Automated Flame Photometry of Serum Sodium and Potassium
Gina Pennacchia, Victor G. Bethune, Martin Fleisher, and Morton K. Schwartz
A simple, rapid, automated procedure for flame
photometry is described for use with the IL flame
photometer and on-line dilutor and Technicon
Sampler II.
Additional Keyphrases
Unopeue
#{149}
IL
Dilutor
The IL 1\Iodel 143 I”lame Photometer
(Instrumentation Laboratory, Inc., Lexington, 1\Tass. 02173) is widely
used. For the determination
of Na and I,
a 200-fold
dilution of sample is made, which has a final Li
concentration
of 15 mmol/liter.
Over several
years
we have tried in various ways to eliminate the tedium
of manual
uated the
sample dilution. Several years ago, we evalfirst model of a dilutor
manufactured
by
Instrumentation
Laboratory and found that both precision and agreement between data obtained with it
and with manually prepared dilutions were unacceptable, as also reported by Habig and Williamson (1).
We next devised an AutoAnalyzer
manifold
which
prepared the dilution and introduced
the specimen
into the flame photometer.
Although the results correlated
acceptably
with
those
for manually
prepared
dilutions,
the response time between aspiration
of
sample and read-out was too long. We then evaluated
the “lJnopette” system (Becton-Dickinson
Co., Rutherford, N.J. 07070) for Na and K determinations.
In
this procedure,
capillary
pipets and prefilled vials
of lithium
solution
are
used.
Correlation
with
our
manual procedure was excellent (Table 1) and, since
this procedure eliminated the need for glassware and
glass washing, it became part of our routine method
for determining
sodium and potassium.
Recently, a
new version of the IL Dilutor, Model 144, became
available and was adapted as described here.
From the Department of Biochemistry,Memorial Hospital
for Cancer
Received
and Allied Diseases,
New York, N.Y. 10021.
Dec. 18, 1970; accepted Jan. 13, 1971.
Experimental Results
The IL 1\Iodel 144 Dilutor
is a peristaltic
pump
consisting
of three rollers that compress
tubing
and
create
a positive
displacement
of the fluids being
pumped. Equal volumes (about 390 ,zl/min) of sample
and of stock lithium
solution
containing
3000 mmol
of lithium per liter are pumped into a mixing chamber
and diluted
200-fold with distilled
water introduced
from a reservoir.
When the dilutor is used according
to the manufacturer’s
instructions
with the Model 143
IL Flame Photometer,
a 12-s aspiration
of sample is
sufficient for accuracy.
In the automated
system, the
IL 1Iodel 144 Dilutor is attached
to the IL Model 143
Flame Photometer
according
to the manufacturer’s
instructions,
except that the sample
feed line is made
twice as long (33 cm) by joining two sample feed lines
with a small metal connector.
The feed line is then
connected
to the aspirator
probe of an AutoAnalyzer
Sampler
II (Technicon
Instrument
Co., Tarrytown,
N.Y. 10591). The sampler
is equipped
with a 120specimen
per hour cam having a 1:2 wash ratio. The
dilutor is connected
to a bottle of LiSO4 (3000 mmol/
liter; 191.95 g LiSO4 dissolved
and diluted
to 1 liter
with distilled water containing
a drop of Triton X-100 (a
surfactant)
and to a reservoir of distilled water.
In operation,
the sample tray is organized
as follows:
The first two sample cups contain
140 mmol of Na+
and 5 mmol I
standard
per liter. In cup 3 there is a
120-mmol/liter
Na
and a 1-mmol/liter
K standard
and in cup 4 a 160-mmol/liter
Na
and a 9-mmol/liter
j#{231}+
standard.
These latter two standards
are used to ensure the linearity
and proper operation
of the instrument. If these standards
do not yield their calculated
value, the instrument
is recalibrated
and the automated
operation
not continued
until the problem
has been
corrected.
Cup 5 contains
an aqueous
quality-control
standard
and cup 6 a quality-control
serum. The unknown sera then follow. A sample-tray
cover must be
used to prevent evaporation.
After every 10 unknown
specimens,a
140-mmol/liter
Na+ and a 5-mmol/liter
I’
standard
and the aqueous quality control are inserted.
CLINICAL CHEMISTRY, Vol. 17, No. 4, 1971 339
Table 1. Results of Serum Sodium and Potassium Determination after Sample Dilution
by Various Means
Potassium,
Unopette
mmol/liter
Unopette
Manual
4.4
4.4
4.3
4.3
4.1
3.9
4.6
4.6
4.5
5.3
4.5
4.2
4.9
5.7
4.6
4.0
4.8
4.4
5.0
4.4
4.1
4.8
5.4
4.4
3.9
4.6
4.9
4.7
3.6
4.8
5.2
4.6
4.6
4.8
4.4
3.5
4.8
5.1
and manual”
method
Sodium,
mmol/llter
Unopette
Potassium,
Manual
Unopette
Unopetto and automated method
mmOI/liter
Sodium,
Automated
Unopette
Automated
131
142
142
130
138
142
5.9
5.1
3.7
5.8
5.1
140
139
3.7
138
137
137
139
139
142
132
135
137
136
142
4.0
4.0
4.2
5.3
4.2
3.9
4.0
4.1
5.3
4.3
133
139
128
134
134
131
137
127
134
135
126
122
4.3
4.5
136
137
145
142
4.8
4.7
135
144
144
4.8
4.6
132
141
138
135
3.5
4.2
133
124
136
134
144
136
142
142
148
a In this procedure, 0.5 ml of serum and 5 ml
mark with de-ionized water.
of
123
mmoI/liter
122
146
3.8
3.5
4.1
3.7
139
133
132
134
123
137
136
142
143
144
4.6
4.7
136
138
3.9
3.2
4.0
5.0
5.6
3.9
3.1
4.0
5.0
5.5
140
140
138
130
126
137
138
130
126
136
Li (300 mmol/ liter) were pipetted into a 100.ml volumetric
In operation, the flame photometer
is lighted in the
usual manner, the dilutor is turned on, and the zero
control and the “Set Li” are adjusted. The sampler
is started
and the first 140-mmol/liter
Na
and 5mmol/liter I standards are aspirated. The sampler is
turned off to allow for continuous sampling. The flame
photometer
is adjusted
to these values. The sampler
is again turned on, and the final instrument
adjustments
are made when the probe withdraws
from the second
cup. Each reading
is made as the aspirator
probe
withdraws
from the sample cup. The values of successive
samples
(about 0.3 ml of serum is required
in each
cup) are then recorded,
and the instrument
is readjusted
if necessary
after every 10 specimens,
when
the standard
is aspirated.
It is essential
that the pump lines in the dilutor
be changed
frequently.
We routinely
do this weekly
(after about 70 h of use). These tubes apparently
change their delivery characteristics
as they are used,
and can eventually
aspirate
aqueous
standards
and
340 CLINICAL CHEMISTRY, Vol. 17, No. 4, 1971
flask and diluted to the
the more viscous
serum at slightly
different
rates.
This phenomenon
becomes
apparent
in the sodium
values,
which will tend to be lower. However,
this
problem is eliminated
by following the suggested
maintenance
program
and changing
tubing
if a decrease
of 2% or more is observed in the sodium quality-control
values.
The automated
method
has been in use in
our laboratory
for months,
during which time it has
proved to be reliable and useful. Table 1 shows data
for a series of specimens
analyzed
by the automated
method and our previously
used Unopette
system. As
can be seen, the values correlated
excellently.
The
coefficient of variation
obtained
by analyzing
the same
specimen in 10 successive cups was less than 0.5%.
Reference
1. Habig, IL L., and Williamson,
W. H., On-linedilutorforuse
with flame photometers.
CLIN. CHEM.
17, 251 (1970).