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

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.