Delves cup

1 Delves Cup. The Delves cup method was first introduced by Delves for the determination of lead in blood samples. The method may be used for the determination of volatile elements such as Ag, As, Bi, Cd, Se, Te, Tl, and Zn. 

The sample amount required is very small and detection limits are lower than by conventional FAAS (Table 16). However, the reproducibility is not good and hence its most common use has been as a readily applied screening method. 

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Amongst other devices used to produce the required atoms in the vapour state are the Delves cup which enables the determination of lead in blood samples the sample is placed in a small nickel cup which is inserted directly into an acetylene-air flame. The tantalum boat is a similar device to the Delves cup in this case the sample is placed into a small tantalum dish which is then inserted into an acetylene-air flame. The use of these devices, especially for small sample volumes, has now been largely superseded by the graphite furnace. 

Daniell cell 64 d.c. arc source 763, 771 Dead-stop end points 635 Decantation 119 Decomposition potential 504 Degreasing agent 80 Delves cup 788 Demasking agents 312, 334 Densitometers 231, 232 Depolariser anodic, 515 cathodic, 509... 

Determination of lead in blood by Delves-cup AAS. Both weighted and unweighted curves of best fit are shown. 

In 1970, Delves15 described the use of 10 mm diameter nickel metal foil micro-crucibles for the atomization of lead in blood samples, after a partial pre-oxidation with hydrogen peroxide at 140 °C. The technique, which became widely known as the Delves Cup Technique , was extensively used for more than a decade in many laboratories around the world, and was also applied to environmental analyses such as the determination of lead in water. A flame-heated nickel tube was again used to overcome the reproducibility problems otherwise caused by the variability in the construction of individual disposable cups. 

The more recent success achieved with Delves cup and heated graphite sources for microsample applications in AAS has widened the applicability of AAS to include major-element analysis of microsamples and trace-element analysis of macrosamples. The range of sensitivities now available affords relatively easy analysis of samples of airbpme materials over the full range of concentrations important in studies of air pollution and occupational health problems. 

Transfer 10 )li1 of the blood sample to a 10x5 mm nickel crucible (Delves cup), add 10 jiil of water, and heat at 150° for 1 minute or until sputtering occurs. Add 20 li1 of strong hydrogen peroxide solution, and evaporate to dryness at 150°. Place the cup in the air-acetylene flame and imder the nickel absorption tube, and record the absorbance at 217 nm. The correct positioning of the cup is crucial. Repeat the procedure using a series of nickel crucibles containing, individually, 10 ll1 of the pooled normal blood and 10 p, of each diluted standard solution. 

The so-called Delves cup method was applied in many laboratories for PbB determination before the graphite furnace technique reached its highly developed present stage. The method was published by Delves (1970) and at that time it was one of the first reliable micro methods requiring only very small amounts of blood. It has been adopted by several authors for the analysis of capillary blood as well as for lead determinations on disks punched from filter paper previously spotted with a drop of blood (Cernik and Sayers, 1971 Cernik, 1974 Delves, 1977). 

El. Ediger, R. D., and Goleman, R. L., A modified Delves cup atomic absorption procedure for the determination of lead in blood. At. Absorption Newslett. 11, 33-36 (1972). 

The multislot or Boling burner gives a wide atom vapour which completely surrounds the radiation signal from the radiation source. Thus, the outer mantel of the flame protects the inner part of the flame against atmospheric air. The multislot burners are employed with the Delves-cup and boat methods (so called semiflame methods). 

A number of methods have been described for improving the sensitivity of conventional FAAS in order to allow the analysis without resorting to more expensive techniques. Best known of these techniques are hydride generation, cold vapour, semi-flame (Delves cup, tantalum boat), and slotted tube atom trap (STAT) methods. 

Table 16 Detection limits for some elements by the Delves cup method (A), and by the sampling boat method (B)...

Sampling Boat. The sampling boat method is even more simple than the Delves cup method. A sample is added to a narrow, deep and long boat (5 cm in length and 2 mm in width). The boat is made of tantalum because of its resistance to heat and good conductivity. A multislot burner is preferred as it heats the boat more uniformly and produces a smooth flow of the combustion gases around the sample. A simple device is made to enable the boat to be loaded about 10 cm away from the flame, then pushed close to the flame to dry the sample, and finally placed in the correct position within the flame. 

The sampling boat method can be applied to the same volatile elements as the Delves cup method (Table 16). 

FIGURE 10-22. Diagram of the Delves cup technique for vaporizing solid samples. 

Application of the Delves cup technique to other metals in aqueous solution has been investigated by Kerber and Fernandez, who found the method useful particularly with metal elements of relatively high volatility. Matrix effects were not studied sufficiently to draw any general conclusions about their effects. Table 10-3 presents absolute detection limits for a series of elements using the Delves cup technique to volatilize the samples. 

Absolute Detection Linnits for a Series of Elements Using the Delves Cup Technique"... 

In international intercomparison programs for the determination of Cd-B and Cd-U, GFAAS was by far the most used method [49,57]. This was also concluded in a review about Cd-B [50]. Other methods used for Cd-B were flame atomic absorption spectrometry (FAAS) with Delves cup [51] or punched paper disk [52], and differential pulse anodic stripping voltammetry (DPASV) [53]. Other methods used for Cd-U were FAAS with Delves cup [51], flame atomic fluorescence spectrometry [58], and DPASV after wet digestion [59]. For Cd-U in the past many modifications of the GFAAS method existed, e.g., extraction with ammonium pyrrolidine dithiocarbamate (APDC) or another compound [60,64], with ammonium dihydrophosphate and Triton-X [61], with diammonium hydrophosphate and nitric acid [62], with water dilution or direct [54,63], and with nitric acid dilution [54,65-67]. 

As compromises between flame and flameless atomization techniques the Delves cup and sample boat methods have been developed (Fig.6.63). In the first of these two techniques the sample is kept in a small cup made of nickel. It is introduced into the flame of an ordinary atomic absorption slit burner. The sample is vaporized and passes through a hole into a nickel... 

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