Pretreatment of samples

Instrumental Quantitative Analysis. Methods such as x-ray spectroscopy, oaes, and naa do not necessarily require pretreatment of samples to soluble forms. Only reUable and verified standards are needed. Other instmmental methods that can be used to determine a wide range of chromium concentrations are atomic absorption spectroscopy (aas), flame photometry, icap-aes, and direct current plasma—atomic emission spectroscopy (dcp-aes). These methods caimot distinguish the oxidation states of chromium, and speciation at trace levels usually requires a previous wet-chemical separation. However, the instmmental methods are preferred over (3)-diphenylcarbazide for trace chromium concentrations, because of the difficulty of oxidizing very small quantities of Cr(III). 

No. Pretreatment of Sample and Treatment Time (min) Reagents Added and Reaction Time (min) Initial Intensity (LU/s)b Total Light Emitted (LU)b... 

The useful life of hplc columns can be extended by proper treatment, in particular by the use of guard and scavenger columns. Pretreatment of samples is often necessary, eg very dilute samples may require concentration, or complex samples may need to be cleaned up. Some of the more important techniques are considered. 

Methods for pretreatment of samples for 13C analysis had been described in Chen et al. (2002a). After pretreatment, soil samples and plant debris were sent to the State Key Laboratory of Loess and Quaternary Geology, Chinese Academy of Sciences (CAS), for 13C analyses. The 13C analyses were conducted using a Finnigan MAT-251 mass spectrometer manufactured by Finnigan-Mat Company, with a precision of 0.2%o. Results are reported as 513C, in parts per thousand of the 13C/12C ratio from that of the International Pee Dee belemnite (PDB) standard, where ... 

Differentiation of inorganic and organic mercury can be achieved in a number of different ways, many of which depend upon the reduction and vapourisation of the inorganic mercury, followed by reduction [84] or oxidation [85,86] of the organic mercury compounds, and a final measurement by atomic absorption or mass spectrometry. Similar methods of separation of the inorganic and organic components are used in the pretreatment of samples where the final analysis for mercury is to be made by neutron activation analysis [87,88]. 

Preservation, transport and storage of samples Investigation methods for soils, soil material and other materials Selection and pretreatment of samples Extraction and elution techniques (Table 4)... 

Development of a micro-pre-column method for pretreatment of samples. Journal of Chromatography 152(2), 341-348, 1978. 

Pretreatment of Samples. For standardization all samples used in IR and DTA studies were pretreated in air at 450°C, followed by a special activation procedure (described below). Samples for ESR studies were heated for 10 hours in air at different temperatures (see Results) and for 10 hours under vacuum (10 4 torr) at the same temperatures. 

Ueda, T. and lgarashi, O. 1990. Determination of vitamin E in biological specimens and foods by HPLC-pretreatment of samples and extraction of tocopherols. J. Micronutr. Anal. 7 79-96. 

Polycyclic aromatic hydrocarbons Polycyclic aromatic hydrocarbons co2 Pretreatment of sample with (a) 15% water, (b) 5% (ethylenedinitrilo) tetraacetic acid tetrasodium salt or (c) 50% methanol then extraction with C02 Use of liquid-solid traps compared to analyte trapping 60 - 98% recovery using Na4 EDTA-C02. Only 7 - 63% recovery with C02 alone [133]... 

ISO/DIS 11464 Soil Quality - Pretreatment of Samples for Physico-Chemical Analyses, 1995 ISO/DIS 14507 Soil Quality - Sample Pretreatment for Determination of Organic Contaminants in Soil, 1995... 

Table 5.7. Methods for Pretreatment of Samples for Spedation of Metals...

One of the most successful applications of microsystem technology is the use of pTAS in diagnostics [332-335]. Microreactors have been integrated into automated analytical systems, which eliminate errors associated with manual protocols. Furthermore microreactors can be coupled with numerous detection techniques and pretreatment of samples can be carried out on the chip. In addition, analytical systems that comprise microreactors are expected to display outstanding reproducibility by replacing batch iterative steps and discrete sample treatment by flow injection systems. The possibility of performing similar analyses in parallel is an attractive feature for screening and routine use. 

The detergent treatment conditions of samples drastically affected the SDS-PAGE of the Chl-protein complexes. Thus, when samples were SDS-treated for different time lengths the A-2 band was affected faster than the other green bands, and no A-2 band could be observed after incubation of samples for 90 min with SDS at a final SDS Chi ratio=20 l (data not shown). However, the effect of the LDAO pretreatment of samples was less apparent... 

The above studies show that the imprinted sorbents can be used in two modes in the reversed phase mode (sample application) and in the affinity mode (dichloromethane washing). Otherwise there are only few reports on the use of MIPs for the pretreatment of samples of environmental concern. Recently an MIP imprinted using the herbicide bentazone as template was synthesised and evaluated by... 

During expeditions with the German research vessel Polarstern sea water was continuously pumped under clean conditions from the front of the ship bow at a depth of 10 m into a laboratory, where samples were collected into precleaned PE bottles. Subsequently, the samples were filtered using a 0.45 pm pore sized filter and then analyzed as soon as possible. For the analysis of VHOCs a 10 1 precleaned steel bucket was also used in some cases. Only ultra pure chemicals were used for the pretreatment of samples. 

Some monitoring tools, particularly online and on-site techniques (Table 2.3.2), may require some pretreatment of samples. Most of them are derived from laboratory... 

Collection, handling and pretreatment of samples prior to testing... 

Collection, handling and pretreatment of samples prior to testing all ensure that the toxicity of the sample obtained at source does not change markedly before a test is conducted. 

Today, the easiest way of sample preparation is the use of disposable cartridges equipped with a Luer connector that can be attached to the disposable syringe. They contain, depending on the application, different packing materials (see Table 8-10). Disposable cartridges can be employed both for the pretreatment of samples and for preconcentration of solute ions. In the former case, it is important that only matrix compo-... 

Problems of intercomparability of data are similar for sedimentary and aquatic samples. Cronin and Morris (1982) discussed the large changes in the amounts and apparent nature of sedimentary humic substances resulting from variations in extraction technique. Factors showing the greatest variability among investigators include the pretreatment of samples for carbonate removal or lipid extraction, concentration and duration of the base extraction step, and the pH of the fulvic-humic acid separation step. 

ISO 11464 1994 Soil quality - Pretreatment of samples for physico-chemical... 

Methyl xanthines in tea extracts have been widely analyzed using reversed-phase Cjg column with UV detection. They have absorption maxima at 210 and 274 nm, the latter being more often reported as it is more specihc. HPLC conditions employed varied according to the level of interferences in the extracts. Fernandez et al. reported simultaneous analysis of five catechins and three methyl xanthines by RP-18 HPLC. Without pretreatment of samples, complete separation was achieved in 18 minutes using a gradient mobile phase of water-formic acid-acetonitrile. Iso-cratic elution with methanol-0.1% ortho-phosphoric acid (20 79.9 0.1, v/v) for the analysis of the same components required 60 minutes. Such time-consuming... 

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