Liquids, automatic sampling

Continuous automatic sampling is carried out from these cells into ordinary liquid scintillation vials by an ISCO brand (Lincoln, N.E.) Retriever III fraction collector whose timing mechanism has been altered so that nine timepoints can be sampled in intervals of up to 99.0 hours for 14 diffusion cells. 

Beta particle calibration sources span energies from about 100 to 3,000 keV for proportional counters, and down to a few keV for liquid scintillation counters. In this experiment, a low-background, gas-flow, end-window proportional counter with automatic sample changer for alpha- and beta-particle counting is calibrated. Beta-particles sources are counted with pulse-height discrimination to eliminate interference from alpha particles the discriminator may be turned off when no alpha particles are present. 

The liquid or solid sample is placed in a vial, which is sealed with a septum and heated to a predetermined temperature for a period of time. Equilibrium between the sample and vapor phase is then established and a portion of the volatiles in the gas phase (headspace) is subsequently injected onto the column. Several different methods have been used to transfer headspace volatiles into the GC, from manual withdrawal that uses a gas syringe, to sophisticated automatic sampling that involves transfer lines, and valves that lead directly onto the column. 

The homogeneity problem is specific to solid samples, as liquid and gaseous samples are considered homogeneous by nature. Thus, for solid samples, an automatic sampling process is recommended to obtain reliable analytical information. To select the most adequate system to obtain a homogeneous sample it is necessary to take into account the sample complexity and the stability of the sample within a certain period of time.37 Further, it is necessary to establish first the nature of analysis that will be used in sample control, especially when the limits of detection are low. One must also be wary of the many contamination risks from reagent impurities, laboratory vessels, laboratory climate, and the operator. 

The automatic sampling of liquids can be carried out with off-line and online samplers. Off-line assemblies consist essentially of an suction pump, a series of flasks and microprocessor allowing programming of the Intervals between successive samplings. An example of this type of set-up is the portable automatic sampler S-4000 of the Philips Environmental Protection Series, a scheme of which Is depicted In Fig. 15.1a. The operational sequence Involved the following events ... 

D-1 Automatic Sampling and Sample Definition of Liquids and Gases... 

Analytical Methods. The analytical method for carbaryl and 1-naphthol by high performance liquid chromatography (HFLC) was recently described for aqueous samples (9). Similarly, these two compounds were analyzed in these studies using a Waters 6000A Solvent Delivery System, WISF Automatic Sample Frocessor, Data Module and Automatic Integrator, and Model 4530 Variable Wave Length Detector, set at 230 nm. A Water uBondapak reverse-phase column (25 cm x 2 mm i.d.) was employed. The following experimental conditions were maintained ... 

AUTOMATIC SAMPLE COMBUSTION MEIHODS FOR TEE DETERMINATION OF SOFT BETA-EMITTING ISOTOPES IN DUAL LABELLED ORGANIC COMPOUNDS AND BIOLOGICAL MATERIALS BY LIQUID SCINTILLATION COUNTING... 

Automatic sample preparation methods for the determination of oarbon-14 and/or tritium, and carbon-14 and/or sulfur-36 in dual labelled samples by liquid scintillation counting are presented. The sample is burnt in a stream of oxygen, and the combustion products carrying radioisotopes are subsequently separated and collected for radioactivity determination. Tritium is measured as water, carbon-14 as "carbamate" and sulfur-35 as sulfuric acid. The procedures run automatically, they are free of memory effect and cross contamination, and provide quantitative recovery. 

All samples of l-14C-acetylated SRL and SRC were weighed in combustocones and mixed with cellulose to insure a slow and uniform oxidation. The samples were then oxidized in a Packard Model 306 automatic sample oxidizer for subsequent liquid scintillation measurement of 002 Problems such as sample solubility and color quenching usually experienced in liquid scintillation counting were eliminated by this procedure. Chemical quenching is minimized and chemllumlnesence is entirely eliminated. Because of this counting efficiency is increased and quench correction is unnecessary. For carbon-14 the oxidizer can accommodate a sample size equivalent up to 40 millimoles of CO2... 

We are grateful to Dr. Surendra S. Parmar for the use of Packard Automatic Sample oxidizer and Dr. Robert C. Nordlle for the use of a liquid scintillator spectrometer. We like to thank Dr. Kalsa Salto for recording C-13 NMR. This work was performed under the auspices of the U.S. Department of Energy, Contract No. (EX-76-C-01-2211). 

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