Dilution of samples

Note that by no means should the amounts of reagents added to the sample be doubled, if very high concentrations of hydrogen sulphide suggest that the reagent concentrations may be insufficient this will change the pH of the sample leading to erroneous results even after dilution. 

If the sample is a solid one, then 1 g should be suspended in 9 ml. of sterile Ringer s solution and homogenised thoroughly. This will give a dilution of 10 , and the above procedure should then be followed to produce more dilute samples. 

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HPLC/MS and HPLC/MS/MS analyses are susceptible to matrix effects, either signal enhancement or suppression, and are often encountered when the cleanup process is not sufficient. To assess whether matrix effects influence the recovery of analytes, a post-extraction fortified sample (fortified extract of control sample that is purified and prepared in the same manner as with the other samples) should be included in each analytical set. The response of the post-extraction fortified sample is assessed against that of standards and samples. Matrix effects can be reduced or corrected for by dilution of samples, additional cleanup, or using calibration standards in the sample matrix for quantitation. 

Figure 4 Dynamic dilution of sample for HPLC analysis of amidation/cyclization reaction. Transfer solvent methoxyethanol flow rate 1 ml/min. Detection refractive index.

Choice of phase type Phase weight Particle size pH of sample Dilution of sample... 

Blood Dilution of sample with ammonium solution containing Triton X-100 ICP/MS 15 pg/L 96-111 Delves and Campbell 1988... 

Urine ( -aminolevuli nic acid) Dilution of sample reaction with ethylacetoacetate and ethylacetate to form -amino-levulinic acid-pyrrole reaction with Erhlich s reagent Spectrophotometry No data No data Tomokuni and Ichiba 1988... 

Urine Dilution of sample bromination and treatment with pyridine- p-phenylenediamine Spectrophotometric (thiocyanate- cyanide determination) -0.07 ppm 88 (thiocyanate at 0.6 ppm) Pettigrew and Fell 1972... 

The system in its current configuration is shown in Fig. 6.9. Since 1988, the system has been moved from a bench top to a custom vented enclosure to minimize exposure to organic fumes. The detectors, solvents and other necessary support devices are located below the robot work surface. Functionally, the robot still performs almost the same procedure as the initial system (dilution of samples), but there are a number of key differences. 

Prepare 1/20 dilutions of samples, standards, and quality control specimens using assay diluent, and add 150 pL to each of the microtiter plate wells Cover the plate with plastic film, and incubate at 37°C for 1 h... 

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... 

In the Hornsey (1956) procedure, the sample was minced thoroughly, and a 10 g sample was mixed in a tall beaker (to prevent undue evaporation) with 10 ml of a solution of 40 ml acetone and 3 ml water. Total fluid volume was 50 ml, including the 7 ml water in the sample. This procedure was preferred over dilution of sample to 50 ml final volume, since calculations were simplified and correction for the volume of insoluble meat tissues was avoided. Later workers have modified the procedure, using smaller samples and less solvent. Pearson and Tauber (1984) used a 2 g sample and capped test tubes to prevent acetone evaporation, and Carpenter and Clark (1995) used 5 g samples. 

An anion-exchange method for the separation and detection of BA and SA in citrus juice required only the filtration and dilution of samples with KH2P04 before injection. The Partisil 10-SAX anion-exchange column was eluted with 0.225 M KH2P04 at ambient temperature. Average recoveries for both BA and SA varied between 94 and 98% (73). 

Dilution of Samples. Samples are generally plated in dilutions of 1-100 or 1-1000. The dilution used will depend upon the number of colonies present on the plates after a 48-hour incubation period, or what previous experience with the product has shown. Dilutions should be adjusted so that the plate counts fall between 30 and 300 colonies per plate. If the count falls outside this range, higher or lower dilutions are necessary. Upon initial plating, when the dilution range is unknown, samples should be plated in dilutions of 1-100, 1-1000, 1-10,000 and made in duplicate. If spoilage is suspected the lower dilutions are not necessary and even higher dilutions made. 

Aqueous samples can be tested directly without any sample extraction steps. An aliquot of the sample (10 to 250 pL) should be suitable for the test. For high analyte concentrations, dilution of samples may be necessary. Follow the assaying procedure given in the kit using appropriate amounts of sample (or extract), enzyme conjugate, and coloring reagent. 

III Toxicity the L(I)C50 is reached in at least one test in the 10-fold dilution of sample, the effect is lower than 50% (1-10 TU)... 

In general, the functional range of a curvilinear regression model is narrower than that of a linear model the assay range is extended by the dilution of samples with concentrations higher than the ULOQ. Dilution linearity also demonstrates the lack of a prozone or hook effect of the assay. A hook (prozone) effect is the phenomenon where the responses of higher concentrations of analyte are lower than expected. 

Narrow inserts ( 2 mm ID) reduce dilution of sample vapors with carrier gas of interest for analyses requiring maximum sensitivity. 

Employee Exposure Monitoring. Industrial hygiene assessment of surface concentrations associated with a potent compound handled solely in liquid form within a chemical laboratory hood was conducted to assess the potential for downstream contamination potential. Handling operations assessed included dilutions of sample solutions and HPLC analysis. Wipe samples were collected from the following surfaces within and outside of the laboratory ... 

Deposition of sample on the sampler, skimmer, ion optics, and other parts of the interface can lead to elevated blank levels as well as drift. This, in combination with the space-charge-induced chemical matrix effects, often requires further dilution of samples than is desirable. This can also limit the range of concentrations that can be measured for a set of samples even though the dynamic range may in theory be sufficient. An improved understanding of the chemical and physical characteristics of the deposition process and means to minimize them is needed. 

Dilution of sample—The dilution of concentrated samples may lead to large errors in counting. Concentrated samples flocculate and settle at higher rates than dilute samples. Consequently, the portions transferred by pipette are not always representative. However, this in itself may not be a serious drawback except when the samples are taken for long periods of time. The dilution of samples should proceed to a point where the average count per one-fourth field is greater than 20 and less than 40 particles. Control samples may be relatively free from particles, but as a rule they average from 4 to 10 per one-fourth field. 

Other authors have reported the use of a simultaneous multielement (SM) AAS instrument to identify the content of Pb and other metals in wines. In a 2000 review the principal characteristics and applications of the technique were discussed and the authors made reference to the determination of Cd and Pb in beverages and other matrices [76], Freschi et al. [77] determined Pb and Cd in 10 white and red table wines. The characteristic mass was approximately 0.6 pg for Cd and 33 pg for Pb and the LoD was found to be 0.03 and 0.8 pg l-1 for Cd and Pb, respectively. The comparative results of diluted and digested wines and recovery values indicated that the simple dilution of samples was sufficient to determine those elements in Brazilian wines. Fernandes and coworkers [78]... 

Field measurement instruments should be checked for their limits of detection, accuracy, and reproducibility, and their measurement errors should be established. This can be done with standards, duplicate samples, and dilution of samples, similar to the checks discussed for laboratory measurements (section 5.9). Such checks should be performed in preparation for field work, and the results should be recorded and reported with the... 

Dilution of sample with deionized water, addition of phosphate buffer and EDTA. 

Aspirate a 1 10 dilution of Sample Solution into the spectrophotometer, read the absorbance in the same manner, and by reference to the standard curve, determine the concentration (Cj of aluminum, in micrograms per milliliter, in the Sample Solution. 

With the help of microprocessors, recalibrations have become so easy and so quick, that a new calibration curve can be plotted using different parameters (a different analytical line, slit width, position of burner or dilution of sample solution). 

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