Comparison of samples

Data collected by modern analytical instalments are usually presented by the multidimensional arrays. To perform the detection/identification of the supposed component or to verify the authenticity of a product, it is necessary to estimate the similarity of the analyte to the reference. The similarity is commonly estimated with the use of the distance between the multidimensional arrays corresponding to the compared objects. To exclude within the limits of the possible the influence of the random errors and the nonreproductivity of the experimental conditions and to make the comparison of samples more robust, it is possible to handle the arrays with the use of the fuzzy set theory apparatus. 

Comparison of Sample Similarities within a Molecule Dataset... 

It is desirable for the record to have an objective statement of the nature and degree of color deterioration. The simplest, but least desirable, method is comparison of sample color with color charts or plates such as those used in the Munsell system, Ridgeway s color standards, or the Maerz and Paul dictionary of color. Such a method is limited in value because of the difficulty of obtaining true color matches, and because of variations due to human error. The use of color charts or plates may be much improved in the Munsell system by employing a disk colorimeter (29). Kramer and Smith (21) have pointed out that the results obtained in its application to foods are sometimes difficult to explain and compare, and that the method requires special training of the operator and is tedious and cumbersome. 

The main characteristics of the ideal extraction method are given in Table 3.47, which at the same time are also criteria for comparison of sample preparation techniques. It is unlikely that a unique best method can be defined, which is analyte and matrix independent. Extraction is affected by polymer functionality, molecular weight and cross-linking. Selective extraction of some additives is basically not possible. Hence, the goal of an ideal extraction would be the complete extraction of all additives from the polymer for subsequent chromatographic separation. 

It became apparent that comparison of samples with similar [r l, Ec cl and C-j would reveal the degree of tensile difference brought about by other structural factors. The matching samples with three structural factors comparable simultaneously were... 

Wong et al. [38] conducted an inter comparison of sampling devices using seawater at 9 m in a plastic enclosure of 65 m in Saanich Inlet, BC, Canada. The sampling methods were ... 

The value of infrared spectrometry as a means of identification of unknown compounds and to investigate structural features is immense. Spectra are used in an empirical manner by comparison of samples with known materials and by reference to charts of group frequencies. A simplified correlation chart is shown in Table 9.8. The interpretation of infrared spectra is best considered by discussing the prominent features of a representative series of compounds. 

So how does the IRMS get its stability Collector slits are several times the width of the ion beams. This gives a flat-topped peak shape (Fig 6) which makes the ion current intensive to drift. The main source of drift is temperature variation which both affects the electronic components used for mass selection and caused expansion and contraction of mechanical parts. Simultaneous measurement of ion beams using a double or triple collector is more precise than sequential measurement by mass scanning with a single detector. Finally, frequent comparison of sample gas under identical conditions also contributes to stability. Ion beam stability is more important than resolution for isotopic measurements. 

Figure 10.1 An illustration of a vertical slab-gel apparatus. Samples are applied in the wells set in the gel using a comb. Side-by-side comparison of samples is possible in slab systems (ref. 7). (Reprinted with permission from reference 7, Figure 11.2, Page 295, copyright (1994) Springer-Verlag.)...

A parametric test for comparison of sample means where... 

Gustavson, K.E. and Haikin, J.M. 2000 Comparison of sampling techniques and evaluation of semipermeable membrane devices (SPMDs) for monitoring polynuclear aromatic hydrocarbons (PAHs) in groundwater. Environ Sci. Technol. 34 4445 451. 

Utvik, T.I.R. Durell, G.S. Johnsen, S. 1999, Deteimining produced water originating polycyclic aromatic hydrocarbons in North Sea waters Comparison of sampling techniques. Mar. Pollut. Bull. 38 977-989. 

In addihon to shape selechvity and acid-site strength, other catalyst characteristics that influence the catalyhc performance of SAPO-34 have also been idenhfied. Variahon in the SAPO-34 gel composition and synthesis condihons have been were used to prepare samples with different median particle sizes and Si contents (Tables 15.3 and 15.4) [104]. In these samples the median parhcle size was varied from 1.4 to 0.6 xm, and the Si mole frachon in the product was varied from 0.14 down to 0.016. A comparison of samples B and E (which have similar parhcle size distributions) shows that reducing Si content decreases propane formation and increases catalyst life. A comparison of samples B and C (which have similar Si contents) illushates an increase in catalyst life with a reduchon in parhcle size. 

H. Wikstrom, l.R. Lewis and L.S. Taylor, Comparison of sampling techniques for in-line monitoring using Raman... 

Kaupp, H., and G. Umlauf, Atmospheric Gas-Particle Partitioning of Organic Compounds Comparison of Sampling Methods, Atmos. Environ., 26A, 2259-2267 (1992). 

Table I. Comparison of Sample Preparation for Sorbate in Chocolate Syrup...

Volatile pheromones from spiders are more difficult to analyze because the site of the pheromone-producing organs is not known. Good results have been obtained by collection of volatiles released into the airspace around a spider. For example, single individuals of A. aperta confined in 50 ml glass chambers emitted enough material for analysis (Papke et al, 2001). Probable pheromone components were deduced by comparison of samples collected from individuals that had been shown to be attractive or unattractive to males. Abdominal wipes afforded similar quantities of... 

Fig. 25 a and b. Analysis of epoxy resin prepregs. a = SEC with UV detection at 280 nm, comparison of sample SP 250 with formulation standard, b = Gradient elution of these samples on a RP 18 column with water/THF gradient program 40 to 80% B in 50 min, non-linear. (From Ref. e9) with permission)... 

Hewitt, A.D., Comparison of sample preparation methods for the analysis of volatile organic compounds in soil samples solvent extraction vs. vapor partitioning, /. Environ. Sci. Technol., 32(1), 143-149, 1998. 

Filtration. To separate the dissolved from the particulate fraction filtration or centrifugation will be necessary. This causes a severe risk of contamination it is therefore often not carried out with open ocean samples, where the concentrations of suspended material are low. The presence of phytoplankton or a variable concentration of suspended matter affects the total concentration and a comparison of samples can thus become difficult. In speciation Studies the presence of particles may influence the results even more (complexation, adsorption), therefore filtration over acid washed membrane or screen filters in an appropriate filtration apparatus is recommended for all natural samples (Bewers et al., 1985). High pressure during filtration should be avoided ruptured (plankton-) cells will contribute organic matter, nutrients and trace metals to the solution. A pressure < 25 kPa is recommended (Florence and Batley, 1980). 

Bewers, 3.M. and Windom, H.C., 1982. Comparison of sampling devices for trace metal determinations in seawater. Mar. Chem., 11 71-86. 

Lewtas, J., Pang, Y., Booth, D., Reimer, S., Eatough, D.J. and Gundel, L (2001) Comparison of sampling methods for semi-volatile organic carbon associated with PM2.5. Aerosol Science and Technology, 34, 9-22. 

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