Stability, Storage, Handling and Temperature Effects of Calibration Solutions

Proper stability, storage, handling, and temperature control are essential for maintaining the accuracy of calibration solutions. Learn how stability, storage, handling, and temperature effects apply to Hamilton liquid calibration solutions and how these aspects relate to Hamilton's ISO 17034‑certified liquid solutions used in regulated and measurement‑critical applications.

Stability & Homogenity

Long‑term stability is a key requirement for pH buffer solutions and conductivity standards used for sensor calibration in regulated environments. Conventional technical buffer solutions have a limited shelf-life, most of them only one year in sealed bottles. Once opened, their shelf life is reduced to a few months. Especially alkaline buffer solutions, which are affected by CO2 contamination from the atmosphere.

DuraCal pH buffer solutions from Hamilton are different. These buffer solutions provide a pH stability never achieved before; their high accuracy is guaranteed for up to 5 years after the date of manufacture. Hamilton DuraCal pH buffers will maintain their published accuracy (±0.01pH or ±0.02pH) during their expiry period, even after the bottle has been opened to air. Each bottle of Hamilton buffer solutions is certified, including the actual pH value and expiration date. The certification is traceable to primary standards from NIST and PTB.

Hamilton ph buffer stability — Stability comparison of Hamilton alkaline buffer to conventional alkaline buffer

Please note that this assumes that good laboratory practices are followed. Exposure to dust or other external contaminants should be avoided. If using glassware for calibration, then both the glassware and the sensor should be properly cleaned prior to use. Hamilton offers a cleaning solution set (Ref 238290) specifically designed for this purpose. After cleaning, a final rinse with deionized water should be applied to avoid contamination of the buffer solution.

The National Institute of Standards and Technology (NIST) recommends nine different buffer solutions for the exact calibration of pH measurement systems. These buffer solutions also serve as reference points for the pH scale, as it is impossible to prove the activity of single hydrogen ions by measurement.

pH Values of Standard Buffer Solutions According to NIST

NBS	A	B	H	C	D	E	F	I	G
Temp (°C)	Potassium tetra‑oxalate	Potassium hydrogen tartrate	Potassium dihydrogen citrate	Potassium hydrogen phthalate	Phosphate (D)	Phosphate (E)	Borax	Sodium carbonate / sodium hydrogen carbonate	Calcium hydroxide
0	–	–	3.863	4.010	6.984	7.534	9.464	10.137	13.423
5	1.668	–	3.840	4.004	6.951	7.500	9.395	10.245	13.207
10	1.670	–	3.820	4.000	6.923	7.472	9.332	10.179	13.003
15	1.672	–	3.802	3.999	6.900	7.448	9.276	10.118	12.810
20	1.675	–	3.788	4.001	6.881	7.429	9.225	10.062	12.627
25	1.679	3.557	3.776	4.006	6.865	7.413	9.180	10.012	12.454
30	1.683	3.552	3.766	4.012	6.853	7.400	9.139	9.966	12.289
35	1.688	3.549	3.759	4.021	6.844	7.389	9.102	9.925	12.133
38	1.691	3.548	3.755	4.027	6.840	7.384	9.081	9.903	12.043
40	1.694	3.547	3.753	4.031	6.838	7.380	9.068	9.889	11.984
45	1.700	3.547	3.750	4.043	6.834	7.373	9.038	9.856	11.841
50	1.707	3.549	3.749	4.057	6.833	7.367	9.011	9.828	11.705
55	1.715	3.554	3.750	4.071	6.834	–	8.985	–	11.574
60	1.723	3.560	3.753	4.087	6.836	–	8.962	–	11.449
70	1.743	3.580	3.763	4.126	6.845	–	8.921	–	–
80	1.766	3.609	3.780	4.164	6.859	–	8.885	–	–
90	1.792	3.650	3.802	4.205	6.877	–	8.850	–	–
95	1.806	3.674	3.815	4.227	6.886	–	8.833	–	–

Temperature Dependence

The value is based on a reference temperature of 25 °C. Changes in ambient temperature will affect the buffer’s pH and must be accounted for during calibration. The label on the bottle provides information for expected pH, ORP, and conductivity values as a function of temperature.

For detailed temperature correction data, Hamilton publishes the temperature dependence of DuraCal pH buffers in 1 °C increments. Equivalent temperature-dependent data are also available for conductivity standards, where temperature significantly affects measured values. Similarly, correct ORP buffer characterization and stability are essential for achieving reliable redox potential measurements.

Certifications and Documentation

A QR code on the bottle leads to the Certificate of Analysis (CoA) and the Safety Data Sheets. Eliminating printed certificates is, alongside the optimized packaging, another step toward greater sustainability through digitalization, reduced material use, and improved efficiency. These documents support the use of Hamilton calibration solutions in regulated and quality‑critical environments.

Different Vessel Sizes

Our wide range of container sizes, allows you to choose the buffer ideally tailored to your worklflow and consumption.

The Calpack bottle is specifically designed to avoid contamination issues. A light squeeze of the bottle allows fresh buffer solution to flow into the specially designed calibration chamber at the top of the bottle. A one-way valve separates the chamber from the buffer below. This design prevents users from recycling buffer back into the bottle, as well as limits any contamination from the sensor reaching the fresh buffer in the bottle below. Additionally, calibration can now be performed within the chamber without the need for a separate beaker, further removing contamination risk. Calpack bottles are used for 250 and 500mL DuraCal buffer solutions.

Storage Conditions

The stated stability and accuracy data are based on the assumption that specified storage conditions are maintained:

5–35 °C (41–95 °F) and a relative storage humidity of 20–80 %

Calibration solutions should not be subjected to extraordinary stress, such as direct sunlight or contamination, to preserve their certified performance.

Metrological Competence and Support of Hamilton

We not only provide top-notch products but also ensure that our customers receive the highest level of support, expert guidance, and hands-on training. Our services include comprehensive training in handling, calibration, and verification procedures, enabling you to operate with confidence, accuracy, and efficiency throughout the entire product lifecycle.