Precipitate knotted reactors

Cd precipitation in a knotted reactor was studied with a 3-variable full design... 

In-line filtration without a filtering element is also feasible. To this end, a three-dimensional reactor [299], also called a knitted or knotted reactor (see 6.2.3.4), can be used, as emphasised in the landmark article reporting the flow injection determination of lead in blood and bovine liver by flame atomic absorption spectrometry [300]. The analyte was co-precipitated the complex formed was retained on the inner walls of a knitted reactor and then released by isobutyl methyl ketone and transported to the detector. Interference from iron(III) at high concentrations was circumvented, sensitivity was markedly improved and precise results were obtained. This innovation was recently exploited to remove organic selenium and determine the speciation of inorganic selenium in a flow-injection system with atomic fluorescence spectrometric detection [301]. 

The advantages of the knotted reactor precipitate collector may be summarized as follows ... 

The foregoing list included almost all the required features of an ideal precipitate collector mentioned in Sec. 7.2.1, except at the moment it may not be applicable to all forms of precipitate, particularly those with a hydrophylic nature. However, much remains to explored in the material of the reactor, and in the types of precipitate which are applicable with the present design. Even during the preparation of this manuscript, dithizone and APDC were added to the list of complexing agents which produced precipitates suitable to be processed in coprecipitation procedures using the knotted reactor... 

Fig.7.6 FI manifold and main operation sequences for on-line coprecipitation ETAAS determination of Cd with the Fe(U)-HMDTC/IBMK system, a, delivery of stored concentrate (from previous sample) b, precipitation of sample with HMA-HMDTC c, washing of precipitate with aqueous solution of HMA-HMDTC and d, precipitate dissolution by IBMK. Pi, P2, peristaltic pumps KR, knotted reactor, B, solvent displacement bottle V, 4 5 channel injector valve C, PTFE concentrate collector tube (60 /xl) GF, graphite furnace and W, waste [23].

Lead, cadmium and other trace metals are coprecipitated from blood and urine matrices and collected on-line on the tube walls of a knotted reactor. Iron(Il), formed by reduction of iron(IIl) using ascorbic acid, is used as a coprecipitation carrier to form a black precipitate with HMDTC. Therefore, 200 mg 1 iron are added to all sample digests to provide a minimum iron concentration. The collected precipitate is subsequently dissolved by IBMK and transported to the flame atomizer of an AAS system. The method features high sensitivity and sample throughput with high tolerance to the principle matrix interferents, including iron and copper. 

Fig.9.4 FI manifold for the FAAS determination of lead and cadmium in blood and urine by on-line coprecipitation, a. sample loading (precipitate collection) sequence b. precipitate dissolution sequence. P, P2, peristaltic pumps V, 4 5 channel injector valve S. sample KR. knotted reactor precipitate collector and W. waste 1.2).

Flow-injection online preconcentration and separation with ion exchange or sorbent extraction in packed microcolumns and/or precipitation and collection in knotted reactors has proved to extend the capabilities of ET-AAS by allowing relative detection limits to be lowered by two to three orders of magnitude and troublesome matrices to be removed. 

Figure 5.11 Steps followed for analyte preconcentration by precipitation with a knotted reactor in ICP-MS.

Yan, X.-P, Kerrich, R., and Hendry, M. J. (1999) Row injection on-line group preconcentration and separation of (ultra)trace rare earth elements in environmental and geological samples by precipitation using a knotted reactor as a filterless collector for inductively coupled plasma mass spectrometric determination. J. Anal. At. Spectrom., 14,215-21. 

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