Sampling devices, contamination from

At the sampling step, contamination from sampling bottles and hydrowire should be minimized [10], Old types of sampling devices such as Nansen and Knudsen are constructed mostly from brass, which may cause contamination of Cu and Zn into seawater. The recently developed Niskin plastic sampling bottle provides less contamination from the sampler walls. However, the materials used for the end-caps or springs, rubber or Teflon-coated stainless steel, sometimes release significant amounts of Ba, Cu, Sb and Zn [14]. 

Sample contamination from sampling apparatus, storage media or by introduction of foreign elements during analytical procedures must be given consideration. This is a particular pro Hem in those determinations carried out using electrothermal atomisers, due to the high sensitivity of these devices. 

Sample Withdrawal from Process A number of considerations are involved in the design of sample-withdrawal devices that wih provide representative samples. For example, in a horizontal pipe that conveys process fluid, a sample point on the bottom of the pipe wih collect a maximum amount of rust, scale, or other solid materials being carried along by the process fluid. In a gas stream, such a location will also collect a maximum amount of liquid contaminants. A sample point on the top side of a pipe will, for liquid streams, collec t a... 

Initially, this method utilized 5-mL conical centrifuge tubes as the collection device for final elution of the extract from the Cig tubes. In practice, these tubes were found to be very difficult to clean and in few instances were the cause of cross-contamination when low-concentration samples were extracted following samples with very high concentrations. Since no commercial graduated tubes were available, disposable culture tubes are used as the receiver. These tubes are individually calibrated before use. A solvent blank sample may be processed through the method from extraction to quantification to determine if contamination from glassware occurs. 

The analysis of tetramethylammonium hydroxide (TMAH) solutions manufactured by SACHEM Inc. of Cleburne, Texas, includes the determination of trace elements. These elements cause less-than-optimum performance of integrated circuit boards manufactured by SACHEM s customers that use these solutions in their processes. Alkali and alkaline earth metals (e.g., Li, Na, K, Mg, Ca, and Ba) can reduce the oxide breakdown voltage of the devices. In addition, transition and heavy metal elements (e.g., Ti, Cr, Mn, Fe, Co, Ni, Cu, Zn, Ag, Au, and Pb) can produce higher dark current. Doping elements (e.g., B, Al, Si, P, As, and Sn) can alter the operating characteristics of the devices. In SACHEM s quality control laboratory, ICP coupled to mass spectrometry is used to simultaneously analyze multiple trace elements in one sample in just 1 to 4 min. This ICP-MS instrument is a state-of-the-art instrument that can provide high throughput and low detection Emits at the parts per thousand level. Trace elemental determination at the parts per thousand level must be performed in a clean room so that trace elemental contamination from airborne particles can be minimized. 

Because SPMDs sequester a wide variety of organic solutes or vapors of hydrophobic chemicals, care must be used to prevent inadvertent contamination of the devices. Of particular concern for SPMDs destined to be used for environmental sampling is the fact that SPMDs clear large volumes of vapor phase chemicals from air. For example, under low flow conditions (<5 cm s ) at about 22 °C the Rs... 

The results of in-process sample testing are important to confirming the proper operation of the equipment. Therefore it is important to ensure the sampling device, wherever used, is clean. If cleaning after each use is not feasible or it is difficult to keep it clean until next used, then the sample device must be stored properly to protect it from environmental contamination. 

Field duplicates for water samples are collected by sequentially filling sample containers with water from a sampling device. Water sample field duplicate precision summarily measures the analytical precision and the reproducibility of the sampling procedure. Unless gross contamination in the form of a separate phase is present, field duplicate precision for properly collected and analyzed duplicate water samples is typically below 30 percent. 

Introduction of external chemical contamination from the sampling devices into the sample should be avoided because binding of metals to biological molecules is possible in vitro, and this can change the distribution of metal-containing species in the sample. Heavy metal contaminants could cause protein precipitation as well as irreversible deactivation of enzymes. 

Sampling devices themselves can be a source of contamination. Contamination may come from the material of construction or from improper cleaning. For example, polymer additives can leach out of plastic sample bottles, and organic solvents can dissolve materials from surfaces, such as cap liners of sample vials. Carryover from previous samples is also possible. Say that a sampling device was used where the analyte concentration was at the 1 ppm level. A 0.1% carryover represents a 100% error if the concentration of the next sample is at 1 part per billion (ppb). 

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