Sodium analysis

Na[Sb(OH)g], respectively. The latter compound is one of the least soluble sodium salts known and is useful in sodium analysis. Numerous polyantimonate(V) derivatives are prepared by heat treatment of mixtures of antimony trioxide and other metal oxides or carbonates. Of these, K Sb O [12056-59-6] and K Sb O [52015-49-3] have been characterized by x-ray. These consist of three-dimensional networks of SbO in which corners and edges are shared with K" ions located in tunnels through the network (23). Simple species such as SbO and Sb20 2, analogous to orthophosphate and pyrophosphate, apparendy do not exist. 

Check for the presence of caustic in the fuel by sodium analysis or by pH determination. 

According to the analysis supplied by Linde, the rare earths were predominantly lanthanum. An independent sodium analysis agreed with that supplied by Linde. 

To measure the volume of the Sephadex at equilibrium the equilibrated samples were contained in a calibrated tube (0.1 mL/division). An apparent volume was obtained from visual observation of the boundary defined by the layer to obtain the true volume an aliquot of the equilibrated solution phase was analysed for sodium by flame photometry. Most of the supernatant solution was then removed until 2.0 zt 0.025 mL of solution remained above the gel-defined boundary. Exactly 1.00 mL of water was added and the mixture was stirred sufficiently to assure a homogeneous aqueous phase. The solution phase was sampled immediately for sodium analysis with the flame photometer. From the observed dilution of the aqueous phase the true volume of the Sephadex gel at equilibrium was obtained. A correction for the matrix volume was based on the monomeric molecular weight of the Sephadex ( 220 25 capacity of 4.5 0.5 meq/dry g). In our samples, which contained about 88% water or 0.12 g acid/g sample, a volume of about 0.13/g is estimated for the matrix by assuming a density of approximately 0.9 for the dehydrated Sephadex. 

Stock solutions were made by dissolving about 100 mg samples from the decomposition residues of sodium alkoxides in dilute hydrochloric acid and distilled water. Necessary dilutions were made by taking aliquot from these stock solutions and used for sodium analysis using AES as explained previously. 

One way to reduce the effect of drift and to give very reproducible sample handling is to use flow-injection analysis (FLA). PVC membranes incorporating the methylketone and methyl ester derivatives were assessed as detectors in a FIA system for blood sodium analysis and the results demonstrated that the bias described above could be greatly reduced while still maintaining excellent correlation [13]. 

However, the best results were presented in a series of papers where the methylester tetramer was used as an element in an ISE array both in conventional dip-type measurements [14] and in a flow-injection analysis system [15,16]. Using sophisticated calibration and sensor modelling techniques, these papers rigorously demonstrated that the methylester tetramer (Table 1,2) could be applied to blood sodium analysis with excellent results (Figure 3). Furthermore, the same ISE was shown to be suitable for the analysis of sodium in mineral water samples. 

Fig. 3. Plasma sodium analysis results obtained with a PVC membrane electrode based on 1 compared with a SMAC analyser. The electrode was part of an array of ISEs which were carefully calibrated before use. Bias in the results was eliminated through the use of a flow-injection analysis (FIA) approach which enabled the entire sample handling and analysis to be automated. These results demonstrate clearly the successful application of calix[4]arene-based ISEs to this important assay (from reference [15] with permission).

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