Electronic circuit is used in a paper chromatograph instrument that has excellent sensitivity and furnishes a printed record of each test. The circuit measures and records changes in conductivity in a strip of chromatographic paper as different solutions are placed on it

Steffensen, G. R.

English

NASA Technical Reports Server

Ratio 
Arm 
Resistor
70 
80 
90 
June 1967	 Brief 67-10201 
NASA TECH BRIEF C' 
NASA Tech Briefs are issued to summarize specific innovations derived from the U.S. space program, 
to encourage their commercial application. Copies are available to the public at 15 cents each 
from the Clearinghouse for Federal Scientific and Technical Information, Springfield, Virginia 22151. 
Electronic Circuitry Used to Automate Paper Chromatography 
DC 
The problem: 
To provide a convenient, easily operated paper 
chromatograph instrument that exhibits excellent sen- 
sitivity and furnishes a printed record of each test. 
The solution: 
An electronic circuit that measures and records 
changes in conductivity in a strip of chromatographic 
paper as different solutions are placed on it. 
How it's done: 
Gold electrodes are attached to each side of the 
adsorption paper and this combination is wired into 
a Wheatstone bridge circuit as one of its resistance 
elements. The bridge is completed by a potentiometer 
and ratio arm resistor, is excited by a l-kc signal 
generated in a lock-in amplifier, and is connected 
in a balanced input through a transformer. Balance 
of the bridge circuit is detected by the combination 
of low noise amplifier, lock-in amplifier, and strip
chart recorder. The system is phase coherent in that 
the output of the lock-in amplifier is a positive or 
negative dc voltage derived by comparing the refer-
ence phase through the transformer with the signal 
output of the low noise amplifier. The dc voltage 
from the lock-in amplifier moves a pen in the strip 
chart recorder in a direction corresponding to the 
polarity of the signal. The circuit is shown in the 
figure at the left. 
In operation, a I microliter sample is placed on 
the paper and its passage down the paper is recorded 
as electrical output versus time from start. The figure 
at the right illustrates the chart readout of the passage 
of a I microliter sample of 10 —
 mole/liter copper 
sulfate. A flow of water carrier down the paper is 
established and the potentiometer adjusted for zero 
bridge output as indicated on the recorder. A drop 
of the CuSO 4 is then placed on the paper and its 
passage down the paper is indicated by a trace of 
the recorder pen. 
sk
(continued overicaf) 
This document was prepared under the sponsorship of the National 
Aeronautics and Space Administration. Neither the United States 
Government nor any person acting on behalf of the United States
Government assumes any liability resulting from the use of the 
information contained in this document, or warrants that such use 
will be free from privately owned rights.
https://ntrs.nasa.gov/search.jsp?R=19670000201 2020-03-11T20:32:14+00:00Z
The lower figure represents separation of constitu-
ents of a mixture. As an example, the first peak could 
indicate a salt of copper, the second, one of iron, the 
third, one of manganese, and the fourth, a substance 
less conductive than the water carrier. 
Notes: 
1. In practice, this device has detected different 
mineral content in drinking water from two differ-
ent buildings at the Jet Propulsion Laboratory. 
2. This instrument could be used in analysis of 
plating baths to establish the relative concentra-
tion of constituents. It would also be useful for 
solution control in hydroponics.
3. Inquiries concerning this innovation may be di-
rected to:
Technology Utilization Officer 
Jet Propulsion Laboratory 
4800 Oak Grove Drive 
Pasadena, California 91103 
Reference: B67-10201 
Patent status: 
No patent action is contemplated by NASA. 
Source: George R. Steffensen 
(JPL-840) 
Brief 67-10201	 Category 01


Electronic circuitry used to automate paper chromatography

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