Organophosphorus sensitivity analyses

FPD measures the phosphorus or sulfur-containing substances. Because most organophosphorus pesiticides contain sulfur atoms, die FPD may be more sensitive and selective. Both these detectors may be used in a dual column dial detector system for analysis. 

The HPLC/MS technique used in EPA Method 8321 is best suited for analysis of thermally unstable compounds that are hard to analyze with conventional GC methods, such as organophosphorus pesticides, chlorinated herbicides, and carbamates. In this technique, the detection with mass spectrometry provides the ultimate selectivity. The sensitivity for each individual compound depends on the interferences in a given environmental matrix and on the chemical nature of the analyte. 

Nonselective 1-D 1H-31P inverse NMR spectroscopic experiments have been applied for analysis of CWC-related organophosphorus compounds (38). With these experiments, the alkyl substituent at the phosphorus can be determined with a better sensitivity than in the 31P 1H experiment, and with elimination of strong background signals. 

Pesticides. There are numerous references to the use of HPLC/MS for the analysis of pesticides and herbicides [14, 16-20]. Some major classes of pesticides and herbicides including carbamate, triazines, organophosphorus, and phenolic acid have been analyzed by HPLC/MS using Cl or ion evaporation ionization. While these ionization techniques often resulted in excellent sensitivity (thermospray/MS full scan detection limits of 1-10 ng), usually only [M+H] and/or [M+NH4] ions were formed. This limitation can be overcome using tandem4MS [20], moving belt [17], and most recently through the use of particle beam HPLC/MS. 

Heteronuclear correlation experiments can be useful in terms of identification and quantification of traces in complex mixtures such as soil or water. The detection of trace amounts of organophosphorus compounds related to the chemical weapons convention impressively demonstrates how the advantages of each nucleus were combined, namely the sensitivity of the H NMR spectra and the freedom from background noise for P NMR spectra [26]. This was achieved by measuring inverse H- P NMR spectra utilizing the HSQC experiments. These techniques will be introduced to drug analysis in body fluids. 

The popularity of the BCD can be attributed to the high sensitivity to organohalogen compounds, which include many compounds of environmental interest, including polychlorinated biphenyls and pesticides. It is the least selective of the so-called selective detectors but has the highest sensitivity of any contemporary detector. The NPD or thermionic ionization or emission detector is a modified FID in which a constant supply of an alkali metal salt, such as rubidium chloride, is introduced into the flame. It is a detector of choice for analysis of organophosphorus pesticides and pharmaceuticals. The FPD detects specific luminescent emission originating from various excited state species produced in a flame by sulfur- and phosphorus-containing compounds. 

Acoustic analysis detects changes in the properties of acoustic waves as they travel at ultrasonic frequencies in piezoelectric materials. The interaction between the waves and the phase-matter composition facilitates chemical selectivity and, thus, the detection of CWA s. These are commonly known as surface acoustic wave (SAW) sensors. Reported studies indicate detection limits as low as 0.01 mg m for organophosphorus analytes within a 2 min analysis [1]. There are several commercially available SAW instruments, which can automatically monitor for trace levels of toxic vapors from G-nerve agents and other CWAs, with a high degree of selectivity. A major advantage of SAW detectors is that they can be made small, portable and provide a real-time analysis of unknown samples. One of the drawbacks of these instruments is that sensitivity and a rapid response time are inversely related. In an ideal instrument, both parameters would be obtained without sacrificing one for the other. 

---