pH buffer solutions
pH buffer solutions reliably calibrate pH electrodes and are essential for obtaining reliable measurement results. LT Laborhandel stocks WTW standard (DIN/NIST) and technical buffer solutions in the common pH levels 4, 7, 9 and 10, some of which are available in trace quality to meet the highest standards. You can also find the right electrodes in our shop; for more information on pH measurement, see the Electrochemistry & pH Measurement category. Any questions about the appropriate calibration interval? We’d be happy to help.
WTW Standard (DIN/NIST) Buffer Solution PL 7, pH 6.865/6.87, PTB/NIST-traceable Calibration Solution in Accordance with DIN 19266-01:2000, ± 0.02 pH, 250 ml, 109120
An electrode that is incorrectly calibrated in the neutral range will introduce a bias into every subsequent measurement, particularly where pH 7, as the zero point of the scale, plays a key role. The WTW Standard (DIN/NIST) buffer solution PL 7 provides a traceable reference for this purpose: a working reference buffer solution in accordance with DIN 19266-01:2000, certified as traceable to PTB/NIST, with an accuracy of ± 0.02 pH at 25 °C. Together with PL 4 and PL 9, it forms the midpoint of a complete, documentable three-point calibration. Standard (DIN/NIST) buffer solution PL 7: higher accuracy class than the technical range The key difference from the ‘technical’ WTW buffer solution range lies in the accuracy class and traceability. The WTW Technical Buffer Solution pH 7 is designed for daily routine calibration and reliably covers everyday laboratory work. The Standard (DIN/NIST) Buffer Solution PL 7 goes one step further: As a working reference buffer solution in accordance with DIN 19266-01:2000, it is certified as PTB/NIST-traceable and specified to ± 0.02 pH at 25 °C. This makes it the ideal choice wherever the calibration itself must be documented and traceable, such as in ISO/IEC 17025-accredited testing laboratories, in pharmaceutical analysis or in metrologically demanding research. Buffer system comprising two phosphate salts PL 7 is based on a mixture of disodium hydrogen phosphate and potassium dihydrogen phosphate as a buffer system and achieves a pH value of 6.87 at 20 °C, stated on the label as pH 6.865 according to DIN or pH 6.87 according to NIST. The density is 1.01 g/cm³, the melting point is -0.3 °C and the boiling point is 100 °C. Under the CLP Regulation, the solution is not classified as a hazardous substance and is not a dangerous good, which simplifies storage, transport and handling in day-to-day laboratory work. Each bottle bears its own batch code with an expiry date, ensuring that the batch used can always be linked to the corresponding test certificate and remains clearly traceable within the documentation of a quality management system. Traceability as part of quality assurance Traceability means that the printed pH value can be traced back through an unbroken chain of reference measurements to the national metrology institutes PTB and NIST. For a testing laboratory accredited to ISO/IEC 17025, this is precisely the difference between a plausible and a robust measurement: not only the electrode itself, but also the reference used to calibrate it, must be documented and traceable. The zero point at pH 7, in particular, affects the entire calibration curve, which is why a traceable, certified buffer is especially important at this point. With PL 7, this requirement can be met directly via the batch identification and the associated test certificate, without the need for additional in-house verifications in the laboratory. Storage and handling Storage in the tightly sealed original container at 15 to 25 °C is recommended. According to TRGS 510, the solution is classified in storage class LGK 12 (non-flammable liquids) and is not considered to pose a risk to water. As PL 7 is neither classified as a hazardous substance nor declared as dangerous goods, no special protective measures are required when opening or dispensing it. Nevertheless, safety goggles with side protection are recommended for the safe handling of the reference solution, and the container should be resealed promptly after use to prevent the reference value from shifting due to evaporation or the absorption of CO2 from the air. Typical applications PL 7 is used wherever the calibration of a pH electrode must not only be ‘adequate’ but also verifiable through documentation: Two- or three-point calibration of pH electrodes in the neutral measuring range, in conjunction with the WTW buffer solutions PL 4 and PL 9 Zero-point adjustment of the pH scale as the central reference point for every calibration routine Traceable calibration in accredited testing laboratories in accordance with ISO/IEC 17025 Quality control in pharmaceutical and active ingredient analysis Calibration prior to the analysis of approximately neutral samples, such as drinking water or cell culture media Research institutions with stringent requirements regarding measurement uncertainty Buffer solutions in accordance with DIN 19266-01:2000 are among the most widely used working reference buffer solutions, as their composition is specified directly in the standard. When PL 7 is used in conjunction with PL 4 and PL 9 for a three-point calibration, this trio covers the entire pH range relevant to practical applications, from acidic through neutral to alkaline, with the same accuracy class and the same traceability to PTB/NIST. This simplifies documentation, as all three calibration points can be included in the same test certificate format. Technical details Trade namePL 7 Buffer systemDisodium hydrogen phosphate, potassium dihydrogen phosphate pH value at 20 °C6.87 (labelling: pH 6.865 according to DIN / pH 6.87 according to NIST) Accuracy± 0.02 pH at 25 °C TraceabilityPTB/NIST StandardDIN 19266-01:2000 Density at 20 °C1.01 g/cm³ Melting point/freezing point-0.3 °C Boiling point100 °C Physical state / Colour / OdourLiquid, colourless, odourless Hazard classification (CLP)Not classified Dangerous goodsNo Storage class (TRGS 510)Class 12 (non-flammable liquids) Recommended storage temperature15-25 °C Container size250 ml Scope of delivery 1 bottle of WTW Standard (DIN/NIST) buffer solution PL 7, 250 ml, with batch number and expiry date Individual requirements and procurement service For a complete three-point calibration, we also stock the WTW Standard (DIN/NIST) buffer solutions PL 4 (pH 4.006/4.01) and PL 9 (pH 9.180/9.18). If you carry out daily routine calibration using the technical accuracy class, you will find the WTW Technical Buffer Solution pH 7 with the same pH value in our range. You can find suitable pH electrodes for calibration in our range of electrodes. Our procurement service is on hand to assist you with additional accessories for your pH measurement technology or with individual procurement enquiries.
Content: 250 ml (€11.60 / 100 ml)
WTW Technical Buffer Solution pH 7, Calibration Standard Series, (50 ml – 1000 ml)
WTW Technical Buffer Solution pH 7 (108802, 108702, 108708), defined as a high-precision electrochemical calibration standard, provides the metrological foundation for the validation of pH measurement chains in pharmaceutical analysis, biotechnology research and industrial quality assurance. In chemical metrology, a pH value of 7.00 represents the electrical zero point (isopotential point) of most commercially available pH electrodes. From a physico-chemical perspective, the effectiveness of this buffer solution is based on a precisely balanced phosphate buffer system consisting of dihydrogen phosphate (H₂PO₄⁻) and hydrogen phosphate (HPO₄²⁻). This system utilises chemical equilibrium to neutralise external acidic or basic influences, thereby maintaining the hydrogen ion activity at a constant level over a wide range. For procurement professionals in the pharmaceutical industry and research, the reliability of this zero point is an essential prerequisite for investment security, as it forms the basis for the linear calculation of the slope across the entire measurement range. Thermodynamics of ion activity and temperature coefficients The thermodynamics of the WTW Technical Buffer Solution pH 7 are characterised by a strictly defined temperature dependence of the dissociation constant. As the pH value is physically defined as the negative decimal logarithm of the H+ activity, changes in temperature affect the chemical equilibrium via the kinetic energy of the system. The TEP 7, TPL 7 and STP 7 variants feature a detailed temperature table, printed on the label, covering the range from 0 °C to 95 °C. This metrological precision is of fundamental importance for modern pH metres with automatic temperature compensation (ATC) in order to calculate the Nernst factor physically correctly and minimise measurement uncertainty. In industrial process analysis, where measurements are often taken far from the standard temperature of 25 °C, this documented temperature coefficient guarantees the full traceability of results to national primary standards. Variant-specific kinetics and application profiles (STP, TPL, TEP) The range of container sizes – 50 ml (STP 7), 250 ml (TPL 7) and 1000 ml (TEP 7) – allows for specific adaptation to the respective laboratory kinetics and sample throughput. The STP 7 variant (108708), supplied in a 50 ml bottle, is ideally designed for mobile field use or for laboratories with low throughput, in order to minimise the time the opened container is left open and thus the risk of carbonation due to atmospheric CO₂. The standard 250-ml TPL 7 (108802) is the universal workhorse for daily routine calibration in university education and research. For high-throughput environments in pharmaceutical production, the 1-litre variant TEP 7 (108702) offers a highly efficient solution for supplying automated calibration stations. Each variant is subject to the same stringent electrochemical specifications, enabling easy scaling of laboratory processes without compromising analytical integrity. Material science of the barrier layer and storage stability A critical quality attribute of the WTW Technical Buffer Solution pH 7 is the chemical composition of the storage containers. The bottles are made of high-density polyethylene (HDPE), which provides an excellent diffusion barrier against atmospheric gases. The ingress of carbon dioxide would physically shift the pH value into the acidic range via the formation of carbonic acid (H₂CO₃), which would lead to significant calibration errors, particularly in the neutral pH range. The stabilised matrix of the WTW buffer solutions also prevents microbiological growth without altering the surface tension of the electrode’s glass membrane. For pharmaceutical buyers, this long-term stability is a key factor in reducing TCO (Total Cost of Ownership), as the solutions exhibit a metrological drift of less than 0.01 pH units over their entire service life, provided that the handling instructions are followed. Electrochemical metrology and compliance in quality assurance Finally, the use of the WTW Technical Buffer Solution pH 7 ensures compliance with the highest regulatory standards, such as GMP, GLP and ISO 17025. When calibrating a measuring chain, the buffer solution is used to determine the asymmetry voltage. The use of technical buffers in accordance with DIN 19267 ensures a high degree of comparability of measured values between different laboratory sites. The solution’s optimised ionic strength reduces the electrode’s response time, which enhances efficiency, particularly in diagnostics and time-critical process controls. By choosing the WTW buffer series, laboratories are investing in a tried-and-tested system solution that harmonises physical excellence with the practical requirements of modern quality management. Technical Details Thermodynamics & Chemical Specifications Nominal pH value (at 25 °C): 7.00 Measurement uncertainty: ± 0.03 pH Buffer system: Phosphate buffer (based on KH₂PO₄ / Na₂HPO₄) Temperature range: 0 °C to 95 °C (with documented table of values) Kinetics: Rapid potential stabilisation through optimised ionic conductivity Metrology & Control Engineering Conformity: Complies with the requirements for technical buffers in accordance with DIN 19267 Traceability: Directly traceable to NIST / PTB primary standards Calibration function: Determination of zero point and asymmetry voltage Stability: Microbiologically stabilised, CO₂-inhibited Materials Science & Variants – Dimensions Container material: High-density polyethylene (HDPE) with barrier properties Variant STP 7 (108708): 50 ml bottle (ideal for field use) Variant TPL 7 (108802): 250 ml bottle (standard size for routine use) Variant TEP 7 (108702): 1000 ml bottle (for high-volume use/automation) Environmental conditions & storage Storage temperature: 15 °C to 25 °C (recommended) Shelf life: Typically 24 months from date of manufacture (depending on batch) Physical state: Liquid, odourless, pH-neutral Contents 1 x WTW Technical Buffer Solution pH 7 (in the selected variant: 50 ml, 250 ml or 1000 ml) 1 x temperature correction table (printed on the label) Important note: Buffer solutions are consumables. To ensure metrological integrity, solution that has been removed must never be returned to the original container. The use of a separate beaker for calibration is physically essential. Individual requirements & accessories For a complete two-point calibration, in addition to the WTW Technical Buffer Solution pH 7, a second standard (e.g. pH 4.01 TPL 4 or pH 10.01 TPL 10) is required to determine the slope of the electrode. For the maintenance of your pH sensors, we also recommend WTW cleaning solutions (e.g. RL 1 for protein removal) and a 3-molar KCl solution for the proper storage of the reference systems. All supplementary standards and maintenance kits are available via our procurement service.
Content: 250 ml (€6.84 / 100 ml)
WTW Technical Buffer Solution TPL 4, 1 bottle of 250 ml: pH 4.01, #108800
WTW Technical Buffer Solution TPL 4, 1 bottle of 250 ml: pH 4.01, #108800
Content: 250 ml (€6.80 / 100 ml)
WTW Technical Buffer Solution TEP 10 Trace, 1 bottle containing 1 L: pH 10.01, #108703
WTW Technical Buffer Solution TEP 10 Trace, 1 bottle containing 1 L: pH 10.01, #108703
Content: 1000 ml (€4.60 / 100 ml)
WTW Standard (DIN/NIST) Buffer Solution PL 4, pH 4.006/4.01, PTB/NIST-traceable Calibration Solution in Accordance with DIN 19266-01:2000, ± 0.02 pH, 250 ml, 109110
Anyone calibrating a pH electrode in an accredited testing laboratory, in pharmaceutical quality control or in research cannot do without a fully traceable reference. The WTW Standard (DIN/NIST) buffer solution PL 4 delivers exactly that: a working reference buffer solution in accordance with DIN 19266-01:2000, which is certified as traceable to both the PTB and NIST and achieves an accuracy of ± 0.02 pH at 25 °C. It thus covers the acidic range of the pH scale and, together with the WTW buffer solutions PL 7 and PL 9, forms the basis for a complete, documentable three-point calibration. Standard (DIN/NIST) buffer solution PL 4: higher accuracy class than the technical range The key difference from the ‘technical’ WTW buffer solution range lies in the accuracy class and traceability. Technical buffer solutions are designed for the daily routine calibration of pH electrodes and reliably cover everyday laboratory work. The Standard (DIN/NIST) buffer solution PL 4 goes one step further: As a working reference buffer solution in accordance with DIN 19266-01:2000, it is certified as PTB/NIST-traceable and specified to ± 0.02 pH at 25 °C. This makes it the ideal choice wherever the calibration itself must be documented and traceable, for example in ISO/IEC 17025-accredited testing laboratories, in pharmaceutical analysis or in metrologically demanding research. Buffer system: potassium hydrogen phthalate PL 4 is based on potassium hydrogen phthalate as the buffer system and achieves a pH value of 4 at 20 °C, stated on the label as pH 4.006 according to DIN or pH 4.01 according to NIST. Its density is 1.01 g/cm³, its melting point is -1.6 °C and its boiling point is 100 °C. Under the CLP Regulation, the solution is not classified as a hazardous substance and is not a dangerous good, which simplifies storage, transport and handling in day-to-day laboratory work. Each bottle bears its own batch code with an expiry date, so that the batch used can be linked to the corresponding test certificate at any time and remains clearly traceable within the documentation of a quality management system. Traceability as part of quality assurance Traceability means that the printed pH value can be traced back through an unbroken chain of reference measurements to the national metrology institutes PTB and NIST. For a testing laboratory accredited to ISO/IEC 17025, this is precisely the difference between a plausible and a robust measurement: not only the electrode itself, but also the reference against which it was calibrated, must be documented and traceable. With PL 4, this requirement can be met directly via the batch identification and the associated test certificate, without the need for additional in-house verifications in the laboratory. Storage and handling Storage in the tightly sealed original container at 15 to 25 °C is recommended. According to TRGS 510, the solution is classified in storage class LGK 12 (non-flammable liquids), is not classified as hazardous to water and, according to the safety data sheet, is considered readily biodegradable. As PL 4 is neither classified as a hazardous substance nor declared as dangerous goods, no special protective measures are required when opening or dispensing it. Nevertheless, for safe handling of the reference solution, safety goggles with side protection are recommended, and the container should be resealed promptly after use to prevent the reference value from shifting due to evaporation or the absorption of CO2 from the air. Typical applications PL 4 is used wherever the calibration of a pH electrode must not only be ‘adequate’ but also verifiable through documentation: Two- or three-point calibration of pH electrodes in the acidic measurement range, in conjunction with the WTW buffer solutions PL 7 and PL 9 Traceable calibration in accredited testing laboratories in accordance with ISO/IEC 17025 Quality control in pharmaceutical and active ingredient analysis Calibration prior to the analysis of acidic samples, such as fruit juices, wine or soil extracts Research institutions with stringent requirements regarding measurement uncertainty Buffer solutions in accordance with DIN 19266-01:2000 are among the most widely used working reference buffer solutions, as their composition is specified directly in the standard. When PL 4 is used in conjunction with PL 7 and PL 9 for a three-point calibration, this trio covers the entire pH range relevant to practical applications, from acidic through neutral to alkaline, with the same accuracy class and the same traceability to PTB/NIST. This simplifies documentation, as all three calibration points can be included in the same test certificate format. Technical details Trade namePL 4 Buffer systemPotassium hydrogen phthalate pH value at 20 °C4 (labelled: pH 4.006 according to DIN / pH 4.01 according to NIST) Accuracy± 0.02 pH at 25 °C TraceabilityPTB/NIST StandardDIN 19266-01:2000 Density at 20 °C1.01 g/cm³ Melting point/freezing point-1.6 °C Boiling point100 °C Physical state / Colour / OdourLiquid, colourless, odourless Hazard labelling (CLP)Not classified Dangerous goodsNo Storage class (TRGS 510)Class 12 (non-flammable liquids) Recommended storage temperature15-25 °C Container size250 ml Scope of delivery 1 bottle of WTW Standard (DIN/NIST) buffer solution PL 4, 250 ml, with batch number and expiry date Individual requirements and procurement service For a complete three-point calibration, we also stock the WTW Standard (DIN/NIST) buffer solutions PL 7 (pH 6.865/6.87) and PL 9 (pH 9.180/9.18). If you carry out daily routine calibration using the technical accuracy class, you will find the WTW Technical Buffer Solution TPL 4 with the same pH value in our range. You can find suitable pH electrodes for calibration in our range of electrodes. Our procurement service is on hand to assist you with additional accessories for your pH measurement technology or with individual procurement enquiries.
Content: 250 ml (€11.60 / 100 ml)
WTW Standard (DIN/NIST) Buffer Solution PL 9, pH 9.180/9.18, PTB/NIST-traceable Calibration Solution in Accordance with DIN 19266-01:2000, ± 0.02 pH, 250 ml, 109130
In the alkaline measuring range, a pH electrode requires the same traceable calibration point as in the acidic and neutral ranges. The WTW Standard (DIN/NIST) buffer solution PL 9 provides a working reference buffer solution in accordance with DIN 19266-01:2000, certified as traceable to PTB/NIST, with an accuracy of ± 0.02 pH at 25 °C. It thus complements PL 4 and PL 7 as the third point in the three-point calibration. Unlike the other two stages in the range, PL 9 also requires hazardous substance labelling; please refer to the separate section below. Standard (DIN/NIST) buffer solution PL 9: higher accuracy class than the technical range The key difference from the ‘technical’ WTW buffer solution range lies in the accuracy class and traceability. Technical buffer solutions are designed for daily routine calibration and reliably cover everyday laboratory work. The Standard (DIN/NIST) buffer solution PL 9 goes one step further: As a working reference buffer solution in accordance with DIN 19266-01:2000, it is certified as PTB/NIST-traceable and specified to ± 0.02 pH at 25 °C. This makes it the ideal choice wherever the calibration itself must be documented and traceable, such as in ISO/IEC 17025-accredited testing laboratories, in pharmaceutical analysis or in metrologically demanding research. Traceability as part of quality assurance Traceability means that the printed pH value can be traced back through an unbroken chain of reference measurements to the national metrology institutes PTB and NIST. For a testing laboratory accredited to ISO/IEC 17025, this is precisely the difference between a plausible and a robust measurement: not only the electrode itself, but also the reference against which it was calibrated, must be documented and traceable. With PL 9, this requirement can be met directly via the batch identification and the associated test certificate, without the need for additional in-house verifications in the laboratory. Buffer system: disodium tetraborate decahydrate (borax) PL 9 is based on disodium tetraborate decahydrate (borax, CAS 1303-96-4, concentration 0.3-<1 % in the mixture) as a buffer system and achieves a pH value of 9.18 at 20 °C, stated on the label as pH 9.180 according to DIN or pH 9.18 according to NIST. The density is 1 g/cm³, the melting point is 0 °C, the boiling point is 100 °C, and the dynamic viscosity at 20 °C is 0.952 mPas. Each bottle bears its own batch code with an expiry date, ensuring that the batch used can be linked to the corresponding test certificate at any time and remains clearly traceable within the documentation of a quality management system. Hazard labelling in accordance with GHS/CLP Unlike PL 4 and PL 7, PL 9 is classified as Repr. 1B under Regulation (EC) No 1272/2008 due to its content of disodium tetraborate decahydrate. The labelling comprises the hazard pictogram GHS08, the signal word ‘Danger’ and the hazard statement H360FD: ‘May impair fertility. May cause harm to the unborn child.’ Precautionary statements: P280 (Wear protective gloves/protective clothing/eye protection/face protection), P308+P313 (If exposed or affected: seek medical advice/attention) and P405 (keep locked up). The hazard-determining ingredient, disodium tetraborate decahydrate (CAS 1303-96-4), is also listed as a substance of very high concern (SVHC) in accordance with Article 57 of REACH, although it is present in the mixture only in a concentration of 0.3 to less than 1 per cent. The product is intended exclusively for professional users. Before use, refer to the safety data sheet, in particular the information on protective equipment and first-aid measures. Storage and handling It is recommended to store the product in the original, tightly sealed container at 15 to 25 °C, kept under lock and key in accordance with P405. According to TRGS 510, the solution is assigned to storage class LGK 6.1D, in contrast to storage class LGK 12 for the unclassified PL 4 and PL 7. For handling, the safety data sheet recommends protective gloves made of nitrile rubber with a material thickness of at least 0.11 mm and a breakthrough time of 480 minutes, as well as safety goggles with side protection. Respiratory protection is only required if aerosols or mists form. The product is non-flammable and is not classified as a dangerous good under the relevant transport regulations (ADR/RID/ADN/IMDG/IATA). Typical applications PL 9 is used wherever the calibration of a pH electrode in the alkaline range must not only be ‘adequate’ but also verifiable through documented evidence: Two- or three-point calibration of pH electrodes in the alkaline measuring range, in conjunction with the WTW buffer solutions PL 4 and PL 7 Traceable calibration in accredited testing laboratories in accordance with ISO/IEC 17025 Quality control in pharmaceutical and active ingredient analysis Calibration prior to the analysis of alkaline samples, such as cleaning solutions or certain process waters Research institutions with stringent requirements regarding measurement uncertainty Buffer solutions in accordance with DIN 19266-01:2000 are among the most widely used working reference buffer solutions, as their composition is specified directly in the standard. When PL 9 is used in conjunction with PL 4 and PL 7 for a three-point calibration, the trio covers the entire pH range relevant to practical applications, from acidic through neutral to alkaline, with the same accuracy class and the same traceability to PTB/NIST. As PL 9 is the only one of the three grades to be classified as a hazardous substance, care should be taken to note the different storage class, LGK 6.1D, when ordering and storing the calibration set together. Technical details Trade namePL 9 Buffer systemDisodium tetraborate decahydrate (borax), CAS 1303-96-4, concentration 0.3-<1 % pH value at 20 °C9.18 (labelled: pH 9.180 according to DIN / pH 9.18 according to NIST) Accuracy± 0.02 pH at 25 °C TraceabilityPTB/NIST StandardDIN 19266-01:2000 Density at 20 °C1 g/cm³ Melting point/freezing point0 °C Boiling point100 °C Dynamic viscosity at 20 °C0.952 mPas Physical state / Colour / OdourLiquid, colourless, odourless Classification (CLP)Repr. 1B Hazard pictogramGHS08 Hazard statementDanger Hazard statement (H-phrase)H360FD: May impair fertility. May harm the unborn child. Precautionary statements (P-phrases)P280, P308+P313, P405 SVHC listing (REACH Art. 57)Yes, disodium tetraborate decahydrate, CAS 1303-96-4 Dangerous goodsNo Storage class (TRGS 510)LGK 6.1D Recommended storage temperature15-25 °C Container size250 ml Scope of delivery 1 bottle of WTW Standard (DIN/NIST) buffer solution PL 9, 250 ml, with batch number and expiry date Individual requirements and procurement service For complete three-point calibration, we also stock the WTW Standard (DIN/NIST) buffer solutions PL 4 (pH 4.006/4.01) and PL 7 (pH 6.865/6.87). For the alkaline range of the technical accuracy class, we also stock the WTW Technical Buffer Solution TPL 10 Trace (pH 10.01). You will find suitable pH electrodes for calibration in our range of electrodes. Our procurement service is on hand to assist you with additional accessories for your pH measurement technology or with individual procurement enquiries.
Content: 250 ml (€11.60 / 100 ml)