Blanking Experiments

Control or blank experiments have frequently to be employed in organic estimations. Their value is twofold ... 

C.HsNH, + CHjCO-O-COCHa = C.R NHCOCHs -h CHjCOOH then hydrolysed with water and the total free acetic acid estimated by titration with standard NaOH solution, the result being compared with that obtained in a control or blank experiment. 

The number of ethylenic linkages In a given compound can be established with accuracy by quantitative titration with perbenzoic acid. A solution of the substance ajid excess of perbenzoic acid in chloroform is allowed to stand for several hours at a low temperature and the amount of unreacted perbenzoic acid in solution is determined a blank experiment is run simultaneously. 

A blank experiment, employing for distillation the residue resulting from the evaporation of 25 c.c. of the alcoholic potash used in 5, previously neutralised by means of sulphuric acid. 

Ester found in 5 less the amount of ester equivalent to the volume of deci-normal sodium hydroxide used up in the blank experiment. 

Care must be taken that the filter paper is free from chlorine. This should be determined by a blank experiment. This process has been strongly recommended by Schimmel Co., but there is considerable doubt whether it will detect minute quantities of chlorine. 

Leerversuch, m. blank experiment or test no-load test. 

NuU-vektor, m. zero vector. -verfahren, n. zero method, -versuch, m. blank experiment, blank teat. -wert, m. zero value, zero, naught. 

For the most accurate work, and particularly when the amount of carbon dioxide is small, a blank experiment must be run with the reagents alone before the determination... 

Follow good experimental practice Always make comparisons with experiments performed under identical conditions. Check for reproducibility and that the experiments are not limited by such trivial factors as thermodynamics. Check for cleanliness and run blank experiments for the reactor and any inert filling material if such has been used. 

Our parallel experiments, in which subtilisin Carlsberg was used to promote hydrolysis of A-acetyl-A-benzyl arenesulfinamides, led to exclusive S-N bond breaking. However, the recovered substrates were racemic. Moreover, blank experiments showed that a spontaneous chemical hydrolysis contributed to the process to a much higher degree than that in the cases shown in Ref. 47. Hence, a conclusion was drawn that in our case the hydrolysis proceeded without involvement of the subtilisin active site Kielbasihski, P. Albrycht, M. Mikolajczyk, M. Unpublished results. 

Similar SSIMS and TDS results were obtained for rhodium on tltanla and fiir hydrogen chemisorption on both substrates. In a blank experiment Involving i o metal over layer, temperature programming while following the T1 and TIO SIMS signals (Fig. 4) shows that the tltanla thin film does not begin to change until the temperature reaches about 760 K, well beyond the 615 K where Tl was first noted to Increase on the systems with thin metal overlayers. ... 

Fig 3 shows the results of two temperature-programmed experiments. In the first (blank) experiment CH4 reacts with a "bare" FeZSM-5 zeolite, while in the second one it reacts with the zeolite after a-oxygen loading on its surface. Obviously, the bare surface is quite inert towards methane (Fig 3a) after reactor opening a weak CH4 adsorption occurs at room temperature. A slight heating results in a complete recovery of the CH4 pressure. 

Figure 1. Conversions of the alkane (filled points) and of NO (open points) in the blank experiment.

Fig. 3.18. Kinetics of conductivity of ZnO film during adsorption of methyl radicals CH3 at room temperature depending on the degree of preliminary alloying of the surface by titanium atoms. 1 - Blank experiment with a clean (Ti-atom free) film (O - before doping - after heating of alloyed film at 350 C, i. e. after the film has been regenerated) 2-5 - Experiments with doped films. Doping degree increases in the following row 2<3<4<5.

Fig. 2.4. (a) Thermal desorption blank experiment. The Pt electrode was held at 0.45 V vs. RHE in the base electrolyte (5 x 10 2 M H2S04) during 120 s and then transferred to the UHV. (b) Thermal desorption spectra of adsorbed CO on Pt after adsorption from an aqueous solution. Temperature scan 5 K/s. 

The MS response after Sn(IV) addition is given in Fig. 4.5 for two oxidation potentials Eox. The C02 signal grows and passes through a maximum after some minutes. A more pronounced response is observed at higher potentials. The lowest potential at which this effect can be observed is ca. 0.425 V. Blank experiments (without addition of tin, dashed curve in Fig. 4.5) show a C02 production at potentials above 0.4 V, but this was always lower than in the presence of tin. 

The current-time response of the system during Sn(Il) addition presents the same features as the mass intensity-time curve. For comparison the i-t curve for a blank experiment (only adsorbed methanol being present, no tin addition) is also shown in Fig. 4.6a. The observed response is not simply the sum of the individual responses of Sn(II) (Fig. 4.2b) and adsorbed methanol (see dashed curve in Fig. 4.6a), to the applied potential step. 

The general experimental procedure employed in the study here has been described previously (7), thus only a brief overview is presented here. For all experiments, 45 mL deionized water and catalyst (50 mg Pd-black for 3-buten-2-ol and 25 mg for l,4-pentadien-3-ol) were added to the reaction cell. For ultrasound-assisted, as well as stirred (blank) experiments, the catalyst was reduced with hydrogen (6.8 atm) in water for 5 minutes at an average power of 360 W (electrical 90% amplitude). The reagents (320 mg 3-buten-2-ol or 360 mg l,4-pentadien-3-ol) were added to the reduced catalyst solution to achieve... 

The results of Ito et a/.101 indicate that careful experiments including enough blank experiments are necessary in studies of photoelectrochemical reduction products of carbon dioxide because, unfortunately, the products observed to date are in very low concentrations. Purification of the carbon dioxide gas itself should also be considered, expecially in experiments in which a continuous flow of C02 gas is used. Accumulation of organics which are present as impurities in C02 gas is often observed. Purification methods for C02 gas used are given in some papers,95"97,102 but establishment of a common recommended method would be helpful. Also, it may be advisable to reexamine earlier work on C02 reduction to exclude meaningless results. In future experiments, the use of labeled 13C02 is to be recommended. 

The quantity k3 may be considered as an instrumental constant to be determined in a blank experiment—that is, without added solute. In this case, the current is given by I(t)/I(0) = (1 - vt/d) exp( - k3 t), from which k can be determined. With the solute added, the current initially decays exponentially (fast decay) from which is determined h + k2 + k3, while the ratio of the initial plateau to the initial current gives k2/(k] + k2 + k ). The detachment rate k2 is now obtained from the last two numbers, and then the attachment rate fe, is also obtained since k3 is already predetermined. In short, both attachment (kj and detachment (k2) rates are obtainable from the time dependence of the cell current following a brief pulse of ionizing radiation. 

As was discussed above, it is essential to determine the effect, if any, that the emersion process has on the double layer. To do this, Wilhelm and colleagues have performed the definitive type of blank experiment. CO was adsorbed onto the Pt working electrode from sulphuric acid electrolyte. After adsorption, the CO-saturated solution was replaced with pure electrolyte. The potential of the electrode was then ramped in order to oxidise off the adsorbate, as C02, and the voltammogram so obtained is shown in Figure 2.118(a). The experiment was then repeated CO was adsorbed as before, but the electrode was emersed and transferred into the UHV chamber, before being re-immersed and the potential ramp applied. The voltammogram so... 

Readily available copper(II) complexes derived from o-nitrosophenols react with dimethyl acetylenedicarbonxylate to give the 1,4-benzoxazine products that would be expected from formal [4 + 2] cycloaddition across the diheterodiene system (Scheme 168).239 No such reaction is observed in blank experiments with uncomplexed tautomeric nitrosophenols hence the copper may cause sufficient electronic perturbation within the heterodiene complex to allow reaction to occur. 

Fig. 4.—Mass Fragmentography (m/e 161) of Methylated Hexose Derivatives from the Disialosy] Ganglioside. [Top, before treatment with neuraminidase bottom, after treatment with Vibrio cholerae neuraminidase. The methylated hexose derivatives identified are (A) 2,4,6-tri-O-methylgalactose (B) 2,3,6-tri-O-methylglucose (C) 2,3,4,6-tetra-O-methylgalactose. The peaks eluting before C are unrelated signals that were also detected in a blank experiment employing the neuraminidase treatment. Conditions 3% of QF-1, at 190°. Reproduced, by permission, from Ref. 80.]...

Table 2 Check and blank experiments showing levels of incorporation of tritium into preformed polyisobutylenes (PIB) and a saturated hydrocarbon (nonadecane) ...

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 term JT A Hi in equations 8.1 and 8.3 is frequently very small compared to the uncertainty in the determination of A/frcp and in many instances can safely be neglected. This should of course be tested by performing blank experiments under normal operating conditions. For example, the enthalpy associated with breaking an ampule (independently from the contribution from vaporization effects) can be determined by breaking ampules partially filled with the calorimetric solvent in the calorimetric solvent. For many systems this contribution is negligible, provided that a well-designed breaker mechanism and ampules ensure that the dissipation of heat is reduced to a minimum. The importance of vaporization effects can be evaluated as described by Vanderzee [129]. 

---