Chemical background, overcoming

Metabolites are small molecules that participate as substrates or products in metabolic reactions essential for the normal function of a cell. This molecular class comprises a wide range of compounds, from amino acids to lipids, organic acids, and nucleotides (11). The wide range of concentration and different chemical properties make the analysis of these compounds a challenging task. Usually, high-resolution mass spectrometers and chemical derivatization strategies are necessary to resolve isobaric interferences, increase ionization efficiency, and overcome chemical background effects from the matrix-assisted laser desorption/ionization (MALDI) matrix or the tissue matrix itself (12). 

ICP-AES and ICP-MS analyses are hampered in almost all cases by the occurrence of sample matrix effects. The origins of these effects are manifold, and have been traced partly to physical and chemical aerosol modifications inside sample introduction components (nebulisation effects). Matrix effects in ICP-AES may also be attributed to effects in the plasma, resulting from easily ionised elements and spectral background interferences (most important source of systematic errors). Atomic lines are usually more sensitive to matrix effects than are ionic lines. There exist several options to overcome matrix interferences in multi-element analysis by means of ICP-AES/MS, namely ... 

A most powerful detection mode under actual investigation in CE is CL. Because CL detection does not require a light source for excitation—the required energy being produced by a suitable chemical reaction—problems in baseline stability limiting detection limits are overcome, providing excellent sensitivities due to the low background noise. Recently, some review articles have been produced in this field [46, 65-68],... 

LGC. To overcome this, the Automation Group had to fill the gap, and the skills of mechanical engineering, electronics and software were important. The author s background experience at the Philips Research Group was important at this stage in terms of accurately specifying what could be done by hardware or software, or explaining how chemical procedures could be modified to suit the requirement. 

However, fluorescence background from chemical compounds or biological media can affect the accuracy of FP. As such fluorescence background mainly arises in the wavelength range between 400 and 550 mn, the use of red dyes emitting above 550 nm can be an effective way to partially overcome this problem. ... 

The occurrence of molecular absorbance and scatter in AAS can be overcome by the use of background correction methods. Various types of correction procedures are common, e.g. continuum source, Smith-Hieftje and the Zeeman effect. In addition, other problems can occur and include those based on chemical, ionization, physical and spectral interferences. 

In atomic emission spectroscopy flames, sparks, and MIPs will have their niche for dedicated apphcations, however the ICP stays the most versatile plasma for multi-element determination. The advances in instrumentation and the analytical methodology make quantitative analysis with ICP-AES rather straightforward once the matrix is understood and background correction and spectral overlap correction protocols are implemented. Modern spectrometer software automatically provides aids to overcome spectral and chemical interference as well as multivariate calibration methods. In this way, ICP-AES has matured in robustness and automation to the point where high throughput analysis can be performed on a routine basis. 

Application of the relationship between density and chemical potential allows one to use both GCMC/MD and GC/MD to calculate chemical potential in model singlecomponent systems of interest (e.g., 35, 36). The application of the schemes to interface systems could follow the general set-up suggested in Refs 26 and 31. One possible way to overcome the problem of slow response to pure GC/MD mentioned earher will be to take a leaf out of the hybrid technique book and periodically freeze the entire system outside the control volumes (the distance between them insures that they do not affect each other). While the GC/MD steps are executed in two control volumes, flie rest of the system is treated as static background. Full and fractional particles alike are confined to control volumes. In between the grand canonical steps it is the number dynamics fliat will be put on hold, with the fractional particles bouncing off the control volume walls in a direction normal to flie interface. 

---