Blank solution

Fig. 1. Voltammograms of AA in 0.1 M H,SO. The top and bottom curves refer to voltammograms for a 0.5 mM AA solution and a blank solution, respectively. One increment in the concenttation is 0.1 mM.

Procedure To an aliquot of the sample solution containing 12.5 - 305 p.g of platinum(IV) were added 5 ml of hydrochloric acid - sodium acetate buffer of pH 2.1, 1 ml of O.IM Cu(II) sulphate solution, and 3.0 ml of 0.5% propericiazine solution. The solution was diluted to 25 ml with distilled water, mixed thoroughly, and the absorbance measured at 520 nm against a reagent blank solution after 10 min. The platinum concentration of the sample solution was determined using a standar d calibration curve. 

The initial concentrations were AC2O, 0.53 M ROH, 0.41 M DMAP, 0.17 M. Portions (5.0 ml) of the sample solution or the blank solution were with-... 

Procedure. Dissolve 0.0079 g of pure lead nitrate in 1 L of water in a graduated flask. To 10.0 mL of this solution (containing about 50 p.g of lead) contained in a 250 mL separatory funnel, add 75 mL of ammonia-cyanide-sulphite mixture (Note 1), adjust the pH of the solution to 9.5 (pH meter) by the cautious addition of hydrochloric acid (CARE ), then add 7.5 mL of a 0.005 per cent solution of dithizone in chloroform (Note 2), followed by 17.5 mL of chloroform. Shake for 1 minute, and allow the phases to separate. Determine the absorbance at 510 nm against a blank solution in a 1.0 cm absorption cell. A further extraction of the same solution gives zero absorption indicative of the complete extraction of the lead. Almost the same absorbance is obtained in the presence of 100 pg of copper ion and 100 pg of zinc ion. 

When plotting the standard curve it is customary to assign a transmission of 100 per cent to the blank solution (reagent solution plus water) this represents zero concentration of the constituent. It may be mentioned that some coloured solutions have an appreciable temperature coefficient of transmission, and the temperature of the determination should not differ appreciably from that at which the calibration curve was prepared. 

Measurement of the absorbance of the test and standard solutions will be carried out in the manner described above for comparing cells, but, of course, choosing the wavelength appropriate to the substance being determined. The blank solution will be of similar composition to the test solution, but without any of the determinand. The prepared solution of the test material must be diluted if necessary so that the absorbance lies in the 0.2-1.5 region. 

Procedure. Transfer the neutral sample solution (<100 gMg), free from calcium and other metals, to a 100 mL graduated flask with calibrated neck. Add 25 mL of the buffer solution, dilute to just below the 90 mL graduation mark, and shake. Add 10.0 mL of the solochrome black solution carefully. Shake to mix and dilute to the 100 mL mark with water. Measure the absorbance immediately at 520 nm (green filter) against that of a blank solution, similarly prepared but containing no magnesium. 

Procedure. To 100 mL of the neutral sample solution (containing not more than 0.4 mg nitrite) add 2.0 mL of solution A and, after 5 minutes, 2.0 mL of solution B. The pH at this point should be about 1.5. Measure the absorbance after 10 minutes in the wavelength region of 550 nm (yellow-green filter), in a spectrophotometer against a blank solution prepared in the same manner. Calculate the concentration of the nitrite from a calibration plot prepared from a series of standard nitrite solutions. 

Fill a test-tube with distilled water or with a blank solution to a depth of not less than 3 cm, and set to zero by means of the zero control. 

Prepare a blank solution by carrying through all the sequences of the separation procedures using a hydrochloric acid solution to which no alloy has been added, and then measure the absorption given by this blank solution, by a series of standard solutions containing from 1 to 10 /rg Pb mL 1 prepared by suitable dilution of the lead caprate stock solution (see Note), and finally of the extract prepared from the sample of alloy. Plot the calibration curve and determine the lead content of the alloy. 

To determine die diffusion current, it is necessary to subtract the residual current. This can be achieved by extrapolating the residual current prior to the wave or by recording die response of the deaerated supporting electrolyte (blank) solution. Addition of a standard or a calibration curve are often used for quantitation. Polarograms to be compared for this purpose must be recorded in the same way. 

Recommendation Dilute the standard solutions twice with blank solutions prepared from each of the blank samples. Impurities in the blank samples reduce the thermal decomposition of the target analytes in the injection port and stabilize the profiles of ionization and fragmentation of the target analytes. 

Residual current in polarography. In the pragmatic treatment of the theory of electrolysis (Section 3.1) we have explained the occurrence of a residual current on the basis of back-diffusion of the electrolysis product obtained. In conventional polarography the wave shows clearly the phenomenon of a residual current by a slow rise of the curve before the decomposition potential as well as beyond the potential where the limiting current has been reached. In order to establish the value one generally corrects the total current measured for the current of the blank solution in the manner illustrated in Fig. 3.16 (vertical distance between the two parallel lines CD and AB). However, this is an unreliable procedure especially in polarography because, apart from the troublesome saw-tooth character of the i versus E curve, the residual current exists not only with a faradaic part, which is caused by reduction (or oxidation)... 

The final blank solution is set at 100% transmittance and the transmittance of the test solution is then measured. Reading from the standard curve, one obtains the number of micrograms of triazole. 

The trick is that bulk Te (Te°), can be stripped at a more negative potential in a supporting electrolyte (blank) solution. In this way, only Te(upD) is left, due to stabilization by bonding with previously deposited Cd, forming CdTe ... 

This is a method involving a two-compartment cell with a salt bridge connection and having two identical indicator electrodes. The sample solution is placed in one compartment and a blank solution having the same total ionic strength in the other. Increments of a standard solution of the species to be determined are added to the blank compartment until the cell potential is zero. At this point, the activities of the species of interest in each compartment are equal and that of the sample solution can therefore be calculated. A concentrated standard solution should be used to minimize dilution errors. This method is particularly useful for the determination of trace amounts or where no suitable titrant can be found. 

Spectral interferences may arise from the close proximity of other emission lines or bands to the analyte line or by overlap with it. They can often be eliminated or minimized by increasing the resolution of the instrumentation, e.g. changing from a filter photometer to a grating spectrophotometer. Alternatively, another analyte line can be selected for measurements. Correction for background emission is also important and is made by monitoring the emission from a blank solution at the wavelength of the analyte line or by averaging measurements made close to the line and on either side of it. 

In practical situations the absorbance of a sample is determined by making two measurements, the first to determine 70 and the second to determine I. The determination of I0 is used to cancel a large number of experimental factors that could affect the result. When measuring I0 the sample container must closely match the unknown container in all ways except for the analyte content. The cuvettes should be a matched pair if a double beam instrument is used and the same cuvette can be used for both the blank and sample with a single beam instrument. The blank solution filling the cuvette should be identical to the solvent that the sample is dissolved in, except for the sample itself. If done correctly, the least-squares line for the calibration graph will come very close to the 0,0 point on the graph. 

FIGURE 7.19 Illustration of the definitions of I and I0. The intensity of the light that has passed through a blank solution is designated I0. The intensity of the light that has passed through the analyte solution is less than I0 and is designated I. 

Beer s law (g) The intensity of light after having passed through a blank solution. 

A Blank solution is prepared by adopting the above operations sequentially, but without the addition of the K2S04 solution,... 

Insert the Blank solution in the nephelometer and adjust to zero reading of the scale by the aid of zero-control-knob,... 

Place the blank solution into the matched test-tube of the nephelometer and adjust the reading to zero. 

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