Republication or reproduction of this report or its storage and/or dissemination by electronic means is permitted without theAbstract: The definition of a "primary method of measurement" [1] has permitted a full consideration of the definition of primary standards for pH, determined by a primary method (cell without transference, Harned cell), of the definition of secondary standards by secondary methods, and of the question whether pH, as a conventional quantity, can be incorporated within the internationally accepted system of measurement, the International System of Units (SI, Système International d'Unités). This approach has enabled resolution of the previous compromise IUPAC 1985 Recommendations [2]. Furthermore, incorporation of the uncertainties for the primary method, and for all subsequent measurements, permits the uncertainties for all procedures to be linked to the primary standards by an unbroken chain of comparisons. Thus, a rational choice can be made by the analyst of the appropriate procedure to achieve the target uncertainty of sample pH. Accordingly, this document explains IUPAC recommended definitions, procedures, and terminology relating to pH measurements in dilute aqueous solutions in the temperature range 5-50 °C. Details are given of the primary and secondary methods for measuring pH and the rationale for the assignment of pH values with appropriate uncertainties to selected primary and secondary substances.

We review the performance of various nanoscaled structures needed to support the propagation of the surface plasmons responsible for surface-enhanced Raman scattering (SERS), and assess the potential for the optimisation of the compromise between enhancement and reproducibility that they provide, and hence their utility for relevant applications. We divide these nanostructures into those comprising structured arrays of discrete nanoparticles in two or three dimensions, and those comprising structured or regularly patterned surfaces in two or three dimensions. The most promising in terms of this compromise are those that involve the tethering of functionalised metal nanoparticles to surfaces. They are not only reproducible, but the functionalisation provides a measure of selectivity to relevant target analytes that the majority of SERS applications require.

Primary methods of measurement play an important role in metrology because they provide the essential rst link in the chain of traceability from the abstract de nition of a unit of the International System of Units (SI) to its practical use in measurement. A de nition of a primary method of measurement has been developed by the Consultative Committee for Amount of Substance (CCQM) that distinguishes between those methods that measure a quantity directly and those that measure the ratio of two quantities. Methods that do not ful l the de nition of being primary also play an important role in measuring amount of substance. In some cases, it is appropriate to refer to these as secondary methods.

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Republication or reproduction of this report or its storage and/or dissemination by electronic means is permitted without the Measurement of pH. Definition, standards, and procedures (IUPAC Recommendations 2002)Abstract: The definition of a "primary method of measurement" [1] has permitted a full consideration of the definition of primary standards for pH, determined by a primary method (cell without transference, Harned cell), of the definition of secondary standards by secondary methods, and of the question whether pH, as a conventional quantity, can be incorporated within the internationally accepted system of measurement, the International System of Units (SI, Système International d'Unités). This approach has enabled resolution of the previous compromise IUPAC 1985 Recommendations [2]. Furthermore, incorporation of the uncertainties for the primary method, and for all subsequent measurements, permits the uncertainties for all procedures to be linked to the primary standards by an unbroken chain of comparisons. Thus, a rational choice can be made by the analyst of the appropriate procedure to achieve the target uncertainty of sample pH. Accordingly, this document explains IUPAC recommended definitions, procedures, and terminology relating to pH measurements in dilute aqueous solutions in the temperature range 5-50 °C. Details are given of the primary and secondary methods for measuring pH and the rationale for the assignment of pH values with appropriate uncertainties to selected primary and secondary substances.