Sample preparation and dilution

Special sample preparation may be necessary for certain antigens. For example, in assays for the eicosanoid PGE2 in serum, it is often recommended that samples be extracted by protein removal before PGE2 is assayed. If such extraction is necessary it should be carefully controlled for by including in every assay set samples of standard antigen spiked into sample matrix, to check that recovery is uniform. Alternatively, it is often the case that sufficient dilution of sample may largely overcome the need for extraction. The errors produced by residual matrix interference may be less significant than those introduced by extraction methods, and also more uniform between samples. 

Sample dilution is also an important consideration. The dilution procedure itself can introduce errors, and obviously very large dilutions can lead to proportionately large errors. This is particularly important with reference to the preparation of the standard curve between assays. Often, purified standard antigens are stored at relatively high concentrations to optimize stability. When devising an assay, it may be better to develop a less sensitive form of the assay rather than making an exquisitely sensitive assay where everything has to be 

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A method to prepare milk powder, bovine liver, and bovine muscle samples for analysis by ET-AAS was proposed by Martins et al. [9]. Samples were mixed with a small amount of TMAH and a stable and homogeneous slurry was produced in ca 2h with heating at 60D70G. After such sample preparation and dilution with water, trace elements (Ag, Cd, Cr, Cu, Ni, and Pb) were determined in CRMs. External calibration was used for every analyte. 

Selecting an antibody 297 Selecting an assay standard 297 Sample matrix 299 Sample preparation and dilution 299 Assay turnaround time 300... 

The accuracy and precision of carotenoid quantification by HPLC depend on the standard purity and measurement of the peak areas thus quantification of overlapping peaks can cause high variation of peak areas. In addition, preparation and dilution of standard and sample solutions are among the main causes of error in quantitative analysis. For example, the absorbance levels at of lutein in concentrations up to 10 mM have a linear relationship between concentration and absorbance in hexane and MeOH on the other hand, the absorbance of P-carotene in hexane increased linearly with increasing concentration, whereas in MeOH, its absorbance increased linearly up to 5 mM but non-linearly at increasingly higher concentrations. In other words, when a stock solution of carotenoids is prepared, care should be taken to ensure that the compounds are fuUy soluble at the desired concentrations in a particular solvent. 

Ultrafiltration processes (commonly UF or UF/DF) employ pressure driving forces of 0.2 to 1.0 MPa to drive liquid solvents (primarily water) and small solutes through membranes while retaining solutes of 10 to 1000 A diameter (roughly 300 to 1000 kDa). Commercial operation is almost exclusively run as TFF with water treatment applications run as NFF. Virus-retaining filters are on the most open end of UF and can be run as NFF or TFF. Small-scale sample preparation in dilute solutions can be run as NFF in centrifuge tubes. 

Beckman Robotic Biomek 1000 automated laboratory The Biomek 1000 integrates the work formerly done by four instruments sample preparation system, diluter/dispenser, plate washer and a spectrometer finish. In can handle assays such as radio-immunoassays (RIA), fluorescence immunoassays (FIA), enzyme immunoassays EIA and enzyme-linked immunoassays (ELISA). 

Filter if necessary and take a precise aliquot of the sample extract and dilute this until its concentration falls at approximately the mid-point of the calibration series prepared using the analytical standard. 

Inject the diluted sample solution into the HPLC system. Replicates of the sample preparation and of the injection of the sample in HPLC may be carried out sample preparation procedures are more likely to give rise to imprecision than instrumental variation. 

The use of the Zymate Laboratory Automation System allows the standardization and automation of many routine operations in an analytical chemistry laboratory. It additionally allows for a closing of the analytical automation loop of sample preparation and analysis therefore potentially decreasing the need for personnel with a resultant increase in productivity. These operations include, but are not limited to, weighing, pipetting, diluting, blending, heating, liquid-solid extraction, and filtration. 

Dissolution testing involves a two-step process sample preparation and sample analysis. In this chapter sample preparation denotes the actual sample dissolution procedure, including sample collection. The samples collected from the dissolution apparatus may be analyzed directly or may be subject to further manipulation (e.g., dilution) to give the final sample solutions. 

Zn2+, Co2+ and Cu2+ ions were incorporated into calcined (A1)MCM-41 via ion exchange performed using very diluted Zn2+and Co2+ nitrate and Cu2+ acetate solutions at ambient temperature. Samples were carefully washed by distilled water, dried at ambient temperature and grained. Detailed conditions of the sample preparation and chemical composition ofMe -(A1)MCM-41 are given in Table 1. 

Calibration curves must be made from chemicals with the highest purity as possible. To avoid dilution errors a multi-level calibration curve (six points) based on three stock solutions is recommended. One must also be aware that low concentrations of for example, PAHs (2 ppm) may be adsorbed by the vials up to -90% (Pinto, Jose and Cordero, 1994). A calibrated and traceable balance or a traceable pipette must be used for accurate preparation and dilution of the standards. The calibration curve must cover the concentration range that is needed for the analysis. Both the slope and the intercept must be used to calculate the concentration in the sample, especially if the intercept is different from zero. 

Uncontrolled species transformations during analysis form another source of error. For methylmercury determinations in sediments it was demonstrated that errors of up to 80% resulted from the formation of the compound from inorganic mercury during separation and analysis [28, 29], For the study of possible species transformations during analysis multiple isotope dilution could be used as a diagnostic tool for identifying the error and bias inherent in specific methods of storage, sample preparation and measurement [30, 31]. 

Some techniques are known to provide higher variability than others. The choice of an appropriate method at the outset can improve precision. For example, a volume of less than 20 mL can be measured more accurately and precisely with a syringe than with a pipette. Large volumes are amenable to precise handling but result in dilution that lowers sensitivity. The goal should be to choose a combination of sample preparation and analytical instrumentation that reduces both the number of sample preparative steps and the RSD. Automated techniques with less manual handling tend to have higher precision. 

Fig. 9 Erratic IS response from a proprietary assay using dilution sample preparation and normal...

In the early years of LC-MS/MS application in clinical laboratories, chromatographic separation was looked upon as rather unnecessary with tandem mass spectrometers being understood as extremely selective measuring devices. Thus, many LC-MS/MS methods with minimal degree of chromatographic resolution and analyte retention times close to the void time of the chromatographic systems ( dilute and shoot approaches) have been described. However, from the issues discussed so far, the requirements of proper sample preparation and sufficient chromatographic separation prior to MS/MS detection have become evident. 

A wide variety of sample types, sample preparations, and processes have been used. Powdered rock samples were fused with K2B07 or K2C03, followed by precipitation of the potassium using perchloric acid, separation with methanol-perchloric acid, evaporation to a residue, and dissolution of the residue in dilute nitric acid. Detection limits in the solid were in the microgram per gram ( xg/g) to nanogram per gram (ng/g) levels in the solid without preconcentration. 

An alternative method involving coupled LC-GC has been proposed (Grob et al., 1992), which considerably reduces analysis time as the only sample preparation is dilution of the oil to a 20% solution in hexane. HPLC removes the large amounts of triglycerides and isolates the steroidal hydrocarbons from other interfering components such as alkanes before online transfer of the steradiene fraction to GC. 

The present chapter has as its focus the use of ready to use (RTU) reagents, sometimes included under the terms pre-diluted reagents or IHC kits. The potential utility of RTUs will be examined with respect to improved standardization of IHC, including indirect benefits that relate to sample preparation and the use and availability of control tissues. 

Procedure Set up an inductively coupled plasma emission spectrometer according to manufacturer s instmctions, using the lead emission line at 220.35 nm. Calibrate the instmment using the Standard Lead Blank Solution and the Diluted Standard Lead Solution. Then analyze the Sample Preparation and the Control Lead Solution. The sample passes the test if the lead concentration found in the Sample Preparation is equal to or less than that in the Control Lead Solution. 

Procedure Fill the titrator buret with the 0.05 N Sodium Hydroxide solution, and following the manufacturer s instructions, set the temperature to 30° and the pH set point to 7.0. Transfer 15.0 mL of the Substrate Emulsion to the titration cell, and add a small stirrer bar. Add 1.0 mL of the diluted Sample Preparation, and actuate the titrator. Record the rate of 0.05 N Sodium Hydroxide addition. Stop the titration after a constant (linear) rate of addition has been observed for 5 min. Determine the addition rate, in milliliters per minute, from the linear portion of the recording and record this value as R. 

Procedure Determine the absorbance of the Sample Preparation and of each of the Standard Dilutions in 1-cm cells at... 

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