Chromatography background

K. Palmer and F. Rabel, Planar Chromatography Background Contaminants Some Causes and Cures, Ainer. Lab. May 1992, p. 28BB-28DD. 

Identification of normal paraffins by chromatography presents no special problems with the exception of biodegraded crudes, they are clearly distinguished. The problem encountered is to quantify, as shown in Figure 3.14, the normal paraffin peaks that are superimposed on a background representing other hydrocarbons. 

A feature of ion exchange chromatography is, of course, that ionic solutions are used as eluants, so that the eluted species are present in an electrolyte background. The problem which now arises in the application of electrical... 

It was against this background and in view of the fact that there is at present no contemporary monograph on thin-layer chromatography that this book was produced. It is intended as an introduction to the method, a reference book, and a laboratory handbook in one, i.e., far more than just a Reagent Book . 

Prechromatographic dansylation has the advantage that chromatography separates excess reagent and also the fluorescent by-products (e g dansyl hydroxide) from the reaction products of the substances to be determined In the case of postchromatographic dansylation the whole of the plate background fluoresces blue, so that in situ analysis is made more difficult... 

In a further study, Rill et al. [325] developed a model of gel permeation chromatography that included a bimodal pore stracture. The smallest mode in the pore-size distribution represents the basic background polyacrylamide pore structure of about 1-mn mean radius, and the second mode was around 5 nm, i.e., in the range of size of the molecular templates. The introduction of this second pore structure was found to substantially improve the peak resolution for molecules with molecular sizes in the range of the pore size. 

In modern times, most analyses are performed on an analytical instrument for, e.g., gas chromatography (GC), high-performance liquid chromatography (HPLC), ultra-violet/visible (UV) or infrared (IR) spectrophotometry, atomic absorption spectrometry, inductively coupled plasma mass spectrometry (ICP-MS), mass spectrometry. Each of these instruments has a limitation on the amount of an analyte that they can detect. This limitation can be expressed as the IDL, which may be defined as the smallest amount of an analyte that can be reliably detected or differentiated from the background on an instrument. 

More recently, liquid chromatography/mass spectrometry (LC/MS) and liquid chromatography/tandem mass spectrometry (LC/MS/MS) have been evaluated as possible alternative methods for carfentrazone-ethyl compounds in crop matrices. The LC/MS methods allow the chemical derivatization step for the acid metabolites to be avoided, reducing the analysis time. These new methods provide excellent sensitivity and method recovery for carfentrazone-ethyl. However, the final sample extracts, after being cleaned up extensively using three SPE cartridges, still exhibited ionization suppression due to the matrix background for the acid metabolites. Acceptable method recoveries (70-120%) of carfentrazone-ethyl metabolites have not yet been obtained. 

Early measurements of " Th were on seawater samples and Th was co-precipitated from 20-30 L of seawater with iron hydroxide (Bhat et al. 1969). This procedure may not recover all of the " Th in the sample, and an alpha emitting Th isotope (e g., °Th or Th) is added as a yield monitor. Following chemical purification of the Th fraction by ion exchange chromatography, the Th is electrodeposited onto platinum or stainless steel planchets. The planchets are then counted in a low background gas-flow beta detector to measure the beta activity and subsequently with a silicon surface barrier detector to determine the alpha activity of the yield monitor. The " Th activity is thus determined as ... 

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