Phosphorus-nitrogen selective detectors

Detectors which are sensitive to specific elements or structures, such as electron capture detectors (ECD) or phosphorus- and nitrogen-selective detectors (TSD) respond even to quantities of substances in the picogram (10"12 g) Qj. femtogram (10 g) ranges. 

The detectors used in HTGC are, apart from the highly versatile flame ionization detector (FID), the phosphorus/nitrogen-selective alkali-flame ionization detector (AFID), the atomic emission detector, the inductively coupled plasma (ICP)-mass spectrometer, and, last but not least, mass spectrometers with electron impact and chemical ionization ion sources (EI/CI-MS). 

A gas chromatograph (GC), equipped with a nitrogen selective detector. A Hewlett-Packard Model 5840A GC fitted with a nitrogen-phosphorus flame ionization detector (NPD) was used for this evaluation. Injections were performed using a Hewlett-Packard Model 7671A automatic sampler. 

The most common selective detectors in use generally respond to the presence of a characteristic element or group in the eluted compound. This is well illustrated by the thermionic ionisation detector (TID) which is essentially a flame ionisation detector giving a selective response to phosphorus- and/or nitrogen-containing compounds. Typically the TID contains an electrically heated rubidium silicate bead situated a few millimetres above the detector jet tip and below the collector electrode. The temperature of the bead is maintained... 

Universal and selective detectors, linked to GC or LC systems, have remained the predominant choice of analysts for the past two decades for the determination of pesticide residues in food. Although the introduction of bench-top mass spectrometers has enabled analysts to produce more unequivocal residue data for most pesticides, in many laboratories the use of selective detection methods, such as flame photometric detection (FPD), electron capture detection (BCD) and alkali flame ionization detection (AFID) or nitrogen-phosphorus detection (NPD), continues. Many of the new technologies associated with the on-going development of instrumental methods are discussed. However, the main objective of this section is to describe modern techniques that have been demonstrated to be of use to the pesticide residue analyst. 

For amines absorption in an acid solution, or preferably adsorption onto an acid ion exchange column (acidified divinylbenzene-styrenesulfonic acid copolymer) is used. 10-50 1 of ambient air is sent over a wet 100 mmx 3 mm I.D. column the ion exchange polymer is put into a vial, made alkaline and the water solution is analysed on packed Carbowax-KOH GC-column with a thermionic selective detector (TSD), which is specific for nitrogen- and phosphorus-compounds. Trimethylamine is detected easily at 1 ppb. 

Where the target analyte contains heteroatoms such as nitrogen, phosphorus and sulfur, atom-selective detectors can provide an ideal detection method. A number of examples appear in the literature of the use of a detector called a thermal energy analyser (TEA) for the measurement of A-nitroso compounds [14-17] and aromatic nitro compounds [18]. This has also been used as an HPLC detector [19, 20], and a modified TEA has been reported to be useful for analysis of amines and other nitrogen-containing compounds [17]. Unfortunately, this technique appears not to have gained in popularity, since no reports have appeared in the literature for over two decades. 

The extracts were also analyzed for OPs and TAAPs by capillary GC equipped with a nitrogen-phosphorus selective detector (GC-NPD) (6, 8). 

Organochlorine pesticides and OPPs have been determined mainly using GC, because of the stability and volatility that most of them show under chromatographic conditions and, particularly, the availability of element-selective detectors that display high selectivity for OCPs (electron-capture detector, ECD), and OPPs (flame photometric detector, FPD, and nitrogen phosphorus detector, NPD). Mass spectrometry-based detection is also more popular in GC than in HPLC (1,2,12,16). 

Highly selective to compounds containing nitrogen and phosphorus Nitrogen-phosphorus detector Organophosphorus pesticides (EPA 8141) Acrylonitrile (EPA 8031) Acetonitrile (EPA 8033) Nitrosamines (EPA 8070) Hydrocarbons, fats, oils, waxes may interfere with organophosphorus pesticides. 

F enitrothion,Aminocarb and phenolic hydrolyses products Nitrogen- phosphorus selective detector Phenols derivitivised to esters with aceticanhydride then methylene chloride extraction, then GLC I 8 [449]... 

Giachetti et al. [60] compared the performance of mass selective detector (MSD), electron capture detector (ECD) and nitrogen-phosphorus detector (NPD) of gas chromatography systems in the assay of six nonsteroidal antiinflammatory drugs in the plasma samples. As a practical test, six NSAIDs (mefenamic, flufenamic, meclofenamic and niflumic acids, diclofenac and clonixin) added to plasma samples were detected and quantified. The analyses were carried out after solvent extraction from an acidic medium and subsequent methylation. The linearity of response was tested for all the detection systems in the range of 1-25 ng/mL. Precision and accuracy were detected at 1, 5 and 10 ng/mL. The minimum quantifiable level for the six drugs was about 1 ng/mL with each of the three detection systems. 

TCD) detector or the flame-ionization (FID) detector, which are the two most common detectors in gas chromatography, respond to all (organic) compounds except the carrier gas. On the contrary, a selective detector responds to a range of compounds with a common physical or chemical property. Representatives of the latter group of detectors are the nitrogen-phosphorus detector (NPD), the electron capture detector (ECD), the mass selective detector (MSD) and - last, but not least - the tandem mass spectrometer (MS/MS). 

The mass-selective detector is more specific and allows a lower limit of quantification than the nitrogen-phosphorus detector (NPD). 

The alkali flame-ionization detector, sometimes called an NP or nitrogen-phosphorus detector, contains a thermionic source, such as an alkali-metal salt or a glass element containing rubidium or other metal, that results in the efficient ionization of organic nitrogen and phosphorus compounds. It is a selective detector that shows little response to hydrocarbons. 

Other detectors in use include the thermal conductivity detector (TCD) and the phosphorus-nitrogen detector (PND) which is much used in toxicology because of its selectivity for nitrogen-containing compounds. It is a feature of gas-liquid chromatography that spectrophotometric detectors can be coupled readily to the outflow for detection this includes IR, NMR and, particularly, mass spectrometers, in combined GC-MS analysers. Spectroscopic analysis allows structural information to be... 

Traditionally, gas chromatography (GC) was the preferred approach for the analysis of pollutants in water, due to the high sensitivity and selectivity achieved, thanks to its selective detectors such as the nitrogen-phosphorus (NPD), the flame photometric detector (FPD), and electron-capture detector (ECD), and to the ease of coupling to mass spectrometry (MS). However, high-performance liquid chromatography (HPLC or LC) is the most powerful approach for the determination of polar, nonvolatile, and thermolabile compounds (i.e., those which are not GC amenable). 

Sensitivity With a flame ionisation detector, the measurement of parts-per-million (ppm) level of almost all volatile organic compounds can be easily achieved. When using selective detectors such as electron-capture and nitrogen-phosphorus detectors, levels as low as parts-per-bilhon (ppb) have been routinely measmed. 

Figure 7. Gas chromatogram of pyrrolizidine alkaloids from comfrey root tea. Nitrogen-phosphorus selective detector all other conditions identical to those...

MSD Mass selective detector NMR Nuclear magnetic resonance NPD Nitrogen-phosphorus detector (used in GC to analyze nitrogen- and phosphorus-containing organics)... 

The persistence of terbuthylazine, simazine, atrazine, and prometryn (r-triazine herbicides) was studied in sea, river, and groundwaters during long-term laboratory incubation (127 days) under different laboratory conditions (light-darkness at 20 °C). Analysis of herbicides was performed by GC-NPD and their identity was confirmed by GC-MSD(NPD = nitrogen phosphorus detector MSD = mass selective detector) <2004SCT87>. 

Detection Femtomole detection limits can be achieved using electron capture detection (ECD). Nitrogen-phosphorus and flame ionization detectors have also been employed. However, the primary advantage of GC is its compatibility with MS. Using a mass-selective detector, amino acids can be determined at the low femtomole level. Figure 6 shows the... 

Residues are determined in the purified extracts by chromatographic or immunochemical techniques. In the chromatographic systems, thin-layer chromatography (TEC), liquid chromatography (LC), and GC, the analytes are separated on plates or columns and determined by colorimetry, by spectrophotometry (ultraviolet (UV), infrared (IR, Fourier transform infrared (FTIR)), by fluorescence, by selective detectors (in GC analysis ECD, flame photometric (FPD), nitrogen/phosphorus (NPD, TSD), etc.), or by MS. Separations may also be achieved by... 

Element selective detectors Element selective detectors applicable in pesticide residue analysis include electron capture detector (ECD), electrolytic conductivity detector (ELCD), halogen-specific detector (XSD), nitrogen phosphorus detector (NPD), flame photometric detector (FPD), pulsed flame photometric detector (PEPD), sulfur chemiluminescence detector (SCD), and atomic emission detector (AED). To cover a wider range of pesticide residues, a halogen-selective detector (ECD, ELCD, XSD) in conjvmction with a phosphorus- (NPD, FPD), nitrogen- (NPD), and/or sulfur-selective detector (FPD, SCD) is commonly used. A practical approach is to spht the column flow to two detectors that reduces the number of injections however, the reduced amoimt of analyte that reaches the detector must be considered. 

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