F. Mas

Monitoring of environmental parameters by sequential injection analysis

The use of sequential injection analysis (SIA), as applied to the control of environmental parameters, is reviewed. Its advantages and drawbacks are compared with those of flow injection analysis (FIA). FIA is simpler and easier to handle, has a higher sample throughput, and may be controlled manually, but SIA is more robust and versatile and better adapted for multiparametric and stopped flow techniques.

New approach to sequential injection analysis: using the sample as carrier

A new way of implementing sequential injection analysis involving the use of the sample as a carrier is proposed. These systems are especially suitable for constructing continuous monitoring set-ups with no restrictions regarding the amount of sample which can be processed. A new standard addition methodology was used to calibrate the proposed system. The methodology was applied to the determination of FeII with o- phenanthroline (a reaction which involves a single reagent) and that of phosphorus by formation of a blue heteropolyacid (a reaction involving two reagents). The analysis rate is 8 min per sample (3 standard additions). The manifold design together with an adequate programme of aspiration–impulsion movements avoids the memory effects between samples. Determination of FeII is linear between 0.25 and 6 mg l–1 FeII. In the analysis of a sample containing 2.3 mg l–1 FeII (n = 10) a relative standard deviation of 1.7% has been obtained. The detection limit (3s) is 0.06 mg l–1 FeII and the determination limit (10s) 0.2 mg l–1 FeII. Determination of P is linear between 0.1 and 1 mg l–1 P and in the analysis of a sample containing 0.75 mg l–1 P (n = 10) a relative standard deviation of 4.1% has been obtained. The detection limit is 0.02 mg l–1 P and the determination limit 0.1 mg l–1. Both methods have been applied to the determination of Fe and P in spiked waters. The use of the methodology based on the standard addition has been evaluated in the case of P determination in order to eliminate interferences of the multiplicative type.

Simultaneous Spectrophotometric Determination of Silicate and Phosphate by Flow Injection Analysis

Abstract A method is reported for the simultaneous determination of phosphate and silicate by flow injection analysis based on the different rate of formation of the heteromolybdic acids of the two anions. Measurements are based on the colour of the ion-pairs formed between the said molybdic acids and Rhodamine B. The method allows the determination of the two anions at a rate of 20 samples/h over the ranges 0.05–2.5 ppm (phosphate) and 0.8–15 ppm (silicate), which allows application to a variety of waters.

Automatic System for Simultaneous Determination of Nitrates and Nitrites in Waters

Abstract An automatic FIA system for simultaneous determination of nitrates and nitrates in waters is described. The method is based on the classical azodye reaction for nitrites. The sample is split into two flows: (a) one is directly treated with the azodye reagent and sent to the sample flow cell of a double beam spectrophotometer, which gives positive absorbance values, allowing direct determination of nitrites in the sample, (b) the other flow goes through a cadmium reduction microcolumn, where nitrates are reduced to nitrites. The sample is then treated with the azodye reagent and the overall mixture is sent to the reference cell of the same double beam spectrophotometer, which gives negative peaks corresponding to the sum of the absorbances of nitrates and nitrites. Thus deducing the nitrate content in the original sample from the difference. The procedure has been automatized by connecting a digital potentiometer, provided with a RS232C interface, to the register output of the spectrophotometer. T...

Determination of phosphate in waters by flow injection analysis

A flow injection system for the determination of phosphate in natural water samples is reported. Phosphate is reacted with molybdate ion and Rhodamine B in an acid medium to yield a complex whose absorbance is monitored at 586 nm. The method thus developed is applicable to the determination of phosphate ion at the ppb level at a sampling rate of 55 samples hr−1.

Spectrophotometric determination of silicate with rhodamine B by flow-injection analysis.

Abstract A spectrophotometric flow-injection method for the determination of silicate based on the formation of an ion pair between molybdosilicic acid and Rhodamine B is proposed. It allows silicate to be determined over the concentration range 0.17–2.0 mg 1 −1 at a sampling rate of 40 h −1 , is reasonably precise and is highly tolerant to ions that commonly occur in waters. It has been applied with satisfactory results to the determination of silicate in various types of water.

Study on the implementation of flow titrations in sequential injection analysis

Several variables that affect flow spectrophotometric titrations in sequential injection analysis (SIA) systems were studied by using titration of a strong acid with a strong base as a model; blue bromothymol was used as an indicator and distilled water was used as a carrier. Both possibilities of performing titrations on SIA systems according to the aspiration sequences (a) titrant B/sample/titrant A and (b) titrant/sample are considered. In case (a) the possibilities regarding the use of different volumes and/or different concentrations of titrant reagents were studied and are discussed. The established methodology allows hydrochloric acid determinations with 0.1 M sodium hydroxide within the range 32–1000 mM by means of logarithmic calibration curves. The analysis rate is of 5 min/sample.

Application of chemometric techniques to the analysis of underground water from the Majorca Island

Summary We applied three multivariate analysis techniques (principal component analysis, correspondence factor analysis and cluster analysis) to physico‐chemical data obtained by analyzing underground waters from the Majorca Island in 1987. We studied the information obtained on plotting samples and variables in the new factor space defined and found conclusions to be consistent throughout the interval studied and the occurrence of redundant information. The sample groups obtained and their relationship to the variables assayed allow hypotheses to be formulated on the geographical origin of the samples.

Automatic system for the determination of boron in ceramic frits

An automatic system for the potentiometric determination of boron in ceramic frits was developed. The system includes a personal computer for instrumental control, data acquisition and processing, which allows up to 13 samples to be analysed sequentially with no human intervention.The system performance was tested on the titration of standard solutions, which it carried out with low errors and RSD. It was subsequently applied to the determination of the B(2)0(3) content in various types of ceramic frits with good results.