Dialysis sample preparation

In sample preparation by dialysis, sample ions transfer or migrate across a membrane from its original matrix into a receiving solution. Then, the receiving solution containing the sample ions is injected into the IC and the ion analysis is performed. An attractive feature of the dialysis process is that it isolates the sample matrix from the sample ions that are injected onto the analytical column. Some appUcations of dialysis sample pretreatment include the determination of ions in 

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There are several processes that are occurring in Donnan dialysis sample preparation. One process involves the normal transport ions of like charge across the membrane. At the start of dialysis there is a strong tendency for the any particular ion to diffuse from a high concentration zone on one side of the membrane to the low concentration zone on the other side. As this process occurs, corresponding transfer of the same charge ion travels back across the membrane in order to preserve electroneutrality. The counter ion does not travel across so there can exist different normality concentrations of ions on each side. The example of 90 % transport of a sample (Na+) Cl at 0.0010 N and a receiving electrolyte (Na" ) OH" at 0.050 N at 1 mL each is shown in Fig. 9.3. 

R. Herraez-Heruandez, A. J. H. Eouter, N. C. van de Merbel and U. A. Th Brinkman, Automated on-line dialysis for sample preparation for gas cliromatogruphy determination of benzodiazepines in human plasma , 7. Pharm. Biomed. Anal. 14 1077-1087 (1996). 

Until this point, the sample preparation techniques under discussion have relied upon differences in polarity to separate the analyte and the sample matrix in contrast, ultraflltration and on-line dialysis rely upon differences in molecular size between the analyte and matrix components to effect a separation. In ultrafiltration, a centrifugal force is applied across a membrane filter which has a molecular weight cut-off intended to isolate the analyte from larger matrix components. Furusawa incorporated an ultrafiltration step into his separation of sulfadimethoxine from chicken tissue extracts. Some cleanup of the sample extract may be necessary prior to ultrafiltration, or the ultrafiltration membranes can become clogged and ineffective. Also, one must ensure that the choice of membrane filter for ultrafiltration is appropriate in terms of both the molecular weight cut-off and compatibility with the extraction solvent used. 

GC, utilizing flame ionization detection (FID), has been used to measure diisopropyl methylphosphonate in meat, grain, or milk (Caton et al. 1994). Sample preparation steps include homogenization, filtration, dialysis, and extraction on a solid sorbent. Two common solid phase extractants, Tenax GC and octadecylsilane bonded silica gel (C18 Silica), were compared by Caton et al. (1994). They reported 70% recovery when using Tenax GC and 85% recovery when using C18 Silica. Sensitivity was not reported. Equilibrium experiments indicate that 8-10 mg of Tenax GC are required to achieve maximum recovery of each g of diisopropyl methylphosphonate (Caton et al. 1994). By extrapolating these... 

The micropipette tip containing solid phases is a relatively new sample preparation technique that permits handling of microliter to submicroliter amounts of liquid samples, using the techniques of SPE, dialysis, and enzyme digestion. Various phases (reversed-phase, affinity, size-exclusion, etc.) are packed, embedded, or coated on the walls of pipette, permitting liquid samples to be transferred without undue pressure drop or plugging (Fig. 2.5). 

FIA star 5010 Modular, semi- or fully automatic operation. May be operated with process controller microprocessor. Can be set up in various combinations with 5017 sampler and superflow software which is designed to run on IBM PC/XT computer 60-180 samples h Dialysis for in-line sample preparation and in-line solvent extraction.Thermostat to speed up reactions. Spectrophotometer (400-700nm) or photometer can be connected to any flow through detector, e.g. UV/visible, inductively coupled plasma, atomic absorption spectrometer and ion-selective electrodes... 

Fio. 3. Sedimentation coefficient and molecular weight as functions of pH. (A) Sedimentation coefficients as a function of pH. (O) s°0 w values were determined for samples adjusted from neutral pH to each pH value. The concentrations were 72 mg/ml, except at pH 5 and pH 4, where they were 4j0 mg/ml in 0.01 Af tris-0.01 Af sodium acetate. (0) s°0 w values were determined for samples adjusted from neutral pH to the given pH. Concentrations were 0.62 mg/ml in 0.1 Af NaCl-0.01 Af tris-0.01 M sodium acetate. ( ) s° w values were determined for samples prepared at pH 2, then dialyzed at the appropriate pH. Concentrations were 0.62 mg/ml in 0.1 M NaCl-0.01 Af tris-0.01 M sodium acetate. (O) Determinations with Schlieren optics all other determinations were made with the use of ultraviolet optics with the photoelectric scanner. (B) Weight average molecular weight as a function of pH. (0) M values were determined for samples adjusted from neutral pH to each pH indicated, by dialysis, 0.62 mg/ml, in 0.1 M NaCl-0.01 M tris-0.01 M sodium acetate. (O) Mw values were determined for samples prepared at pH 2, then dialyzed at the appropriate pH, 0.62 mg/ml in 0.1 M NaCl-0.01 Af tris-0.01 Af sodium acetate. 

Dialysis has been applied to the preparation of a wide range of sample types, ranging from foodstuffs to physiological fluids. Membrane-based sample preparations for chromatography have been reviewed by Van de Merbel et al.60 In ordinary dialysis, solutes are transferred from a concentrated to a more dilute solution as a consequence of the concentration gradient. 

While it is wonderful to be able to inject neat samples directly, sample preparation can often improve selectivity and sensitivity. If the resolution is poor, the salt content of the sample too high, or the capillary fouls, consider a sample cleanup. This can include liquid-liquid extraction, solid-phase extraction, supercritical fluid extraction, protein precipitation, or dialysis, depending on the solutes and application [38]. The final sample diluent should be a solution that is CE-Mendly. That usually means low ionic strength compared to the BGE. 

Dialysis can also be used as an on-line sample preparation technique for the deproteinization of biological samples prior to HPLC. Selecting the appropriate semipermeable membrane for the dialyzer can prevent interference from large macromolecules. Samples are introduced into the feed (or donor) chamber, and solvent is pumped through the lower acceptor (or recipient) chamber. The smaller molecules diffuse through the membrane to the acceptor chamber and are directed to an HPLC valve for injection. In case of low concentrations of compounds of interest, a trace enrichment step may be required this is accomplished with a column placed downstream of the dialyzer that will retain the analyte until the concentration is sufficient for detection. After this step, the analyte can be backflushed into the HPLC system. The technique is useful for blood studies as sampling can be achieved continuously without blood withdrawal. A commercial on-line system, such as Asted from Gilson, used for both cleanup and enrichment by a combination of dialysis with SPE, is shown in Fig. 7. 

All of the samples analyzed using a chromatographic technique need special preparation before they are introduced into the column. This process is laborious, not reliable enough, and often expensive. There are several steps involved in sample preparation dialysis, dilution, extraction (selective extraction or concentration), and derivatization. Sometimes, the derivatiza-tion step is part of the extraction process. The expenses refer to the reagents and solvents of chromatographic purity grade. The sample preparation will become easier and not so expensive by automation. 

The ideal system for sample preparation in a chromatographic method is that the operation of all the steps between sample dissolution and chromatography is done through a SIA technique (Fig.l). The first part of the system will consist of a sample dialysis (unit 1) and the outlet will be channeled into the second unit consisting of concentration or dilution steps and extraction of the analyte. It is always assumed that the concentration, dilution, and derivatization steps can be done by extraction — in most cases, it is absolutely necessary. 

An extensive examination of the different conditions affecting CZE separation (sample preparation, type of loading buffer and pH of CE buffer) of wine proteins reveals as optimum conditions the sample preparation by either ultrafiltration or dialysis and dissolution and separation... 

In some instances, microdialysis sampling can be coupled on-line with mass spectrometry without prior separation or cleanup with techniques such as GC or LC. Continuous flow fast atom bombardment (cfFAB) has been used for the ionization of microdialysis samples without prior sample preparation. Coupling micro-dialysis directly to mass spectrometry via FAB was more feasible with cfFAB because it provided for a more robust, efficient ionization and prevented source fouling. 

Metrohm literature. On-line sample preparation in ion chromatc aphy - no problem with the novel 754 dialysis unit, Metrohm Information, 74 ed., 26,3,1999. 

Sample preparation (Chapter 9) includes simple procedures such as centrifugation or filtration. Other more complex sample preparation procedures include passive or active dialysis, preconcentration, combustion or precipitation of matrix ions. In some cases, choosing the correct eluent/column/detector system will negate the need for sample preparations. A selective detector will be able to detect a minor analyte in the presence of other ions. Ion exclusion allows the passage of strong acid anions prior to separation of weak acid anions. Methods that require the least sample preparation or minimal sample preparation directly prior to injection are the most desirable. 

Sodium and potassium levels are difficult to analyze by titrimetric or colorimetric techniques but are among the elements most easily determined by atomic spectroscopy (2,38) (Table 2). Their analysis is important for the control of infusion and dialysis solutions, which must be carefully monitored to maintain proper electrolyte balance. Flame emission spectroscopy is the simplest and least expensive technique for this purpose, although the precision of the measurement may be improved by employing atomic absorption spectroscopy. Both methods are approved by the U.S. (39), British (40), and European (41) Pharmacopeias and are commonly utilized. Sensitivity is of no concern, due to the high concentrations in these solutions furthermore, dilution of the sample is often necessary in order to reduce the metal concentrations to the range where linear instmmental response can be achieved. Fortunately, the analysis may be carried but without additional sample preparation because other components, such as dextrose, do not interfere. 

Sample preparation Adjust pH of serum samples to 7.4 and dialyze 3 mL serum against 5 mL dialysis buffer at 37° in I FE chambers for 4 h. Inject 1 mL mobile phase, 1 mL water, 2 mL dialysate, 1 mL water, and 1 mL MeCN water 50 50 onto column A. Elute coliram A onto column B with mobile phase for 30 s then remove it from the circuit. Elute coliunn B with mobile phase and monitor the effluent. (Dialysis buffer was 3.998 g Na2HP04.2H20 +... 

Snippe, N. Van de Merbel, N.C. Ruiter, F.P.M. Steijer, O.M. Lingeman, H. Brinkman, UA.T. Automated column liquid chromatographic determination of amoxicihin and cefadroxil in bovine serum and muscle tissue using on-line dialysis for sample preparation. J.Chromatogr.B, 1994, 662, 61-70 [serum muscle cow post-column reaction LOD 50 ng/mL LOD 200 ng/g SPE extracted cefadroxil dialysis]... 

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