Spiked filters

It is necessary to add a small leading edge spike filter to the current sensing output. To keep the time delay to a reasonable value, I will use a 1K ohm resistor and a 470 pF capacitor. 

A leading edge spike filter of 1K and 470pF will also be added before inputting the eurrent signal to pin 4. 

The spiked filters were placed in a 50-mL beaker with the spiked side up and 1 mL of water was added. The beaker was shaken so that all of the filter area had been washed by the water. One mL of the reduction-buffer solution without the sodium hydrosulfite was added to the filter and water. The beaker was shaken a second time. The filter was then turned over (spiked side down) and the beaker placed in an ultrasonic bath for 15 minutes. At the end of this period, the solution in the beaker was colored. A 1-mL aliquot of this solution was transferred to a 4-mL vial. One mL of a freshly prepared solution of 100-mg sodium hydrosulfite in 10-mL phosphate reduction buffer was then added to the vial. The vial was then capped and shaken several times during the course of an hour. During this time, the original color of the solution disappeared or changed to a different color, depending on the dye present. This solution was then injected into the liquid chromatograph. A 10-yL aliquot was used, giving a measurement limit of 0.38 ng benzidine/yL. The analytical reproducibility at this limit was 10% coefficient of variation (CV). 

Since no chemically pure dyes (greater than 95 purity) were available, recovery studies were done by reducing and analyzing a liquid sample of the dye along with the spiked filter. These liquid samples were prepared by adding a quantity of dye solution (2-200 yL) equivalent to one-half the amount present on the spiked filter to 1 mL of the reduction buffer solution. To this solution 10 mg of sodium hydrosulfite in 1 mL of the reduction buffer was added. The sample was then analyzed in the same manner as the spiked filter sample. The amount of dye contained in the filter and liquid spiked samples was the same, but concentration did vary. However, volume variations became greater than 9 ... 

To investigate the storage stability of these dyes, a 28-day storage study was undertaken. Filters were spiked and dried by the procedure described in the experimental section. Sixty liters of humidified air (75% relative humidity) were drawn through each spiked filter before storage, using the previously described vacuum pump system. During the... 

Store Spiked Filters in Refrigerator Three Days Before Extracting (3)... 

Figure 1. Experimental design used to test and compare the stability of organoarsenicals on cellulose ester, Fluoropore, and Mitex filters. Triplicate spiked filters were used for each experiment.

The percent recoveries of MMA and p-APA from cellulose ester filters are significantly better if the filter samples are extracted the same day as they axe spiked rather than storing the spiked filters for 3 days. 

A test of the recovery of 25 xg of PAHs ranging from phenanthrene (PH) to BghiP was performed by passing clean air through the spiked filter followed by two PUF disks for 24 h (the temperature was unstated). Except for PH, PAHs volatilized from the GF filter were 90-95% trapped and recovered from the PUF plugs. The losses of BghiP and BaP from the filter were 0 and 3%, respectively (79). 

Table 13.5 Uptake of technetium and rhenium from oxic seawater by BioRad AGlx8 (100-200 mesh) anion-exchange resin (501 spiked, filtered seawater passed through series columns each 100 mm x 20 mm diameter)...

Both solution samples and spiked filter samples containing Cr (III) and Cr (VI) as Cr y were prepared. Samples were solubilized using both a nitric acid and a nitric-perchloric acid digestion. 

The data presented in Table X show that low (64 to 71 percent) recoveries and decreased precision for Cr analysis are obtained when either synthetic solutions or spiked filters are digested using a procedure requiring samples containing HCIO4 to be taken to dryness. This is true whether Cr (III) exists in solution. along with other analytes (Cd, Co, Ni, Pb) or as a single analyte Cr (VI) C Oj solution. 

Spike filter / Spatial filter / Pre-monochromator Beam expander... 

Figure 8.35. Spectra of sucrose in water, with water and cuvette spectrum subtracted. Spectrum A is a single 10 sec integration, containing cosmics at 800 and 1700 cm . Spectrum B is an average of ten 10 sec spectra, with the spikes filtered by comparing successive spectra. See text for details.

The 488.0 nm Coherent Radiation Model 520-B argon-ion laser of 300 mW power was focused on the center of the drop and the Raman light is detected perpendicular to both the laser beam and the sample tube. Qualitative polarization measurements were made by rotating the plane of polarization of the laser beam with a half-wave plate. In most of the spectra, it was not necessary to use a spike filter to attenuate the plasma lines. The spectra were recorded using a modified Cary 81 spectrophotometer employing a 9558A EMI photo-multiplier counting detection system. 

Previously, both filters and PUF plugs spiked with standards were extracted and analyzed together. In order to determine whether the above ASE optimized conditions were suitable for filter as well as PUF samples, the ASE extractions were applied by two static cycles to standard-spiked filter/PUF samples, respectively, as described above. All recoveries of POPs by ASE are shown in Table 3. 

Fig. 2 Calibration of Cr, Cu and Pb performed by LA-ICP-MS analysis of spiked filters. Filters standards were prepared on three different days...

PMio samples collected at two sites in Boston, USA were analysed by LA-ICP-MS with quantification based on the analysis of spiked filters. 

Table 2 Detection limits for the analysis of spiked filters and airborne particulate matter...

However, the concentrations of these elements are often too low to have a significant impact on the determination of selected analytes. The analysis of spiked filter enables the estimation of interference formation and the contribution of interference to the measured signal in the samples (Rauch et al. 2001). Interferences were found to represent <2% of the measured signal for all elements, except for Zn and Fe for which interferences represent <5 and <25%, respectively. Interferences were corrected mathematically following the method described by Rauch et al. (2001). 

Load 20 PSDs each with one treated filter and determine desorption efficiency as described in Section 3.2.7. Spiked filters may be stored either in the PSD housings (inside the specimen jars) or in clean centrifuge tubes. Conditions should be chosen which most resemble actual storage conditions of samples. 

The air-dried spiked filters were digested and analyzed for their cadmium content by flame atomic absorption spectroscopy (AAS) following the procedure described in Section 3. The 0.02 to 2.0 pg/mL cadmium standards (the suggested working range) were used in the analysis of the spiked filters. 

The average recovery of the six spiked filter samples at 0.1 times the TWA PEL target concentration was 118.2% with a coefficient of variation (CV ) of 0.128. The average recovery of the spiked filter samples in the range of 0.5 to 2.0 times the TWA target concentration was 104.0% with a pooled coefficient of variation (CV ) of 0.010. Consequently, the analytical bias found in these spiked sample results over the tested concentration range was -1-4.0% and the OAE was 6.0%. 

Taking into account dilution of the volatilized fission products before reaching it, the monitoring station has to have the capability of measuring down to 10(xBqm of Ba. The measurement system is called RASA -Radionuclide Aerosol Sampler/Analyser. Detectors of at least 40% relative efficiency are specified to allow the required limit to be achieved in a reasonable time. Direct calibration over the range 88 to 1836 keV using spiked filter standards is used. Monte Carlo and other mathematical methods are not used. The measurement scheme is ... 

Figure 3.5 shows a similar solution for 0.5 mil-thick polyester (Mylar) film under about the same temperature conditions. Here the strong polyester absorption band from 7.7-8.2 pm dictates the use of a 7.9-pm spike filter placed in front of the same broadband detector. 

Variable Spike Filters. Multilayer interference filters of the longwave-pass type as used for order elimination were discussed on p. 37. By variation in the design of the coatings it is possible to make filters which pass only a narrow band of wavelengths. Such a device is called a spike filter. Recent developments in coating techniques have led to the availability of variable spike filters. In these, the thickness of the layers is varied as a function of angular position on a circularly shaped disc. If a narrow beam from an infrared source impinges on the disc the... 

Sensor problems are often associated with the small-diameter lines that transport process fluids to the sensors. For example, the presence of solid material, ice, or bubbles in a line can result in erroneous measurements. Simple diagnostic checks can be performed to detect certain types of sensor problems. An abnormally small amount of variability in a set of consecutive measurements can indicate a dead sensor (see Section 10.3), while a break in an instrument line (e.g., a thermocouple) can be detected by a rate-of-change or noise-spike filter (see Chapter 17). 

Noise-spike filters (or rate-of-change filters) are used to limit how much the filtered output is permitted to... 

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