Difference between revisions of "Measuring the Conductivity of a Liquid in a Pipette Tip"

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(Created page with "‘’The ER818 Octal Contactless Conductivity System https://www.edaq.com/ER818 was used to measure the conductivity of a solution in a pipette tip.’’ === Introduction =...")
 
(Equipment Required)
Line 29: Line 29:
 
** ER815  Contactless Conductivity Detector https://www.edaq.com/ER815
 
** ER815  Contactless Conductivity Detector https://www.edaq.com/ER815
 
** ET128 Octal headstage
 
** ET128 Octal headstage
* A computer with your own software to record the data (for example, Tera Term, LabVIEW, C#, WinWedge or HyperAccess)
+
* A computer with your own software to record the data (for example, Tera Term, LabVIEW, C#, WinWedge or HyperACCESS)
 
* Your pipette tips with samples
 
* Your pipette tips with samples
 
* A standard solution with conductivity in the middle of the measuring range, say 5 mS/cm
 
* A standard solution with conductivity in the middle of the measuring range, say 5 mS/cm

Revision as of 18:14, 2 January 2017

‘’The ER818 Octal Contactless Conductivity System https://www.edaq.com/ER818 was used to measure the conductivity of a solution in a pipette tip.’’

Introduction

The ER818A system was developed to enable the measurement of conductivity of samples with the following general characteristics:

  • Low Sample Volumes
  • Low Sample Wastage
  • Zero Cross contamination
  • 100 µS/cm to 20,000 µS/cm conductivity range
  • Ready operation in an automated system


Typical sample mediums are shown below. All are based on individual samples, except for the 1600 µm outer diameter (OD) capillary, which allows for either a continuous or sampled liquid to be monitored.

1 Straight tube tip

2 Tapered tube tip

3 Capillary tubing with 1600 µm OD

4 Melting point disposable glass tube with 1600 µm OD

5 NMR tube with 5mm OD


Equipment Required

  • ER818 Octal Contactless Conductivity System https://www.edaq.com/ER818, which includes:
  • A computer with your own software to record the data (for example, Tera Term, LabVIEW, C#, WinWedge or HyperACCESS)
  • Your pipette tips with samples
  • A standard solution with conductivity in the middle of the measuring range, say 5 mS/cm

Experiment Procedure

A Quick Start guide describes how to connect the system, how to use Tera Term software to calibrate the system using a standard solution, adjust the gain and measure the conductivity of an unknown sample. The Quick Start guide can be downloaded from here.


Notes

Important Note about Temperature

The volumes of liquid involved in these measurements are very small and subject to temperature variation. Typically there will be a 4 to 5 °C temperature difference between the ambient laboratory air and the internal temperature of the headstage. This corresponds to a potential error of approximately 5-6%.

Since the internal temperature of the headstage is available – some temperature compensation can be performed.

Allowing some time for the temperature to equalise can also help in reducing the temperature error. Another approach could be to measure the conductivity as quickly as possible before the sample temperature increases.


Use of a Reference Channel

In some applications where small changes in conductivity are to be measured, a reference channel is provided which operates as follows.

A reference solution is selected, say 3 mS/cm. The unknown solutions to be tested have a conductivity of say 3 mS/cm +/- 1 mS/cm. By selecting the reference solution, it effectively subtracts this value from the unknown solutions so that only the changes are displayed. An advantage of this technique is that any temperature drift in the reference will be removed from the unknown solutions, thereby providing temperature compensation.