Blank equivalent concentration

Table 4.7 Recommended isotopes for selected elements and blank equivalent concentrations (BEC) for selected elements obtained using ICP-MS X7 CCT Thermo-Elemental (by the permission of Thermo-Elemental)...

Table 4.7 presents typical recommended analytical masses and indicative blank equivalent concentration (BEC) for analytes. The quantification limits... 

LOQ) will typically be higher than the instrumental detection limit (IDL), because of background analyte and matrix-based interferences. The BEC (blank equivalent concentration) used in Table 4.7 is the apparent concentration of an analyte normally derived from intercepted point of its calibration curve or by reference of the actual counts for that analyte in a blank solution. The BEC gives a good indication of the blank level, which will affect the IDL. Most often, the detection limits are calculated as three times the normal standard deviation of the BEC in a within batch replicate analytical measurement of a blank solution. Therefore, if the instrument is stable enough, this will give a better IDL than the BEC itself. The BEC is a combination of the contamination of the analyte in the solution, the residual amount of the analyte in the spectrometer and the contribution of any polyatomic species in the analyte mass. 

Analytical results for sulfate ions are for the net change in rainfall composition, after the rainfall flows over the surface of the exposed stone (Tables I and II). The net concentration, resulting from the interaction of rain with the stone surface, is calculated by subtracting the blank-sample concentration value from the value measured for the stone runoff. For very small rain amounts (typically 2 to 4 millimeters), blank volumes were too small to allow complete chemical analysis. Sulfate ion net concentration, in excess of that possible from sulfate loading, was calculated to identify the presence of soluble sulfate-containing minerals on the rock surface. Loss of rock mass, measured by the calcium concentration in the runoff, is expressed as surface recession, in micrometers of rock surface lost per rainstorm. The net calcium concentration in the runoff solution is converted to an equivalent volume of rock removed this result divided by the surface area of the exposed rock, yields a measurement of surface recession. ... 

The standard redox potential is 1.14 volts the formal potential is 1.06 volts in 1M hydrochloric acid solution. The colour change, however, occurs at about 1.12 volts, because the colour of the reduced form (deep red) is so much more intense than that of the oxidised form (pale blue). The indicator is of great value in the titration of iron(II) salts and other substances with cerium(IV) sulphate solutions. It is prepared by dissolving 1,10-phenanthroline hydrate (relative molecular mass= 198.1) in the calculated quantity of 0.02M acid-free iron(II) sulphate, and is therefore l,10-phenanthroline-iron(II) complex sulphate (known as ferroin). One drop is usually sufficient in a titration this is equivalent to less than 0.01 mL of 0.05 M oxidising agent, and hence the indicator blank is negligible at this or higher concentrations. 

At least four chromatographic standards prepared at concentrations equivalent to 50-70% of the limit of quantitation (LOQ) up to the maximum levels of analytes expected in the samples should be prepared and analyzed concurrently with the samples. In LC/MS/MS analysis, the first injection should be that of a standard or reagent blank and should be discarded. Then, the lowest standard should be injected, followed by two to four blanks, control samples, fortifications or investigation samples, followed by another chromatographic standard. This sequence is then repeated until all the samples have been injected. The last injection should be that of a standard. In order to permit unattended analysis of a normal analysis set, we recommend that samples and standards be made up in aqueous solutions of ammonium acetate (ca 5 mM) with up to 25% of an organic modifier such as acetonitrile or methanol if needed. In addition, use of a chilled autosampler maintained at 4 °C provides additional prevention of degradation during analysis. 

Residue was incorporated to a volumetric flask. Determinations of REE were carried out with an ICP mass spectrometer VG Elemental model PQ3. Detection limits were calculated as the concentration equivalent to three times the standard deviation of five replicates of the blank... 

Figure 3 illustrates a conductivity experiment with four successive additions of styrene whenever more styrene was added, the equivalent conductance (referred to the total perchloric acid concentration) fell abruptly, but not quite down to its original value during the first latency period. This is not because some carbonium ions remained after the styrene addition, but because the free acid present after the end of the polymerisation reacted with the tungsten leads, as mentioned above. This was confirmed by a blank experiment without styrene which gave the dotted base-line in Figure 3. 

The area under curve for the sample (AUCsaj pie), reduced by the area under curve plotted for the blank sample (AUCbianJ is referred to as "net AUC". Moreover, the net AUC is calculated for a series of dilutions of Trolox and a calibration curve is plotted, showing the relationship between net AUC and the concentration of Trolox. The results of the assay which refer the net AUC of the sample to the calibration curve are expressed as Trolox equivalent. 

In all of the functional group tests of kerogen, the inorganic material removed from the oil shale by attrition grinding was used as a mineral blank. Because pyrite was concentrated with the kerogen and was not separated with the mineral, pyrite equivalent to that present in the kerogen concentrate was added to the mineral blank. 

For blanks one can use ethanol, water or methanol, whichever the tissue extract was dissolved in last. Since this is a spectrophotometric assay, it is important to have a standard curve to relate the absorbance value to a concentration. Common compounds used to generate a standard curve are chlorogenic acid (1.18) or gallic acid (1.5). The concentration of phenolic compounds is then reported as chlorogenic acid or gallic acid equivalents, respectively. 

At least the double blank value (Bq) is required for evidence of a significant concentration value ( xg equivalents per g or ml). 

Calibration Blank Solution Tare a clean, dry 4-oz polyethylene bottle (or equivalent). Add approximately 50 g of High-Purity Water. Slowly add 28 1 g of concentrated nitric acid, mix thoroughly, slowly add 12 1 g of concentrated hydrochloric acid, and mix thoroughly again. Dilute the solution to 100.0 0.1 g with High-Purity Water, and mix thoroughly. 

Calibration Extract a sample of the Standard Solution as directed under Procedure (below) and inject it into the gas chromatograph, or equivalent. Determine a blank for each lot of reagent-grade Hydrochloric Acid and perchloroethylene by extracting the Hydrochloric Acid in the same way as for the standard. Calculate a response factor (R) by dividing the concentration (C), in milligrams per kilogram, for each component by the peak area (A) for that component (subtract any area obtained from the blank sample) ... 

Assay Dissolve about 100 mg of sample, accurately weighed, in 20 mL of water add 40.0 mL of 0.1 N ceric sulfate prepared as directed for Volumetric Solutions under Solutions and Indicators (or use a commercially available solution) mix well and add 2 mL of silver sulfate solution (5 g of Ag2S04 dissolved in 95 mL of concentrated sulfuric acid). Cover, heat nearly to boiling, and continue heating for 30 min. Cool to room temperature, and titrate with 0.1 A ferrous ammonium sulfate to a pale yellow color. Add 2 drops of orthophenanthroline TS, and continue the titration to a salmon-colored endpoint, recording the volume required, in milliliters, as S. Perform a residual blank titration (see General Provisions), and record the volume required as B. Each milliliter of the volume B - S is equivalent to 2.650 mg of NaH2P02H20. 

Preparation of the Standard Curve Dilute the Folic Acid Stock Solution with water to a measured volume such that after incubation, as described below, response at the 5.0-mL level of this solution is equivalent to a titration volume of 8 to 12 mL. This concentration is usually 1 to 4 ng of folic acid per mL but can vary with the culture used in the assay. Designate this solution as the Folic Acid Working Standard Solution. To duplicate test tubes, addO.O (for uninoculated blanks), 0.0 (for inoculated blanks), 1.0,2.0,3.0,4.0, and 5.0 mL, respectively, of the Folic Acid Working Standard Solution. Add water to each tube to make a final volume of 5.0 mL. Add 5.0 mL of the Basal Medium Stock Solution to each tube, and mix. Cover the tubes suitably to prevent bacterial contamination, and sterilize by heating in an autoclave at 121° for 10 min. Cool tubes rapidly to keep color formation to a minimum. 

Six 50-mg blank hair samples were extracted by SFE and the noise was integrated for the ion used for quantification (m/z = 355 for codeine, 369 for ethylmorphine, 383 for 6-MAM, and 397 for morphine) in a retention time window of tj + 0.5 min. The LOD and LOQ were determined (n = 6) using lUPAC methods. For each substance the standard deviation of the blank value (Sg) was determined. The mean area converted from the noise was calculated as concentration equivalent based on a calibration graph. The LOD is defined as 3Sg and the LOQ as lOSg. 

The nature of our concern is best illustrated by a specific example. Blank and Kidwell use a cocaine solution of 100,000 ng/mL for their contamination experiments, to which they add approximately 1 pCi of tritium-labeled cocaine, i.e., approximately one million counts per minute. Therefore, they have approximately a sensitivity of 10 cpm/ng of sample. Decontamination of hair means that residual drug concentration must drop below the endogenous cutoff level of 5 ng/10 mg of hair, i.e., to 50 cpm/10 mg hair. Now if the labeled cocaine has a radiochemical impurity of as little as 0.1%, this corresponds to 1000 cpm or to 100 ng of residual cocaine equivalents. Since self-irradiation of tritium-labeled material tends to form polymeric impurities, and since these are likely to preferentially bind to hair, one incurs a major risk of concluding erroneously that the residual radioactivity represents residual cocaine contamination rather than contamination by polymeric degradation products. 

Concentration of actin is determined photometrically at 290 nm against G-buffer as blank an extinction of 0.62 is equivalent to 23.8 nM actin. 

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