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Blank determinations

Due to the strong adsorption properties of glass, plastic beakers should be employed throughout. [Pg.157]


Running a blank determination. This consists in carrying out a separate determination, the sample being omitted, under exactly the same experimental conditions as are employed in the actual analysis of the sample. The object is to find out the effect of the impurities introduced through the reagents and vessels, or to determine the excess of standard solution necessary to establish the end-point under the conditions met with in the titration of the unknown sample. A large blank correction is undesirable, because the exact value then becomes uncertain and the precision of the analysis is reduced. [Pg.131]

The method may be standardised, if desired, with pure potassium dihydrogen-orthophosphate (see below) sufficient 1 1 hydrochloric acid must be present to prevent precipitation of quinoline molybdate the molybdophosphate complex is readily formed at a concentration of 20 mL of concentrated hydrochloric acid per 100 mL of solution especially when warm, and precipitation of the quinoline salt should take place slowly from boiling solution. A blank determination should always be made it is mostly due to silica. [Pg.304]

Carry out a blank determination on the acetic anhydride/ethyl acetate solution following the above procedure without adding the carbohydrate. Use the difference between the blank titration, Vb, and the sample titration, Vs, to calculate the number of hydroxyl groups in the sugar (Note 2). [Pg.307]

As the acetonitrile may contain basic impurities which also react with the perchloric acid, it is desirable to carry out a blank determination on this solvent. Subtract any value for this blank from the titration values of the amines before calculating the percentages of the two amines in the mixture. [Pg.308]

The titration error will increase with increasing dilution of the solution being titrated and is quite appreciable (ca 0.4 per cent) in dilute, say 0.01 M, solutions when the chromate concentration is of the order 0.003-0.005M. This is most simply allowed for by means of an indicator blank determination, e.g. by measuring the volume of standard silver nitrate solution required to give a perceptible coloration when added to distilled water containing the same quantity of indicator as is employed in the titration. This volume is subtracted from the volume of standard solution used. [Pg.344]

Discussion. One very important application of potassium dichromate is in a back-titration for the environmental determination16 of the amount of oxygen required to oxidise all the organic material in a sample of impure water, such as sewage effluent. This is known as the chemical oxygen demand (C.O.D.) and is expressed in terms of milligrams of oxygen required per litre of water, mg L l. The analysis of the impure water sample is carried out in parallel with a blank determination on pure, double-distilled water. [Pg.378]

Carry out a blank determination, preferably before passing the iron solution through the reductor, by running the same volumes of acid and water through the apparatus as are used in the actual determination. This should not amount to more than about 0.1 mL of 0.02M permanganate, and should be deducted from the volume of permanganate solution used in the subsequent titration. [Pg.411]

It is advisable to carry out a blank determination with the hydrofluoric acid, and to allow for any non-volatile substances, if necessary. [Pg.487]

After the acetylation, the analytical finish is not based on non-aqueous titration, but consists in acid titration after complete conversion of the anhydride with water and by comparison with a blank determination. [Pg.254]

The concentration of dimethylketene is determined by titration of an aliquot at ice temperatures with 0.1 N sodium hydroxide using phenolphthalein indicator. Under these conditions, blank determinations indicate that ethyl acetate is not hydrolyzed. [Pg.16]

Dissolve about 300 mg of Miconazole, accurately weighed, in 40 mL of glacial acetic acid, add 4 drops ofp-naphtholbenzein TS, and titrate with 0.1N perchloric acid VS to a green endpoint. Perform a blank determination, and make any necessary correction. Each mL of 0.1 N perchloric acid is equivalent to 41.61 mg of C18EL4CI4N2O. [Pg.31]

In contrast, a systematic error remains constant or varies in a predictable way over a series of measurements. This type of error differs from random error in that it cannot be reduced by making multiple measurements. Systematic error can be corrected for if it is detected, but the correction would not be exact since there would inevitably be some uncertainty about the exact value of the systematic error. As an example, in analytical chemistry we very often run a blank determination to assess the contribution of the reagents to the measured response, in the known absence of the analyte. The value of this blank measurement is subtracted from the values of the sample and standard measurements before the final result is calculated. If we did not subtract the blank reading (assuming it to be non-zero) from our measurements, then this would introduce a systematic error into our final result. [Pg.158]

Determinate errors may be constant or proportional. The former have a fixed value and the latter increase with the magnitude of the measurement. Thus their overall effects on the results will differ. These effects are summarized in Figure 2.1. The errors usually originate from one of three major sources operator error instrument error method error. They may be detected by blank determinations, the analysis of standard samples, and independent analyses by alternative and dissimilar methods. Proportional variation in error will be revealed by the analysis of samples of varying sizes. Proper training should ensure that operator errors are eliminated. However, it may not always be possible to eliminate instrument and method errors entirely and in these circumstances the error must be assessed and a correction applied. [Pg.628]

The recovery of these herbicides was checked by adding known volumes of standard solutions to lOg portions of the ten air-dried soil types followed by removal of solvent by a gentle stream of air. The soils were allowed to stand for 24h and then treated as described above. The results obtained are shown in Table 9.20. Blank determinations carried out on these soils showed that any herbicide present was below the limit of detection. [Pg.261]

Here the concentration range of the analyte in the ran is relatively small, so a common value of standard deviation can be assumed. Insert a control material at least once per ran. Plot either the individual values obtained, or the mean value, on an appropriate control chart. Analyse in duplicate at least half of the test materials, selected at random. Insert at least one blank determination. [Pg.88]

Longer (e g. n > 20) frequent runs of similar materials Again a common level of standard deviation is assumed. Insert the control material at an approximate frequency of one per ten test materials. If the run size is likely to vary from run to run it is easier to standardise on a fixed number of insertions per run and plot the mean value on a control chart of means. Otherwise plot individual values. Analyse in duplicate a minimum of five test materials selected at random. Insert one blank determination per ten test materials. [Pg.88]

Here the concept of statistical control is not applicable. It is assumed, however, that the materials in the run are of a single type. Carry out duplicate analysis on all of the test materials. Carry out spiking or recovery tests or use a formulated control material, with an appropriate number of insertions (see above), and with different concentrations of analyte if appropriate. Carry out blank determinations. As no control limits are available, compare the bias and precision with fitness-for-purpose limits or other established criteria. [Pg.88]

Bilirubin is eliminated by dializing the incubated /Miitrophenolate ion (at pH 10.5, and maintaining at 38°C for 30 minutes) into 2-amino-2-methyl-l-propanol, without carrying out the blank determination stated... [Pg.60]

In order to ascertain the effect of the impurities present in the reagents employed and reaction vessels used besides establishing exactly the extent to which an excess of standard solution required to locate the exact end-point under the prevailing experimental parameters of the unknown sample—a blank determination is an absolute necessity. It may be accomplished by performing a separate parallel estimation, without using the sample at all, and under identical experimental parmeters as employed in the actual analysis of the given sample. [Pg.76]

Calibration of instruments and apparatus (if) Parallel control determination (// / ) Blank determination... [Pg.89]

Procedure Weigh accurately about 0.4 g, previously dried and stored in a vacuum desiccator, and dissolve in 50 ml of glacial acetic acid, add 10 ml of mercuric acetate solution, one drop of crystal violet solution and titrate with 0.1 N perchloric acid to a blue-green end point. Perform a blank determination and make any necessaiy correction. Each ml of 0.1 N perchloric acid is equivalent to 0.01957 g of C8H18C1N02. [Pg.111]

In summing up, the net reaction in the process of standardization has been expressed. The interaction between the water in the solvent (DMF) and the titrant is equivalent to the volume of sodium methoxide consumed by DMF or may be considered as a blank determination. [Pg.118]

Procedure Weigh accurately about 0.2 g of acetomenaphthone and boil it with 15 ml of glacial acetic acid and 15 ml of dilute hydrochloric acid under a reflux condenser for 15 minutes. Cool the contents carefully and taking adequate precautions to avoid any atmospheric oxidation. Add 0.1 ml of ferroin sulphate solution as indicator and titrate with 0.05 N ammonium ceric sulphate. Repeat the assay without the substance being examined (blank determination) and incorporate the correction, if any. Each ml of 0.05 N ammonium ceric sulphate is equivalent to 0.006457 g of C15H1404. [Pg.135]

In direct titration, usually an appropriate buffer solution and a suitable indicator are added to the M2+ (metal-ion) solution and subsequently the resulting solution is titrated with previously standardized disodium-EDTA until the indicator just changes colour. Sometimes, a simultaneous blank determination is also recommended to have a check for the presence of traces of metallic impurities in the reagents. [Pg.166]

A blank determination is always performed simultaneously to account for the losses caused by the bromine as well as iodine vapours due to the interaction of excess bromine on potassium iodide. [Pg.216]

Whatman No. 2 filter paper, collecting the filtrate in a boron-free tube inside the filter flask. Terminate the filtration after 5 min, and retain the filtered extract for the determination of boron. Carry out a blank determination. [Pg.59]

Carry out a blank determination using 2 g of sucrose in place of the sample. [Pg.77]

Procedure (extraction). Transfer 5 ml (scoop filled and struck off level without tapping) of air-dry soil, sieved to 2 mm into a bottle (e.g. wide-mouth, square HDPE). Add 100 ml of sodium bicarbonate reagent, pH 8.50, cap the bottle and shake on a reciprocating shaker, at approximately 275 strokes of 25 mm length per minute, for 30 min at 20°C. Filter a portion immediately through a Whatman No. 2 filter paper, rejecting the first few millilitres of filtrate. Carry out a blank determination. [Pg.84]

Calculation. Read from the standard graph the number of pg of P equivalent to the absorbances of the sample and blank determinations. Subtract the blank from the sample value, and multiply the difference by 4. The result gives the... [Pg.85]

The extraction method of Hislop and Cooke (1968), has been outlined in Chapter 4, Phosphate extractants. A blank determination without soil should be carried out. The autoanalysis manifold is shown in Fig. 5.4. Some adjustments to dilution and/or readout sensitivity may be necessary to handle both... [Pg.87]


See other pages where Blank determinations is mentioned: [Pg.107]    [Pg.185]    [Pg.392]    [Pg.395]    [Pg.401]    [Pg.857]    [Pg.226]    [Pg.117]    [Pg.207]    [Pg.76]    [Pg.78]    [Pg.95]    [Pg.97]   
See also in sourсe #XX -- [ Pg.7 ]

See also in sourсe #XX -- [ Pg.76 ]

See also in sourсe #XX -- [ Pg.7 ]

See also in sourсe #XX -- [ Pg.207 ]




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