Automatic Dilution

When a test result for a particular specimen is found to have an elevated, out of method range value, some analy2ers, eg, Beckman CX3, can automatically repeat the sampling from the same specimen. For elevated concentrations, the precision of the optical system is reduced so an automatic dilution of the sample, eg, by aspiration of a reduced amount of sample, is provided during the second sampling. 

Pressure/Vaccum Sensor Flowmeter Automatic Diluter... 

The random-access sampler can go to any sample cup position, any number of times, at any time during a run. This abihty to sample cups in any order and to return to sample cups more than once, allows system automation to be greatly extended. It saves time and work by allowing automatic re-run of sample(s) following off-scale peaks and also the automatic dilution and re-analysis of off-scale samples. The sampler also saves cup positions, allowing more samples and longer unattended runs. For example, one set of standards provides initial cahbration, drift correction, carry-over correction and periodic quality control. In addition, samples or standards can be sampled in repHcate form from a single cup. The random-access sampler can be controlled and either the operator or the computer can make the decision as to which cup the sampler must go to. 

As a final illustration of the use of computers in coulometric titrations, a method of automatic dilution of samples developed by Ruzicka, Christian, and co-workers is discussed. Flow injection (FI) involves the injection of a solution of analyte into a flowing carrier stream contained in narrow-bore tubing (e.g., 0.5 mm diameter) where controlled dispersion of the injected solution takes place... 

Horiba Autoreservoir, available for the LA-910 and LA-920, is a three-chamber tank with a built-in pump. The unit supplies liquid to the analyzer in response to commands. Concentrated surfactant solutions can be added to two of the tanks and then automatically diluted during the fill sequence. This automates the supply of dispersant solution for fill, sample dilution and rinses. 

The ET is suitable for on-line monitoring of the raw milk sterilization process. Here, immobilized catalase is inserted into the ET, raw milk samples with H202 are automatically diluted within a FIA-system and continuously analyzed. Figure 19 shows on-line data of a H202 decomposition experiment. After addition of 0.1% H202 to raw milk, the ET signal increases tremendously whereas addition of catalase obviously causes H202 decomposition. Thus, raw milk s own catalase seems to have a too low activity. 

Work-simplification devices on the laboratory bench will be detailed under the headings of automatic dispensers, automatic diluters, and flowthrough colorimeters with digital read-out. In each group, examples will be given of equipment of which the authors have had personal experience, but a choice of alternative apparatus will be available in most instances. The instruments mentioned are not necessarily the simplest or cheapest obtainable for performing a particular function. 

Automatic diluters. The simplest form of automatic diluter was described by Seligson (SI) and this type of instrument is now widely used. Seligson diluters (or pipets) can be constructed in the laboratory, or complete precalibrated instruments can be obtained commercially. An important feature of the operation of all diluters is the wash-out of the... 

Most mechanical automatic diluters incorporate two syringes suitably connected via a valve mechanism. One syringe is calibrated to meter the... 

A further application for sample diluters arises when an initial extraction or dilution is required before the normal sequential operations of an AutoAnalyzer can be started. Examples of this can be considered in relation to the assay of serum cholesterol and blood glucose. For the AutoAnalyzer serum cholesterol method an initml extraction is required before the extract can be placed in the AutoAnalyzer cup, and difficulties can arise if an automatic diluter is used to perform this, since the extracting fluid precipitates the serum proteins at the interface in the diluter... 

Preliminary extraction done, using an automatic diluter (Section 5.4.2.2). 

J.M.P.J. Garrido, R.A.S. Lapa, J.L.F.C. Lima, C. Delerue-Matos, J.L.M. Santos, FIA automatic dilution system for the determination of metallic cations in waters by atomic absorption and flame emission spectrometry, J. Autom. Chem. 18 (1996) 17. 

M.F. Gine, A.P. Packer, T. Blanco, B.F. Reis, Flow system based on a binary sampling process for automatic dilutions prior to flame atomic spectrometry, Anal. Chim. Acta 323 (1996) 47. 

I. Lopez-Garcia, J. Arroyo, P. Vinas, M. Hemandez-Cordoba, A manifold for the automatic dilution of concentrated solutions in flame atomic absorption spectrometry, Anal. Bioanal. Chem. 372 (2002) 587. 

Another limitation of light scattering techniques is that it must be assumed that the concentration of crystals is sufficiently low so that there is no significant multiple scattering. To extend the use of these techniques to the case of high slurry concentration, an automatic dilution unit has been developed for fast and representative dilution of samples (Jager et al. 1987). 

Both ends of the atomic absorption analysis are subject to automation. At one end, there is the automatic dilution and presentation of samples to the instrument. The results are then fed directly to a computer or other storage device, via cards, punched tape, or magnetic tape. Thus, it will eventually be possible to complete an entire series of analyses, possibly including interpretation of the meaning of the data, without intervention of the operator. 

Recent improvements in FAAS include the addition of a flow injection sample delivery system. This allows for automatic dilution and reagent addition, and also provides for automated cold vapour or hydride generation needed for As, Se and Hg (e g., Saraswati et al., 1995). Other new techniques are improving the sensitivity of FAAS. A slotted silica tube placed in the flame improves the sensitivity 8 fold forCd and c. 3 fold forCu, Pb, and Zn. Experimental application of graphite tubes in the flame can improve Pb sensitivity 50 fold (Alvarado Jaffe, 1998). 

In the 1970s (Pella and von Baeckman 1969 von Baeckman 1971), an instrument was developed for the automatic dilution and L-X-ray fluorescence analysis (XRFA) of U and Pu in spent fuel solutions with a precision and accuracy of about 1%. 

Analyte detection and quantification is accomplished using spectrophotometer devices. These are usually photoamplifier tubes or diode array assemblies. A computerized control system allows for continuous signal monitoring. This system can be interfaced with an autosampler/diluter system which uses a feedback loop based on signal intensity to automatically dilute overrange samples until they reach calibration range. 

Figure 10.409 Analysis of inorganic cations in an automatically diluted fracking flow-back wastewater. Separator column lonPac CS16 with guard column column dimensions ...

Dionex Technical Note No. 84 Automatic Dilutions Using Chromeleon AutoDilution and Two Injection Loops. Dionex Corporation (now part of Thermo Fisher Scientific), Sunnyvale,... 

Persulfate digestion can be also carried out in an automated online apparatus, constituted by a digestor online with an autoanalyzer system [133]. In this case, the sample is mixed with PO reagent and pumped in a digestor coil, made by a P)n ex tube immersed in an oil thermostatic bath (115°C). The length of the coils and the velocity of the peristaltic pump assure a time of digestion of about 30 min. After the samples are passed through the coil, they are automatically diluted and injected in the colorimetric system. 

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