Richard Tykva

Estimation of radioactivity in electrophoresis gels by a scanning semiconductographic procedure

Abstract A fully automatized procedure for determination of radioactivity in a polyacrylamide gel is described that utilizes a semiconductor detector and a selectable preset program. This method is simple, provides high resolution, and permits either stepwise or continuous registration of radioactivity. The record of radioactivity is displayed both graphically and numerically. Partially depleted surface barrier silicon detectors are used for the measurement. In view of the high-energy resolution of the semiconductor detectors, the procedure is particularly suitable for the determination of two or more radionuclides present simultaneously in a gel. A quantitative comparison with results obtained with a liquid scintillation spectrometer and with a windowless flow counter is presented.

Analysis of errors and accuracy of simultaneous H3 and C14 assay in organic substances by means of an internal gas counter

Abstract Accuracy is calculated and the individual procedures are studied with regard to possible sources of errors in the method using the internal gas counter for radioactivity determinations of H 3 and C 14 in double-labelled solid organic compounds. The method facilitates the preparation of a filling of constant composition and determines the relative radioactivity of the individual radionuclides simultaneously. The procedure is designated for dry samples of up to 50 mg and is essentially unaffected by their character and composition. The method is especially suitable for the determination of low radioactivity of both isotopes in biological material, on paper chromatograms and thin-layer chromatograms or in substances causing considerable quenching after introduction into the liquid scintillator.

Exclusion of the sample sorption effects on the instability of liquid scintillation by emulsion counting.

Abstract In activity assays of labeled compounds by liquid scintillation spectrometer, the effects due to sample sorption to the counting vial may be excluded by the use of the Triton X-100-toluene-based mixture in a 1:2 ratio by volume. For the ratio (v/v) of water to this mixture within the interval 1:4 to 1:1, the counting rates in particular channels, corrected to the disintegration half-time, are constant.

Semiconductographic determination of labelled substances in thin-layer chromatography.

Abstract A method is presented for the radioactive detection of β-nuclide-labelled substances in thin-layer chromatography. The method is based on a scanning device with a semiconductor detector; the detection proceeds in the laboratory atmosphere and at room temperature. The measurement and recording may be programmed on a computer. Conditions are considered for 3H- and 14C-detection and also for the detection of simultaneously present 14C and 35S, after the chromatographic separation of nucleic acid components.

The Possible Role of Auxin in Reversing Photoperiodic Induction of Flowering in a Short-day Plant, Chenopodium rubrum L.

Summary IAA (3.10 -4 M) inhibited the photoperiodic induction of flowering in the short day plant Chenopodium rubrum L. when applied during the inductive period to the shoot apex. When applied instead to the cotyledons it is much less effective, but only if the transport of auxin to the apex is inhibited by internode elongation due to gibberellic acid application. In some cases, as with TIBA treatment, this transport was reduced to less than 1 %. The rate of auxin transport was estimated using analytical methods or by semiconductography. The step-wise application of IAA during three or four inductive short days revealed that the inhibitory effect is restricted to the later stage of induction not inhibitable by actinomycine D or cycloheximide. The possible role of auxin in evocation is discussed.

Nondestructive and quantitative evaluation of radioactive spots on two-dimensional peptide maps by an automated procedure

Abstract A semiconductographic scanning method has been described for determination of radioactivity distribution on two-dimensional peptide maps of proteins. In each scanned site, the activity record is printed in counting rates per time interval used. The topographic resolution and measurement interval in particular sites are programmed according to the required measurement accuracy and the activity applied. With a 2 × 2 mm topographic resolution and 2-min counting intervals, all 14 C-labeled peptides were reliably detected on a 10 × 10 cm Whatman 3MM paper down to the minimum activity of 50 nCi of the applied sample. In the case of elongated spots, a procedure is described which makes it possible to determine whether two partly overlapping peptides are involved.

Correction of the continual scanning record of radioactivity distribution I: Smoothing☆

Abstract A method is described of smoothing the graphical record of the counting rate obtained in measuring the radioactivity distribution during continual scanning of a plane sample by the detector. The smoothing is based on using a smoothing operator with coefficients optimized according to the recorded curve. The method enables on-line smoothing if the curves are similar in shape. Its use is demonstrated on the example of the simultaneous determination of the distribution of 14C and 32P.

Radio gas chromatography of carbon-14-labelled compounds using continuous activity assay by a semiconductor detector

A method and apparatus are described for the direct measurement of 14C activity in fractions leaving a gas chromatograph by means of a silicon-diffused detector; the simple device can readily be attached to a conventional chromatograph. The method was tested on substances boiling between 31.5° and 205.8°. With use of a preparative gas chromatograph, with thermal-conductivity mass detection, the limit of detection of the device described was 0.15 μCi.

Correction of the continual scanning record of radioactivity distribution II: Deconvolution☆

Abstract A procedure has been developed to eliminate the “smudging” of the imaging of the one-dimensional radioactivity distribution in a plane sample due to the counting geometry in the scanner. The procedure, based on the regularization method, simultaneously enables the error of the measurement due to the statistical nature of radioactive decay to be estimated. The advantages of the described procedure for determining the distribution of substances labelled by beta emitters are demonstrated on two examples.