Transmittance sample containers

Attenuation of radiation as it passes through the sample leads to a transmittance of less than 1. As described, equation 10.1 does not distinguish between the different ways in which the attenuation of radiation occurs. Besides absorption by the analyte, several additional phenomena contribute to the net attenuation of radiation, including reflection and absorption by the sample container, absorption by components of the sample matrix other than the analyte, and the scattering of radiation. To compensate for this loss of the electromagnetic radiation s power, we use a method blank (Figure 10.20b). The radiation s power exiting from the method blank is taken to be Pq. 

In many projects involving a transformation or isolation of carbohydrates, it is important to quantify the amount of product obtained. It is sometimes difficult to measure the content of a specific component in a mixture. The process can be laborious with instrumentation such as HPLC or GC, especially if the sample contains major impurities of different natures. Fortunately, knowledge of the properties of the desired product can suggest a specific method of analysis, several of which involve colorimetric analysis. With colorimetric analyses, a selective chemical transformation will produce color. The absorbance or transmittance of the colored sample is directly correlated with the presence of a certain functional group or product in the mixture. Various reactions that produce color are known to be selective for certain types of carbohydrates. 

Now, when infrared radiation of a particular frequency is passed through a sample containing molecular species, it may or may not be absorbed. If all frequencies are passed through, some will be absorbed to varying degrees, depending on the molecular species involved. For example, a typical spectrum of transmittance (%) versus wave number (cm 1) (wave number = 1/wavelength)... 

Transflectance is not likely to be more successful than transmittance for analysis of milk by NIR, because the surface presented to the instrument will be changing in composition, due to the progressive changes in fat content. Transmittance or reflectance of the sample in a large cell, with continuous agitation is the recommended method of sample presentation for NIR analysis of milk, or any other type of liquid sample containing suspended material that is liable to settling at the bottom or surface of the cell. 

Let us recall the mle of thumb given at the start of this chapter (i.e., a strong band in a 10-pm film of a pure material has a typical absorbance of about 1 AU). Furthermore, we will assume that the strongest band in the spectmm of the analyte must have an absorbance of at least 0.001 AU (1 mAU) for the analyte to be identified above the noise level, interference by atmospheric water vapor, and small variations of the baseline. These constraints imply that the thickness of a sample containing 1 ppm of the analyte must be 1 cm if a trace component is to yield a recognizable spectmm. However, the transmittance of most samples that are 1 cm thick is well below 0.1% in those spectral regions where chemically useful information is to be found (3100 to 2700 and 1800 to 400 cm ). Thus, windows in the spectmm of the matrix material must be found where at least one characteristic band of analyte absorbs. An example of just such a case is found in the determination of antioxidants in polyolefins. Many polyolefins have weak absorption between... 

A water sample was run through the colorimetric procedure for the analysis of nitrate, giving 55.0% transmittance. A sample containing 1.00 ppm nitrate run through the exactly identical procedure gave 24.6% transmittance. What was the concentration of nitrate in the first sample ... 

The results obtained by the authors were comparable to products produced from conventional cellulose paper [82]. Dahman and Oktem obtained an optically transparent nanostructured biocomposite composed of surface-modified BNC and poly(hydroxyethyl methacrylate). Composite samples containing 1% (w/w) nanofiber transmitted over 80% of the light, whereas samples with less than 1% (w/w) BNC content exhibited higher light transmittances [83]. Transparent NCC films open the doors to new applications for cellulose devices, e.g., paper displays, smart packaging, radiofrequency identification, and smart labels [82,83]. 

Laws of Photometry. The time rate at which energy is transported in a beam of radiant energy is denoted by the symbol To for the incident beam, and by P for the quantity remaining unabsorbed after passage through a sample or container. The ratio of radiant power transmitted by the sample to the radiant power incident on the sample is the transmittance T ... 

Procedure. Transfer the almost neutral sample solution of beryllium (containing 5 to 80jug of the element in a volume of about lOmL) to a 25 mL graduated flask, add 2.8 mL of 2.0M sodium hydroxide (or more if much aluminium is present), 5.0 mL of 0.64M boric acid solution, and 6.0 mL of the dye solution (see Note), dilute to the mark with distilled water, and mix well. Measure the transmittance at 520 nm, or with a green filter preferably using a 2 cm cell. 

The probe contains the electronics designed to detect the tiny NMR signal. The central component of the probe is a wire that receives the Rf pulse from the transmitter and dissipates it into the sample. It also receives the signal from the sample and transfers it to the receiver... 

Probe Region of the spectrometer where the sample is held during the acquisition of a spectrum. It contains the transmitter and receiver coils and gradient coils (if fitted). 

OL behavior is assessed simply by monitoring the transmission of a (usually solution) sample as a function of the incoming laser fluence measured in joules per square centimeter (rather than intensity in watts per square centimeter).22,23 Limiting thresholds Fth, defined as the incident fluence at which the actual transmittance falls to 50% of the corresponding linear transmittance, are then commonly quoted. Since excited-state absorption processes generally determine the OL properties of molecules, the excited-state structure and dynamics are often studied in detail. The laser pulse width is an important consideration in the study of OL effects. Compounds (1-5)58-62 are representative non-metal-containing compounds with especially large NLO and/or OL... 

When using a spectrophotometer for a colorimetric analysis, both the 0% and 100% transmittance (oo and 0 absorbance) readings must be set. Once the instrument has warmed up, with the light beam blocked and with nothing in the sample compartment, the readout is set to 0% transmittance (oo abs.). Again, this measurement is done to set / in the absorbance equation shown earlier. A blank, a solution containing all the components used in the analysis except the analyte being measured, is placed in a cuvette, placed in the sample... 

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