Recent advances in biological sample preparation methods coupled with chromatography, spectrometry and electrochemistry analysis techniques
Introduction
The development of biological sample analysis methods has become more and more challenging over the past years due to very demanding requirements in terms of method reliability, sensitivity, speed of analysis and sample throughput. The aim of quantitative analytical method is to provide accurate and reliable determination of the amount of a targeted or untargeted analyte, usually a drug, a metabolite or a biomarker, in complex biological samples. The biological samples usually encompass whole blood, serum, plasma, urine, saliva, breast milk, sweat, cerebrospinal fluid, gastric fluid, exhaled breath, and tissue samples (i.e., hair, nail, skin, bone, muscle) [1], cells, cell culture, culture media and so on. Types of biological samples used in CE-MS metabolomics studies were listed [2]. Except tissue and cell, urine and serum are the most often used samples. However, matrix effects, such as the presence of endogenous or exogenous macromolecules, small molecules and salts which interfere with analysis, low analyte concentration and biological matrix that are incompatible with instrument, all necessitate sample preparation before analysis [3]. Therefore, sample preparation starting from enhancement of selectivity and sensitivity of the analysis to improving analytical criteria and/or protecting the analytical instrument from possible damage might be employed. Sample preparation is of utmost importance for obtaining the analytes of interest in a suitable injection solution able to provide reliable and accurate results. It has substantial objectives before sample injection, including [4]:
- 1.
reducing or eliminating matrix interferences or undesired endogenous compounds;
- 2.
increasing selectivity for targeted analyte(s);
- 3.
preconcentrating the sample to enhance sensitivity; and
- 4.
stabilizing the sample by reconstituting it in an inert solvent.
A number of research efforts dealing with biological sample preparation methods have been reported. There are also some valuable reviews about biological sample preparation.
Soltani et al. [3] and Namera [5] gave reviews focused on the achievements in the pretreatment of biological samples and investigated sample pretreatments in six categories (i.e., dilution, filtration/dialysis, precipitation, extraction (solid-phase extraction, liquid liquid extraction]), novel techniques (turbulent flow chromatography, immunoaffinity method, electromembrane extraction) and combined methods.
Nováková [6] reviewed some traditional biological sample preparation techniques, such as solid phase extraction (SPE), liquid liquid extraction (LLE), protein precipitation (PP), and modern biological sample preparation techniques such as solid phase microextraction (SPME), stir-bar sorptive extraction (SBSE), microextraction by packed sorbent (MEPS), disposable pipette tips extraction (DPX), single drop microextraction (SDME), hollow-fiber liquid phase microextraction (HF-LPME), dispersive liquid-liquid microextraction (DLLME) and dried blood spot (DBS) prior to liquid chromatography-mass spectrometry method (LC-MS).
Lum et al. [7] discussed four aspects of the recent development in metal preconcentration methods in clinical samples, namely the use of ionic liquids (ILs) in DLLME and SDME extraction, sorption by nanomaterials in SPE, preconcentration using surfactants in CPE and liquid phase extraction, and automation (on-line SPE and DLLME). Delafiori et al. [8] introduced some sample preparation methods of arsenic (As), selenium (Se) and mercury (Hg) elements in various clinical matrices.
Fernández-Peralbo and Luque de Castro [9] presented an overview of researches on preparation of urine samples prior to targeted or untargeted metabolomics mass-spectrometry analysis.
Oh and Lee [10] described sample preparation methods such as PP, LLE and SPE for liquid chromatographic analysis of phytochemicals in biological fluids.
An important bottleneck of biological sample preparation is the presence of matrix effects, which have recently received lots of attention. Biological matrices are complex and often contain proteins, lipids, drugs, salts, acids, bases and various other organic and inorganic compounds with similar properties to the analytes, which may interfere with the analytes measurement. Therefore, sample preparation is a very vital part prior to the instrument analysis. However, sample preparation step still remains the most time-consuming and labor-intensive step of biological analysis. An important trend shared by the fundamental researches on the above sample preparation techniques relates to the development of more accurate, precise, selective and robust preparation methods. It has become a hot issue to new sorbents, on/in-line sample preparation methods coupled with chromatography, spectrometry and electrochemistry analysis. In this review, we therefore summarized some biological samples such as urine, blood, plasma, serum, hair, human breast milk, saliva, sweat and skin surface lipids, fecal, some tissue samples and so on, highlighted sample preparation techniques of these samples. We provided an updated, essential summary of the most important sample preparation methods coupled with chromatography, spectrometry and electrochemistry analysis for biological samples. We also discussed the present limitations and expected future trends of biological sample preparation methods for better advancement. There is no restrict definition of sample pretreatment and preparation in the published researches. Some may consider both steps as a single step, they called them sample preparation. In this review, the former step, consisting of sampling time and collection, preservative addition, volume correction, pH adjustment, dilution, enzymatic hydrolysis and so on, is called sample pretreatment; the following step, consisting of PP, LLE, SPE, SPME, LPME and so on, is called sample preparation.
Section snippets
Urine
Urine is composed of over 95% water, plus sodium, ammonia, phosphate, sulfate, urea, creatinine, proteins and products processed by the kidney and liver, including drugs and metabolites [9]. Urine is slightly acid in the morning (pH = 6.5–7.0), generally becoming more alkaline (pH = 7.5–8.0) by evening in healthy people primarily because no food or beverages are consumed while sleeping. As a sample for analysis, it has its own advantages compared with serum:
- (1)
can be obtained in large volume by
Sample preparation
Related description about liquid and solid phase extraction such as LLE, LPME (DLLME, SDME, HF-LPME and etc.), SPE, SPME, stir-bar sorptive extraction (SBSE), and matrix solid phase dispersion (MSPD) is presented in our previous review [39], [40]. Also, these methods used for biological samples are reviewed in detail by other research groups [3], [5], [6], [7], [9], [10], [41], [42], [43], [44]. Sample preparation methods applied in bioanalytical sample and their important features including
Applications
In order to obtain high sensitive results of analytes and protect the analytical instrument (including chromatography, spectrometry and electrochemical instrument), sample pretreatment/preparation must be an important part of the whole analysis. Below, we provide an elaborated update on the simple introduction of these sample preparation methods application.
Conclusions and perspectives
This review of sample preparation for biological samples coupled with chromatography, spectrometry and electrochemistry technique includes an enormous variety of methods (LLE, LPME, LLLME, DLLME, CPE, SPE, SPME, SBSE and so on). Undoubtedly, the sample preparation/pretreatment of biological samples is an important bottleneck of bioanalytical methods and has become a hot topic in analysis. Important features of some solid and liquid extraction methods, such as extraction time, solvent volume,
Acknowledgements
Financial support from the National Natural Science Foundation of China (No. 81660355, 81460328, 41676141), and Training Foundation of Hainan Medical University (No. HY2013-04, HY2013-16) are gratefully acknowledged.
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