Francisco J. Krug

Merging zones in flow injection analysis

Abstract A double proportional injector is described, and an improvement of the continuous flow-injection method is discussed. Sample and reagent are both injected into an inert carrier stream; the reagent is consumed only in the presence of the sample, and can otherwise be recovered continuously. The main characteristics of the flow injection system, e.g. high sampling rate and good accuracy, precision and sensitivity, are maintained. The proposed system is compared with other flow-injection systems suggested earlier. The determination of phosphate in plant material by the molybdenum blue flowinjection method was chosen to demonstrate the feasibility of the system; the consumption of ascorbic acid is only 9% of that in the original method.

Zone-sampling processes in flow injection analysis

Abstract In flow injection analysis, it is possible to select a small portion of a dispersed zone and inject it into another carrier stream. The potentialities of such zone-sampling processes are discussed, and the main factors involved are investigated by spectrophotometric measurements. The usefulness of zone sampling in routine work is demonstrated in the atomic absorption spectrometry of potassium in plant digests. The simple system, which provides automatic dilution, allows analysis of 120 samples per hour, although the required sample dispersion factor was 0.0076; the results agreed with those obtained by conventional a.a.s. after hundredfold manual sample dilution.

Commutation in flow injection analysis

Abstract Recent advances in flow injection analysis, including the introduction of zone-sampling and zone-trapping processes and the incorporation of ion exchangers, have involved electronically operated injector/commutators. Other techniques based on manual commutation, such as manifold modifications and intermittent and alternating streams, have been reported. A comprehensive review of these techniques is given. The use of commutation for difference injection procedures (loop-based, time-based, hydrodynamic, sequential and nested injection) is emphasized. An alternative stopped-flow approach without stopping the pump is suggested.

Rapid determination of sulphate in natural waters and plant digests by continuous flow injection turbidimetry

The turbidimetric determination of sulphate as barium sulphate has been adapted to the continuous flow injection procedure of Růžicka and co-workers. The effects of reagent composition, reagent flow-rates and length of mixing coils have been investigated. Optimum conditions were established for the determination of sulphate in natural waters and in plant digests. The results agree satisfactorily with those obtained by a standard turbidimetric method and analyses can be carried out at a rate of up to 180 samples per hour.

Merging zones in flow injection analysis: Part 2. Determination of Calcium, Magnesium and Potassium in Plant Material by Continuous Flow Injection Atomic Absorption and Flame Emission Spectrometry

Abstract A flow-injection analysis system is described for the automatic determination of calcium, magnesium and potassium in plant material by atomic absorption and flame emission Spectrometry. Flow rates and damping factors were studied; the sample undergoes a dispersion of ca. 40-fold with automatic incorporation of lanthanum when necessary. The proposed method allows 300 determinations per hour with a typical relative standard deviation of 0.5% and a reagent consumption of only 500 μg of lanthanum per determination, which is about 1% the usual amount. The results for plant digests agree with those obtained by the standard a.a.s. procedure.

Mercury fluxes in a natural forested Amazonian catchment (Serra do Navio, Amapá State, Brazil).

Mercury (Hg total) fluxes were calculated for rainwater, throughfall and stream water in a small catchment located in the northeastern region of the Brazilian Amazon (Serra do Navio, Amapá State), whose upper part is covered by a natural rainforest and lower part was altered due to deforestation and activities related to manganese mining. The catchment area is 200 km from the nearest gold mining (garimpo). Minimum and maximum Hg concentrations were measured monthly from October 1996 to September 1997 and were 3.5-23.4 ng l(-1) for rainwater, 16.5-82.7 ng l(-1) for throughfall (March-August 1997) and 1.2-6.1 and 4.2-18.8 ng l(-1) for stream water, in natural and disturbed areas, respectively. In the natural area, the inputs were 18.2 microg m 2 year(-1) in rainwater and 72 microg m(-2) year(-1) in throughfall. This enrichment was attributed to dry deposition. The stream output of 2.9 microg m(-2) year(-1) indicates that Hg is being recycled within the forest as other chemical species or is being retained by the soil system, as confirmed by the cumulative Hg burden in the 0-10 cm surface layer, which was 36480 microg m(-2). When the disturbed area of the catchment was included, the stream output was 9.3 microg m(-2), clearly indicating the impact of the deforestation of the lower part of the basin on the release of mercury. The Hg burden in the disturbed area was 7560 microg m(-2) for the 0-10 cm surface layer.

flow injection systems wiht inductively-coupled argon plasma atomic emission spectrometry: Part 2. The generalized standard addition method

Abstract In multicomponent analysis by inductively-coupled argon plasma emission spectrometry, the generalized standard addition method is useful in overcoming matrix and/or spectral interferences. As this method requires many standard additions, it becomes cumbersome when done manually if many elements are to be determined. By using a flow injection system, the standard addtion manipulations required can be significantly simplified and completed within a shorter period of time with much less sample material. A flow injection system with merging zones is used to demonstrate the method for analyses of a Ni/Cu/Zn standard and of alloys. The reproducibility of measurements of the injected sample, with or without additions of standards is always better than 99%. The results obtained compare well with those obtained by the manual procedure and also with those obtained by atomic absorption spectrometry.

Flow injection systems with inductively-coupled argon plasma atomic emission spectrometry: Part 1. Fundamental Considerations

Abstract Flow injection systems with inductively-coupled argon plasma atomic emission spectromeiry are proposed. Effects of flow rates, injected volumes and mixing Coil lengths are investigated and conditions for the measurement of the flow injection transient signal are discussed. The peak profile measured with the spectrometer corresponds well with the estimate of the true sample zone distribution near the inlet of the spectrometer made by a zone-sampling process; thus the plasma is not a limiting factor in the proposed systems. For plant analysis, the system provides nearly zero sample dispersion and so the inherent sensitivity of the spectrometric method is preserved. The results obtained for 10 elements in the NBS Orchard Leaves reference material (SRM 1571) are in good agreement with the certified values. For determinations of calcium and magnesium in dolomitic limestones, cadmium is used as internal standard and so the merging zones configuration is employed. The proposed system provides medium sample dispersion and permits about 100 samples to be analysed per hour. Relative standard deviations of 1.34% and 1.23% were calculated for the calcium and magnesium data, respectively. The analytical results compare favorably with those obtained by normal i.c.p. spectrometry with pneumatic sample aspiration, after manual sample dilution.

Determination of iron in natural waters and plant material with 1,10-phenanthroline by flow injection analysis

A flow injection analysis procedure for the determination of total iron in natural waters and plant digests by the 1,10-phenanthroline method is described. Effects of mixing-coil lengths, sample volume, flow-rates, reagent concentrations and interfering species were investigated. The proposed procedure allows the determination of iron concentrations in the range 0.1–30 p.p.m. at a rate of up to 180 samples per hour with a relative standard deviation of lower than 1%. The results agree with those obtained by atomicabsorption spectrometry, and an iron concentration identical with the certified value was found by analysis of an NBS standard reference material.

Turbidimetric determination of sulphate in plant digests and natural waters by flow injection analysis with alternating streams

Abstract An improved flow injection system with alternating streams of reagents is described for the turbidimetric determination of sulphate. Samples are injected into an inert carrier stream which is mixed with barium chloride to form a barium sulphate suspension. The range of the method can be extended to low concentrations by continuously adding sulphate to the sample carrier stream. System performance is improved by automatic alternate pumping of the reagent stream and an alkaline EDTA solution at high flow rate. All operations are controlled by an electronically-operated proportional injector-commutator. Even after routine analysis of 3000 samples of natural waters and plant digests, baseline drift was not observed. The proposed method is suitable for 120 samples per hour with a relative standard deviation less than 1% for sulphate concentrations in the range 1–30 ppm (waters) or 5–200 ppm (plant digests). The results compare well with those obtained by standard manual procedures.