Dynamic end-point total organic fluoride measurement
An embodiment provides a method for measuring an amount of total organic fluoride content of a PFAS containing sample, including: placing a sample comprising a PFAS compound in a measurement device, wherein the measurement device comprises an oxidation cell and a non-oxidation cell, wherein the oxidation cell comprises a boron-doped diamond electrode; measuring, using the measurement device, an amount of total inorganic fluoride of the sample before an oxidation; applying an electrical potential to a portion of the sample in the oxidation cell, wherein the electrical potential oxidizes the PFAS compound; measuring, using the measurement device, an amount of total organic fluoride of the sample after the oxidation to provide a measurement signal of the total organic fluoride; and determining a first derivative of the measurement signal of the total organic fluoride. Other aspects are described and claimed.
1 . A method for measuring an amount of total organic fluoride of a polyfluoroalkyl substance (PFAS) compound in a sample, comprising:
placing the sample comprising the PFAS compound in a measurement device, wherein the measurement device comprises an oxidation cell and a non-oxidation cell, wherein the oxidation cell comprises a boron-doped diamond electrode;
measuring, using the measurement device, an amount of total inorganic fluoride of the sample before an oxidation;
applying an electrical potential to a portion of the sample in the oxidation cell, wherein the electrical potential oxidizes the PFAS compound;
measuring, using the measurement device, the amount of total organic fluoride of the sample after the oxidation to provide a measurement signal of the total organic fluoride;
determining a first derivative of the measurement signal of the total organic fluoride; and
comparing the first derivative to a predetermined value, wherein if the first derivative is greater than the predetermined value then adjusting the electrical potential provided to the oxidation cell.
2 . The method of claim 1 , wherein the sample circulates between the oxidation cell and the non-oxidation cell.
3 . The method of claim 1 , wherein the electric potential provides a step wise electrochemical oxidation.
4 . The method of claim 1 , further comprising determining a second derivative of the measurement signal of the total organic fluoride.
5 . The method of claim 1 , further comprising periodically turning off the electrical potential to the oxidation cell for a temperature stabilization.
6 . The method of claim 1 , further comprising periodically turning off the electrical potential to the oxidation cell to reduce an electrical noise as measured by the measurement device.
7 . The method of claim 1 , further comprising shielding the measurement device from the electrical potential applied during the oxidation.
8 . The method of claim 1 , further comprising filtering the first derivative to reduce electrical noise.
9 . The method of claim 1 , wherein the oxidation generates fluoride from a digestion of the PFAS compound using the boron-doped diamond electrode.
10 . The method of claim 1 , wherein the first derivative approaches an asymptote representing a linear background of the measurement device.
11 . The method of claim 1 , wherein the first derivative approaching an asymptote defines a dynamic end point of the oxidation.
12 . The method of claim 1 , wherein a total fluoride content equals a summation of the total inorganic fluoride and the total organic fluoride.
13 . The method of claim 1 , wherein a duration of the oxidation is determined by the first derivative reaching a threshold value.
14 . The method of claim 1 , further comprising subtracting a linear background from the measurement of the total inorganic fluoride and from the measurement of the total organic fluoride.
15 . The method of claim 14 , wherein the linear background comprises system contribution variables, wherein the system contribution variables are selected from the group consisting of: a rate constant of oxidation at the surface of the boron-doped diamond electrode, a penetration depth and diffusional rate of hydroxyl radicals, a total volume of the oxidation cell, and an exchange rate of the sample between the oxidation cell and the non-oxidation cell.
16 . The method of claim 1 , wherein the measurement device is selected from the group consisting of: an electrochemical device and an optical device.
17 . A device for measuring an amount of total organic fluoride of a PFAS compound in a sample, comprising:
a non-oxidation cell;
an oxidation cell comprising an ion selective electrode and a boron-doped diamond electrode; and
a processor;
wherein the processor is configured to:
measure an amount of total inorganic fluoride of the sample before an oxidation;
apply an electrical potential to a portion of the sample in the oxidation cell, wherein the electrical potential oxidizes the PFAS compound;
measure the amount of total organic fluoride of the sample after the oxidation to provide a measurement signal of the total organic fluoride;
determine a first derivative of the measurement signal of the total organic fluoride; and
compare the first derivative to a predetermined value, wherein if the first derivative is greater than the predetermined value then adjusting the electrical potential provided to the oxidation cell.