Injection technique high salt content

Clearly, trouble-free universal methods are the ideal for trace analysis of oxide materials. Numerous materials can only be dissolved via melting fusion they then cannot be diluted overmuch and therefore contain a relatively high salt content. However, many laboratories are not yet equipped with furnace atomisers so the flame method must be used. 

During trace analytical analyses with the flame technique a separation and therefore concentration, e.g. via ion exchange, can be introduced if the concentrations during normal sample preparation are likely to be below the detection limit of the instrument [92], 

The direct use of the Hoesch injection technique is useful for trace analysis of oxide substances after fusion [31, 99, 142]. It is possible to take up the fused substance in small quantities (max. 10 ml, usually 1 ml). It is best to use an acid mixture which contains 400ml HC1 (6 = 1.15gml-1) and 40g citric acid in 1000 ml. Generally, 10 pi, and in special cases 50 pi, of the analytical solution are injected. It is thus possible to determine all important ascertainable elements in 1 ml of analytical solution several times over. Salt concentrations of 100 mg ml-1 are no problem for the injection technique. 

The following general methods can also be recommended for the analysis of almost all oxide products. 

A combination of the rapid procedures of spectroscopy and corresponding control methods is presently the only analytical procedure with the necessary precision and accuracy and at a reasonable cost. In the field discussed AAS is an essential technique for routine work. 

---

The flow injection AAS system with online preconcentration will challenge the position of the graphite furnace technique, because it yields comparable sensitivity at much lower cost by using simpler apparatus and separation mode. The method offers unusual advantages when matrices with high salt content (e.g., seawater) are analysed, because the matrix components do not reach the nebuliser. 

Statistical data on the analysis of oxide products should be based on the same criteria as for iron and steel analysis. Reproducibility limits of about 1—2rel.% are valid in the case of direct analysis with A AS. The use of the injection technique leads to reproducibilities of 2—5rel.% for high salt content and 10—20rel.% for the graphite tube technique (low salt content) used as a trace method. 

If the total salt content of a solution is high or if only small amounts of sample are available the injection technique may be used. If a piston burette is used for the injection, individual errors cannot be avoided, and reproducibility becomes somewhat poorer than with continuous aspiration. Also, the uncertainty of the volume measurement with small injection volumes becomes noticeable in the reproducibility. In Table 4 the data and statistical values of a simultaneous copper and nickel determination are shown. 

---