Trace analysis biological samples

Treatment of ICPAES from different perspectives and to varying degrees of comprehensiveness appears in a number of chapters in volumes not solely dedicated to ICP-AES, but treating spectrometry and analysis in general. An early excellent chapter on ICP-AES is by Tschopel (1979) on plasma excitation in spectrochemical analysis, in Wilson and Wilson s Comprehensive Analytical Chemistry. A very brief historical introduction to ICP-AES, basic principles and considerations of absorption and emission lines, and applications to food analysis is in a book on modern food analysis (Ihnat (1984), and Van Loon (1985), in his practical analyst-oriented book on selected methods of trace analysis biological and environmental samples includes a chapter (pp. 19-52) on techniques and instrumentation including ICPAES. Moore (1989) (Introduction to Inductively Coupled Plasma Atomic Emission Spectrometry) provides... 

Van Loon, J. G. Selected Methods of Trace Metal Analysis Biological and Environmental Samples. Wiley-lnterscience New York, 1985. 

Trace enrichment and sample clean-up are probably the most important applications of LC-LC separation methods. The interest in these LC-LC techniques has increased rapidly in recent years, particularly in environmental analysis and clean-up and/or trace analysis in biological matrices which demands accurate determinations of compounds at very low concentration levels present in complex matrices (12-24). Both sample clean-up and trace enrichment are frequently employed in the same LC-LC scheme of course, if the concentration of the analytes of interest are Sufficient for detection then only the removal of interfering substances by sample clean-up is necessary for analysis. 

Byrne AR, and Kucera J (1991) Radiochemical neutron activation analysis of traces of vanadium in biological samples A comparison of prior dry ashing with post-irradiation wet ashing. Fresenius f Anal Chem 340 48-52. 

The acceptance criterion for recovery data is 98-102% or 95-105% for drug preparations. In biological samples, the recovery should be 10%, and the range of the investigated concentrations is 20% of the target concentrations. For trace level analysis, the acceptance criteria are 70-120% (for below 1 ppm), 80-120% (for above 100 ppb), and 60-100% (for below 100 ppb) [2]. For impurities, the acceptance criteria are 20% (for impurity levels <0.5%) and 10% (for impurity levels >0.5%) [30], The AOAC (cited in Ref. [11]) described the recovery acceptance criteria at different concentrations, as detailed in Table 2. A statistically valid test, such as a /-test, the Doerffel-test, or the Wilcoxon-test, can be used to prove whether there is no significant difference between the result of accuracy study with the true value [29],... 

Two methods were examined for digestion of biological samples prior to trace element analysis. In the first one a nitric acid-hydrogen peroxide-hydrofluoric acid mixture was used in an open system, and in the second one nitric acid in a closed Teflon bomb. The latter method was superior for Ge determination, however, germanium was lost whenever hydrogen fluoride had to be added for disolving sihcious material. End analysis by ICP-AES was used for Ge concentrations in the Xg/g range13. 

Flame emission spectrometry is used extensively for the determination of trace metals in solution and in particular the alkali and alkaline earth metals. The most notable applications are the determinations of Na, K, Ca and Mg in body fluids and other biological samples for clinical diagnosis. Simple filter instruments generally provide adequate resolution for this type of analysis. The same elements, together with B, Fe, Cu and Mn, are important constituents of soils and fertilizers and the technique is therefore also useful for the analysis of agricultural materials. Although many other trace metals can be determined in a variety of matrices, there has been a preference for the use of atomic absorption spectrometry because variations in flame temperature are much less critical and spectral interference is negligible. Detection limits for flame emission techniques are comparable to those for atomic absorption, i.e. from < 0.01 to 10 ppm (Table 8.6). Flame emission spectrometry complements atomic absorption spectrometry because it operates most effectively for elements which are easily ionized, whilst atomic absorption methods demand a minimum of ionization (Table 8.7). 

Probably the most effective use of XRF and TXRF continues to be in the analysis of samples of biological origin. For instance, TXRF has been used without a significant amount of sample preparation to determine the metal cofactors in enzyme complexes [86]. The protein content in a number of enzymes has been deduced through a TXRF of the sulfur content of the component methionine and cysteine [87]. It was found that for enzymes with low molecular weights and minor amounts of buffer components that a reliable determination of sulfur was possible. In other works, TXRF was used to determine trace elements in serum and homogenized brain samples [88], selenium and other trace elements in serum and urine [89], lead in whole human blood [90], and the Zn/Cu ratio in serum as a means to aid cancer diagnosis [91]. 

Mady N, Smith D, Smith J, et al. 1979. Analysis of Kepone in biological samples. In Trace organic analysis A new frontier in analytical chemistry, Proceedings of the 9th Materials Research Symposium, National Bureau of Standards, April 10-13, 1978. Gaithersburg, MD National Bureau of Standards Special Publications, 519 341-343. 

The technique is useful for the quantitation of many metals including lead, copper, mercury, cadmium and zinc with detection limits as low as lOpg. Its sensitivity makes it a very suitable method for trace metal analysis in biological samples. 

MS has been successfully interfaced to both gas and liquid chromatography and the interface to CE has also been successfully developed. CE—MS is serving an analytical role in the area of small sample sizes commonly found in biological, biomarker, or cellular samples. Liquid chromatography is ideally suited for trace analysis when large amounts of sample are available. Compared to HPLC, CE offers different selectivity, higher efficiency, fast method development, and shorter analysis times. 

Kfivankova, L., Pantiickova, P., Gebauer, P., Bocek, P., Caslavska, J., and Thormann, W. (2003). Chloride present in biological samples as a tool for enhancement of sensitivity in capillary zone electrophoretic analysis of anionic trace analytes. Electrophoresis 24, 505—517. 

Helbing KS, Schnid P, Schlatter C (1994) The trace analysis of musk xylene in biological samples problems associated with its ubiquitous occurrence. Chemosphere 29 477-484... 

Biological matrices usually require sample preparation prior to trace element analysis. These sample preparations, such as acid digestion or extractions, are labour intensive and can benefit significantly from laboratory automation to reduce both time and manual manipulations. 

Both microwave closed-vessel dissolution and laboratory robotics are relatively new to the analytical laboratory. However, it is this marriage of new methods which provides useful combinations of flexible laboratory automation to meet a variety of individualized needs. Because of the large number of biological samples which are prepared for analysis each day, it is reasonable to assume that this type of innovative automation wiU be of great benefit. It should be evaluated for its ability to improve the preparation technology for trace element analysis of biological materials. 

Flame atomic absorption spectrometry can be used to determine trace levels of analyte in a wide range of sample types, with the proviso that the sample is first brought into solution. The methods described in Section 1.6 are all applicable to FAAS. Chemical interferences and ionization suppression cause the greatest problems, and steps must be taken to reduce these (e.g. the analysis of sea-water, refractory geological samples or metals). The analysis of oils and organic solvents is relatively easy since these samples actually provide fuel for the flame however, build-up of carbon in the burner slot must be avoided. Most biological samples can be analysed with ease provided that an appropriate digestion method is used which avoids analyte losses. 

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