Sample preservation volatilization

Sample Preservation Without preservation, many solid samples are subject to changes in chemical composition due to the loss of volatile material, biodegradation, and chemical reactivity (particularly redox reactions). Samples stored at reduced temperatures are less prone to biodegradation and the loss of volatile material, but fracturing and phase separations may present problems. The loss of volatile material is minimized by ensuring that the sample completely fills its container without leaving a headspace where gases can collect. Samples collected from materials that have not been exposed to O2 are particularly susceptible to oxidation reactions. For example, the contact of air with anaerobic sediments must be prevented. 

Total petroleum hydrocarbons as gasoline and other volatile petroleum products SW-846 5035/8015 G, ACD 5 to 25 g 2 to 6°C, NaHS04 to pH <2 Methanol 48 h for unpreserved samples 7 days for samples preserved, with NaHS04 14 days for samples preserved, with methanol... 

A.D. Hewitt, Storage and Preservation of Soil Samples for Volatile Compound Analysis, USA Cold Regions Research and Engineering Laboratory, Special Report 99-5, [US Army Corps of Engineers, 1999a]. 

Campos, M.L.A.M., R.F.P. Nogueira, P.R. Dametto, J.G. Francisco, and C.H. Coelho. 2007. Dissolved organic carbon in rainwater Glassware decontamination and sample preservation and volatile organic carbon. Atmos. Environ. 41 8924-8931. 

The first step in sampling is sample pickup. It is recommended that this step to be done by the analyst, because the quality of the results will be given by the repartition of the analyte in the sample (e.g., for a solid sample, it is recommended to take small amounts from different parts of the solid and to homogenize of the sample collected). For this step, the best instruments and containers must be used for sample collection and sample preservation. Automation of this step increases its quality and objectivity and decreases the possibility of contamination of the operator in the case of samples that are radioactive, toxic, or volatile with high toxicity. 

A trip blank is shipped to and from the field with the sample containers. It is not opened in the field and, therefore, provides a test for contamination from sample preservation, site conditions, and transport as well as sample storage, preparation, and analysis. It is most commonly used for volatile organics. 

See also Air Analysis Sampling. Chromatography Overview Principles. Clinical Analysis Sample Handling. Drug Metabolism Metabolite Isolation and Identification. Extraction Solid-Phase Extraction. Food and Nutritional Analysis Sample Preparation. Forensic Sciences Volatile Substances. Headspace Analysis Purge and Trap. Perfumes. Sample Handling Sample Preservation Automated Sample Preparation. Sampling Theory. 

Method development for spedation involves answering several questions. Is the sample photoredudble or photosensitive. Are any analyte species volatile, thermally unstable, or unstable when exposed to air. Could redox conditions change because of sampling, sample preservation, or sample preparation. The loss or conversion of nonanalyte sample components may also affect the balance of analyte spedes. The reader is advised to consider the chemistry closely and follow established spedation methods to prevent incorrect measurements of the various elemental spedes. 

To preserve volatile components, which may be in some samples, do not uncover samples any longer than necessary. Analyze samples as soon as possible after taking from the bulk supplies to prevent loss of nitrogen or contamination due to exposure or contact with sample container. 

To reduce the loss of contaminants from the collected samples due to volatilization and bacterial degradation, the majority of environmental samples must be preserved by storage within a temperature range of 2-6 °Celsius (C). Samples collected for VOC analysis are particularly susceptible to such losses even at slightly elevated temperatures. Preserved samples represent the sampling point conditions at the time of sampling, and that is why proper preservation upon sample collection is necessary to assure the collected sample representativeness. 

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