Ultratrace

Scale of Operation Molecular UV/Vis absorption is routinely used for the analysis of trace analytes in macro and meso samples. Major and minor analytes can be determined by diluting samples before analysis, and concentrating a sample may allow for the analysis of ultratrace analytes. The scale of operations for infrared absorption is generally poorer than that for UV/Vis absorption. 

Scale of Operation Atomic absorption spectroscopy is ideally suited for the analysis of trace and ultratrace analytes, particularly when using electrothermal atomization. By diluting samples, atomic absorption also can be applied to minor and major analytes. Most analyses use macro or meso samples. The small volume requirement for electrothermal atomization or flame microsampling, however, allows the use of micro, or even ultramicro samples. 

Scale of Operation The scale of operations for atomic emission is ideal for the direct analysis of trace and ultratrace analytes in macro and meso samples. With appropriate dilutions, atomic emission also can be applied to major and minor analytes. 

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. 

The essential mineral nutrients are classified either as principal elements or as trace and ultratrace elements. The distinction between these groups is the relative amounts ia the dietary requirement (see Table 1). 

As early as 1967, IFF chemists (11), in an in-depth study of jasmin absolute, identified an ultratrace amount of one of the key compounds in the entire fragrance repoitoire, hydroxycitroneUal [107-75-7] (21). This chemical has been used for many years in almost every "white flower" fragrance to give a very diffusive and lasting lily-of-the-valley and jasmin note, but this represents the only known identification of the compound in nature. This illustrates that the human nose can often predict the presence of a molecule well before the instmmentation becomes sufficiently sensitive to detect it. 

Sampling. A sample used for trace or ultratrace analysis should always be representative of the bulk material. The principal considerations are determination of population or the whole from which the sample is to be drawn, procurement of a vaUd gross sample, and reduction of the gross sample to a suitable sample for analysis (15) (see Sampling). 

Statistically designed studies should be performed to determine accuracy, precision, and selectivity of the methodology used for trace or ultratrace analyses. The rehabihty requirements for these studies are that the data generated withstand iatedaboratory comparisons. 

Trace or ultratrace and residue analyses are widely used throughout chemical technology. Areas of environmental investigations, explosives, food, pharmaceuticals, and biotechnology rely particularly on these methodologies. 

Pharmaceuticals. Examples of trace and ultratrace analyses of various dmgs and pharmaceuticals have been provided throughout. The purity of the active ingredient, its content and availabiUty in dosage form, therapeutic blood levels, deflvery to target areas, elimination (urine, feces, and metabohtes), and toxicity are always of importance. 

Complete qualitative and quantitative bulk elemental analysis of conducting solids to ultratrace levels... 

Because GDMS can provide ultratrace analysis with total elemental coverage, the technique fills a unique analytical niche, supplanting Spark-Source Mass Spectrometry (SSMS) by supplying the same analysis with an order-of-magnitude better accuracy and orders-of-magnitude improvement in detection limits. GDMS analy-... 

Since then, TXRE has become the standard tool for surface and subsurface microanalysis [4.7-4.11]. In 1983 Becker reported the angular dependence of X-ray fluorescence intensities in the range of total reflection [4.12]. Recent demands have set the pace of further development in the field of TXRE - improved detection limits [4.13] in combination with subtle surface preparation techniques [4.14, 4.15], analyte concentrations extended even to ultratraces (pg) of light elements, e. g. A1 [4.16], spe-dation of different chemical states [4.17], and novel optical arrangements [4.18] and X-ray sources [4.19, 4.20]. 

Trace element analysis has become sufficiently important, especially to industrial users, that commercial laboratories specialising in trace and ultratrace elemental analysis are springing up. One such company specialises in high-resolution glow-discharge mass spectromety , which can often go, it is claimed, to better than parts per billion. This company s advertisements also offer a service, domiciled in India, to provide various forms of wet chemical analysis which, it is claimed, is now nearly impossible to find in the United States . 

When the sample weight is small (0.1-1.0mg), the determination of a trace component at the 0.01 per cent level may be referred to as subtrace analysis. If the trace component is at the microtrace level, the analysis is termed submicrotrace. With a still smaller sample (not larger than 0.1 mg) the determination of a component at the trace level is referred to as ultratrace analysis, whilst with a component at the microtrace level, the analysis is referred to as ultra-microtrace. 

The apparatus required for classical procedures is cheap and readily available in all laboratories, but many instruments are expensive and their use will only be justified if numerous samples have to be analysed, or when dealing with the determination of substances present in minute quantities (trace, subtrace or ultratrace analysis). 

---