A multilaboratory-evaluated reference method for the determination of serum sodium.

We carried out a statistically designed, multilaboratory study to evaluate a flame atomic emission spectroscopic (FAES) method for serum sodium as a Reference Method. definitive values for the serum pools for the study, with sodium in the 110-160 mmol/L range, were determined at the National Bureau of Standards by an ion-exchange/gravimetry method. The multilaboratory FAES results were judged against the preselected performance criteria for the Reference Method: maximum imprecision 1.5 mmol/L, maximum bias 2.0 mmol/L. The standard error of a single laboratory's performance of the method varied with concentration from 0.46 to 0.86 mmol/L with a maximum bias of 1.0 mmol/L; thus, the criteria were satisfied. The cooperating laboratories performed the method with either manual or semi-automated pipetting. Although both modes of pipetting satisfied our acceptability criteria, only the method with semi-automated pipetting is described here as the Reference Method. The statistical results indicate that the precision criterion can be fulfilled with fewer than four replicate analyses.

Polarization Effects on Fluorescence Measurements.

Polarization effects on fluorescence measurements are a function of four independent variables. The first is F, the polarization ratio of the exciting light which reaches the sample. The second is r, the emission anisotropy of the sample, which is the polarization "response" of the sample to plane polarized exciting light. The third is G, the polarization ratio of the emission detection system, which is the ratio of the sensitivities of the detection system to vertically and horizontally polarized light. The fourth is α the viewing angle, which is the angle bet ween the direction of the propagation of the exciting light and the direction from which the emission is being detected. The intensity and the degree of polarization of the fluorescence emission that the sample exhibits are functions of F, r, and a, while the actual readings obtained with a typical spectrofluorimeter are functions of all four variables, F, r, α, and G. A theoretical analysis is made taking all these factors into account, and proper mathematical models are developed for the different modes of operation in which a fluorimeter can be used. These are verified experimentally with data obtained for a sample which has a high degree of emission anisotropy (Nile Blue A Perchlorate in glycerol). A recently designed goniospectrofluorimeter was used. Calibration procedures are developed and recommendations are made for modes of operation and fluorescence standards.

Considerations on Organic Compounds in Solution and Inorganic Ions in Glasses as Fluorescent Standard Reference Materials.

The use of various organic compounds in solution and inorganic ions in glasses has been investigated as possible fluorescence Standard Reference Materials. Emphasis was placed on measuring physical and chemical parameters such as stability, reproducibilities of absorbance and fluorescence measurements, relative quantum efficiencies as a function of excitation wavelength, etc., for quinine derivatives and selected organic compounds. A brief discussion is included on the use of rare earth and non-rare earth inorganic ions in glasses as standards.