Samples, nature

Application of rotating coiled columns has become attractive for preparative-scale separations of various substances from different samples (natural products, food and environmental samples) due to advantages over traditional liquid-liquid extraction methods and other chromatographic techniques. The studies mainly made during the last fifteen years have shown that using rotating coiled columns is also promising for analytical chemistry, particularly for the extraction, separation and pre-concentration of substances to be determined (analytes) before their on-line or off-line analysis by different determination techniques. 

Restrictions on sample nature (excluding aqueous samples and polar compounds)... 

Coplen, T.B., C. Kendall, and J. Hoppell. 1983. Comparison of stable isotope reference samples. Nature 302 236-238. 

The strict regulations of the pharmaceutical industry have a significant effect on the quality control of final products, demanding the use of reliable and fast analytical methods. The capacity that the technique has for the simultaneous determination of several APIs with no need of, or with minimum, sample preparation has considerably increased its application in pharmaceutical analytical control. The main limitation of NIR is the relatively low sensitivity that limits the determination of APIs in preparations when their concentration is less than 0.1%. Nevertheless, instrumental improvements allow the determination below this limit depending on the nature of the analyte and the matrix, with comparable errors to the ones obtained with other instrumental techniques. The reference list presents an ample variety of analytical methodologies, types of samples, nature of analyte and calibration models. A detailed treatment of each one is beyond the scope of... 

The final temperature selected should be near the boiling point of the highest-boiling component present in the sample. Naturally, the practical limitations of the column substrate volatility must be taken into account. 

Wilkinson F, Willsher CJ, Warwick P, Land EJ, Rushton FAP (1984) Diffuse reflectance pulse radiolysis of opaque samples. Nature 311 40-42... 

Chlorotriazine in environmental samples (natural waters and sediment samples) MAA MIP-based SPE cartridge with LC diode array detection 0.05-0.2 ug/L depending on the type of pesticide Ferrer et al., 2000... 

Difficulties have been observed in the preservation of samples for speciation of chromium. Chromium speciation in seawater was determined on board ship shortly after samples had been collected (Abollino et at., 1991). Some samples were frozen, and analysed later in a laboratory. However, significantly lower concentrations of Crvl were observed in these latter samples. Thus, sea-going analytical methods for the determination of Crm and total chromium are of particular importance (Mugo and Orians, 1993). The volatile trifluoroacetyl-acetone derivative of Crm was formed and then concentrated by extraction into toluene. Chromium was determined by means of a gas chromatograph equipped with an electron capture detector. Total chromium was determined as Cr111 after reduction. The detection limits were 0.062 and 0.255 nmol dm 3 total chromium. A useful method was described for sampling natural water in the field, and for the preservation of Crm and Crvl species for subsequent analyses in a laboratory (Cox and McLeod, 1992). Water samples were drawn through small columns packed with activated alumina, which had been prepared previously. Chromium species were retained on the columns. 

A technique for the determination of methylmercury in aqueous samples (natural and seawater) involved the conversion of methylmercury to gaseous methyl-ethylmercury by reaction with sodium tetraethylborate (Bloom, 1989 Bloom and Watras, 1989). The volatile derivative was purged from the solution and concentrated on a graphitic column at room temperature. The derivative was thermally desorbed from the column, and then analysed by cryogenic gas chromatography with cold vapour atomic fluorescence detection. In addition to methylmercury, labile Hg11 species could be determined (as diethylmercury) as well as dimethylmercury (which is not ethylated). The detection limit for... 

This chapter aims at presenting the various approaches to sample preparation prior to As and Se speciation from the standpoint of method types rather than of sample nature. As already noted above, there is in fact usually no ideal method for a given sample type, since the purpose of the analysis may require different degrees of extraction efficiency. In the following, the most common sample types have been associated with the most frequently recommended preparation methods as a function of specific requirements. Examples are given to illustrate such sample-method couples. 

Residual solvents, volatiles, initial survey of sample nature, MW distribution, determination of saturate types... 

In a review of the performance of combinatorial chemicals alongside natural product extracts in several biochemical assays, there no comprehensive significant differences (Table 1). Natural products and combinatorial chemicals were screened in three different biochemical assays of current pharmaceutical relevance. In one assay, natural products resulted in more confirmed active samples than combinatorials. In another assay, the reverse was true. In a third assay, both sample types performed about the same. In the majority of assays formatted for high throughput, both combinatorial chemicals and natural products will provide adequate numbers of active samples for drug candidate lead identification programs. There is a perception however, that for biochemical assays for which combinatorial chemicals fail to produce a significant number of active samples, natural products are likely to provide some possibilities. 

As with other solutes, sampling natural waters for arsenic and selenium require (i) the sample to... 

The performance of ablation lasers depends largely on two factors, namely the nominal laser wavelength and intensity, and whether the continuous or pulsed mode of irradiation is used. Studies on the first two factors have yielded controversial results that can be ascribed to differences in sample nature or grain size. Thus, ruby (694 nm), Nd YAG (1064, 532, 266 and, recently, 213 nm) and excimer (308, 248, 222, 193 and, recently, 157 nm) lasers have been used for laser ablation (LA). A comparison of the Nd YAG laser operating at 1064 nm and 266 nm revealed better absorption of UV wavelength by most types of samples and also decreased fractionation. The particle sizes produced during ablation were smaller with 266 than with 1064 nm, which was possibly the reason for the reduced... 

Earlier work on Gorleben aquifers (7-3) has identified two organic phases in the sampled groundwaters the distinction between the two phases was dictated by the ultrafiltration methodology deployed to sample natural aquatic colloids. Thus, colloids (operational size range 1 to 1000 nm) were identified as made up mostly of humics (HA) and the organic macromolecules associated with solution... 

Recently we completed an evaluation of the effectiveness of the Aflatest (Vicam) immunoaffinity column for analysis of corn, peanuts and peanut butter for aflatoxin (11). In this procedure the sample is extracted with Me0H/H20, filtered, and the extract diluted to <30% MeOH with water. An aliquot is then applied to the immunoaffinity column. The column is then washed with water and the aflatoxins eluted with methanol. Total aflatoxins are then determined by solution fluorometry with bromine (SFB), or individual toxins by reverse phase high performance liquid chromatography with post column I2 derivatization (PCD). In the collaborative study corn samples naturally contaminated with aflatoxins and samples of corn, peanuts and peanut butter spiked at 30, 20 and 10 ng/g, were analyzed by 24 collaborators. The results of this study are tabulated in Table V. 

Estimation by using known values of carbonyls absorption coefficients [12] revealed that the surface density of Ce cations is less than 1% of a monolayer. Hence, those sites are clearly defects. For Me centers including weak ones filled only in the presence of gas phase CO, the integral surface density amounts up to 30-40 % of a monolayer, weakly depending on the sample nature. Hence, the predominant part of those sites can be assigned to 7-coordinated regular cations located on the most developed faces of the (111) type [13],... 

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