Practical Sampling

It is important that the sample should be representative of the water being examined. Certain precautions need to be taken to ensure that the water does not change significantly between the sample being collected and assayed. These are  

The HMSO report also makes recommendations for sampling from a variety of other sources such as reservoirs, wells and storage tanks. 

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Another method, called photobleaching, works on robust soHds but may cause photodecomposition in many materials. The simplest solution to the fluorescence problem is excitation in the near infrared (750 nm—1.06 pm), where the energy of the incident photons is lower than the electronic transitions of most organic materials, so fluorescence caimot occur. The Raman signal can then be observed more easily. The elimination of fluorescence background more than compensates for the reduction in scattering efficiency in the near infrared. Only in the case of transition-metal compounds, which can fluoresce in the near infrared, is excitation in the midvisible likely to produce superior results in practical samples (17). 

P. B. Coleman, ed.. Practical Sampling Techniquesfor Infrared Mnaljsis, CRC Press, Boca Raton, Fla., 1993. 

Although mechanical sampling methods are to be the focus of attention, manual sampling methods are also employed for practical sample collecdion in commerce. Techniques of mechanical sampling should be emulated as closely as possible for best results with sampling by manual procedures. 

Sample quantity to estimate moisture for specific material is influenced to various levels of significance by properties such as particle-size range as well as relative amounts or moisture distributed among denoted forms of retention. Practical sample size estimates require background knowledge of parameters derived from experience for specific materials. More detailed examination of moisture-sampling aspects is provided in reference texts (Pitard). 

However, with practical samples the way the (k ) values of the individual components for any given complex solute mixture are distributed is not predictable, and will vary very significantly from mixture to mixture, depending on the nature of the sample. Nevertheless, although the values for the theoretical peak capacity of a column given by equation (26) can be used as a reasonable practical guide for comparing different columns, the theoretical values that are obtained will always be in excess of the peak capacities that are actually realized in practice. 

The theoretical lateral spatial resolution achievable with Raman imaging using the optical arrangements of our system (50 x objective with NA = 0.75, 633 nm HeNe laser) should be about 1 pm. In this investigation the resolution is worse than predicted. In practice, sample drift during long acquisition times, uneven surface structures and penetration of laser light into the material worsen the lateral spatial resolution to a value of about 2 pm (estimated). 

To assess the regional variations of Rn-222 in Norwegian dwellings, a simple and practical sampling procedure was chosen. The local health authorities in 75 municipalities were asked to select about 20 houses in their municipality, and dosemeters were sent by mail to the local health inspectors who in their turn contacted the householders. 

With the dump command, we cause the program to discard the minerals present in the initial system before beginning the reaction path. In this way, we simulate the separation of the fluid from reservoir minerals as it flows into the wellbore. The precip = off command prevents the program from allowing minerals to precipitate as the fluid cools. In practice, samples are acidified immediately after they have been sampled and their pH determined. Preservation by this procedure helps to prevent solutes from precipitating, which would alter the fluid s composition before it is analyzed. 

Quality assurance (QA) is a generic term for all activities required to maintain quality in analytical results. These include laboratory management structures and sample documentation procedures, as well as the more practical sample preparation and analysis requirements (as described above). The ISO (International Organization for Standardization) develops standards across a wide range of areas, from screw threads to banking cards. The majority of ISO standards are specific to certain areas they are documented agreements containing technical specifications or precise criteria to be used... 

Practical sampling makes use of an increment, which may, or may not be identical to a sample. Composite samples are by definition made up of several increments. 

In contrast, the sampling process itself gives rise to three complementary so-called incorrect sampling errors (ISE), to be delineated in full as these constitute the main culprits with respect to all practical sampling if no action towards their elimination is taken. 

ISEs are the root cause of all sampling bias. Elimination of ISE is therefore of the highest priority for all practical sampling. Eor process sampling the most frequent problems are associated with IDE. After... 

Four practical procedures - often nsed several times over, in varions problem-dependent sequences and combinations during practical sampling ... 

V(0) is identical to the estimate the minimal practical sampling error MPE. From this further breakdown of the constituent error sources is often possible [2,3,9,12,13,]. 

Practice samples (for method validation) of known and declared composition should be available. 

The parameter can change in a vessel being part of the analytical instrument, for example, an ultraviolet-visible (UV-Vis) spectrophotometric cell [39,41,45,14,47, 48], an infrared (IR) cell [42, 46], or a fluorometer cell [45, 51], or a polarimetric tube [27, 49]. It can change in a reactor vessel where the analytical signal can be read in some way, for example using an optical fiber cell for spectrophotometry [52-54] or a conductometric cell [16,34,40]. Another possibility is to transport the solution from the reaction vessel to the analytical instrument by a peristaltic pump [38]. When altenative ways are not practicable, samples can be taken at suitable time intervals and analyzed apart [29,31,35,39,43,50]. 

Coleman, P.A. (1991). Practical Sampling Techniques for Infrared Analysis. Boca Raton, FL CRC Press. 

When the average relaxation time exceeds the longest practical sampling interval times the number of correlator channels, meaningful equilibrium data can still be... 

Coleman. P.B. Practical Sampling techniques for Infrared Analysis, CRC Press, LLC.. Bocu Raton, FL, 1993,... 

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