Sample Changers

Metrohm have also designed the 672 Titroprocessor with the 655 Dosimat (Fig. 5.14 and p. 319) as a rapid routine titrator with three functions SET as an end-point titration, GET as a titration to find one or more equivalence points and KFT for Karl Fischer or other titrations with polarized electrodes it can be expanded into an automatic series titrator by connecting the 624 Sample Changer for ten samples. 

By connecting the PRS 12 Alpha Printer, complete documentation of titration results, stored methods or other user input is available. The SAC 80 sample changer can be connected for fully automatic titrations or pH measurements on 20 samples, while the sample weights can be keyed into the TTT 85 titrator. 

The sample is introduced into the spectrometer, locked onto the deuter-ated solvent (here CDC13) and the homogeneity optimized by shimming as described by the instrument manufacturer (this can often be done automatically, particularly when a sample changer is used). 

An automatic probe tuning and matching (ATM) accessory allows one to automatically tune the NMR probe to the desired nuclei s resonant frequency and match the resistance of the probe circuit to 50 Q [7]. Traditional NMR instruments are designed so that one must perform these adjustments manually prior to data acquisition on a new sample. The advent of the ATM accessory allows the sampling of many different NMR samples without the need for human intervention. The ATM in conjunction with a sample changer enables NMR experiments to be conducted under complete automation. The sample changers are designed so that once the samples are prepared, they are placed into the instrument s sample holders. Data are then acquired under software control of both the mechanical sample delivery system as well as the electronics of the spectrometer. 

The titration process has been automated so that batches of samples can be titrated non-manually and the data processed and reported via printouts and screens. One such instrument is the Metrohm 670 titroprocessor. This incorporates a built-in control unit and sample changer so that up to nine samples can be automatically titrated. The 670 titroprocessor offers incremental titrations with variable or constant-volume steps (dynamic or monotonic titration). The measured value transfer in these titrations is either drift controlled (equilibrium titration) or effected after a fixed waiting time pK determinations and fixed end points (e.g. for specified standard procedures) are naturally included. End-point titrations can also be carried out. 

The automation of sample preparation is clearly a requirement if one wants to measure a reasonably high number of test compounds. While sample changers have been used for a long time in analytical NMR laboratories, sample preparation robots have been introduced only recently, especially in the field of biomolecular NMR. They offer the great advantage that the samples are freshly prepared under identical conditions and delivered to the NMR instrument in a just-in-time fashion. Thus, they circumvent the disadvan-... 

Figure S.ll shows the flow diagram of the microprocessor-controlled preconcentration equipment, which is configured here for off-line operation, and consists of a sample changer, three separate peristaltic pumps (PI, P2 and P3) for the sample solution, buffer and add, three magnetic valves (VI, V2 and V3), the preconcentration column filled with chelating ion-exchange material (7 mm i.d., 10—30 mm height) and a fractionating unit for the addic column eluate. The flow-rates for the sample solution, buffer and add are adjusted to S ml/min.

PI - P2- P3 - 2 Start next sample with step 1 Actuate sample changer... 

The system, which is shown in Fig. 7.3, consists of the sample changer, rinsing units, control computer and the Aroma software. Existing measuring instruments may he used subject to compatibility. The software currently supports the following instruments ... 

The microprocessor control also enables the instrument to be set to calculate pA"a values directly from the pH profile it obtains by titration of a sample. A sample changer can be incorporated so that several samples can be automatically titrated. 

Optional) Robotic sample changer to facilitate exchange of samples for diffraction analysis (reeNote 8). 

In principle there is no label, if not set by the user, to identify the given DISNMR file as an FID or spectrum, or if the NMR data is from a H or C experiment. However the Bruker automation software, primarily developed to connect older type spectrometers (AC, AM) to a sample changer, allows the user to structure the name in such a way that it carries additional information with respect to the type of experiment. The user is referred to the corresponding automation manual available from Bruker and to the name conventions set by the key NMR operator at your site. 

In LC-NMR this problem does not arise in the same way as it does in standard sample changer automation systems, where a change between such different solvents as water and chloroform is possible. In LC-NMR, the samples are eluted from a column in a mixture of solvents, in which only the relative composition changes ... 

Changing solvents also has an effect on the homogeneity of the magnetic field. Again, the observed changes in LC-NMR systems are not as large as those found in normal sample changer automated devices ... 

The LC-NMR probe is a fixed set-up, where the sample container is the flow cell and is fixed in the probe. Different filling heights or qualities of sample tubes will not affect the homogeneity as in normal sample changer operation. 

An early spectrophotometric method [ 1 ] for aluminium in soil involves the use of a Technicon sample changer, proportioning pump and automatic colorimeter. The method is based on the measurement of the rate of colour development in the reaction between aluminium and xylenol orange in ethanolic media. The calibration graph is rectilinear up to 2.7 mg/1 aluminium and the coefficient of variation is 4.5%. 

Finally, radioactivity with its counters, scalers, sample changers, and print-out devices has not been covered in spite of intriguing possibilities in the clinical use of radioactive enzyme substrates. 

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. 

Low background gas-flow, end window proportional counter with automatic sample changer for alpha and beta counting (or equivalent counting system)... 

An automatic sample changer (ASC) often is an option for a spectrometer. The operator sets the samples into the rack of the ASC and predefines the experiments, which are then performed with automatic homogeneity adjustment, processing,... 

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