Solid-phase extraction sample filtration

Samples rarely come in a form that can be injected directly into the instrument some form of sample preparation usually is required. Sample preparation includes any manipulation of the sample prior to analysis, including techniques such as weighing, dilution, concentration, filtration, centrifugation, and liquid- or solid-phase extraction. Sample preparation can be performed either on-line or off-line, but it is usually performed offline. Off-line preparation can be time-consuming and tedious, and the more steps that are required, the more susceptible the analytical method is to operator error and irreproducibility. 

Sample injection in gas chromatography often seems deceptively simple a microlitre aliquot is rapidly injected into an inlet system, and elution and detection follow. Samples containing substantial amounts of non-volatile material, however, require one or more preparation steps in order to isolate volatile analytes from non-volatiles that would otherwise contaminate the inlet system and column, eventually leading to impaired chromatographic performance. Examples of such procedures include liquid-liquid extraction, solid-phase extraction and filtration. The use of a pre-column (viz. a retention gap or a guard column) is often required, even if prepared samples are used. 

W whole (unfiltered) water sample P particulate phase D dissolved + colloidal phase. LLE liquid - liquid extraction F - SPE filtration - solid phase extraction F filtration GC-MS gas chromatography - mass spectrometry GC - FH) gas chromatography - flame ionization detection HPLC - FI high perfomance liquid chromatograph - fluorescence spectrophotometry C18 - FI Cl8 column chromatography - fluorescence spectrophotometry. 

This sample preparation involved, firstly, an extraction and the elimination of the solid matrix by filtration and, secondly, a concentration procedure employing a solid phase extraction cartridge. The compounds of interest were separated solely by dispersive interactions with the reversed phase. In the example given, the corn meal was spiked with the aflatoxins. 

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... 

However, the solution obtained after denaturation might include, depending on the application, other components besides the liberated marker ( matrix ). If a small amount of target material is used in the binding assay, the quantity of remaining matrix will be so low that it hardly disturbs the quantitation and the sample can be measured directly by LC-MS without further sample preparation (e.g. membrane filtration or solid phase extraction [78]). 

As well as typical sample preparation methods such as filtration and liquid-liquid extraction, newer developments are now extensively used. The first of these is solid-phase extraction (SPE). This is a rapid, economical, and sensitive technique that uses several different types of cartridges and disks, with a variety of sorbents. Sample preparation and concentration can be achieved in a single step. Interfering sugars can be eluted with aqueous methanol on reversed-phase columns prior to elution of flavonoids with methanol. 

Prior to analysis of -lactam residues in liquid foods such as milk, a pretreatment step for fat removal, accomplished by centrifugation (69-71), is usually required. In instances where milk is to be submitted to ultrafiltration, dilution with water/acetonitrile (72-76) or water/acetonitrile/methanol (77-79) is often needed. Milk filtration (80) or dilution with acetate (81, 82) or phosphate buffers (83) is sometimes essential prior to solid-phase extraction. Unlike milk, semisolid food samples such as muscle, kidney, and liver require normally more intensive sample pretreatment. Tissue break-up is mostly carried out by the combined use of a mincing apparatus and a tissue homogenizer. 

This method is used to simplify a chromatogram by reducing the number of compounds in a sample to the six aglycons. This protocol describes the dilution, preparation (including solid phase extraction and acid hydrolysis), filtration, and reversed-phase HPLC analysis of the sample. 

This fractionation step may be optional. Some samples can be directly analyzed by HPLC after filtration (step 2) without solid-phase extraction. Anthocyanins that can be detected at 280 nm can interfere with the separation of some polyphenolics. If the analyst is interested in nonanthocyanin polyphenolics, and especially if plant materials containing high levels of anthocyanins are being analyzed, this fractionation technique should be utilized. 

Adjustment of pH Adjustment of pH (to 3 and 11) provides additional information on the nature of the toxicants, and provides blanks for subsequent pH adjustment tests performed in combination with other treatments (/.< ., filtration, aeration). Samples are adjusted to pH 3 and 11, and then subjected to filtration, aeration, or solid phase extraction with a Cl8 column. The treated samples (including the pH adjusted samples without additional treatment) are re-adjusted to the initial pH of the effluent (pH 7) prior to testing. 

Copper speciation in water was investigated by means of spectrophotometry of Cu+-bathocuprine complex formation (Bjoerklund and Morrison, 1997). The complex was separated by means of solid-phase extraction on PTFE-supported octadecyl (Qg) bonded silica discs. The discs provided rapid filtration and contributed low blanks. After filtration, the copper complex was eluted, and the copper concentration was measured by spectrophotometry. Total copper concentrations in the samples were measured after UV irradiation. The bathocuprine-available copper detection limits (for 500 ml samples) were 0.4 and 3.8 mg dm-3 copper for pure and polluted water, respectively. 

Both column chromatography and HPLC are used routinely for sample preparation, particularly for protein samples after particulate contamination has been removed by filtration or centrifugation. In addition, the use of ultrafiltration or solid-phase extraction techniques prior to chromatography often will result in a simplified, more concentrated sample. 

Sample preparation includes any manipulation of the sample prior to analysis, including such techniques as weighing, dilution, concentration, filtration, centrifugation, and liquid- or solid-phase extraction. These techniques may be performed with the aid of devices such as... 

The Prelude" Workstation, which is capable of automating solid sample treatments and includes options such as weighing, mixing, filtration and solid-phase extraction of samples for automatic insertion into HPLC systems, transfer to UV-Vis spectrophotometers and gathering in an EasyFill Sample Collection Module. 

Determination of these compounds is carried out frequently in biological fluids. Analysis in urine requires a previous filtration to remove cells and other particulate matter then, the samples are diluted and directly injected onto the column. With cerebrospinal fluid, the samples are obtained by lumbar puncture each ahquot is centrifuged and decanted before analysis. Often in plasma or semm, some form of protein removal is needed because the presence of these compounds in injected samples can cause modifications of the column and bias in chromatographic results. Protein removal can be performed by various methods such as protein precipitation, ultrafiltra-tion, centrifugation, liquid-phase or solid-phase extraction, and column-switching techniques. 

Before any sample can be subjected to chromatography, some type of sample preparation is required, which can be as simple as filtration or an involved solid-phase extraction protocol. Sample preparation is that activity or those activities necessary to prepare a sample for analysis. The ultimate goal of sample preparation is to provide the component of interest in solution, free from interferences and at a concentration appropriate for detection. This entry will briefly discuss seven topic areas included in sample preparation standard methods, solid-phase extraction (SPE), matrix solid-phase dispersion (MSPD), solid-phase microextraction (SPME), microdialysis, ultraliltration (UF), and automated systems. 

There are many sample preparation techniques listed in texts, from a simple filtration or centrifugation to many other kinds of extraction procedures, including both liquid-liquid and solid-phase extraction. When any type of sample preparation is used, it often is done manually if only a few samples are involved. If a large number of samples are to be analyzed, the entire procedure should lend itself to automation. Regardless of the number of samples, most sample preparation is done off-line that is, the samples are prepared first with one of the methods listed, then placed into an automated sample injection system for sequential analysis of all samples. 

Chapter 8 provides practical guidance on the use of widely used extraction and isolation techniques from the sample preparation perspective. The first two sections, solid-phase extraction and liquid-liquid extraction deal with liquid samples. The sections on supercritical fluid extraction and accelerated solvent extraction focus mainly on solid samples while the centrifugation and filtration sections handle suspensions. A successful sample preparation protocol accounts for specificity and homogeneity as well as recovery and final physical state of the targeted material. The ultimate aim is to produce a sample that is compatible with the desired analytical technique to assure generation of maximum information. 

Sometimes the sample preparation is a difficult problem, especially in clinical and environmental chemistry. General procedures are filtration (perhaps by means of a dedicated membrane which retains compounds selectively), solid phase extraction with disposable cartridges (also with dedicated selectivity), protein precipitation and desalting. A special case is sample preparation for biopolymer analysis. 

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