Reagentless dissolution and quantification of particulate analyte in a sample via membrane electrolysis
Described herein are methods and devices of detecting a particulate analyte in a sample solution, using an electrochemical cell having an anodic compartment and a cathodic compartment, wherein the anodic and cathodic compartments are separated by a semi-permeable membrane. The sample solution is acidified by applying a positive current to the anodic compartment and maintaining the positive current to permit anions to flow from the cathodic compartment to the anodic compartment through the semi-permeable membrane. The analyte is deposited on an electrode disposed in the anodic compartment by applying a negative current. The deposited analyte is stripped from the electrode and an electrochemical voltammogram is generated by measuring the current as the analyte is stripped from the electrodes. The voltammogram is used to determine the concentration of the analytes in the sample solution based on the generated electrochemical voltammogram.
1 . A method of detecting a particulate analyte in a sample solution, the method comprising
loading the sample solution into an anodic compartment of an electrochemical cell;
loading an electrolyte solution into a cathodic compartment of the electrochemical cell, wherein the anodic and cathodic compartments are separated by a semi-permeable membrane;
acidifying the sample solution by applying a positive voltage to the anodic compartment to provide oxonium cations, and maintaining the positive voltage to permit anions to flow from the cathodic compartment to the anodic compartment through the semi-permeable membrane, whereby the oxonium cations and the anions in the anodic compartment form an acid that dissolves the particulate analyte;
depositing the dissolved analyte on an electrode disposed in the anodic compartment by applying a negative voltage to the anodic compartment;
stripping the deposited analyte from the electrode by applying a potential to the electrode;
generating an electrochemical voltammogram by measuring a current as the deposited analyte is stripped from the electrode; and
determining a concentration of the particulate analyte in the sample solution based on the generated electrochemical voltammogram.
2 . The method of claim 1 , wherein the positive voltage applied to the anodic compartment is about +4.5 V.
3 . The method of claim 1 , wherein the positive voltage is applied to the anodic compartment for about 60 minutes.
4 . The method of claim 1 , wherein the positive voltage is applied to the anodic compartment with a first working electrode.
5 . The method of claim 4 , further comprising removing deposited analyte from the first working electrode prior to depositing the particulate analyte on the electrode by applying a voltage and cycling the voltage from about −0.1 V to about +0.1 V.
6 . The method of claim 5 , wherein the voltage is cycled 100 times.
7 . The method of claim 1 , wherein the negative voltage applied to the electrode is about −1.5 V.
8 . The method of claim 1 , wherein the negative voltage is applied to the electrode for about 3 minutes.
9 . The method of claim 1 , wherein stripping the deposited analyte from the electrode further comprises applying a square wave potential pulse to the electrode, wherein the square wave potential pulse comprises alternating the potential between a base potential and a peak potential.
10 . The method of claim 9 , wherein the base potential is about −1.0 V and the peak potential is about +0.7 V.
11 . The method of claim 1 , wherein the particulate analyte is lead.
12 . The method of claim 1 , wherein acidifying the sample solution comprises lowering the pH of the sample solution to about 2.
13 . A method of detecting lead in tap water solution, the method comprising
placing the tap water and potassium nitrate in an electrochemical cell, the electrochemical cell comprising:
an anodic compartment configured to hold the tap water,
a cathodic compartment, configured to hold the potassium nitrate, wherein the cathodic compartment is in fluid communication with the anodic compartment through an anion exchange membrane;
a first electrode system comprising:
a platinum mesh working electrode disposed in the anodic compartment,
a first wire counter electrode disposed in the cathodic compartment;
a second electrode system disposed in the anodic compartment, the second electrode system comprising:
a glassy carbon working electrode,
a second counter electrode, and
a potentiostat communicatively coupled to the glassy carbon working electrode and configured to generate a current therein;
acidifying the tap water in the anodic chamber comprising:
generating a positive voltage in the platinum mesh electrode, wherein the positive voltage generates oxonium cations in the anodic compartment;
maintaining the positive voltage on the platinum mesh electrode, thereby allowing nitrate to flow from the cathodic compartment into the anodic compartment through the anion exchange membrane;
forming nitric acid in the anodic compartment, thereby lowering the pH of the tap water and dissolving the lead;
applying a negative voltage to the glassy carbon electrode, thereby depositing the dissolved lead on the glassy carbon electrode;
stripping the deposited lead from the glassy carbon electrode by applying a square wave potential pulse to the glassy carbon electrode, wherein the square wave potential pulse comprises alternating the potential between a base potential and a peak potential; and
measuring a current response at the glassy carbon electrode as a function of the applied potential to generate an electrochemical voltammogram to determine the concentration of the lead in the tap water.