Multivariate optimisation of a rapid and simple automated method for bismuth determination in well water samples exploiting long path length spectrophotometry

ABSTRACT

An automated spectrophotometric system is proposed for the determination of bismuth in well water samples, using multi-syringe flow injection analysis (MSFIA) and exploiting a liquid waveguide capillary cell (LWCC). This method is based on the colorimetric reaction of bismuth and methylthymol blue (MTB) in the presence of polyvinylpyrrolidone (PVP) in acid medium (0.1 mol L⁻¹ HNO₃). The Bi(III)–MTB complex was measured at 600 nm. The method was optimised by multivariate techniques. Some figures of merit of the proposed system are worth being highlighted, such as its wide linear working range (between 4.9 and 600 μg L⁻¹), its low detection limit (1.5 μg L⁻¹ of bismuth) and its high intra-day precision and inter-day precision (0.7% (n = 12) and 1.4% (n = 5), respectively, both expressed as RSD). Moreover, a high injection frequency of 30 h⁻¹ is achieved, as the proposed analyser is a powerful tool for fast Bi(III) determination. The method developed was successfully validated by analysing reference samples (pharmaceutical samples) by comparing the results with those obtained by ICP-OES and it was satisfactorily applied to well water samples. Besides, the present system is miniaturised allowing in situ measurements in control processes and field analysis.

KEYWORDS:

• bismuth
• long path spectrophotometry
• multi-syringe flow injection analysis (MSFIA)
• methylthymol blue (MTB)
• environmental water samples
• automation

Acknowledgements

The authors acknowledge financial support from Spanish Ministry of Economy and Competitiveness (MINECO) through Project CTQ2013-47461-R co-financed by FEDER funds. J. Avivar acknowledges to the Torres Quevedo Program of the MINECO co-financed with European Funds for the financial support through the PTQ-2012-05755. C. Calderilla acknowledges to the National Council of Science and Technology in Mexico (CONACYT) for the allowance of a grant.

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

The authors acknowledge financial support from Spanish Ministry of Economy and Competitiveness (MINECO) through Project CTQ2013-47461-R co-financed by FEDER funds. J. Avivar acknowledges to the Torres Quevedo Program of the MINECO co-financed with European Funds for the financial support through the PTQ-2012-05755. C. Calderilla acknowledges to the National Council of Science and Technology in Mexico (CONACYT) for the allowance of a grant.