 2 12, causing coprecipitation with
calcium phosphate. The phosphate precipitate is dissolved
in a little hydrochloric acid, and after a reduction with hypophosphite the arsenic is determined in this solution photometrically as brown arsenic sol. The range of applicability
is 20 pg to the mg region per 5 0 ml of absorbing solution for
stibine, and 5 pg to 60 pg per 50 ml for arsine. There is no
interference with the determination o f arsine unless more
than 10 mg of antimony is present in the absorbing solution.
Interpretation of Potentiometric and Photometric
Titration Curves Obtained on Recording A p p a r a t u s
E. Greuter, Herisau (Switzerland)
Automatically recorded titration curves have the advantage
of showing the complete course of the titration, so that
anomalies can be recognized immediately. A potentialvolume curve is produced. For its generation the advance of
the paper and the addition of the reagent must be accurately
proportional. The equivalence point is preferably determined
graphically from the curve; parallel tangents to the curve
are drawn in front of and behind the equivalence point; a
parallel line drawn midway between these two tangents cuts
the curve at the equivalence point.
Tests have been made to determine what faults can arise o n
use of automatically recording analytical apparatus. The
errors observed are caused by the recording itself and during
measurement along the volume axis of the potentiogram.
Titrations of hydrochloric and acetic acid with sodium
hydroxide, with various experimental programs, gave deviations of + 3 . 3 %, + 1.8 %. -2.0 %, and + 1.9 % in the results
relative t o the standard values.
677
Unsymmetrical curves are harder to evaluate; no mathematically sound method is known for this purpose.
Electrical differentiation of the potentials arising during the
titration with respect to the time, and recording of the
derivatives against volume, are often advantageous. Endpoints close to each other often give only one potential
jump on the integral curve, whereas the derivative curve
often shows the two equivalence points separated. The
simplest method of electrical differentiation is by means of a
capacitance-resistance circuit.
Photometric titration curves can be recorded by coupling a
potentiograph to a spectrophotometer. Acid-base titrations
give symmetric curves if the pK of the indicator equals that
of the acid (or base) to be titrated. The photometric titration
curve can be obtained by graphical addition of a potentiometric titration curve to the curve showing the change in
extinction of the indicator in relation to pH.
Micromethod for Analytical Determination of Lower
Oxidation States
R . Gruehn, Miinster (Germany)
A new method permits determination of lower oxidation
states in substances that react in a KOH melt with evolution
of Hz. 0.5-15 mg samples, including single crystals, are
added to a degassed KOH melt in a vacuum; all the substance
dissolves in its highest oxidation state, while an equivalent
amount of hydrogen is set free. The hydrogen is pumped
off, compressed in a Topler pump, and measured in a
Hg buret; it can be identified by combustion over CuO.
For instance, the compositions of six NbO, phases have
been accurately determined, giving the following values of x:
2.417
0.003 (2 modifications); x = 2.454 + 0.002; x =
2.462 f 0.002 to x = 2.467 i 0.001 (phase range); x = 2.467
0.001 to 2.479 + 0.001 (phase range): x = 2.483
0.001.
Moreover, the lower phase limit of the H modification of
niobium pentoxide has x 2.489 & 0.001. Other lower oxides,
oxide halides, and halides of Mo, W, Nb, Ta, and Ti have
been investigated. The oxidation states of the compounds
NbC12.33, Ta6C114.8H20, and TahBrl4-8 H20 have been
confirmed by this method.
*
*
-
DirectW - S p e c t r o p h o t o m e t r i c Evaluation ofThin-Layer
Chromatograms
H . Jork, Saarbrucken (Germany)
In thin-layer chromatography one obtains discrete zones, for
the localization, identification, and/or quantitative analysis
of which spectrophotometric methods can be used. By use
of the Zeiss chromatogram-spectrophotometer, reflection
fluorescence and absorption spectra can be obtained directly
from the chromatogram layer, both for the visible and the
ultraviolet region.
For localization of invisible, absorbing zones the whole
chromatogram is examined at a wavelength specific for the
compound in question. Then differences in the amount of
reflection are found for various parts of the layer.
The reflection spectrum of a zone that has thus been located
is best taken with a slit width corresponding approximately
to the radius of the spot. It usually corresponds exactly to
the absorption spectrum measured in solution (2.g. for
p-ethoxyacetanilide and trimethylxanthine). If this is not the
case, as for 2,3-dimethyl-4-dimethylamino-l
-phenylpyrazol-5one or acetylsalicyclic acid, then these medium effects, e.g.,
that of Kieselgel G as a layer, can be used for characterization
of the substance present. The sensitivity obtained by taking
the spectrum directly is at least ten times greater than for
measurement in the usual cells. For absorption spectra at
least 3 pg of substance is required, for fluorescence spectra
only 30 to 50 ng.
Direct quantitative evaluation of thin-layer chromatograms
is possible with the Kubelka-Munk function (relative
deviation f 3 %).
678
Analytical Use of Infrared Spectroscopy with Gratings.
Quantitative Analysis of Gas Traces
G . Kemmner, G . Nonnenmacher, and W . Wehling
uberlingen (Germany)
The sensitivity and detection limits of the quantitative infrared-spectroscopic analysis of gas traces depend on the cell
length and on factors related t o the apparatus: resolving
power, signal-to-noise ratio, and the scale of the ordinate.
The cell thickness can be varied independently of the instrument; the recording parameters, on the other hand, are
connected with the design of the instrument, and are essentially determined by energy relationships.
The influence of the apparatus parameters on the quantitative
analysis of CzH2, Nz0, and CO has been tested on dilution
series of these gases in nitrogen. Concentrations between
100 ppm and close to the detection limit (see below) were
determined by means of two grating instruments and one
NaC1-prism instrument in a 1 m gas cell and at various
scanning conditions.
According to the distance between their rotational lines the
investigated absorption bands show varying dependence on
the spectral slit width AS. The effect is slight in the case of
Nz0. CO and CzH2 exhibit increasingly resolved fine structure
with decreasing AS; the molar extinction coefficients of the
analytical lines increase by a factor of 4 to 6 when AS is
reduced from 4 to 0.6 cm-1 in the case of C2H2, and from
18 to 0.5 cm-1 in the case of CO.
The high dispersion of grating instruments gives flexibility
in the adjustment of the recording parameters under the
conditions of the quantitative analysis: narrow slits for
the highly sensitive measurement of larger concentrations,
and wide slits for a favorable signal/noise ratio with relatively
good resolving power for measurements in the lower ppm
range with ordinate scale expansion.
The smaller the spectral slit width and the greater the signal/
noise ratio, the lower are the detection limits. For an optical
path of 1 m, the detection limits in the most favorable case
(Perkin-Elmer 225 with a 50-fold expansion of the ordinate)
were found to be 2.5 ppm for CO, 0.4 ppm for NzO, and
0.1 ppm for CzH2. These values lie in a range that, without
ordinate scale expansion, is analytically attainable only by
the use of a 10 m gas cell.
Element-Specific Determination of Gas-Chromatographically Separated Metal C o m p o u n d s b y Use of
Atomic Absorption Spectroscopy; Determination of
L e a d Alkyls in Gasoline
B. Kolb, G . Kemmner, Fr. H . Schleser, and E. Wiedeking
Uberlingen (Germany)
Atomic absorption spectroscopy can be used for determination of the concentration, in a sample, of an element
amenable to this method. Since, however, a given element
may occur as various compounds, these must be separated
when it is necessary to differentiate between them. For
volatile compounds this is most simply done by gas chromatography, the column being connected directly to the burner
of an atomic absorption spectrophotometer. The recorder
draws a chromatogram in which, of all the components
separated, only the compounds to be analysed appear as
peaks. The combination of gas chromatography with atomic
absorption spectroscopy is particularly suitable for analysis
of traces of volatile metal compounds in complex mixtures.
Since the process is specific to an element no compoundspecific response factor is required.
In the determination of tetramethyl- and tetraethyl-lead in
gasoline, use of the 217 mp line of a lead hollow-cathode
lamp gave a detection limit of 4x 10-11 g-atom of Pb per sec,
which under the given working conditions and a sample size
of 5 p1 corresponds to a concentration of 32 mg Pb(CHd4
and 85 mg Pb(CzH5)4 per liter of gasoline, respectively.
Angew. Chem. internal. Edit. 1 Vol. 5 (1966) 1 No. 7
Use of Activation Analysis for Determination of Traces
in the White Lead of Paintings
Spectrochemical Determination of Impurities in Very
Pure A l u m i n u m after Removal of the M a t r i x b y
Distillation as Organometallic C o m p o u n d
F. Lux and L. Bvannsfein, Munich (Germany)
K. H. Neeb, Erlangen (Germany)
In coliaboration with the Dorner Institut of the Bavarian
State Collection of Paintings a study has been begun of the
use of activation analysis for determining the content of trace
components in the white lead of paintings. Its object is to
test the possibility of dating pictures and of ascribing them to
various schools o n the basis of the trace components in the
white lead,the chief pigment all paintings.This can be achieved
only by activation analysis since only microgram samples
are available from a painting and the content of trace
material often amounts to only a few ppm, so that the
amounts of the trace ingredient will sometimes lie in the
range 10-11 to 10-10 g. In similar studies of the white lead of
paintings by Dutch artists, Houtmnn and Turkstvrc121 concluded that the trace content decreased after about 1850.
In our work the content of Ag, Ba, Cr, Cu, Mn, and Sb in the
white lead was determined. The samples were taken from
undoubtedly white parts of the pictures, e.g. white spots.
Each sample was subdivided into one for short irradiation
(irradiation time 4 hr; 139Ba, 64Cu, 56Mn) and another for
long irradiation (irradiation time 300 hr; IlomAg, 5lCr, 122Sb).
The samples were irradiated in the research reactor at
Munich (FRM) with a flux of 5x 1012 or 3x 1013 neutrons
cm-2 sec-1. The individual nuclides were determined by a
combination of radiochemical separation and gammaspectrometric measurement. A 1600 channel pulse-height
analyser was used for this measurement. Counting times for
the longer-lived nuclides were up to 800 min. The limits of
detection were 5x 10-10 g for Ba, 2x 10-10 g for Cr, 1O-lO g for
Ag and Cu, and 10-11 g for Mn and Sb. Samples of white
lead were taken o n the one hand from paintings by Dutch
masters of the 16th and 17th century, namely Rubens, Vevmeer, and the mannerists Hemessen, Janssens, and Roymerswaele, and o n the other from paintings of the Venetians
Titinn and Tintoretto. The results are given in Fig. 1.
Metallic aluminum reacts with ethyl bromide with formation
of triethylaluminum tribromide, which can be vacuumdistilled without decomposition, leaving some important
impurities as a nonvolatile residue. This simple method of
separation can be utilized to determine traces of other elements in very pure aluminum. For evaluation of the behavior of ppm amounts of impurities, control mixtures
containing radioactive isotopes were studied; the distillation
residue was analysed spectrographically. Recoveries in the
residue and the lower limits of determination (for 1 g of
aluminum) are shown in the table.
Impurity
Recovery(%)
Lower lim. of
detn. (ppm)
1 I 1 1 1 1
1 Fe 1 C o 1 P b 1 A g I Cr 1 M n 1 Co 1 Ni
I99
I99
0.3 0.02
99
0.5
99
0.02
95
0.1
94
0.07
98
0.05
lo?
0.4
Low background values were obtained by confining the
reagents used to low-boiling liquids such as ethyl bromide,
bromine, and nitric acid that areeasy to purify by distillation.
The process is not limited t o final use of spectroscopic determination.
A Novel Pulse Process with Digital R e a d o u t for
A u t o m a t i c Titration
F. Oelzme, Glattbrugg-Zurich (Switzerland)
Except where the reagent is generated coulometrically, almost
all accurate automatic titrators involve use of syringe
burets. Induction motors used for control of the buret have
the disadvantage, due to inertia of the control mechanism,
that the volume added does not correspond to the duration
of the dosage command when the latter is short: a further
result of the inertia is that a small excess may be added when
the cut-off is very sudden.
Step motors do not suffer from these disadvantages. Single
impulses delivered as signals by a pulse generator are passed
o n as defined rotations of the buret control mechanism
even if the pulse duration is only '/loo sec. For example, a
step motor rotates about 18 per pulse. The motor stops at
once when the current stops and remains magnetically
arrested.
The step-motor drive and the pulse generator o n which it is
based have the following advantages:
(a) The volume added is shown directly by counting the
pulses, e.g. by a mechanical counter.
They show that the Dutch and the Venetian white leads differ
in Ag, Sb, and Mn content. It is thus proved in principle
that there is a characteristic distribution pattern for the
trace ingredients in white lead of paintings of about the same
age.
As regards the recognition of imitations, our studies and the
conclusions reached by Houtmnn et al. [21 show that modern
white lead differs from the old material in a distinctly lower
copper content (<1 ppm) and sometimes in the very marked
occurrence of a single trace ingredient, to the extent of some
tenths of a percent (e.g., Ba in our work or Zn[ZJ).
-
~
~
[2] J. P.W . Ifouttiion and J . Tnrkstro: Radiochemical Methods
of Analysis. Vol. I, Conf. Proc. Salzburg 1964, IAEA Vienna
1965, p. 85.
Angew. Cheni. internat. Edit. I Vol. 5 (1966) I No. 7
(b) Very great resolution of the volume used can be achieved
by a simple program. For instance, 1 ml can be added in 1000
separate portions.
(c) If the recorder used for drawing a titration curve includes
a step-motor drive for advancing the paper, the two motors
can be actuated by a single, common pulse generator. A
cable connection (impulse conductor) can be used for synchronization of control of the buret and movement of the
paper.
(d) The impulse feeder mentioned in (c) can be as long as
desired, which opens obvious possibilities for remote control.
(e) The frequency of the impulse generator can be so related
to the signal from the servo-generator of a potentiometer
recorder that the rate of addition can be related to the
steepness of the titration curve.
679
Use of Thin-layer Chromatography and Infrared
Spectroscopy for Elucidation of the Thermolysis
Products of Triphenylphosphine
H . Schindlbauer and F. Mitterhofer,
Vienna (Austria)
Phosphines and phosphine sulfides can be readily separated
on thin-layer chromatograms run o n silica gel layers with
weakly or moderately polar solvents. The R F values increase
rapidly in the order tertiary > secondary > primary phosphines. Positional isomers of phosphines (e.g. the three
tritolylphosphines) are best separated on basic alumina
with hexane/benzene (5:l v/v) as solvent; the RF values
increase in the order p - > m- > 0-.Phosphine oxides are well
separated by use of ether/ethyl acetate. Replacement of a
phenyl group by methyl greatly decreases the RF value of all
organophosphorus compounds.
Phosphines can be oxidized to phosphine oxides on the plate
before running by spotting with iodine in C C 4 ; similarly
they can be converted with methyl iodide into phosphonium
salts, which run in their dissociated form in acetone/HCI but
in their undissociated form in acetone/NH3. Phosphinss are
best made visible by iodine in CC14 (yellow spots), whereas
compounds of quadrivalent phosphorus are well disclosed by
permanganate-sulfuric acid (white on pink). The two-dimensional technique and the wedge method make separation of
organophosphorus compounds possible.
The decomposition products (66 hr at 4OO0C under N2) of
triphenylphosphine have been identified by this technique.
All the products were also studied by infrared spectroscopy.
When no reference sample was available for thin-layer
chromatography, the spots of the unknown were isolated on
a preparative scale and analysed infrared-spectroscopically,
and the assumed product was then synthesized.
The decomposition products of triphenylphosphine were
proved to contain substantial amounts of phosphorus,
benzene, biphenyl, and p-biphenylyldiphenylphosphine,with
smaller amounts of 0-,m-,and p-terphenyl, p-phenylenebis(diphenylphosphine), m-biphenylyldiphenylphosphine, and
diphenylphosphine, with only traces of 9-phenyl-9-phosphafluorene detectable.
New Analytical Separations of Traces of Material on
D e x t r a n Gel
H . Spitzy, Graz (Austria)
Dextran gels can be used for other analytical purposes besides
gel filtration. Reversible adsorption of aromatic and heterocyclic compounds is the basis for a separation of thyroid
hormones from blood serum 131.
Pentadiene- 1,5-Halogen-Oxygen Exchange
A . Roedig, Wiirzburg (Germany)
Compounds of general structure ( I ) - with the cis-configuration at C-2/C-3 - rearrange rapidly and quantitatively
in boiling C C 4 into the acid halides (3) when R = C1 or
Br and R " = H, CH3, or C6H5. The term "1,Spentadiene
halogen-oxygen exchange" is proposed to designate this
thermal rearrangement. Its mechanism has been largely
clarified by radioactive labelling and kinetic measurements 111.
A further use of dextran gels arises from the fact that the
strength of adsorption of solvents varies in accord with their
polarities. This effect (known also for ion-exchange resins)
has the result that with methanol/water mixtures the water is
enriched in the gel phase compared with the mobile outer
phase. During passage through a column filled with Sephadex
swollen in methanol/water a mixture of alkali chlorid:s is
separated by virtue of the different solubilities of these
chlorides in methanol/water mixtures (more correctly, in
methanol/water mixtures of different compositions). Under
suitable conditions (methanol concentration, 75 vol.- %;
column dimensions, 42x 1 cm; gel type, Sephadex G-25 fine;
rate of addition, 4.40 ml hr-1 cm-2) all the alkali chlorides can
be separated quantitatively at concentrations of 10-4 M
downwards. For an addition of 0.5 ml this corresponds to
340 ng of Li to 6.3 pg of Cs. Yields are 95-100 %. Microgram
quantities of Li and K are separated quantitatively from a
~
more than 1000-fold excess of sodium (1600 pg) on a 7 . 5 1.5
cm column. For Li, Na, and K it is a matter of pure distribution chromatography, but for Cs and Rb adsorption
phenomena enter, so that quantitative elution is adversely
affected at concentrations below 10-4 M.
Photometric Determination of Small A m o u n t s of Tin
with Bromopyrogallol Red
D . Thierig and F. Umland, Miinster (Germany)
The 1:1 complex formed by Bromopyrogallol Red (1) with
Sn(I1) or Sn(1V) in acetate-buffered solution of pH 3 is
suitable for photometric determination of tin. Direct analysis
can be effected in presence of at least a 100-fold molar excess
of alkalis, alkaline earths, lead, and mercury(l1); interference
OH
OH
0s03H
by most of the heavy-metal ions can be avoided by separation
of the tin as %I4 before the determination; then there is no
interference by 1000-fold excesses of Be, As, Bi, Ti(IV),
V(V), Cr(III), Mn(II), Fe(II), Fe(III), Cu, Zn, Ce(III), or
W(V1). Only Sb causes a too high and Ag a too low extinction. The extinction coefficient was determined as E = 18 000 I
mole-1 cm-1 at 515 mp. The most favorable concentration
limits are 6-90 pg of tin in 25 ml of solution.
[VB 998 IEI
German version: Angew. Chem. 78, 718 (1966)
[3] H. Spitzv and H. Orfner, Microchem. J. 10, 194 (1966).
Furthermore, experiments with [1-14C]perchloropentadienoyl chloride (If) have shown that pentadienal 1,5halogen-oxygen exchange is not restricted to aldehydes and
R"
R"
R"
This reaction was discovered with cis-perchloropentadienal
( l a ) 121 but is not restricted to perchlorinated pentadienal
systems, as has been shown by study of compounds ( I d )
to ( I d ) . The cis-compound (Ie) avoids the pentadiene-1,5halogen-oxygen exchange by rearrangement to its transisomer; however, pentadienals containing chloro or bromo
substituents on C-3 and C-2 are more stable in the cis-form 131.
680
Angew. Chem. internnt. Edit. 1 Vol. 5 (1966) / No. 7
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