This work describes a simple and sensitive high performance liquid chromatography (HPLC) method, with mass spectrometry (MS)
and ultraviolet (UV) detection, for the analysis of up to 32 pesticides in a mixture. The analytes from substance classes
such as carbamates, organophosphates, pyrazoles, triazines, or ureas were separated on C18 reversed-phase monolithic silica
capillary columns using a gradient elution profile and directly transferred to a mass spectrometer. To improve resolution,
capillaries were coupled, enabling identification of all pesticides. In addition, a porcine kidney sample was spiked with
a set of seven pesticides and after a typical solid-phase extraction (SPE) procedure all analytes were detected using liquid
chromatography–mass spectrometry (LC–MS). For selected compounds, calibration curves were prepared as well as limits of detection
Since humans started to settle and grow crops, fighting pests has been an important issue to securing food supply. Approximately
4500 years ago, sulphur was used in pest control; and approximately 2500 years ago, arsenic was used for the repelling of
insects (1). Until the middle of the 19th century, various inorganic chemicals were applied in pest control, including copper
sulphate (smut or bunt), mercury (rats or insects), sodium chloride (weeds), or even simple water (to protect plants from
caterpillars or lice ). Since then methods have become increasingly elegant. In the late 19th century, herbal agents, such
as pyrethrum or rotenon, were discovered and used as insecticides (3,4). Over time, synthetic pesticides were developed —
copper-, lead-, or mercury-containing compounds and organic molecules, such as dithiocarbamates, became the first choice of
fungicides (5,6), with dinitrocresol as the first synthetic insecticide. Later developments in the field of pesticide synthesis
resulted in tetraethylpyrophosphate, dichlorodiphenyltrichloroethane (DDT), 2,4-dichlorophenoxyacetic acid, esters of thiophosphoric
acid, and triazines (6). In the late 1970s, traps were developed containing the pheromone of the spruce bark beetle Ips typographus.
According to the US Environmental Protection Agency (EPA), any substance intended for preventing, destroying, repelling,
or mitigating any pest is referred to as a pesticide (7). However, pesticides differ in their properties — while molecules
such as pyrethroids (for example, allethrin) or esters of thiophosphoric acid are easily biodegradable, other active agents
from substance classes such as organochlorines (DDT, dieldrin), organophosphates (chlorfenvinphos, parathion), carbamates
(carbetamide, carbofuran), or phenylureas (isoproturon, or linuron) are persistent and can accumulate in the environment (8).
Pesticides can be divided into three categories based on their half-lives (9):
- Nonpersistent pesticides: Half-life = <30 days; for example, pyrethroids.
- Moderately persistent: Half-life = 30–100 days; for example, many carbamates, chloroacetanilides, organophosphates, or ureas.
- Persistent pesticides: Half-life = >100 days; for example, organochlorines.
The toxicological risk of persistent compounds is high, especially with regards to accumulation in ground water resources
or the food chain and the list of incidents is almost endless. In the US, atrazine and its microbial degradation products,
deisopropylatrazine and deethylatrazine, were found to contribute to both surface and groundwater contamination in samples
from coastal sediments, golf courses and a commercial harbour. Isoproturon and chlortoluron were found to be contaminating
the Rhine as a drinking water resource. These important findings demonstrate the importance of establishing methods such as
liquid chromatography–mass spectrometry (LC–MS) (10) for fast, sensitive and accurate analysis of pesticides.
This article describes the qualitative analysis of different pesticide standard mixtures, as well as of a spiked porcine kidney
sample, using monolithic silica column technology combined with liquid chromatography–ultraviolet (LC–UV) and LC–MS detection.
The pesticides analysed are applied as herbicides, algaecides, acaricides, insecticides, fungicides, nematicides, and rodenticides
and belong to substance classes such as triazinones, carbamates, triazines, carbamates, phenylureas, chloroacetanilides, pyrazoles,
chloroacetanilides, organophosphates, and ureas (see Figure 1). This list shows that the analysis of this substance class
is challenging because of the different nature of the target molecules. To improve resolution, column coupling was performed.
Limits of detection (LOD), as well as calibration curves, were determined for two of the pesticides.
Figure 1: Chemical structures of pesticides from different substance classes analysed in this work. 1 = metamitron (substance
class: triazinone), 2 = carbetamide (carbamate), 3 = prometryne (triazine), 4 = carbofuran (carbamate), 5 = isoproturon (phenylurea),
6 = metazachlor (chloroacetanilide, pyrazole), 7 = metolachlor (chloroacetanilide), 8 = chlorfenvinphos (organophosphate),
9 = pencycuron (urea).