Samples filtration

Sample Cleanup. The recoveries from a quick cleanup method for waste solvents based on sample filtration through a Elorisd and sodium sulfate column are given in Table 2 (40). This method offers an alternative for analysts who need to confirm the presence or absence of pesticides or PCBs. 

Samples are generally prepared and analyzed in sets of 30 that include at least one control and one fortified control water sample. Optima-grade bottled water may be used as the matrix for the controls and the laboratory-fortified samples for all water types. Depending on the appearance of the samples, filtration may be required. 

Marvin et al. [302] have discussed the effects of sample filtration on the determination of copper in seawater, and concluded that glass filters could seriously affect the reliability of subsequent analysis. 

Figure 6.27 presents the sample preparation process. Accurate and reproducible control of the depth of the autosampler needles permitted the sampling of the supernatant solution without perturbing the precipitate, thus avoiding the need for sample filtration, as shown in Figure 6.28. Of course, a step could be added to sample preparation to filter the solutions prior to analysis.

Most manufacturers of dissolution testing devices offer semi-automated systems that can perform sampling, filtration, and UV reading or data collection. These systems automate only a single test at a time. Fully automated systems typically automate entire processes including media preparation, media dispensing, tablet or capsule drop, sample removal, filtration, sample collection or analysis (via direct connection to spectrophotometers or HPLCs), and wash cycles. A fully automated system allows automatic performance of a series of tests to fully utilize unused night and weekend instrument availability. 

Broyles, B. S., S. C. Jacobson, and J. M. Ramsey. Sample filtration, concentration, and separation integrated on microfluidic devices. Anal. Chem. 75, 2761-2767 (2003). 

Dilution. It is important to be aware that the dilution process utilized by the automated workstation may differ from a manual process. Adjustments in dilution factors may be required and considerations of the density value of the diluting solvent and sample filtrate are valuable. In some cases the dilution step can be avoided when designing the automated sample preparation through initial volume adjustment whenever possible and/or through changes in the injection loop size to achieve proper column loading. 

Hornsey (1956) also found that extraction with an acidified 80% acetone solution for 1 hr gave a hemin solution, derived from oxidation of the heme moiety of both NO-heme and non-nitrosylated heme pigments. Hemin absorption spectra exhibited distinct peaks at 512 and 640 nm. Hornsey (1956) used the A640 of sample filtrates as a measure of the total heme pigments. Solutions of both hemin and NO-heme in 80% acetone conformed with Beer s... 

In another application, Esy-GC-ECD was applied to the extraction of 14 organochlorine pesticides (OCPs) in spiked and contaminated complex samples, such as raw leachate water and soil-water slurry samples.94 A downsized filtration vessel was deemed crucial for sample filtration after acidification and the addition of activated copper granules (to remove elemental sulfur) and 20% acetonitrile (to prevent adsorption and enhance enrichment). Under optimal conditions, extraction of a 3-mL leachate water sample dispensed at a flow rate of 100 pL min-1 gave Ee values between 32 and 242 and LODs between 1 and 20 ng I. It was also demonstrated that, since ESy extraction is dynamic and its extraction efficiency low, calculation of relative recovery was more relevant than extraction efficiency in all ESy applications. 

Traditionally, in order to prevent oxidation of unstable Fe(II) species, the water sample has to be filtered immediately after sampling (filtration of the sample in the field needs to be carried out under completely oxygen-free conditions) and stabilized stabilization depends on the subsequent analytical method.51 Even when all sample treatment protocols are rigorously applied, Fe(II) is so easily oxidized that the initial speciation can be distorted simply by contact of the sample with air. Mn(II) oxidizes much more slowly than Fe(II) this reaction is about 107 times slower than that of Fe(II) at pH 8 and 25°C,52 reducing the risk of error during the speciation procedure. After filtration, only Mn(II) and Mn(IV) colloids remain in the sample. Filtered samples, mostly acidified, are commonly stored in precleaned Teflon bottles at 4°C. 

CDFs) to sample filtration, homogenization, acid digestion (Modification of for TCDD ( 20%) 1996... 

To trap particles, a filter consisting of a l- im-deep channel was constructed on a quartz chip. This filter was employed for sample filtration before CEC separation [148],... 

One of the most important sensors needed is one that reliably monitors cell density. An IR fiber-optic cell density probe has been used for this because it can directly monitor cell growth (without dilution) in high-cell-density bacterial fermentations. The ability to do an online sample filtration through the use of hollow fibers or rotating filters has made possible continuous, online measurement of glucose, lactate, and other metabolites. However, glucose, nitrogen substrate, and phosphate sensors that can withstand repeated system sterilization are still needed. 

Determine the absorbance of each sample filtrate in a 1-cm cell, at 275 nm, with a suitable spectrophotometer, using the filtrate from the substrate blank to set the instmment at zero. Correct each reading by subtracting the appropriate enzyme blank reading, and record the value so obtained as Au. 

In recent years the study of mobile soil and groundwater colloids has received considerable attention because of concerns that such a vector may enhance the mobility of strongly sorbing contaminants, a process that is often referred to as facilitated transport. 15-16 However, our ability to predict colloid movement and deposition is often confounded by the complexities of surface interactions in such dynamic, unstable systems. The lack of universally accepted analytical techniques and failure to realize instrumental limitations have made it difficult to compare and critically evaluate the results of different studies. Artifacts associated with ground-water sampling, filtration, and storage, and the dilute nature of most soil and ground-water suspensions further hamper characterization efforts.17-21... 

This separation step requires first the addition to the sample of an acid such as trichloroacetic add (TCA), which also serves to terminate the enzymatic reaction. However, since TCA also precipitates the RNA and any radioactive amino acid covalently linked to it, the reaction product RNA- AA will be precipitated as well. And since the precipitate can be separated from the soluble components by a sample filtration step, the separation of the bound from the free amino acid can be accomplished. As illustrated in Figure 1.3, the reaction product, which is trapped on the filter as a precipitate, can be detected by transferring the filter to a scintillation counter for quantitation and, of course, measuring the amount of product formed. Since assays of this design usually focus on one component at a time, no information is obtained about the amount of ATP, AMP, PPj, or free amino acid during the course of the reaction. 

The objective is to demonstrate that the sample filtration does not affect the analytical result due to adsorption and/or extraction of leachables. A word of caution here is that filter studies should be performed to ensure that no adsorption of the compound on the filter is observed. This is particularly the case with protein and peptide samples. Note that for proteins and peptides the impact of centrifugation (speed and time) must be investigated because this may lead to increased aggregate formation. Also, for protein and peptides the initial concentration of the sample could also have an impact on the concentration gradient of the sample in the centrifuge tube, and the concentration of the top, middle, and bottom portions should be assessed. 

The analytical process involves preliminary operations, measurement of the analytical signal, and acquisition and prooessing of the information it provides. The first step in the prooess varies and inoludes operations such as sampling, dissolution or leaching (of solid samples), filtration, olean-up, preconcentration and derivatization. 

Fig. 7 a) shows both base and maximum pressure loss (just before and after regeneration respectively) for some sample filtration series. The base pressure loss (APo) shows a linear dependency of Increase in the residual pressure drop due to depth filtration, dust re-entrainment and fractional cleaning is well known to cause serious filter degrading and may lead to total filter blinding. During the 80 hours of field operation such systematic degrading effects has not been observed. 

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