Classification and Selection of Electrode Solutions: pH Calibration, ORP Maintenance, and Supporting Systems for Ion-Selective Electrodes

Electrode solutions are used in multiple steps, including calibration, storage, soaking, cleaning, internal filling, ionic strength adjustment, and standard curve establishment. For pH electrodes, ORP combination electrodes, conductivity electrodes, and ion-selective electrodes, solution selection directly affects response speed, slope, zero-point drift, ion activity correction, and long-term stability.

Keywords: electrode solutions; pH standard buffer; pH electrode protection solution; ORP standard solution; conductivity standard solution; ion-selective electrode; TISAB solution; electrode cleaning solution

1 Basic Classification of Electrode Solutions

1.1 Classification by Use Stage

Electrode solutions should first be classified according to their use stage rather than only by chemical composition. The same type of salt solution may function as an internal filling solution, salt bridge solution, standard solution, or background electrolyte in different scenarios. These functions are different and cannot be simply substituted for one another.

(1) Calibration solutions

Calibration solutions are used to establish the relationship between instrument readings and standard values, including pH standard buffers, ORP standard solutions, and conductivity standard solutions. Their core requirements are clearly defined standard values, specified temperature conditions, and avoidance of contamination after opening.

(2) Protection and soaking solutions

Protection and soaking solutions are used to maintain the stability of electrode membranes, reference junction interfaces, and sensing elements. pH electrodes should not be stored in pure water for extended periods when not in use; the corresponding electrode protection or soaking solution should be used instead.

(3) Cleaning solutions

Cleaning solutions are used to remove contamination from the liquid junction, glass membrane, or combination electrode surface. General contamination can be treated with pH/ORP cleaning solution, while delayed responses caused by protein-containing samples are more suitably treated with protein cleaning solution.

(4) Standard solutions

Ion-selective electrode standard solutions are used to establish the response curve for the target ion. A 0.1 M standard solution is more suitable for preparing molar concentration gradients, whereas a 1000 ppm standard solution is more suitable for mass concentration systems and environmental sample analysis.

(5) Filling solutions

Filling solutions are used to maintain a stable internal ionic environment in ion-selective electrodes. Filling solutions for different ion-selective electrodes are not interchangeable and should be matched to the target electrode type.

(6) Ionic strength adjusters

Ionic strength adjusters are used to equalize the total ionic strength of standards and samples so that electrode response mainly reflects the activity of the target ion. Fluoride detection commonly uses a TISAB system to control pH, ionic strength, and complexation interference simultaneously.

1.2 Classification by Electrode Type

(1) pH electrodes

pH electrodes mainly use pH standard buffers, pH electrode protection solutions, pH/ORP combination electrode soaking solutions, and cleaning solutions. The key is to maintain the hydration layer of the glass membrane and ensure normal conduction at the reference junction.

(2) ORP electrodes

ORP electrodes mainly use ORP standard solutions, soaking solutions, and cleaning solutions. ORP standard solutions are used to check whether the electrode potential response has shifted; they are not used to adjust the redox state of samples.

(3) Conductivity electrodes

Conductivity electrodes require conductivity standard solutions for calibration. The selected standard should be close to the conductivity range of the sample. Low-conductivity water samples and conventional electrolyte solutions should not be covered simply by the same calibration point.

(4) Ion-selective electrodes

Ion-selective electrodes usually require standard solutions, filling solutions, and ionic strength adjusters as a supporting system. If only standard solutions are used while filling solutions and ionic strength adjusters are ignored, abnormal slope, response drift, or sample matrix bias may occur.

Table 1 Classification and functional positioning of electrode solutions

Solution Type	Main Function	Typical Product Type	Applicable Electrode/System	Selection Focus
pH standard buffer	Establish pH calibration curve	pH 2.00, 4.00/4.01, 6.86/7.00, 9.18, 10.00 buffers	pH meter, pH combination electrode	Calibration points should cover the sample pH range
Electrode protection solution	Maintain membrane hydration and liquid junction stability	pH electrode protection solution	pH glass electrode, combination electrode	Avoid long-term storage in pure water
Electrode soaking solution	Restore electrode response	pH/ORP combination electrode soaking solution	pH/ORP combination electrode	Used for electrodes long unused or with delayed response
Electrode cleaning solution	Remove contaminants	pH/ORP cleaning solution, protein cleaning solution	pH electrode, ORP electrode	Select according to contamination type
ORP standard solution	Check redox potential response	ORP standard solution	ORP electrode	Pay attention to temperature and electrode surface condition
Conductivity standard solution	Calibrate conductivity readings	KCl conductivity standard solution, electrolyte conductivity reference material	Conductivity electrode	Standard value should be close to the sample range
ISE standard solution	Establish target ion response curve	0.1 M standard solution, 1000 ppm standard solution	Ion-selective electrode	Select according to target ion
ISE filling solution	Maintain internal electrode stability	Filling solutions for different ion-selective electrodes	Ion-selective electrode	Different electrodes are not interchangeable
Ionic strength adjuster	Equalize ionic strength and reduce matrix effects	ISA, TISAB solution	Ion-selective electrode	Match target ion and sample system

2 Solutions for pH and ORP Electrodes

2.1 pH Standard Buffers

pH standard buffers are used for pH electrode calibration, not for electrode storage. In practice, calibration points should be selected according to the pH range of the sample, and single-point calibration should not be used to cover the entire measurement range.

(1) Acidic calibration points

pH 2.00, pH 4.00, and pH 4.01 buffers are suitable for calibration before measuring acidic samples. If samples are in a strongly acidic range, a pH 2.00 buffer helps improve the reliability of readings in the low-pH range.

(2) Neutral calibration points

pH 6.86 or pH 7.00 buffers are commonly used as calibration points near the zero point to check the reference reading of the electrode and instrument status. In routine two-point or three-point calibration, the neutral point should generally not be omitted.

(3) Alkaline calibration points

pH 9.18 and pH 10.00 buffers are suitable for measuring alkaline samples. Alkaline buffers are easily affected by CO₂ in air. After opening, exposure time should be minimized, and electrodes should not directly introduce contaminants into the buffer.

2.2 pH Electrode Protection and Soaking Solutions

pH electrode protection solution and pH/ORP combination electrode soaking solution are used to maintain glass membrane hydration, reference system stability, and liquid junction continuity. When an electrode is stored for a long time or shows delayed response, the condition of the protection solution, soaking solution, and liquid junction should be checked first.

(1) Protection solution

pH electrode protection solution is used for electrode storage and can reduce the risk of glass membrane drying, reference solution dilution, and liquid junction instability. Pure water is suitable only for short-term rinsing and is not suitable for long-term electrode storage.

(2) Soaking solution

pH/ORP combination electrode soaking solution is suitable for restoring electrode response before use, especially for electrodes that have been unused for a long time, show reading drift, or have a significantly prolonged response time.

(3) Application boundaries

Protection and soaking solutions are not standard buffers and cannot be used as pH calibration solutions. After storage, the electrode should be rinsed and surface liquid gently removed before calibration in standard buffer solutions.

2.3 pH/ORP Cleaning Solutions

Electrode cleaning should be selected according to the type of contamination. General inorganic salts, mild contamination, and sample residues can be treated with pH/ORP cleaning solution. Delayed response caused by protein-containing samples, biological samples, culture media, or colloidal systems is more suitably treated with pH/ORP protein cleaning solution.

(1) General contamination

General contamination is manifested by reading drift, slower response, or decreased calibration slope. After cleaning, the electrode should be rinsed with pure water and then placed in protection or soaking solution for recovery.

(2) Protein contamination

Protein contamination often blocks the liquid junction or covers the glass membrane surface, and simple rinsing with water is usually insufficient to restore response. Protein cleaning solution is suitable for electrodes used in serum, culture media, protein solutions, and biological sample measurements.

(3) Calibration after cleaning

After cleaning, pH or ORP electrodes should be recalibrated or checked against standard solutions before they are used for critical sample measurements.

2.4 ORP Standard Solutions

ORP standard solutions are used to check whether the response of an oxidation-reduction potential electrode has shifted. ORP readings are jointly affected by electrode surface condition, reference system, temperature, and sample chemistry. Therefore, checking with a standard solution is mainly used to evaluate electrode status, not to correct the sample itself.

(1) Response check

If the reading in an ORP standard solution deviates significantly, platinum electrode surface contamination, reference system condition, and soaking/maintenance conditions should be checked first.

(2) Temperature effect

The reference potential of an ORP standard solution is usually temperature-dependent, so reading interpretation should be based on the measurement temperature.

(3) Maintenance logic

After long-term storage, ORP electrodes should first be soaked to restore response, then checked with a standard solution. If necessary, they should be cleaned and retested.

3 Solutions for Ion-Selective Electrodes

3.1 Selection Logic for Supporting Solution Systems

Ion-selective electrode detection usually requires a coordinated system of “standard solution, filling solution, and ionic strength adjuster.” The standard solution establishes the response curve, the filling solution maintains the internal electrode environment, and the ionic strength adjuster reduces differences in sample matrix so that results more closely reflect changes in target ion activity.

(1) Standard solutions

0.1 M standard solutions are suitable for preparing molar concentration gradients, while 1000 ppm standard solutions are suitable for environmental water samples, industrial water samples, and routine mass concentration systems. The concentration range of standards should cover the sample concentration range, and a single high-concentration point should not be used to extrapolate low-concentration samples.

(2) Filling solutions

Filling solutions should be selected according to electrode type. Fluoride, chloride, sodium, potassium, calcium, nitrate, ammonium, and heavy metal ion electrodes have different internal systems, and filling solutions are not interchangeable.

(3) Ionic strength adjusters

Ionic strength adjusters are used to equalize the ionic strength of standards and samples. For complex matrices, high-salt systems, or samples containing complexes, it should first be confirmed whether the adjuster changes the free form of the target ion.

3.2 Fluoride Ion Electrodes and the TISAB System

Fluoride detection is sensitive to pH, metal complexes, and ionic strength; therefore, TISAB solution is commonly used. TISAB I, TISAB III, and TISAB IV can be used in fluoride determination to control pH, adjust ionic strength, and reduce complexation interference.

(1) pH control

Under acidic conditions, fluoride ions may form HF, affecting electrode response. The TISAB system can control pH within a range suitable for fluoride determination.

(2) Control of complexation interference

Metal ions such as Al³⁺ and Fe³⁺ may form complexes with fluoride ions, reducing the concentration of free fluoride. TISAB can reduce part of this complexation interference, making the measurement closer to the total fluoride level responsive to the electrode.

(3) Matching of standards and samples

Fluoride standard solutions and samples should be mixed with the same volume ratio of TISAB to ensure consistent conditions for calibration curves and sample measurements.

3.3 Common Anion-Selective Electrode Solutions

Chloride, nitrate, bromide, iodide, cyanide, sulfide, and other anion-selective electrodes all require corresponding standard solutions, filling solutions, and ionic strength adjusters. These measurements should focus on similar anions, strongly complexing ions, and the redox state of the sample.

(1) Chloride ion electrodes

Chloride ion-selective electrodes are suitable for Cl⁻ detection in water samples, environmental samples, and industrial samples. If samples contain Br⁻, I⁻, or Ag⁺, electrode selectivity and precipitation interference should be considered.

(2) Nitrate ion electrodes

Nitrate ion electrodes are suitable for water bodies, soil extracts, or nutrient-related testing. Strongly interfering anions or high ionic strength backgrounds can affect response, so supporting adjusters should be used.

(3) Bromide and iodide ion electrodes

Bromide and iodide detection requires attention to cross-interference among halide ions. Standard solutions, filling solutions, and ionic strength adjusters should be matched to the target ion system.

3.4 Common Cation-Selective Electrode Solutions

Sodium, potassium, calcium, ammonium, silver, copper, lead, cadmium, and other cation-selective electrodes can be used for water quality, industrial process, environmental sample, and selected experimental system analysis. Metal ion detection requires particular attention to complexing agents, precipitants, and sample pH.

(1) Sodium and potassium ion electrodes

Sodium and potassium electrodes are commonly used for ion activity analysis in water samples, electrolyte solutions, or biological-related systems. High concentrations of background ions and similar cations may affect electrode selectivity.

(2) Calcium ion electrodes

Calcium ion electrodes measure responses related to free Ca²⁺. EDTA, phosphate, proteins, and organic ligands in the sample can alter free calcium concentration, so sample chemical composition must be considered during interpretation.

(3) Ammonium and ammonia ion electrodes

Ammonium- and ammonia-related systems are strongly affected by pH. Standard solutions, filling solutions, and ionic strength adjusters should be matched to the target detected species to avoid bias caused by changes in the NH₄⁺/NH₃ equilibrium.

(4) Heavy metal ion electrodes

Copper, lead, cadmium, silver, and other ion-selective electrodes are suitable for target metal ion detection, but complexing agents, sulfides, halide ions, and precipitation reactions in samples may significantly affect free ion response.

Table 2 Key points for selecting supporting solutions for ion-selective electrodes

Electrode Type	Required Supporting Solutions	Main Purpose	Selection Focus
Fluoride ion electrode	Fluoride standard solution, filling solution, TISAB solution	Control pH, ionic strength, and complexation interference	Standards and samples should contain the same TISAB ratio
Chloride ion electrode	Chloride standard solution, filling solution, ionic strength adjuster	Establish Cl⁻ response curve	Pay attention to Br⁻, I⁻, and Ag⁺ interference
Sodium ion electrode	Sodium standard solution, filling solution, ionic strength adjuster	Determine Na⁺ activity	Control potential interference from K⁺, NH₄⁺, etc.
Potassium ion electrode	Potassium standard solution, filling solution, ionic strength adjuster	Determine K⁺ activity	Pay attention to NH₄⁺ and high Na⁺ background
Calcium ion electrode	Calcium standard solution, filling solution, ionic strength adjuster	Determine free Ca²⁺	Avoid complexation by EDTA, phosphate, and proteins
Nitrate ion electrode	Nitrate standard solution, filling solution, ionic strength adjuster	Determine NO₃⁻	Pay attention to strongly interfering anions and high-salt backgrounds
Ammonium/ammonia electrode	Ammonium/ammonia standard solution, filling solution, ionic strength adjuster	Determine ammonium ion or ammonia-related indicators	pH affects NH₄⁺/NH₃ equilibrium
Heavy metal ion electrode	Copper, lead, cadmium, silver standard solutions and supporting solutions	Determine free metal ion response	Pay attention to complexation, precipitation, and sample pH

4 Selection of Electrochemical Test Media and Supporting Electrolytes

4.1 Role of Supporting Electrolytes

Supporting electrolytes are mainly used to increase solution conductivity, reduce ohmic drop, stabilize ionic strength, and minimize the influence of migration current from target electroactive species on test results. In cyclic voltammetry, chronoamperometry, open-circuit potential measurement, corrosion electrochemistry, and sensor evaluation, the choice of supporting electrolyte affects background current, potential window, peak shape, and repeatability.

(1) Aqueous systems

Aqueous systems commonly use chloride, nitrate, sulfate, or buffer salt systems. If the test target is sensitive to Cl⁻, or if the system contains ions such as Ag⁺, Pb²⁺, or Hg²⁺ that readily precipitate or complex with Cl⁻, KCl or NaCl should not be used directly as the background electrolyte.

(2) Buffer systems

pH-sensitive reactions, enzyme electrodes, biosensors, and environmental water sample testing usually require buffer systems to maintain stable pH. Phosphate, acetate, Tris, and other systems can be used across different pH ranges, but their interactions with metal ions, calcium/magnesium ions, or target analytes should be considered.

(3) Non-aqueous systems

Non-aqueous electrochemistry is often used for organic molecules, complexes, or testing within wide potential windows. These systems require supporting electrolytes compatible with organic solvents, and water, oxygen, and background impurities must be strictly controlled. If the article focuses on routine ready-to-use electrode solutions, non-aqueous systems can be included as a supplementary note rather than as the key focus for product selection.

4.2 Matching Counter Electrode Solutions with the Test System

Counter electrode solutions are used in specific electrochemical test devices to maintain charge transfer and system stability at the counter electrode side. Selection should consider compatibility with the working electrode reaction system, separator, reference electrode, and sample solution. If the counter electrode solution differs greatly in ionic composition from the sample system, liquid junction potential, ion migration, or background reaction interference may be introduced.

5 Selection of Calibration Solutions, Standard Solutions, and Electrode Maintenance Solutions

5.1 pH Standard Buffers

pH standard buffers are used for pH electrode calibration, not for electrode storage. In practice, calibration points should be selected according to the sample pH range. Acidic samples can be calibrated with pH 4.00/4.01 and pH 6.86/7.00 buffers, while alkaline samples can be calibrated with pH 6.86/7.00 and pH 9.18/10.00 buffers. Three-point calibration is recommended for high-precision measurements.

(1) Acidic calibration points

pH 2.00, pH 4.00, or pH 4.01 buffers are suitable for calibration before measuring acidic samples. If the sample is strongly acidic, a pH 2.00 calibration point should be included to improve accuracy in the low-pH range.

(2) Neutral calibration points

pH 6.86 or pH 7.00 buffers are commonly used as calibration points near the pH electrode zero point to check electrode response and instrument baseline.

(3) Alkaline calibration points

pH 9.18 or pH 10.00 buffers are suitable for alkaline sample measurement. Alkaline buffers are susceptible to CO₂ in air, so prolonged exposure after opening should be minimized.

5.2 pH/ORP Electrode Storage and Cleaning Solutions

pH electrode protection solutions and pH/ORP combination electrode soaking solutions are used to maintain glass membrane hydration, liquid junction stability, and electrode response speed. pH/ORP cleaning solutions are used to remove general contamination, while protein cleaning solutions are more suitable for liquid junction blockage or delayed response caused by protein-containing samples.

(1) Storage solutions

Storage solutions are used for electrode standby and long-term storage and cannot be replaced with pure water. Pure water is suitable only for short-term rinsing, not for soaking storage.

(2) Soaking solutions

Soaking solutions are suitable for restoring response before electrode use, especially for pH/ORP combination electrodes that have been unused for a long time, respond slowly, or show reading drift.

(3) Protein cleaning solutions

Protein samples, culture media, biological samples, or colloidal samples can readily contaminate the liquid junction. Such contamination should be treated with protein cleaning solution rather than rinsing with water alone.

5.3 ORP Standard Solutions and Conductivity Standard Solutions

ORP standard solutions are used to check whether oxidation-reduction potential electrode readings have shifted. Conductivity standard solutions are used to calibrate conductivity electrodes. Both belong to standard systems for confirming instrument and electrode status and cannot replace sample test solutions.

(1) ORP standard solutions

ORP standard solutions are mainly used for response checks. If the reading deviation is large, platinum electrode surface contamination, reference system condition, and temperature should be checked first.

(2) Low-conductivity standard solutions

Low-conductivity standard solutions such as 147.4 μS/cm are suitable for calibration before measurement of low-ionic-strength water samples or purified water.

(3) Conventional conductivity standard solutions

Standard solutions such as 1000 μS/cm and 1410 μS/cm are suitable for conductivity calibration of routine water samples, buffers, and general electrolyte solutions.

6 Cleaning, Maintenance, and Troubleshooting of Common Abnormalities

6.1 Delayed Response of pH/ORP Electrodes

Delayed response of pH/ORP electrodes is often associated with glass membrane drying, liquid junction contamination, protein residue, or improper storage. The recommended workflow is cleaning first, soaking for recovery, and recalibration afterward.

(1) Mild contamination

pH/ORP cleaning solution can be used for mild contamination. After cleaning, rinse with pure water, gently remove surface droplets, and then place the electrode in protection or soaking solution for recovery.

(2) Protein contamination

Serum, culture media, protein solutions, and biological samples can readily cause liquid junction blockage and should be treated with pH/ORP protein cleaning solution.

(3) Long-term unused electrodes

Electrodes that have been unused for a long time should first be restored using soaking solution. Calibration should be performed only after stable readings are confirmed.

6.2 Abnormal Conductivity and ORP Readings

Abnormal conductivity readings are usually related to calibration solution selection, temperature compensation, probe contamination, or changes in the electrode constant. Abnormal ORP readings are often associated with platinum surface contamination, reference system condition, or instability of the sample redox system.

(1) Conductivity abnormalities

Conductivity standard solutions close to the sample range should be used first for checking. Low-conductivity samples should not be judged only by extrapolation from high-conductivity standards.

(2) ORP abnormalities

The ORP electrode status should first be checked with an ORP standard solution, and then the stability of the sample redox system itself should be evaluated.

(3) Retesting after maintenance

After cleaning or soaking, electrodes should be verified again using standard solutions. Normal electrode function should not be inferred only from faster reading recovery.

Table 3 Electrode contamination and abnormality troubleshooting directions

Abnormality	Possible Cause	Recommended Treatment	Notes
pH reading drift	Insufficient glass membrane hydration, unstable liquid junction	Restore using protection or soaking solution	Recalibration is required before retesting
Slow pH response	Protein contamination, sample residue, membrane surface contamination	Use pH/ORP cleaning solution or protein cleaning solution	Select cleaning solution according to contamination type
ORP reading shift	Platinum surface contamination, abnormal reference system	Check with ORP standard solution; clean if necessary	ORP standard solution is used for checking, not for adjusting samples
Conductivity deviation	Mismatched standard solution, abnormal temperature compensation	Use conductivity standard solution close to the sample range	Low-conductivity samples require low-conductivity standards
Abnormal ISE slope	Expired standard solution, wrong filling solution, mismatched ISA	Replace standard solution, filling solution, and adjuster	Standard and sample matrices should be consistent
Poor ISE repeatability	Large differences in sample ionic strength, interfering ions	Add corresponding ionic strength adjuster	Do not substitute ISA between different electrode systems

7 Common Errors in Solution Selection

7.1 Using Storage Solution as Calibration Solution

Storage solutions are used to maintain electrode condition and cannot serve as standard measurement systems. The pH value of a pH electrode storage or soaking solution does not represent a standard pH buffer.

7.2 Long-Term Storage of pH Electrodes in Pure Water

Pure water disrupts the ionic balance of the glass membrane and reference system, causing slower response and increased drift. Pure water is suitable for rinsing, but not for long-term storage.

7.3 Performing Only Single-Point pH Calibration

Single-point calibration only corrects readings near one range and cannot verify electrode slope. Acidic, alkaline, or high-precision samples should be measured after two-point or three-point calibration.

7.4 Using Only Standard Solutions for Ion-Selective Electrodes

ISE detection requires not only standard solutions, but also filling solutions and ionic strength adjusters. If ionic strength adjustment is ignored, systematic errors may arise from differences in activity coefficients between standards and samples.

7.5 Ignoring the Chemical Form of the Target Ion

Fluoride, calcium, ammonium, and heavy metal ions can all be affected by pH, complexation, precipitation, or ionic equilibrium. During detection, attention should be paid to the difference between free ion concentration and total concentration.

8 Related Reagent and Material Selection

Table 4 Selection of electrode calibration, maintenance, and ion-selective electrode supporting solutions

Cat. No.	Product Name	Specification/Concentration	Application Module	Application Positioning
P492949	PH Buffer Standard Solution		pH calibration	Used for routine pH electrode calibration and instrument status checking
P118684	pH Buffer Standard Solution（pH=2.00±0.02）	pH=2.00±0.02 (20℃)	pH calibration	Used for pH electrode calibration in strongly acidic measurement ranges
P118681	pH Buffer Standard Solution（pH=4.00±0.02）	pH=4.00±0.02 (25℃)	pH calibration	Used for pH electrode calibration before acidic sample measurement
P118675	pH Buffer Standard Solution（pH=4.01）	pH=4.012 (25℃)	pH calibration	Used for calibration and slope checking in acidic pH measurement ranges
P118679	pH Buffer Standard Solution（pH=6.86±0.02）	pH=6.86±0.02 (25℃)	pH calibration	Used for pH electrode calibration of near-neutral samples
P118676	pH Buffer Standard Solution（pH=6.86）	pH=6.863(25℃)	pH calibration	Used as a neutral calibration point and for routine two-point/three-point calibration
P118682	pH Buffer Standard Solution（pH=7.00±0.02）	pH=7.00±0.02 (25℃)	pH calibration	Used for neutral calibration, instrument zero-point checking, and routine pH measurement calibration
P118677	pH Buffer Standard Solution（pH=9.18）	pH=9.184 (25℃)	pH calibration	Used for pH electrode calibration and slope checking in alkaline ranges
P118683	pH Buffer Standard Solution（pH=10.00±0.02）	pH=10.00±0.02 (25℃)	pH calibration	Used for strongly alkaline samples or high-pH range measurement calibration
P1513148	Electrode Preserving Solution	BioReagent	pH electrode storage	Used for glass electrode membrane hydration, reference junction stability, and routine electrode storage
E743272	Electrode Soaking Solution		pH/ORP electrode maintenance	Used for pH/ORP combination electrode soaking, response recovery, and routine maintenance
P123956	pH/ORP Cleaning Solution		pH/ORP electrode cleaning	Used to remove general contamination and improve pH or ORP electrode response speed and stability
P123957	pH/ORP Protein Cleaning Solution		Protein contamination cleaning	Used to treat liquid junction blockage or delayed electrode response caused by protein-containing samples
O743259	ORP Standard Solution		ORP calibration/checking	Used for oxidation-reduction potential electrode response checking and potential shift assessment
BWW349374	Aqueous electrolytic conductivity-KCl	1000μS/cm(25℃)in H2O,Uncertainty:0.25%	Conductivity calibration	Used for calibration and quality control of conductivity electrodes in low-to-medium conductivity ranges
P119551	Aqueous electrolytic conductivity-KCl	147.4μs/cm(25°C)	Conductivity calibration	Used for calibration before low-conductivity sample measurement
P119550	Potassium chloride	1410μs/cm(25℃)	Conductivity calibration	Used for conductivity calibration of routine water samples, electrolyte solutions, and laboratory buffers
E359114	Electrolyte conductivity reference material		Conductivity calibration	Used for conductivity measurement standardization and instrument performance validation
C494287	CELS Counter Electrode Solution		Electrochemical supporting solution	Used for counter electrode solution preparation or maintenance in specific electrochemical electrode systems
T488118	TISAB I solution		Fluoride ion detection	Used for ionic strength adjustment and pH control in fluoride ion-selective electrode detection
T488117	TISAB III solution		Fluoride ion detection	Used for fluoride ion-selective electrode analysis to reduce ionic strength differences and complexation interference
T485682	TISAB IV solution	Skip to the end of the images gallery	Fluoride ion detection	Used for pH control, ionic strength adjustment, and interference control in fluoride determination
I123800	Fluoride Ion Selective Electrode Solutions		Fluoride ion-selective electrode	Used as a supporting solution for fluoride ion-selective electrode detection systems
I123818	Fluoride Ion Selective Electrode Solutions	0.1M Standard	Fluoride standard solution	Used for establishing standard curves with fluoride ion-selective electrodes
I123834	Fluoride Ion Selective Electrode Solutions	1000ppm Standard	Fluoride standard solution	Used for fluoride detection calibration, quality control, and method validation
I123782	Fluoride Ion Selective Electrode Solutions	Fill Solution	Fluoride electrode maintenance	Used for internal filling and stable response of fluoride ion-selective electrodes
I123797	Chloride Ion Selective Electrode Solutions	ISA	Chloride ion detection	Used to equalize ionic strength in chloride ion-selective electrode detection
I123816	Chloride Ion Selective Electrode Solutions	0.1M Standard	Chloride standard solution	Used for establishing standard curves with chloride ion electrodes
I123832	Chloride Ion Selective Electrode Solutions	1000ppm Standard	Chloride standard solution	Used for chloride detection calibration and quality control
I123779	Chloride Ion Selective Electrode Solutions	Fill Solution	Chloride electrode maintenance	Used for filling and maintenance of chloride ion-selective electrodes
I123809	Sodium Ion Selective Electrode Solutions	ISA	Sodium ion detection	Used to control ionic strength in sodium ion-selective electrode detection
I123825	Sodium Ion Selective Electrode Solutions	0.1M Standard	Sodium standard solution	Used for establishing standard curves with sodium ion electrodes
I123841	Sodium Ion Selective Electrode Solutions	1000ppm Standard	Sodium standard solution	Used for sodium detection calibration and quality control
I123790	Sodium Ion Selective Electrode Solutions	Fill Solution	Sodium electrode maintenance	Used for filling and response stabilization of sodium ion-selective electrodes
I123806	Potassium Ion Selective Electrode Solutions	ISA	Potassium ion detection	Used to control ionic strength in potassium ion-selective electrode detection
I123823	Potassium Ion Selective Electrode Solutions	0.1M Standard	Potassium standard solution	Used for establishing standard curves with potassium ion electrodes
I123839	Potassium Ion Selective Electrode Solutions	1000ppm Standard	Potassium standard solution	Used for potassium detection calibration and quality control
I123787	Potassium Ion Selective Electrode Solutions	Fill Solution	Potassium electrode maintenance	Used for filling and maintenance of potassium ion-selective electrodes
I123777	Calcium Ion Selective Electrode Solutions	Fill Solution	Calcium electrode maintenance	Used for internal filling of calcium ion-selective electrodes
I123814	Calcium Ion Selective Electrode Solutions	0.1M Standard	Calcium standard solution	Used for establishing standard curves with calcium ion electrodes
I123830	Calcium Ion Selective Electrode Solutions	1000ppm Standard	Calcium standard solution	Used for calcium detection calibration and quality control
I123795	Calcium Ion Selective Electrode Solutions	ISA	Calcium ion detection	Used to equalize ionic strength and improve response stability in calcium ion-selective electrode detection
I123791	Ammonia Ion Selective Electrode Solutions	ISA	Ammonia ion detection	Used to control ionic strength in ammonia ion-selective electrode detection
I123810	Ammonia Ion Selective Electrode Solutions	0.1M Standard	Ammonia standard solution	Used for establishing standard curves with ammonia ion electrodes
I123773	Ammonia Ion Selective Electrode Solutions	Fill Solution	Ammonia electrode maintenance	Used for filling and maintenance of ammonia ion-selective electrodes
I123792	Ammonium Ion Selective Electrode Solutions	ISA	Ammonium ion detection	Used to equalize ionic strength in ammonium ion-selective electrode detection
I123811	Ammonium Ion Selective Electrode Solutions	0.1M Standard	Ammonium standard solution	Used for establishing standard curves with ammonium ion electrodes
I123827	Ammonium Ion Selective Electrode Solutions	1000ppm Standard	Ammonium standard solution	Used for ammonium ion detection calibration and quality control
I123774	Ammonium Ion Selective Electrode Solutions	Fill Solution	Ammonium electrode maintenance	Used for filling and maintenance of ammonium ion-selective electrodes
I123804	Nitrate Ion Selective Electrode Solutions	ISA	Nitrate detection	Used to control ionic strength in nitrate ion-selective electrode detection
I123822	Nitrate Ion Selective Electrode Solutions	0.1M Standard	Nitrate standard solution	Used for establishing standard curves with nitrate ion electrodes
I123838	Nitrate Ion Selective Electrode Solutions	1000ppm Standard	Nitrate standard solution	Used for nitrate detection calibration and quality control
I123786	Nitrate Ion Selective Electrode Solutions	Fill Solution	Nitrate electrode maintenance	Used for filling and maintenance of nitrate ion-selective electrodes
I123796	Carbon Dioxide (Carbonate) Ion Selective Electrode Solutions	ISA	Carbonate/carbon dioxide detection	Used to control ionic strength in carbonate or carbon dioxide ion-selective electrode detection
I123815	Carbon Dioxide (Carbonate) Ion Selective Electrode Solutions	0.1M Standard	Carbonate/carbon dioxide standard solution	Used for establishing standard curves with carbonate or carbon dioxide electrodes
I123831	Carbon Dioxide (Carbonate) Ion Selective Electrode Solutions	1000ppm Standard	Carbonate/carbon dioxide standard solution	Used for carbonate or carbon dioxide detection calibration and quality control
I123778	Carbon Dioxide (Carbonate) Ion Selective Electrode Solutions	Fill Solution	Carbonate/carbon dioxide electrode maintenance	Used for filling and maintenance of carbon dioxide or carbonate ion-selective electrodes
I123793	Bromide Ion Selective Electrode Solutions	ISA	Bromide ion detection	Used to control ionic strength in bromide ion-selective electrode detection
I123812	Bromide Ion Selective Electrode Solutions	0.1M Standard	Bromide standard solution	Used for establishing standard curves with bromide ion electrodes
I123828	Bromide Ion Selective Electrode Solutions	1000ppm Standard	Bromide standard solution	Used for bromide detection calibration and quality control
I123775	Bromide Ion Selective Electrode Solutions	Fill Solution	Bromide electrode maintenance	Used for filling and maintenance of bromide ion-selective electrodes
I123801	Iodide Ion Selective Electrode Solutions	ISA	Iodide ion detection	Used to control ionic strength in iodide ion-selective electrode detection
I123819	Iodide Ion Selective Electrode Solutions	0.1M Standard	Iodide standard solution	Used for establishing standard curves with iodide ion electrodes
I123835	Iodide Ion Selective Electrode Solutions	1000ppm Standard	Iodide standard solution	Used for iodide detection calibration and quality control
I123783	Iodide Ion Selective Electrode Solutions	Fill Solution	Iodide electrode maintenance	Used for filling and maintenance of iodide ion-selective electrodes
I123802	Lead Ion Selective Electrode Solutions	ISA	Lead ion detection	Used to control ionic strength in lead ion-selective electrode detection
I123820	Lead Ion Selective Electrode Solutions	0.1M Standard	Lead standard solution	Used for establishing standard curves with lead ion electrodes
I123836	Lead Ion Selective Electrode Solutions	1000ppm Standard	Lead standard solution	Used for lead ion detection calibration and quality control
I123784	Lead Ion Selective Electrode Solutions	Fill Solution	Lead electrode maintenance	Used for filling and maintenance of lead ion-selective electrodes
I123798	Cupric Ion Selective Electrode Solutions	ISA	Copper ion detection	Used to control ionic strength in copper ion-selective electrode detection
I123817	Cupric Ion Selective Electrode Solutions	0.1M Standard	Copper standard solution	Used for establishing standard curves with copper ion electrodes
I123833	Cupric Ion Selective Electrode Solutions	1000ppm Standard	Copper standard solution	Used for copper ion detection calibration and quality control
I123780	Cupric Ion Selective Electrode Solutions	Fill Solution	Copper electrode maintenance	Used for filling and maintenance of copper ion-selective electrodes
I123807	Silver Ion Selective Electrode Solutions	ISA	Silver ion detection	Used to control ionic strength in silver ion-selective electrode detection
I123824	Silver Ion Selective Electrode Solutions	0.1M Standard	Silver standard solution	Used for establishing standard curves with silver ion electrodes
I123840	Silver Ion Selective Electrode Solutions	1000ppm Standard	Silver standard solution	Used for silver ion detection calibration and quality control
I123788	Silver Ion Selective Electrode Solutions	Fill Solution	Silver electrode maintenance	Used for filling and maintenance of silver ion-selective electrodes
I123794	Cadmium Ion Selective Electrode Solutions	ISA	Cadmium ion detection	Used to control ionic strength in cadmium ion-selective electrode detection
I123813	Cadmium Ion Selective Electrode Solutions	0.1M Standard	Cadmium standard solution	Used for establishing standard curves with cadmium ion electrodes
I123829	Cadmium Ion Selective Electrode Solutions	1000ppm Standard	Cadmium standard solution	Used for cadmium ion detection calibration and quality control
I123776	Cadmium Ion Selective Electrode Solutions	Fill Solution	Cadmium electrode maintenance	Used for filling and maintenance of cadmium ion-selective electrodes

9 Frequently Asked Questions

9.1 Can pure water be used instead of pH electrode storage solution?

It is not recommended. Pure water has low ionic strength, and long-term storage in pure water can disrupt the ionic balance of the glass membrane and reference system, leading to delayed response and reading drift. Pure water is suitable only for rinsing electrodes, not for long-term soaking or storage.

9.2 Can pH standard buffer be used as an electrode protection solution?

It is not recommended. pH standard buffers are used for calibration, while electrode protection solutions are used for storage and maintaining membrane hydration. Their functions are different. Long-term storage of electrodes in standard buffers may cause contamination, crystallization, or reference system instability.

9.3 Why should pH electrodes be calibrated using two or three points?

Two-point or three-point calibration can check both zero point and slope. Single-point calibration cannot determine whether the electrode maintains a normal response in acidic or alkaline ranges.

9.4 Is ORP standard solution used to calibrate the sample potential?

No. ORP standard solution is mainly used to check electrode response and potential shift. It is not used to adjust the redox state of the sample. ORP measurement depends more strongly on electrode surface condition and the sample system itself.

9.5 Why do ion-selective electrodes require ionic strength adjusters?

Ion-selective electrodes respond to ion activity rather than simple concentration. Changes in ionic strength affect activity coefficients, making standards and samples incomparable. Ionic strength adjusters improve response stability and linearity.

9.6 Why is TISAB commonly used in fluoride ion detection?

TISAB controls pH, equalizes ionic strength, and reduces the effect of metal ion complexation on fluoride detection. Standards and samples should receive the same addition ratio to ensure consistent response conditions.

9.7 Can standard solutions, filling solutions, and ionic strength adjusters be used interchangeably?

No. Standard solutions are used for calibration, filling solutions maintain the internal electrode environment, and ionic strength adjusters standardize conditions between samples and standards. Their functions are different, and interchange may cause abnormal response or reduced electrode performance.

Electrode solution selection should be based on electrode type, measurement target, and sample matrix. pH measurement focuses on standard buffers, protection solutions, and cleaning solutions; ORP measurement focuses on standard solution checks and electrode surface maintenance; conductivity measurement requires standards close to the sample range; and ion-selective electrodes require matched standard solutions, filling solutions, and ionic strength adjusters.

For more related articles, please see below:

[1] The Practical Guide to “For Ion-Selective Electrodes” Reagents

[2] Experiments on the determination of fluoride content in agricultural products by fluoride ion selective electrode method

[3] Determination of trace fluorine in water by fluoride ion selective electrode experiment