Blank absorbance

Step 4 If you analyze an unknown solution at a future time, run a blank at the same time. Subtract the new blank absorbance from the unknown absorbance to obtain the corrected absorbance. 

In most spectrophotometric analyses, it is important to prepare a reagent blank containing all reagents, but with analyte replaced by distilled water. Any absorbance of the blank is due to the color of uncomplexed ferrozine plus the color caused by the iron impurities in the reagents and glassware. Subtract the blank absorbance from the absorbance of samples and standards before doing any calculations. 

The blank absorbance was 0.038 at 562 nm in a 1.000-cm cell. A serum sample had an absorbance of 0.129. After the blank was subtracted from each standard absorbance, the points in Figure 18-8 were obtained. The least-squares line through the standard points is... 

E. Bill The figure below shows an infrared absorption peak for solutions containing 10 to 50 vol% acetone ([CH3]2C=0) in water. The shape of the spectrum is somewhat different for each mixture, which shifts the baseline (dotted line) and position of the absorption peak. The baseline is the blank absorbance that must be subtracted from each peak absorbance to obtain corrected absorbance. 

Note that the observed absorbance is equal to the absorbance from Cu in the rock plus the blank absorbance. In the lab we measure the observed absorbance and subtract the blank absorbance from it to find the absorbance due to copper. 

Calculate true absorbance of the sample by subtracting blank absorbance from sample absorbance. Use the true sample absorbance and the glucose standard curve to determine pg of glucose in the sample. 

Prepare the titration reaction mix in each reaction tube as shown in the following tables. Add all the components except the main counterion that would mediate folding (Mg2-1- for Mg titration and K+ for K titrations). For each reaction mix, prepare a reference solution of slightly excess volume but with identical reagent concentrations, for blank absorbance measurements. [Note For K+ titrations, prepare two tubes with 10 mM MgCl2 for comparison of the final states of the RNA in highest K+ concentration and in 10 mM Mg2 1.]... 

Vessels Blank Absorbance Value Due to Adsorption [Blank] (Rg r1) L.D (p.g kg-1)... 

The improvement of the procedural blank signal using FEP and PFA tubes instead of glass and quartz tubes is shown in Fig. 1.3. The last shows a better decrease of the signal (blank absorbance) and therefore a lower concentration level will be reached. Fluoromaterials possess a series of unique properties such as wide operational temperature range (-200 to +260°C) and high chemical resistance, thus being particularly useful in trace and ultratrace work. Needless to say, a low analytical blank can substantially improve the limits of detection (LoDs) and the accuracy of the method [10]. 

FIGURE 6.3 Comparison of MTT tetrazolium and tritiated thymidine incorporation assays to measure effects of hGM-CSF on proliferation of TF-1 cells. A no-cell blank absorbance of 0.065 was subtracted from all MTT values before plotting. Similar ED50 values are shown for both assays. (Source Modified from Promega Corporation Technical Bulletin 112. CellTiter 96 Non-Radio active Cell Proliferation Assay.)... 

Calculations Determine the corrected absorbance values by subtracting the Sample Blank absorbance from each of the Diluted Standard Lead Solutions and from the Sample Preparation absorbances. Prepare a standard curve by plotting the corrected Diluted Standard Lead Solutions absorbance values versus their corresponding concentrations expressed as micrograms per milliliter. Determine the lead concentration in the Sample Preparation by reference to the calibration curve. Calculate the quantity of lead, in milligrams per kilogram, in the sample taken by the formula... 

Subtract the blank absorbance from the sample absorbance (the difference should be between 0.100 and 1.000). Determine the acid phosphatase activity (HFU/mL) from the standard curve, and multiply by the dilution factor. For the activity of solid samples, use the following equation ... 

The blank absorbance (AB) in determined in the same way except that the reagents are added to the water sample in the order acetic acid, ammonium hydroxide, sodium nitrite. Colored nitro compounds are not formed in the basic solution and thus the blank absorbance is due to the reagents and the substances originally present in the water. The net absorbance (As) is calculated as the difference between Ax and AB. 

Hydroxide concentration. The initial rate of reaction is pseudo first order with respect to hydroxide concentrations above 0.5 mmol/L however, at 500 mmol/L there is an increased degradation of the Jaffe complex. Furthermore, at hydroxide concentrations above 200 mmol/L, the blank absorbance increases significantly. 

Absorbance of sample - Absorbance of sample blank Absorbance of standard - Absorbance of standard... 

Calculate the percent displacement using the following equation % displacement = 100 x (absorbance value of blank-absorbance value of lOng/mL cotinine (/absorbance value of blank (tec Note 12). 

Triethylamine purification - if a blank absorbance is >0.01, reflux 100 mL ET3N with 20 mL HjO and 2 g Na hydrosulfite at least 8 hours. Wash with HjO, dry by distilling into a Dean-Stark trap, then distill, collecting the first 75 mL. Store over anhydrous Na2C03 or K2CO3. 

Each time a series of samples is run, the absorbance of one or more blank solutions is read versus pure solvent and, if appreciable (sO.Ol A with a Spectronic 20), this is subtracted from all analyte solution readings. Actually, if file blank solution is essentially colorless (i.e., its absorbance is small), this solution is often used in place of the solvent for adjusting the 100% transmittance reading. Any blank absorbance is then automatically corrected for (subtracted). This method... 

There is probably an impurity in the blank which absorbs at the analytical wavelength. The impurity appears to be present at constant concentration since subtraction of the blank absorbance from all values results in a linear plot with zero intercept. 

A nitrite analysis conducted by the procedure in Section 18-4 gave data in the table on the next page. Fill in corrected absorbance, which is measured absorbance minus the average blank absorbance (0.023). Construct a calibration line to find (a) ppm nitrite nitrogen uncertainty and (b) molar concentration of nitrite in the aquarium. Use the average blank and the average unknown absorbances. 

The plot indicates a linear concentration/absorbance relationship, i.e., calibration has to consider a calibration factor (slope of the regression line, F= 5.1286) and a non-zero blank absorbance of the ZW (A ero = 0.0369 equivalent to a concentration of 0.0318/[Pg.168]

To calculate the concentration of the diluted sample, multiply the absorbance (sample absorbance - blank absorbance) by the dilution factor of 1.91 (105/55) and the calibration factor. 

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