Analytes in complex matrices

Often interference effects from either solvents [74] or other components in sample matrices can cause significant problems especially with direct injection of such solutions. Headspace analysis has been shown to be of great value for residual solvent analysis in drug substance [75] and dmg product [76] because the drag itself is not introduced into the system. Similarly, residual solvent analysis in pharmaceuticals using thermal desorption [77] and solid phase microexttaction (SPME) [78] has been shown to be of benefit. For more con ilex matrices such as 

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Precision Precision is generally limited by the uncertainty in measuring the limiting or peak current. Under most experimental conditions, precisions of+1-3% can be reasonably expected. One exception is the analysis of ultratrace analytes in complex matrices by stripping voltammetry, for which precisions as poor as +25% are possible. 

Preparing a Volatile Sample Gas chromatography can be used to separate analytes in complex matrices. Not every sample that can potentially be analyzed by GG, however, can be injected directly into the instrument. To move through the column, the sample s constituents must be volatile. Solutes of low volatility may be retained by the column and continue to elute during the analysis of subsequent samples. Nonvolatile solutes condense on the column, degrading the column s performance. 

Flow systems are developed mainly for liquid samples and their complexity can range from simple to very complex manifolds to deal with ultratrace amounts of the target analyte in complex matrices, which often require on-line separation/preconcentration steps. As a wide variety of chemical manipulations can be carried out in an FI manifold, the scope of the FI applications is enormous. Not only liquid samples, but also both gas and solid samples, can be also introduced into the liquid flow manifold if special adaptations are made. Gas samples simply require impermeable tubing. Solids can be either introduced into the system and leached with the help of auxiliary energy e.g. ultrasound) or introduced as slurries. 

Although composed of weak and overlapping spectral features, near-infrared spectra can be used to extract analytical information from complex sample matrices. Chemical sensing with in-line near-infrared spectroscopy is a general technique that can be used to quantify multiple analytes in complex matrices, often without reagents or sample pretreatment.7-9 Applications are widespread in the food sciences, agricultural industry, petroleum refining, and process analytical chemistry.10-13 These activities demonstrate that near-infrared spectroscopy can provide selective and accurate quantitative measurements both rapidly and nondestructively. 

A capillary-scale particle beam interface was used for the analysis of phenols in red wine by LC with MS detection. The interface allows very low mobile phase flows and sensitive detection of the analytes in complex matrices . 

Another example connected with the sensitivity, selectivity, and complexity of the matrix is illustrated by the utilization of amperometric biosensors in chemical analysis. It is well known that amperometric biosensors represent the best equilibrium between selectivity and sensitivity needed for an analytical method. Their selectivity can be highly variable in a very complex matrix such as the environment. By using amperometric sensors, the total amount of substances from a certain class are determined. That is the reason these amperometric biosensors cannot assure the accuracy of the analytical methods for analysis of analytes in complex matrices. In food analysis, the complexity of the matrix decreases considerably. Therefore, amperometric biosensors can be used with higher accuracy for the assay of certain compounds. The main field of applicability of amperometric biosensors is clinical analysis, since the matrices in clinical analyses assure for amperometric biosensors the maximum selectivity. 

The advent of new receptors based on nucleic acids, called aptamers, is a new challenge in piezoelectric sensing, not based on the hybridization reaction. The development of aptasensors has analogies to the introduction of immunosensing almost two decades ago the direct detection of analytes in complex matrices by immobilizing an optimized receptor on the sensing surface. 

Several modifications of MALDI have been developed to couple additional sampling and reaction capabilities to this technique. Surface-enhanced laser desorption ionization (SELDI) is one type of modified MALDI and describes an ionization process that involves reacting a sample with an enhanced surface. With SELDI, the sample interacts with a surface modified with some chemical functionality prior to laser desorption ionization and mass analysis. For example, an analyte could bind with receptors or affinity media on the surface, and be selectively captured and sampled by laser desorption. A SELDI surface can be modified for chemical (hydrophobic, ionic, immunoaffinity) or biochemical (antibody, DNA, enzyme, receptor) interactions with the sample. This technique can act as another dimension of separation or sample cleanup for analytes in complex matrices. As discussed before, one disadvantage of MALDI is that the matrix (usually a substituted cinnamic acid) that is mixed with the sample can directly interfere with the analysis of small molecules. There have been several areas of research to overcome this issue.Direct ionization on silicon (DIOS) is an example of a modification of MADLI that eliminates the matrix. In this case, analytes are captured on a silicon surface prior to laser desorption and ionization. Other examples of matrix-free laser desorption techniques include the use of siloxane or carbon-based polymers. 

Immunoassays are an analytical technique based on the highly specific interaction between an antibody and an antigen. Due to their ability to measure trace amounts of analyte in complex matrices, immunoassays are widely used in clinical, pharmaceutical, and environmental chemistry. Person and Yalow were the first to use antibodies as an analytical tool, reporting picogram detection of insulin [131]. Immunoassays are the primary method used in diagnosing diseases such as acquired immunodeficiency syndrome (AIDS) [132], cysticerocosis [133], and schistosomiasis [134, 135]. Due to their widespread use, growth in the field has been tremendous over the past decades. 

The combination of UHPLC with MS detection seems to be an appropriate approach to carry out key requirements in terms of selectivity, sensitivity, and peak-assignment certainty for the rapid determination of analytes in complex matrices [85],... 

Mass spectrometry is only the final step in an integrated procedure, involving many other kinds of apparatus, designed to provide accurate and precise quantitation of trace level analytes in complex matrices. The proper choice and use of these other apparatus, although less glamorous than mass spectrometers, is equally essential for this purpose and a significant part of this chapter is devoted to this aspect. 

Based on these considerations, it could be summarized that MlPs-CNTs composites represent useful innovative materials for analytical determination of target analytes in complex matrices. 

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