Alternating sampling

Natural Deposits. Natural deposits, eg, minerals and fossil fuels, are located by drilling operations. An auger, eg, a screw or worm, is turned in the earth and pulled out, and material is scraped from the auger for analysis. Alternatively, samples can be taken by hoUow core drills which, when withdrawn, enclose a core of the earth that is representative of the strata through which the drill has passed. Such core samples are used in geological surveys for fossil fuels. As the drill drives deeper into the strata, each core is extracted and placed in a shallow box and coded so that a complete cross section of the geological strata can be reconstmcted. From this, the relative thickness of coal and mineral seams can be directly measured. 

Sample reduction in successive stages—primaiy to secondaiy, secondary to tertiary etc.—can be fulfilled using automatic sampling equipment while observing design principles of statistical sampling. Alternatively, sample quantity reduction may be carried out in a lab-oratoiy. 

Alternately, samples subjected to controlled tensile loading are preserved for post-shock analysis, and sectioned so that internal cracks, their morphol-... 

The exposure of sensors in a by-pass stream (which can be valved off), is an alternative way of collecting monitoring data although correlation is required between the main-stream and the by-pass The use of a side-stream taken either side of a choke in the main-stream can provide a useful monitoring point. Traps where product streams can be condensed can offer alternative sampling systems. 

As an alternative, sampling BW from a point just below the extra-low-level alarm point usually is also suitable. However, the BW is not always at its most concentrated point at the water column connection. A sample taken from this point may contain a mix of BW and steam, which leads to errors in sampling and hence, testing, reporting, interpretation, and subsequent actions. 

At the end of the 2D experiment, we will have acquired a set of N FIDs composed of quadrature data points, with N /2 points from channel A and points from channel B, acquired with sequential (alternate) sampling. How the data are processed is critical for a successful outcome. The data processing involves (a) dc (direct current) correction (performed automatically by the instrument software), (b) apodization (window multiplication) of the <2 time-domain data, (c) Fourier transformation and phase correction, (d) window multiplication of the t domain data and phase correction (unless it is a magnitude or a power-mode spectrum, in which case phase correction is not required), (e) complex Fourier transformation in Fu (f) coaddition of real and imaginary data (if phase-sensitive representation is required) to give a magnitude (M) or a power-mode (P) spectrum. Additional steps may be tilting, symmetrization, and calculation of projections. A schematic representation of the steps involved is presented in Fig. 3.5. 

The administrators or users of the study results must supply the objectives and required precision. Statisticians can develop the models for alternative sampling strategies. The estimates of variance components and costs can come from a number of places ... 

As microwave sample preparation has evolved, standard microwave procedures have been developed and approved by numerous standard methods organisations (ASTM, AOAC International, EPA, etc.), see ref. [64]. Examples are standard test methods for carbon black/ash content (ASTM Method D 1506-97), lead analysis in direct paint samples (ASTM Method E 1645-94), etc. Table 8.15 shows some microwave ashing references (detection weight). A French AFNOR method utilises the atmospheric pressure single-mode microwave method as an alternative sample preparation procedure for Kjeldahl nitrogen determination [84], The performance of a microwave-assisted decomposition for rapid determination of glass fibre content in plastics for QC has been described [85]. 

Self-monitoring for cyanide must be conducted after cyanide treatment and before dilution with other streams. Alternatively, samples may be taken of the final effluent, if the plant limitations are adjusted based on the dilution ratio of the cyanide waste stream flow to the effluent flow. 

For solid-phase samples or for membrane interaction studies, it can be very useful to use the alternative sampling technique of attenuated total reflectance (ATR). Films or solutions can be placed on a specially... 

FIGURE 13.2 Schematic of a comprehensive 2DLC (IEX/RP) configuration with alternating sampling of first-dimension IEX eluent by two RP trap columns, and a single downstream analytical RP column. A salt diversion valve is present to divert salts from the IEX dimension to waste, and prevent contamination of downstream collected fractions or mass analyzer. 

Figure 2. Ratio of the unattached Po-218 concentration to the radon concentration for different flow rates during sampling. The daughters are alternately sampled with ( ) and without (O) the detection head.

Collusion might take place between laboratories so that independent data are not submitted. Proficiency testing schemes should be designed to ensure that there is as little collusion and falsification as possible. For example, alternative samples could be distributed within a round. Also instructions should make it clear that collusion is contrary to professional scientific conduct and serves only to nullity the benefits of proficiency testing. 

Laser-induced desorption can be utilized quantitatively to remove adsorbates in a localized area of a surface, without substantially altering the temperature of the surrounding sample. This provides a viable technique for measuring surface diffusion kinetics . Alternatively, sampling different... 

Specific sensor or probe head is often significantly smaller than the physical increment volumes extracted by an alternative sampling valve. 

Alternate Sample Introduction — Obviously, elimination of the sample dissolution stage would greatly reduce analytical time, as it is the slowest step in the analytical scheme. Pulsed-laser vaporization using a CO2—TEA laser seems promising(63, 64). Another possibility is the introduction of a suitable prepared slurry of the sample into the nebullzer(65). Thermal vaporization studies using heated substrates such as tanta-lum(66), carbon filaments(67), or carbon rods(39) have been reported. Silvester(39) de fined the problems of vapor transport, carrier gas expansion, and solid phase chemistry associated with electrothermal sample introduction to an ICP. 

Alternatively, samples are quickly screened by thermal methods, such as DSC or ITC. This alternative approach eliminates the necessity for stability set-downs hence cycle times and sample consumption are reduced. However, the data obtained are difficult to interpret and may be misleading false positives and negatives are routinely encountered [14]. 

An alternative sample-introduction approach is the electrospray (ESP) interface that also constitutes a widely applicable soft ionization technique (103). ESP operates at the low 1/min flow rate, necessitating use of either capillary columns or postcolumn splitting of the mobile phase (104-106). 

Alternative sample extraction techniques include an approach that combines the deproteinizing efficiency of dichloromethane with the ion-pairing ability of phenylbutazone for isolating tetracyclines from eggs (308). Another approach that was employed for extracting oxytetracycline from milk (285) or swine tissues (309), and tetracycline, oxytetracycline, and chlortetracycline from milk (284), was based on ultrafiltration. With ultrafiltration, however, not all low molecular-mass proteins are retained in the cut-off filters while interfering substances pass through the filter. 

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