Clinical determinations, trace

The 3-OH FAs have had great utility in the determination of LPS levels in indoor air. However, in tissues and body fluids it has been determined that 3-OH FAs are naturally present at low levels as products of mammalian metabolism (mitochondrial fatty acid p oxidation). Due to this background GC-MS/MS for 3-OH FAs is not recommended as a general marker to determine trace LPS levels in clinical samples [14]. However, in certain situations the assessment of 3-OH FAs has been successfully used, for example, in the diagnosis of chronic peridontitis [15]. There is great potential for the utility of 3-OH FAs as markers for LPS contamination in pharmaceutical products, where often the background matrix would be anticipated to be much less complex. 

Gas chromatography-mass spectrometry is selective and sensitive for measuring ethanol and other alcohols. As a result of its cost and maintenance requirements, it has not been used for routine testing of ethanol in biological fluids. Headspace GLC with FID has sufficient specific, accurate, and easy to detect ethanol in body fluids for both forensic and clinical purposes. In addition, selective ion monitoring (SIM) is also useful for determining trace amounts of endogenous aliphatic alcohols such as ethanol and n-propanol in body fluids. 

National Institute of Standards and Technology (NIST). The NIST is the source of many of the standards used in chemical and physical analyses in the United States and throughout the world. The standards prepared and distributed by the NIST are used to caUbrate measurement systems and to provide a central basis for uniformity and accuracy of measurement. At present, over 1200 Standard Reference Materials (SRMs) are available and are described by the NIST (15). Included are many steels, nonferrous alloys, high purity metals, primary standards for use in volumetric analysis, microchemical standards, clinical laboratory standards, biological material certified for trace elements, environmental standards, trace element standards, ion-activity standards (for pH and ion-selective electrodes), freezing and melting point standards, colorimetry standards, optical standards, radioactivity standards, particle-size standards, and density standards. Certificates are issued with the standard reference materials showing values for the parameters that have been determined. 

Analytical Applications. Chemiluminescence and bioluminescence are useful in analysis for several reasons. (/) Modem low noise phototubes when properly instmmented can detect light fluxes as weak as 100 photons/s (1.7 x 10 eins/s). Thus luminescent reactions in which intensity depends on the concentration of a reactant of analytical interest can be used to determine attomole—2eptomole amounts (10 to 10 mol). This is especially useful for biochemical, trace metal, and pollution control analyses (93,260—266) (see Trace and residue analysis). (2) Light measurement is easily automated for routine measurements as, for example, in clinical analysis. 

The list of elements and their species listed above is not exhaustive. It is limited to the relatively simple compounds that have been determined by an important number of laboratories specializing in speciation analysis. Considering the economic importance of the results, time has come to invest in adequate CRMs. There is a steadily increasing interest in trace element species in food and in the gastrointestinal tract where the chemical form is the determinant factor for their bioavailability (Crews 1998). In clinical chemistry the relevance of trace elements will only be fully elucidated when the species and transformation of species in the living system have been measured (ComeUs 1996 Cornelis et al. 1998). Ultimately there will be a need for adequate RMs certified for the trace element species bound to large molecules, such as proteins. 

Caroli S, Forte G, Iamiceu AL, Galoppi B 1999) Determination of essential and potentially toxic trace elements in honey by inductively coupled plasma-based techniques. Talanta 50 327-336. Chiswell B, Johnson D (1994) Manganese. In Seiler HG, Sigel A, Sigel H, eds. Handbook on metals in clinical and analytical chemistry. Dekker, New York. 

The POCL reaction has been used for trace determinations of hydrogen peroxide, most commonly in environmental and clinical analysis [26-52], The latter applications often include various enzyme systems [34-52], where a number of substrates can be indirectly determined by measuring the hydrogen peroxide that is produced as a by-product in the enzymatic reaction. 

Trace level analyses are frequently required for forensic, clinical and toxicological applications and for better understanding of the fate of individual pollutants in the environment, where not only the element is determined but the organic species are also identified and individualy quantified. These analyses can be performed with or without actual separation of the individual species. 

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). 

If the size of the literature is a reliable indicator, the analysis of compo-uents fotmd In nvironmfntnl samples has not been developed t the same extent as clinical applications of re versed-phase chromatography. More attention has been paid to the analysis of volatile species by gas phase chromatography. This is due in part to the difficulty in identifying large molecular weight complex molecules which are present in water at trace levels. However, determination of a variety of analytes in water, soil, or other matrices has been reported and the wider use of RPC in the evaluation of water quality especially can be expected. The apolar phases used in RPC may be a boon in the determination of dilute analytes. Frei (4M) has discussed how relatively unpolar compounds dissolved in water can be concentrated at the top of a reversed-phase column and then eluted as a narrow band with an appropriate solvent. This technique can be used for the analysis of environmental samples in which the analyte of interest is in exceedingly low concentration. 

Notwithstanding the excellent analytical features inherent in molecular phosphorimetric measurements, their use has been impeded by the need for cumbersome cryogenic temperature techniques. The ability to stabilize the "triplet state" at room temperature by immobilization of the phosphor on a solid support [69,70] or in a liquid solution using an "ordered medium" [71] has opened new avenues for phosphorescence studies and analytical phosphorimetry. Room-temperature phosphorescence (RTF) has so far been used for the determination of trace amounts of many organic compounds of biochemical interest [69,72]. Retention of the phosphorescent species on a solid support housed in a flow-cell is an excellent way of "anchoring" it in order to avoid radiationless deactivation. A configuration such as that shown in Fig. 2.13.4 was used to implement a sensor based on this principle in order to determine aluminium in clinical samples (dialysis fluids and concen-... 

Another disadvantage of the small, hydrophilic agents is that they tumble very rapidly in the extracellular fluid. In water at 25 °C, for example, Gd-DTPA has a rotational correlation time (rR) of 58 ps as determined by the fitting of NMRD data [3], and 105 ps by EPR simulation in the VO++-DTPA analog [4]. This very rapid motion dominates the relaxivity of the PCA in the frequency range of typical clinical interest (42-63 MHz). The reasons for this dominance of rR can be traced to the fact that small Gd3+ chelates like Gd-DTPA have a relaxivity at clinical frequencies that is determined predominantly by an inner sphere process for Gd-DTPA at 50 MHz, Chen et al. calculate that the relaxivity in water is 43 % inner sphere, 25 % second sphere, and 32 % outer sphere [4]. In turn, the inner sphere contribution to relaxivity is often modeled by the Solomon-Bloem-bergen equations [5,6]... 

Mass spectrometry has provided a wealth of information on chemical structural determination, identification, and a trace level chemical analysis. It has many applications in the biochemistry, pharmaceutical, and clinical diagnostic research field. 

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