Square Wave Voltammetry Variable Acquisition Window

Abstract

One embodiment provides a method of measuring a component of an aqueous sample using square wave modulation, the method comprising: introducing the aqueous sample into a chamber of a square wave modulator; applying a step of a stimulation voltage to the aqueous sample, the step voltage comprising a stepped voltage, each step of the stepped voltage defining a group, the group having one or more cycles of the square wave modulation; adjusting a time acquisition window that is a portion of each half-period of the stimulation voltage; measuring a resultant current output resulting from the stimulation voltage within the time acquisition window; and averaging the resultant current output over at least one or more cycles of the group. Other aspects are also described and claimed.

Description

[Technical field]

[0001] This application claims priority to U.S. patent application Ser. No. 17 / 714,464, entitled "SQUARE WAVE VOLTAMMETRY VARIABLE ACQUISITION WINDOW," filed April 6, 2022, the contents of which are incorporated herein by reference.

[0002] This application relates generally to the measurement of chemical species in solution using square wave voltammetry, and more particularly to voltammetry using a variable acquisition window. [Background technology]

[0003] Voltammetry is a technique used in electrochemical measurements. It involves applying a varying voltage between two electrodes in a solution and recording the resulting current response. Typically, this current response is measured at a third electrode. The resulting curve of response current versus applied voltage provides useful information about the fluid sample being measured. A typical voltammogram shows one or more quasi-Gaussian response peaks, the peak positions of which are related to the redox potentials of the chemical species in the solution being analyzed. Summary of the Invention [Means for solving the problem]

[0004] In summary, one embodiment provides a method for measuring components of an aqueous sample using square wave modulation comprising: introducing the aqueous sample into a chamber of a square wave modulator; applying a step of a stimulation voltage to the aqueous sample, the step voltage comprising a stepped voltage, each step of the stepped voltage defining a group, the group having one or more square wave modulation cycles; adjusting a time acquisition window that is a portion of each half-cycle of the stimulation voltage; measuring a resultant current output resulting from the stimulation voltage within the time acquisition window; and averaging the resultant current output over at least one or more cycles of each of the groups.

[0005] Another embodiment provides an apparatus for measuring a component of an aqueous sample using square wave modulation, the apparatus comprising: a voltammetric electrode, at least one reference electrode, at least one counter electrode, and a memory storing instructions executable by a processor, the instructions including: applying to the aqueous sample a step of a stimulation voltage comprising a stepped voltage, each step of the stepped voltage defining a group, the group having one or more cycles of square wave modulation; adjusting a time acquisition window that is a portion of each half-period of the stimulation voltage; measuring a resultant current output resulting from the stimulation voltage within the time acquisition window; and averaging the resultant current output over at least one or more cycles of each of the groups.

[0006] A further embodiment provides a system for measuring components of an aqueous sample using square wave modulation comprising a voltammetric electrode, at least one reference electrode, at least one counter electrode, and a memory device storing code executable by a processor, the code having: code for applying a step of a stimulation voltage comprising a stepped voltage to the aqueous sample, each step of the stepped voltage defining a group, the group having one or more cycles of square wave modulation; code for adjusting a time acquisition window that is a portion of each half-period of the stimulation voltage; code for measuring a resultant current output resulting from the stimulation voltage within the time acquisition window; and code for averaging the resultant current output over at least one or more cycles of each of the groups.

[0007] The foregoing is a summary and, as such, may contain simplifications, generalizations, and omissions of detail. As such, those skilled in the art will appreciate that this summary is illustrative only and is not intended to be in any way limiting.

[0008] For a better understanding of the embodiments, as well as other further features and advantages, reference is made to the following description taken in conjunction with the accompanying drawings, the scope of the invention being set forth in the appended claims. [Brief description of the drawings]

[0009] [Figure 1] FIG. 1 shows example simulation results of the effect of 60 Hz AC power line interference on square wave voltage measurements when sweeping from −0.5 V to +0.5 V with 101 ramp steps at fmod=25 Hz. [Diagram 2] FIG. 2 shows the similarity of AC power line noise rejection in the signal and measurement curves for a square wave voltammetric sweep with fmod=30 Hz, which is an integer fraction of fline=60 Hz. [Diagram 3]FIG. 3 shows an example of one square wave cycle including an excitation waveform (top) and a response waveform (bottom) with an acquisition window for the positive and negative half cycles. [Figure 4] FIG. 4 shows example images captured on an oscilloscope using square wave drive (top), response current (middle), and gating signal (bottom) in a 20% to 30% acquisition window. [Diagram 5] FIG. 5 shows an example of a control panel for a square wave voltammetry apparatus according to the present invention. [Figure 6] FIG. 6 is a flow chart showing the procedure for measuring components in an aqueous sample using square wave voltammetry. [Figure 7] FIG. 7 is a diagram illustrating an example of a computer circuit. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] It will be readily understood that the components of the embodiments as generally described and illustrated in the Figures herein could be arranged and designed in a wide variety of different configurations in addition to the example embodiments described. Thus, the following more detailed description of the example embodiments, as represented in the Figures, is not intended to limit the scope of the claimed embodiments, but is merely representative of example embodiments.

[0011] Throughout this specification, the reference to "one embodiment" or "an embodiment" (or similar phrases) means that a particular feature, structure, or characteristic described in connection with that embodiment is included in at least one embodiment. Thus, the appearances of phrases such as "in one embodiment" or "in an embodiment" in various places throughout this specification are not necessarily all referring to the same embodiment.

[0012] Furthermore, the described features, structures, or characteristics may be combined in any suitable manner in one or more embodiments. In the following description, numerous specific details are provided to provide a thorough understanding of the embodiments. However, one of ordinary skill in the art will recognize that various embodiments may be practiced without one or more of the specific details, or with other methods, components, materials, etc. In other instances, well-known structures, materials, or operations are not shown or described in detail. The following description is for illustrative purposes only and merely illustrates examples of specific embodiments.

[0013] Traditional stimulus waveforms often involve step changes in voltage. In the simple case of a cyclic voltammetry (CV) sweep, multiple steps are the result of what were originally analog ramp generating circuits being replaced by designs using digital-to-analog converters (DACs) that output numerically generated ramps or triangle waves that are closer to the continuous waveforms used historically.

[0014] The "step changes" are caused by the finite resolution of the transducer, and are typically very small in amplitude. Some instruments combine "oversampling" with analog low-pass filtering to interpolate between successive samples and remove the step changes. The effect depends on the slope of the ramp. Other commonly used stimulus waveforms use intentionally larger voltage steps. In staircase voltammetry (SCV), the desired voltage range is traversed in several intentionally larger steps.

[0015] Square wave voltammetry (SWV) involves superimposing a square wave modulation on top of a step-continuous ramp or step sequence. The amplitude of the modulation steps can be tens of millivolts, much larger than the inherent resolution of the DAC. Instruments performing SWV scans typically acquire the current response to the positive and negative going portions of the square wave modulation separately. Often the latter is subtracted from the former to cancel the "background" response current. Note that instruments capable of SWV measurements are often forced to perform SCV measurements by setting the square wave amplitude to zero and recording only either the positive or negative half-cycle response, not the difference. Many other stimulus waveforms, including step changes, have been devised and used. The invention is not limited to those described herein and applies to any stimulus waveform that includes a series of periodic edge transitions.

[0016] Thus, the systems and methods described herein provide techniques for enhancement of conventional SWV. This may be referred to as adjusting the time acquisition window. The time acquisition window may be adjusted for the forward and reverse portions of the SWV protocol. The systems and methods may use a potentiostat in which the start and end delays of the acquisition window relative to the modulation edge are each user-controllable and are not fixed relative to the modulation or step frequency, but rather adjustable as a percentage thereof. Alternatively, the start and end delays may be specified in any convenient time units with respect to one or more modulation edges. With this instrument, electrochemical experiments can be benchmarked against the conventional "fixed window" potentiostat described herein by adjusting the start and end timing. Optimizing the adjustment of the acquisition window position and length produces integrated current responses up to five times (x5) stronger than those obtained with conventional window timing. Also, the signal-to-noise ratio of the resulting SWV response curve may be improved accordingly. This, along with the SWV modulation frequency or SCV step rate, can be individually set for optimum line noise rejection, providing significant advantages over conventional methods and enabling new measurement applications in challenging environments.

[0017] A voltage step can induce a time-varying response current. A current surge can occur when stepping due to capacitive charging of the double-layer electrochemical capacitor at the electrode-fluid interface. This capacitive charging current decays exponentially. Once the capacitive charging current disappears, a second current component becomes dominant. This second current, the so-called faradaic current, is the result of ion diffusion and its amplitude depends on the applied stimulus voltage compared to the activation potential of the reaction occurring near the electrode-fluid interface. This dependence is the basis for the general characterization of fluid samples in voltammetric instruments.

[0018] To separate the faradaic current from the capacitive charging current, it is common to measure the response current with a fixed delay after each edge transition. For example, a conventional laboratory potentiostat may integrate the SWV response current during the second and fourth quarters of each square wave cycle, ignoring the current response during the first and third quarters. The position and length of each "acquisition window" are fixed relative to the square wave modulation period. When the same instrument is used in SCV mode, the response current is integrated during the second half of each step. In this mode, the acquisition window is fixed relative to the step interval.

[0019] The faradaic response current may also change with time. Many electrochemical experiments exhibit a "diffusion-limited" response according to Cotterell's theory. In these cases, the faradaic current decreases as the inverse of the square root of the time after each edge transition. Ideally, the acquisition window is set early enough to delay until the (exponentially decaying) capacitive charge component is negligibly small, and to measure before the faradaic current drops too low for reliable observation. A skilled user of a conventional potentiostat may select the step interval or square wave modulation frequency to achieve this desired result.

[0020] In laboratory experiments, the step rate or square wave modulation frequency may be considered as free parameters that the experimenter can adjust to obtain optimal results, but disadvantages arise when applying these experimental protocols to heavy industrial and field measurement applications.

[0021] The faradaic current responses observable using the methods under consideration tend to be small. The net difference current of SWV may be only tens of nanoamperes in some experiments. Larger currents are observed using SCV. These are proportional to the step size, and their amplitudes may be measurable in the tens of microamperes. Thus, both of these measurement protocols can be subject to interference from external noise sources, especially noise induced from alternating current (AC) power circuits. Electrochemists take various measures to address this issue, including careful laboratory execution and careful experiments in shielded enclosures. Such stringent measures may not be practical for field or factory measurement applications. At the same time, the levels of electrical interference in heavy industrial environments may be orders of magnitude higher than those observed in typical laboratory environments.

[0022] Careful selection of the measurement setup can help in mitigating power-line related interference. In SCV experiments, integrating the response current over an acquisition window whose length is exactly equal to an integer multiple of the power-line cycle will cancel out the interference. Typically, the acquisition window is a fixed fraction of the step period, so the step period must be adjusted to achieve the appropriate window length. The technique of matching the acquisition window length to the power-line period is also valid for SWV, but a less restrictive protocol is possible. Because SWV needs to calculate the difference between the current response in the positive and negative half-cycles of the square-wave excitation, it is advantageous to choose the square-wave modulation frequency to be equal to the AC line frequency (or an integer fraction of it). In that way, the power-line interference will be identical in both the positive and negative half-cycles and will be cancelled out in the subsequent subtraction. If the length or position of the acquisition window is the same in both the positive and negative half-cycles, no special restrictions are necessary.

[0023] The noise cancellation strategies described herein can be an important tool for mitigating line-related interference, but they can limit users by removing the ability to adjust the modulation frequency as a free parameter. In SWV, the modulation frequency must be constrained according to the local power line frequency. In SCV, the step rate must be adjusted to create an acquisition window length that removes the power line frequency. Only discrete values ​​are suitable in both cases, resulting in a maximum modulation frequency above which power line removal cannot be achieved. To alleviate these constraints, a new form of potentiostat is needed that allows the acquisition window timing to be specified independent of the step rate or modulation frequency. The reader is also referred to U.S. Patent Application No. 17 / 698,263, filed March 18, 2022, entitled “REPEATED CYCLES SQUARE WAVE VOLTAMMETRY,” the contents of which are incorporated herein by reference, which describes how the use of a repeating cycle square wave can relax the upper limit on the modulation frequency.

[0024] The aforementioned problems are exacerbated when studying certain types of surface-bound reactions where reactive species are depleted very rapidly. A skilled experimental chemist may program a regular potentiostat with an appropriately fast step rate or modulation frequency. Alternatively, some potentiostats offer a choice of two SCV acquisition protocols: in "fast mode", a very short acquisition window is generated at the end of each "staircase step", while in "surface mode", it occupies the entire duration of the staircase step. In "fast mode", the priority is given to the elimination of capacitive charging currents, which is not suitable for the study of many surface reactions. In "surface mode", on the other hand, these priorities are reversed.

[0025] Thus, there is a need for an instrument that allows for adjustable start and duration of the acquisition window to optimize the measurement of various fast surface reactions while substantially eliminating the initial charging current.Furthermore, it will be apparent to one skilled in the art that an instrument with user programmable start and end times for the acquisition window can be used to separate the current responses of two or more simultaneous reactions with different decay rates.

[0026] In one embodiment, the potentiostat has an acquisition window start and end time that is user controllable, and adjustable as a percentage of the modulation or step frequency, rather than fixed. This instrument allows electrochemical experiments to be compared to the conventional "fixed window" potentiostats mentioned above. Optimal adjustment of the acquisition window position and length can produce integrated current responses up to five times (x5) stronger than those obtained with conventional window timing, and the signal-to-noise ratio of the resulting SWV response curve can be improved accordingly. This, together with the ability to independently set the SWV modulation frequency or SCV step rate to achieve the best line noise rejection, offers significant advantages over the current state of the art and enables new measurement applications in challenging environments.

[0027] The illustrated exemplary embodiments will be best understood with reference to the drawings, in which: The following description is for purposes of illustration only and merely illustrates specific example exemplary embodiments.

[0028] Figure 1 shows an idealized SWV response plot in one embodiment where the potential effects of power line interference are with and without additive AC noise. In this example, AC interference can shift the response peak position by 30 mV. If this experimenter's approach were used to measure a Nernstian pH response, this would result in an error in pH of over 0.5.

[0029] As mentioned above, the square-wave modulation frequency can be selected with a fixed relationship to the frequency of the AC power grid to mitigate the possibility of SWV measurements being corrupted by induced power line noise. Similarly, in SCV mode, the length of each acquisition window is ideally equal to a fixed multiple of the AC line period. As a result, the step duration or modulation frequency is no longer a free parameter but is restricted to a set of discrete values. For conventional SWV to eliminate power line interference, the selected modulation frequency must be half the power line frequency or an integer fraction of it. In conventional instruments, unless a square-wave voltammetry protocol with repeated cycles is used, higher modulation frequencies cannot be used because they compromise AC line immunity.

[0030] The aforementioned limitations can be troublesome when studying certain types of surface-bound reactions where reactive species are depleted very rapidly. A knowledgeable and skilled laboratory analyst can program a potentiostat with a modulation frequency fast enough to measure the current response before it decays. However, the presence of power line-related interference makes it impossible to do this without compromising the integrity of the measurement, unless the protocol uses square wave voltammetry with repeating cycles.

[0031] In repeated cycle square wave voltammetry, each single cycle of the conventional SWV voltage excitation is replaced by a shorter cycle divided by an integer number r, such that the total time of these repeated cycles is equal to the duration of the original single cycle, ideally the period of an even number k of power line periods. In repeated cycle SWV, a single square wave cycle of the conventional SWV can be replaced by several shorter square wave cycles. The time intervals are preferably selected to ensure removal of the AC line.

[0032] As the modulation period is shortened, it may be desirable to increase the percentage of each half period used in the acquisition window to better filter out high frequency interference. In one embodiment, high frequency noise unrelated to power line noise may be filtered out as the "noise bandwidth" is reduced as the acquisition window is lengthened. Square wave voltammetry with repeating cycles is described in the related applications referenced above and incorporated herein by reference.

[0033] Referring to FIG. 3, an example of a current output of an embodiment is shown. For example, forward and reverse currents corresponding to forward and reverse voltage changes around the bias voltage of the voltammetry electrode are shown. In one embodiment, a portion of the current output is used to determine the current. This may be referred to as the acquisition window. The acquisition window may be set for the forward current, for the reverse current, or for both the forward and reverse currents. As an example, the portion used is displayed as a highlighted portion of the current trace. The acquisition window may be set after the charge delay. The portion that adds the charge delay and the acquisition window may be referred to as the acquisition end delay. The window, delay, etc. may be expressed as a percentage of the current resulting from the voltage step, as described herein. Other periods or intervals may also be used for the measurement, and the illustrated trace is an example. In this manner, the method and system may measure the current. The acquisition window may adjust the start and end times depending on the analyte being measured. This may be based on the current response to a given analyte in the aqueous sample.

[0034] 4, an example of an oscilloscope captured image in one embodiment is shown, showing the square wave drive (top), response current (middle), and gating signal for a 20% to 30% acquisition window.

[0035] 5, a sample graphical user interface (GUI) for one embodiment is shown. A user, system, etc. may configure the parameters described herein for a particular use case.

[0036] In one embodiment, the measurement of an analyte of the sample is possible. In this embodiment, the timing of the acquisition window may be set by the user before starting the measurement. The analyte may be any ion, component, or feature of the sample. In step 601, in one embodiment, an aqueous sample may be introduced into the sample chamber or region. The aqueous sample may be placed or introduced into the sample chamber manually by a user or using mechanical means, such as gravity flow, pumps, pressure, fluid flow, etc. For example, the aqueous sample for testing may be introduced into the chamber by a pump. In one embodiment, there may be one or more chambers in which one or more method steps may be performed. In one embodiment, valves, etc., may be present to control the flow of aqueous solution into and out of one or more chambers. Once the sample is introduced into the measurement system, the system may measure the analyte or property of the sample.

[0037] In step 602, in one embodiment, the system and method can apply a step of a stimulation voltage to the aqueous sample, including a step voltage, where each step of the step voltage defines a group and includes two or more repeating square wave modulations of equal or similar voltage amplitude. In step 603, the method or system can adjust the time acquisition window. There may be cases where the time acquisition window is set at both forward and reverse potentials. The time acquisition can be adjusted for every repeat cycle, or for each voltage step in the group or step protocol. The time acquisition window can be expressed as a percentage of the total voltage step.

[0038] At step 604, in one embodiment, the system and method may measure the resultant current output resulting from the stimulation voltage, which measurement may include square wave voltammetry. At step 605, in one embodiment, the system and method may average the resultant current output over at least one cycle of each group. Further details and structures related to this step are described in the referenced patent applications.

[0039] One or more combinations of the step-shaped width and the additional square wave modulation define a complete excitation voltage waveform and may be referred to as an electrical signal. The electrical signal may be applied using one or more electrodes, for example, a series of electrodes. The electrodes may include a working electrode, a counter (auxiliary) electrode, a reference electrode, etc. In one embodiment, the electrodes may include pH-sensitive voltammetric electrodes. In one embodiment, the one or more series of electrodes may be boron-doped diamond (BDD) electrodes. Other electrode materials are also disclosed and contemplated. Electrodes of carbon-based or metallic materials (e.g., silver, gold, mercury, nickel, etc.) may eventually oxidize themselves, thereby generating interfering signals and contributing to errors in measurements. The use of BDD may serve as a better electrode material than these materials. One or more electrodes may be operably coupled to the electrical circuitry and / or any square wave voltammetry circuitry described herein. Such circuits may allow for the delivery of voltage protocols, the receipt of current responses, the collection, filtering, weighting, averaging, storage, output, etc. of data.

[0040] In one embodiment, the electrodes may be disposed completely or at least partially within the volume of the aqueous solution or sample. For example, when the aqueous solution is introduced into a chamber having one or more electrodes, the aqueous solution may at least partially cover the one or more electrodes. As another example, one or more electrodes may be partially disposed within the chamber, with other portions of the electrodes disposed outside the chamber. Thus, when the aqueous solution is introduced into the chamber, the aqueous solution covers only the portions of the electrodes disposed within the chamber.

[0041] The method and system may determine the analyte, analyte concentration, or characteristic of the sample in step 606. This determination may be made based on the previous voltage step and the resultant current from the method or system.

[0042] However, if an analyte or property can be determined in step 606, the system may output the property of the aqueous sample, the ion concentration of the analyte, etc., in step 607. In an embodiment, the output may be in the form of a display, storing the data in a memory device, transmitting the output by a connected or wireless system, printing the output, etc. The system may be automated such that the system may automatically output the results. The system may also have associated alarms, limits, or predefined thresholds. For example, if a measurement reaches a threshold, the system may respond by raising an alarm, alerting the system / personnel of a fault, altering the flow of the aqueous solution, etc. The data may be analyzed in real time, stored for later use, or a combination thereof.

[0043] In one embodiment, the step voltage may be controlled in real time by the processor. In one embodiment, the square wave modulation amplitude and other parameters may be preset. The adjustable parameters in one embodiment are shown in FIG. 5. In one embodiment, the timing of each cycle may be controlled by a "hardware state machine" rather than each edge being directly controlled by the processor. Alternatively, some or all of the processing may be performed using dedicated logic circuits including hardware state machines. These parameters may be controlled by a user, a configuration program, a circuit, a processor, etc. In one embodiment, the primary interfaces between the processor and the components may be I2C, SPI, and RS-485, in addition to the other hardware disclosed. These may be local serial buses and / or serial field buses used between the measurement instrument and an external computer, and they may include USB support.

[0044] Thus, various embodiments described herein provide technical improvements over conventional methods and instruments of square wave voltammetry. Using the techniques described herein, in one embodiment, methods and apparatus for instruments for measuring analytes using square wave voltammetry may be used. This is in contrast to conventional methods that have the aforementioned limitations. Such techniques provide better construction methods and instruments for measuring analytes using square wave voltammetry.

[0045] While various other circuits, circuit configurations, or components may be utilized in an information processing device, an example is illustrated in FIG. 7 for an apparatus for measuring an analyte using square wave voltammetry according to any of the various embodiments described herein. The device circuit configuration 10′ may include, for example, a measurement system on a chip design found in a particular computing platform (e.g., mobile computing, desktop computing, etc.). The software and processor are integrated into a single chip 11′. The processor includes an internal arithmetic unit, registers, cache memory, buses, I / O ports, etc., as is well known in the art. Essentially, all peripherals (12′) may be connected to the single chip 11′, although the internal buses, etc., are vendor dependent. The circuit configuration 10′ integrates the processor, memory control, and I / O controller hub all into the single chip 11′. Common peripheral connection methods include, for example, SPI and I2C. For example, communication with flash memory may use a high speed connection method such as SDIO.

[0046] A power management chip 13', such as a battery management unit BMU, manages the power provided, for example via a rechargeable battery 14', which can be recharged by connecting to a power source (not shown). In at least one design, a single chip, such as 11', is used to provide BIOS-like functionality and DRAM memory.

[0047] The system 10' typically includes one or more of a WWAN transceiver 15' and a WLAN transceiver 16' to connect to various networks, such as telecommunication networks and wireless Internet devices (e.g., access points). Additionally, the system 10' typically includes devices 12', such as, for example, transmit and receive antennas, oscillators, PLLs, etc. The system 10' includes an input / output device 17' for data input and display / rendering (e.g., a computing location remote from the single beam system that is easily accessible to a user). The system 10' also typically includes various memory devices, such as, for example, flash memory 18' and SDRAM 19'.

[0048] The electronic components of one or more systems or devices may include at least one processing unit, a memory, and a communication bus or means coupling various components including the memory to the processing unit, but not limited thereto, as can be seen from the above description. The system or device may include or have access to various device-readable media. The system memory may include device-readable storage media in the form of non-volatile and / or volatile memory, such as read-only memory (ROM) and / or random access memory (RAM). By way of example and not limitation, the system memory may also include an operating system, application programs, other program modules, and program data. The disclosed system may be used in one embodiment of an instrument for square wave voltammetry.

[0049] As will be appreciated by those skilled in the art, various aspects may be embodied as a system, method, or apparatus program product. As such, the aspects may take the form of an entirely hardware embodiment or an embodiment including software, all of which may be generally referred to herein as a "circuit," "module," or "system." Additionally, the aspects may be embodied in the form of an apparatus program product, in one or more device-readable mediums having device-readable program code embodied therein.

[0050] It should be noted that various functions described herein may be implemented using instructions stored on a device-readable storage medium, such as a non-signal storage device, and those instructions are executed by a processor. In the context of this specification, a storage device is not a signal, and "non-transitory" includes all media other than signal media.

[0051] The program code that performs the operations may be written in any combination of one or more programming languages. The program code may run entirely on a single device, partially on a single device, as a stand-alone software package, partially on a single device and partially on another device, or entirely on other devices. In some forms, the devices may be connected via any manner of connection or network, including a local area network (LAN) or a wide area network (WAN), or the connection may be effected via another device (e.g., via the Internet using an Internet Service Provider), via a wireless connection such as near field communication, or via a hardwired connection such as via a USB connection.

[0052] Example embodiments are described herein with reference to figures illustrating methods, apparatus, and products according to various example embodiments. It will be understood that operations and functions may be implemented, at least in part, by program instructions. These program instructions may be provided to a processor of an apparatus, such as a measurement apparatus as shown in FIG. 11, or other programmable data processing apparatus to create a machine, such that the instructions executed via the apparatus's processor implement the specified functions / operations.

[0053] It should be noted that values ​​provided herein should be construed to include equivalent values ​​as indicated by the use of the term "about." Equivalent values, as would be apparent to one of ordinary skill in the art, include at least values ​​obtained by ordinary rounding of the last significant figure.

[0054] The present disclosure has been presented for purposes of illustration and description, and is not intended to be exhaustive or limiting. Many modifications and variations will be apparent to those skilled in the art. The illustrated embodiments have been selected and described in order to explain the principles and practical applications, and to enable others skilled in the art to appreciate the disclosure of various embodiments with various modifications as appropriate for the particular use envisioned.

[0055] Thus, while illustrative embodiments have been described herein with reference to the accompanying drawings, it should be understood that this description is not limiting and that various other changes and modifications may be made by those skilled in the art without departing from the scope or spirit of the present disclosure.

Claims

1. 1. A method for measuring components of an aqueous sample using square wave modulation, comprising: introducing the aqueous sample into a chamber of a square wave modulator; applying a step of a stimulation voltage comprising a staircase voltage to the aqueous sample, each step of the staircase voltage defining a group, the group having one or more cycles of square wave modulation; adjusting a time acquisition window that is a portion of each half cycle of the stimulation voltage; measuring a resultant current output resulting from said stimulation voltage within said time acquisition window; and each of said groups averaging said combined current output over at least one or more cycles.

2. The method of claim 1 , wherein the averaging step comprises uniform weighting of each of the groups within the time acquisition window.

3. The method of claim 1 , wherein the averaging step includes unequal weighting of each of the groups within the time acquisition window.

4. The method of claim 3 , wherein the averaging step further comprises selecting the non-uniform weighting to achieve a desired frequency response.

5. The method of claim 1 , wherein a single square wave cycle protocol is used for each ramp step.

6. The method of claim 1 , wherein a plurality of response current measurements are taken at equally spaced intervals within the acquisition window.

7. The method of claim 1 , wherein the length of the cycle averaged over the modulation group is equal to an integer multiple of the length of the power supply period.

8. The method of claim 1 , wherein the duration of the acquisition window is equal to an integer number of power supply cycles.

9. The method of claim 1 , wherein the start and end times of the acquisition window are selected to favor a response to an ionic species being measured in the aqueous sample.

10. 10. The method of claim 1, wherein the stimulation voltage step comprises a square wave voltammetry protocol having repeated cycles.

11. 1. An apparatus for measuring components of an aqueous sample using square wave modulation, comprising: A voltammetric electrode; At least one reference electrode; At least one counter electrode; a memory for storing instructions executable by a processor; The instruction: instructions to apply a step of a stimulation voltage to the aqueous sample, the step voltage comprising a staircase voltage, each step of the staircase voltage defining a group, the group having one or more cycles of square wave modulation; instructions to adjust a time acquisition window that is a portion of each half-cycle of the stimulation voltage; instructions for measuring a resultant current output resulting from said stimulation voltage within said time acquisition window; and instructions for each of said groups to average said composite current output over at least one or more cycles.

12. The apparatus of claim 11 , wherein the averaging instructions include uniform weighting of each of the groups within the time acquisition window.

13. The apparatus of claim 11 , wherein the averaging instructions include unequal weighting of each of the groups within the time acquisition window.

14. The apparatus of claim 13 , wherein the instructions to average further comprise instructions to select the non-uniform weighting to achieve a desired frequency response.

15. The apparatus of claim 11 , wherein a single square wave cycle protocol is used for each ramp step.

16. The apparatus of claim 11 , wherein a plurality of response current measurements are taken at equally spaced intervals within the acquisition window.

17. The apparatus of claim 11 , wherein the length of a cycle averaged over a modulation group is equal to an integer multiple of a power supply period.

18. The apparatus of claim 11 , wherein a duration of the acquisition window is equal to an integer number of power cycles.

19. The apparatus of claim 11 , wherein the start and end times of the acquisition window are selected to favor a response to an ionic species being measured in the aqueous sample.

20. 1. A system for measuring components of an aqueous sample using square wave modulation, comprising: A voltammetric electrode; At least one reference electrode; At least one counter electrode; a memory device for storing code executable by the processor; The code is code for applying a step of a stimulation voltage to the aqueous sample, the step voltage comprising a staircase voltage, each step of the staircase voltage defining a group, the group having one or more cycles of square wave modulation; code for adjusting a time acquisition window that is a portion of each half-cycle of the stimulation voltage; code for measuring a resultant current output resulting from said stimulation voltage within said time acquisition window; and code for each of said groups averaging said composite current output over at least one or more cycles.

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