Modern qualitative analysis by miniaturized and microfluidic systems

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Highlights

  • Qualitative analysis in miniaturized and microfluidic analytical systems.

  • Progress in identification of compounds by miniaturized and microfluidic systems.

  • Recent progress in screening samples by miniaturized and microfluidic systems.

  • Selected applications in clinical, food, and environmental fields.

  • Advantages and disadvantages of qualitative analysis in miniaturized systems.

Abstract

The evolution toward miniaturization has affected many facets in our life and similarly is also a clear trend in modern analytical science and laboratories, resulting in miniaturized devices and measurement processes with interesting, advantageous practical implications. This article presents a general view of miniaturized analytical systems, covering devices giving qualitative information. Qualitative information is more than the simple identification of compounds in samples, as the modern concept of qualitative analysis also includes the analytical information not represented by numbers (as is characteristic of quantitative analysis). Thus, classification of samples by screening methods, or the definition of an analytical profile of analytes in a sample, as diagnostic tests provide, must be viewed as a type of qualitative analysis. Following this concept of qualitative analysis, different miniaturized analytical approaches are described, as are future trends, pointing out advantages, disadvantages and challenges.

Introduction

Analytical science is the scientific discipline dealing with the production of information (qualitative, quantitative and structural) about materials or target systems, in general. This information is mainly addressed to satisfy client information needs according to specific requirements (“fitness for purpose”). It is generated through the implementation of the analytical process. Simplification, automation and miniaturization are clear trends for laboratories, characterizing new analytical processes that are more efficient and have greater potential to provide information. These trends in laboratories are possible because of technological developments in the past few years, in parallel with an evolution towards simplification and the miniaturization affecting many other facets of our life (e.g., computers and telephones). Simplification, automation and miniaturization have produced a revolution in laboratories in every field of application.

Miniaturization is rapidly growing with novel ideas in recent years [1]. As in other fields, analytical systems have been affected by this tendency. Concretely, the capacity to carry out laboratory operations on a small scale using miniaturized devices is very appealing. Thus, micro-total analysis systems (µTAS), also called lab-on-a-chip (LOC), have renewed interest in the scaling laws of 20–25 years ago [2]. To this end, small scale reduces the required time to synthesize and to analyze a product, as greater control of molecular interactions is achieved at the microscale level. In addition, reagent cost and the amount of chemical waste can be very much reduced. Now, at the beginning of this century, it is clear that lab-on-a-chip approach is starting to be considered as a potential analytical tool in many application fields. However, some miniaturized analytical systems, such as capillary gas chromatography (CGC), micro-liquid chromatography (µGC) and micro-capillary electrophoresis (µCE), which can be considered as intermediate level of miniaturization (partial miniaturization), have been consolidated in routine laboratories for the analysis of complex samples. Miniaturized analytical systems really do constitute powerful tools in modern chemical analysis, although facing existing challenges [3].

One primary, important part of chemical analysis is qualitative analysis. As previously reported by the Valcárcel group, qualitative analysis cannot be considered a declining branch of analytical science [4]. Instrumental analysis and other recent “at home” alternatives, such as kit or spot tests (e.g., the popular pregnancy test), reinforce the role of qualitative analysis viewed in a modern way {i.e., not only for identification of compounds in the sample [5], but also classification of samples following screening strategies [6]}.

This modern view of qualitative analysis connects very well with the present needs of laboratories. This new view received practical support on the publication, in Europe, of the Decision of the European Commission 2002/657/EC about the analytical requirements of screening methods applied to the analysis of residues of organic pollutants for food-safety-control purposes. In this way, the support of the EC for the clear establishment of the principles of metrology in qualitative chemical analysis through the G6MA-CT-2000-01012 project (MEQUALAN) [7], [8], allowed reporting the implementation of quality principles in qualitative analysis.

From this background, the convergence of qualitative analysis and miniaturization opens up new approaches and opportunities to solve a good number of real-world analytical problems. This goal is the objective of this article.

Section snippets

Miniaturized analytical systems

Miniaturization means “small or very small scale”, and is therefore associated with the size of the systems. From this point of view, we can distinguish three different levels:

  • mini-scale (several mm or µL);

  • micro-scale (a few mm to 50 µm and processing samples between a few µL and 10 nL); and,

  • nano-scale (below 50 µm – even 1 µm in some cases, and with sample size below 10 nL, or even at the pL or fL level).

But, in any case, the association with the reduction of size can be somewhat confusing,

Modern qualitative analysis

Qualitative analysis is the first step of chemical analysis, and is characterized by information not represented by numbers. Traditionally, it has been associated with the identification of compounds [5], [12], but today this is only a partial view of the qualitative analysis, as Fig. 2 shows. The classification of samples according to preset criteria is increasingly routine work in analytical laboratories. The analytical features of this type of qualitative analysis are not exactly the same as

Qualitative analysis using miniaturized analytical systems

The immediate approach to implement qualitative analysis using miniaturized analytical systems is coupling or integrating detectors with high qualitative capabilities. In a recent article, Yue et al. summarized very well the latest contributions on the integration of spectroscopic analyses into µTAS [14]. The common detection modes used in miniaturized systems are laser-induced fluorescence (LIF), electrochemical detection (ED), and mass spectrometry (MS). MS is recognized for the

Conclusions

Miniaturized analytical systems can be used for qualitative purposes, covering the different aspects of qualitative analysis: identification of compounds, classification of samples (screening methods), and, in a wider view, “diagnosis” testing for diseases (clinical) or fraud detection (food). Partial miniaturization of the analytical process can be of interest for solving or improving some specific analytical problems, but the main achievements and revolutionary approaches involve

Acknowledgements

Financial support from the Spanish Ministry of Economy and Competitiveness (CTQ2013-48411-P) and Junta Comunidades Castilla-La Mancha (Project PEIC-2014-001-P) are gratefully acknowledged. The support given through an “INCRECYT” research contract to M. Zougagh is also acknowledged.

References (45)

  • W.T. Liu et al.

    Environmental microbiology-on-a-chip and its future impacts

    Trends Biotechnol

    (2005)
  • A. Ríos et al.

    Miniaturization of Analytical Systems

    (2009)
  • A. Ríos et al.

    Challenges of analytical microsystems

    Trends Anal. Chem

    (2006)
  • B.L. Milman

    Chemical Identification and Its Quality Assurance

    (2011)
  • M. Valcárcel et al.

    Analytical features in qualitative analysis

    Trends Anal. Chem

    (2005)
  • European Commission

    Metrology of qualitative chemical analysis, EUR 20605 EN

    (2002)
  • A. Ríos et al.

    Quality assurance of qualitative analysis in the framework of the European project “MEQUALAN”

    Accredit. Qual. Assur

    (2003)
  • D. Belder

    Integrating chemical synthesis and analysis on a chip

    Anal. Bioanal. Chem

    (2006)
  • J. Yue et al.

    Integration of Microreactors with spectroscopic detection for online reaction monitoring and catalyst characterization

    Ind. Eng. Chem. Res

    (2012)
  • M. Brivio et al.

    Integrated microfluidic system enabling (Bio)chemical Reactions with on-line MALDI-TOF mass spectrometry

    Anal. Chem

    (2002)
  • R.M. Fratila et al.

    Multinuclear nanoliter one-dimensional and two-dimensional NMR spectroscopy with a single non-resonant microcoil

    Nat. Com

    (2014)
  • A. März et al.

    Droplet formation via flow-through microdevices in Raman and surface enhanced Raman spectroscopy – concepts and applications

    Lab Chip

    (2011)
  • Cited by (0)

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