Source blank

If analyte-free water is not available, the field crew may use tap or bottled water for the final rinsing. A sample of source water, called the source blank may be also analyzed for the project contaminants of concern. 

If VOCs are not among the contaminants of concern, bottled drinking water or commercially available deionized water often serves as an equitable substitute for analyte-free reagent water. (Certain VOCs are present in drinking water as the artifacts of water disinfection process.) If VOCs are among the project contaminants of concern, commercially available distilled water may be used for a final rinse. When bottled water is not available, and water of unknown quality is used for equipment blank collection, a source blank of such water is analyzed. The only situation when a source blank may be needed is when the sampled medium is water and low contaminant concentrations of organic compounds and metals are a matter of concern. 

Spectrophotometric Measurements. Spectrophotometric measurements were made with a Cary Model 14 recording spectrophotometer. Absorption spectra of solutions were obtained in silica cells. Absorption spectra of the crystalline salts were obtained using mixtures of the materials with petrolatum between glass or silica plates using the Cary Model 1417200 source. Blanks for the solid spectra were CaCOa mulls in petrolatum plus aqueous starch solution if necessary to produce a flat base line. The reference was adjusted so the base line was flat in the 520 to 600 m/x region where the U(VI) acetate complexes do not absorb. Slit widths for spectra of solids were typically <0.1 mm. 

Obtained from data in "Vapor-Liquid Equilibria for Mixtures of Low-Boiling Substances," by H. Knapp, R. Ddring, L. Oellricli, U. Pldcker, and J. M. Prausnitz, DECHEMA Chemistry Data Series, Vol. VI, Frankfurt/Main, 1982, and other sources. Blanks indicate no data are available from which the kn could be evaluated. In such case use estimates from mixtures of similar compounds. 

Two scans are required to obtain an absorption spectrum. First, a blank reference scan is taken that characterizes the broadband light source. Then a scan with the sample in place is recorded. The ratio of the sample power spectrum to the reference power spectrum is the transmission spectrum. If the source has stable output, then a single reference scan can be used with many sample scans. 

In a single-point standardization, we assume that the reagent blank (the first row in Table 5.1) corrects for all constant sources of determinate error. If this is not the case, then the value of k determined by a singlepoint standardization will have a determinate error. 

In discussing ways to standardize a method, we assumed that an appropriate reagent blank had been used to correct S eas for signals originating from sources other than the analyte. At that time we did not ask an important question— What constitutes an appropriate reagent blank Surprisingly, the answer is not intuitively obvious. 

That all four methods give a different result for the concentration of analyte underscores the importance of choosing a proper blank but does not tell us which of the methods is correct. In fact, the variation within each method for the reported concentration of analyte indicates that none of these four methods has adequately corrected for the blank. Since the three samples were drawn from the same source, they must have the same true concentration of analyte. Since all four methods predict concentrations of analyte that are dependent on the size of the sample, we can conclude that none of these blank corrections has accounted for an underlying constant source of determinate error. 

A reagent blank corrects the measured signal for signals due to reagents other than the sample that are used in an analysis. The most common reagent blank is prepared by omitting the sample. When a simple reagent blank does not compensate for all constant sources of determinate error, other types of blanks, such as the total Youden blank, can be used. 

Since all samples and standards are prepared using the same volume of ammonium acetate buffer, the contribution of this source of iron is accounted for by the calibration curve s reagent blank. 

Determining Concentration by Turbidimetry In turbidimetry the measured transmittance, T, is the ratio of the transmitted intensity of the source radiation, fy, to the intensity of source radiation transmitted by a blank, Iq. 

Eliminate sources of fuel Blank unused lines at switching station Provide emergency cooling activated by external fire (e.g., fusible link, plastic tubing)... 

It is crucial in quantitative GC to obtain a good separation of the components of interest. Although this is not critical when a mass spectrometer is used as the detector (because ions for identification can be mass selected), it is nevertheless good practice. If the GC effluent is split between the mass spectrometer and FID detector, either detector can be used for quantitation. Because the response for any individual compound will differ, it is necessary to obtain relative response factors for those compounds for which quantitation is needed. Care should be taken to prevent contamination of the sample with the reference standards. This is a major source of error in trace quantitative analysis. To prevent such contamination, a method blank should be run, following all steps in the method of preparation of a sample except the addition of the sample. To ensure that there is no contamination or carryover in the GC column or the ion source, the method blank should be run prior to each sample. 

In a different set of experiments solutions of Pu(III) or Pu(VI) in H2O (Ar saturated, pH adjusted to 7, 2 x 10-5 M in Pu) were irradiated in the ANL 60Co-y source at a position where the dose was 1 megarad/hr (Jj) 1 mM H2O2 produced/hr. Cation exchange column behavior was used in an attempt to identify Pu oxidation states, see Table III. The results obtained after an irradiation of 1 hr. were indistinguishable from the "blank", i.e. a solution not subjected to irradiation. The irradiation for a 24 hr. period failed to demonstrate a marked increase in the amount of Pu(IV) produced that could be ascribed to the effects of radiolysis. 

In our application of the transformation given in Equation 1 to these data, we restrict t to positive values. This restriction is based on models of the various sources of processing contamination. Possible sources of contamination include the chemical reagents which might add a constant level to the blank and air borne particles which might add a variable level with positive skewness. There does not seem to be any reason to include a constant level that is negative. Therefore, we have adopted this restriction. 

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