Measurement procedure established for Cl- trace analysis using a HMDE

This method requires a VoltaLab 50 or a VoltaLab 80.

Abstract

To illustrate the outstanding capabilities of VoltaMaster 4 version 4 regarding trace analysis, we offer you to review a measurement procedure established for Cl- trace analysis using a HMDE model MDE150 and the Analytical Electrochemical Laboratory model VoltaLab 50.

Specification of the test

Standard addition:
Sample = 20 µl of [Cl-] 40 mg/l
Standard addition = 20 µl of [Cl-] 40 mg/l

Working Electrode : Mercury drop (HMDE)
Reference Electrode : Ag // AgCl + protecting tube filled with 1M HNO3
Auxiliary Electrode : Pt

Apparatus

• MDE150 Polarographic Stand

  

• VoltaLab 50 (or VoltaLab 80) Analytical Electrochemical Laboratory

  

• ABU901 burette (optional)

Electrodes

• TR020 Reference Electrode with its protecting tube
• TM010 Platinum Electrode
• MDE/CAP 70 µm Capillary

Reagents

• Supporting Electrolyte: 0.1M HNO3.
• Use reagent grade chemicals for reagent preparation..

Settings – Experimental

The "Cl^- with HMDE.EXP" sequence available in the demonstration set of experiment from VoltaMaster 4 is used.
The "Run External Unit" method is used to control the MDE in order to organise the purge, the blanketing, the agitation and the mercury drop renewal (hammer stroke).
Connect your PGZ402 or PST050 to serial port 1 (COM1) and the MDE to serial port 2 (COM2).

Message methods promt the operator to perform each standard addition.

A Potentiostatic Universal Differential Pulse stripping is run after a preconcentration step. The Potentiostatic Universal Differential Pulse enables the supervisor to select the acquisition window within each step to achieve higher selective signal.

Protocol

The protocol includes an automatic evaluation of the blank stability. This stability protocol can also be implemented for the sample and the additions.

Calculation

You can calculate from Peak magnitudes, Peak positions and Peak surfaces. This means that even if the peak is rather weak, you are still capable of performing calcula-tions. This is often the case when the blank does not generate a well-defined peak.

Curve examination

The curves are automatically smoothed and the quantitative analysis is automatically performed after each standard addition. The peak potential can be compared to the half wave potential given by [1]. The signals are linear with the concentrations. It is also possible to run the calculation in post run processing using the virtual mode.

Printed results

Standard addition results:

Y = A * X + B,
A = 17.32,
B = 1.11238e-006,
Linear corr. coeff. = 0.99895
Sample: 64.22 ng/l , 1.130 µC I W/cm²

Analysis result : 35.39 µg/l

Conclusion

Standard addition method can be used to perform trace analysis with VoltaLab.
The CHLORIDE are detected and STANDARD ADDITION method provides quantitative information.
It is necessary to use blank subtraction.

References and notes

[1] Electroanalytical Stripping Methods - Kh. BRAININA and E. NEYMAN

Ordering information

VoltaLab 50 - Analytical Voltammetry

VoltaLab 50 is an analytical quantitative laboratory which automates and simplifies any type of electrochemical analysis using standard addition, standard calibration and calibration by addition. Everything is made easy and practical. For instance the spectrums can be automatically compared to reference spectrum in order to establish a "pass or failed "protocol. User-selectable unit, blank and dilution factor management are some of the fundamental features provided. Every DC technique can be set and run, including the extraordinary powerful Universal Differential Pulse method. VoltaLab 50 is an analytical system which offers the convenience required for routine use of cyclic voltammetry in quantitative analysis. It is the obvious choice to set up a routine DC analysis.

Analytical Electrochemical Laboratory automates and simplifies electrochemical analysis. Either with the MDE150 Hanging Mercury Drop Electrode or the RDS010 Rotating Disc Stand, VoltaLab 50 offers you to achieve a superb analytical station with outstanding capabilities in terms of performance (powerful supervisor level) and ease of use (secure operator level for routine analysis).

• Compliance voltage: ±30 V Up to 100 V with HVB100 (R11V008)
• Measured current: ±1 A Best resolution: 30 fA
• Polarisation voltage: ±15 V Best resolution: 125 µV
• A/D converter 16 bits
• Measurement period 500 µs
• Max. scan rate 20 V/s

MDE150 - Polarographic Stand

The MDE150 Polarographic Stand accommodates either the MDE/HGDROP Hanging Mercury Drop Electrode or the EDI101 Rotating Disc Electrode driven from a separate CTV101. Nitrogen humidifier vessels prevent reduction of the sample volume due to evaporation. The glass sample cell (volume = 5 ml) fits in place without any risk of the geometry of the electrodes being modified. In operation, full automation is organised from VoltaMaster 4 with either VoltaLab 50 or VoltaLab 80 regarding hammer stoke, mercury drop size (growth time), stirring, bubbling and leaking. Pressurised Hg ensure minimum Hg consumption with hig reproducibility.

Methods available for calculation

• Standard Addition
• Calibration by Addition
• Standard Calibration
• Cyclic Voltammetry Standard Titration (CV ST)

Key benefits

• Calculation
  
  You can calculate from Peak magnitudes, Peak positions and Peak surfaces. This means that even if the peak is rather weak, you are still capable of performing calcula-tions. This is often the case when the blank does not generate a well-defined peak.
  
  
• Blank
  
  You can choose whether to take the blank into account for the calculations. As a rule, the blank is used when the signal at no concentration is large compared to the signal at maximum concentration.
  
  
• Dilution factors
  
  Dilution factors are taken in account so that you get the results for your sample in addition to your "cell" result.
  
  
• Selectable unit
  
  You can select your personal unit and a factor in order to get a figure which makes sense in your analytical context.
  
  
• Calibration "curves"

  The full spectrums are recorded. In post-run processing, if you decide to recalculate versus the integration of the peak rather than the peak magnitude, it is not a problem. You will use the same set of spectrums.

• "Curve" or "method"

  The calculation method addresses either a method within the sequence or a file on your hard disc. This enables you to create a sequence which generates the calibration "spectrums" independently from the sequence used to run your sample.

• No limit

  When several peaks (which correspond to several elements) are recorded, you can use the same spectrums to detect and calculate their respective concentrations.