APCI phenylureas

Liquid chromatography -APCI-MS is applicable to many different types of pesticide structures, such as triazines, phenylurea herbicides, acetanilides, and OPPs. A study of 12 pesticides and pesticide degradation products demonstrated the sensitivity of the technique for OPP determination, with detection limits for water samples of about 0.001-0.005 /zg/L (32). 

A comparison between APCI-LC/MS and PB-LC/MS was conducted for the determination of a priority group of herbicides in water, including phenylureas, triazines, and chlorophenoxy acids. The potential of both ionization techniques for the monitoring of environmental matrixes was demonstrated. However, APCI was approximately ten-fold more sensitive than PB, both in negative and positive ionization mode. ... 

In a SPE-LC-APCI-MS/MS study of 37 polar herbicides in water, (mainly triazines, phenylureas, and phenoxy acids), a 5- to 50-fold improved detectability was observed for the combined acetonitrile desorption-methanol gradient procedure, compared to the traditional acetonitrile only approach. 

APCI-LC-MS [325] was applied to determine phenylurea herbicides in water samples with detection limits all in the low pg range, whereas ESI-LC-MS was used to analyse the acidic polar pesticides. Under APCI conditions the specific fragment ion of phenylureas mjz 72 corresponding to [0=C=N (CH3)2] could be observed [325]. Fragmentation pathways were presented. In a TSP-LC-MS study covering 15 phenylurea and thiourea pesticides APCI-LC-MS/MS was used to elucidate fragmentation behavior observed under TSP conditions [175]. 

Surface water samples from Southeastern regions of France and from the St. Lawrence River in Canada were monitored by APCI-LC-MS and MS/MS in the positive mode. Diuron and isoproturon were confirmed by MS/MS. Results obtained by LC-MS and ion trap LC-MS/MS were found to be comparable [374]. A substance-specific robust APCI-LC-MS/MS method using short columns for trace analysis of phenylureas was elaborated and vaUdated. Despite the low quantity of sample applied (15 mL) detection limits of < 5 pg L in full-scan and < 750 ng L in SIM mode, respectively, could be achieved. Product ion spectra were obtained from [M-i-H] parent ions and by means of a pesticide MS/MS Hbrary... 

Liquid chromatography-mass spectrometry The initial attempts to couple LC with MS lacked important attributes for trace analysis sensitivity, robustness, and reliable quantitation. Moreover, the cost of the early LC-MS instruments was prohibitive for most laboratories. The revolutionary introduction of atmospheric pressure ionization (API) techniques, mainly electrospray (ESI) and atmospheric pressure chemical ionization (APCI), resulted in greater applicability of LC-MS and manufacture of more reliable, affordable, and user-friendly instruments. Thus, LC-MS is now becoming an indispensable part of the analytical strategy in many routine laboratories, enabling direct, selective, and sensitive multiclass, multiresidue analysis of more polar, low volatile, and/or thermolabile pesticides, such as carbamates, phenylureas, sulfonylureas, imidazoles, triazoles, imidazolinones, chlorophenoxy acids, and many others. 

Triazines, amides, phenylureas, triazoles, triazinones, benzimidazoles, phenoxyalkanoic herbicides LC/MS and LC/MS/MS ESI (-) for acidic compounds APCI ( + ) 20-100 pgmr 2-6pgmr Environmental water... 

Most of the modern pesticides and their degradation products are characterized by medium to high polarity and thermal lability. Neutral and basic compounds (phenylureas, triazines) are more sensitive using APCI (especially in positive ion mode), while cationic and anionic herbicides (e.g., bipyridylium ions, sulfonic acids) are more sensitive using ESI (especially in negative ion mode). Based on comparative analysis of 75 pesticides, the so-called ionization-continuum diagram illustrates the relationship between compound acidity and appropriate ionization modes (Figure 2). 

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