Food safety is a topic of great interest globally. With recent contamination issues in a wide range of commodities, ensuring the quality of our food supply is becoming increasingly important. Pesticide residue content is one area of concern. While pesticides have typically been monitored by gas chromatography, polar and/or thermally unstable pesticides are difficult or impossible to monitor using this approach. Thus, traditional HPLC techniques are used for select pesticide classes, such as the carbamate and phenylurea pesticides.
With recent advances in LC/MS/MS instrumentation, this technique is quickly gaining acceptance for pesticide residue testing. LC/MS/MS can be used to simultaneously monitor hundreds of potential contaminants—including those difficult to detect by GC. Using both LC/MS/MS and GC approaches allows for a faster, more complete picture of pesticide residues. MS/MS technology also permits identification of the target pesticides through the selection of specific MRM transitions for each compound. For example, aldicarb, a carbamate pesticide, uses two MRM transitions of 208.2 > 89.1amu and 208.2 > 116.1amu.
While the MS/MS detector allows for specific, sensitive detection of the pesticide species, the LC separation is still important to ensure the highest quality data. Conventional C18 stationary phases are typically used for pesticide monitoring, but the selectivity and retention is poor for more polar species. In contrast, Ultra Aqueous C18 columns are ideal for multi-pesticide residue monitoring methods. In Figure 1, the analysis of more than 280 pesticides using the 3μm Ultra Aqueous C18 is shown. Optimized stationary phase selectivity allows for an even distribution of the compounds throughout the retention time window. As well, retention of more polar pesticides is greatly improved, as demonstrated in Figure 1C. The Ultra Aqueous C18 column, in a 100 x 2.1mm, 3μm configuration is the column of choice for LC/MS/MS pesticide monitoring methods.
Ultra-high pressure LC (UHPLC) can also be used with MS/MS detection for monitoring pesticide residues. UHPLC allows for higher sample throughput when used in conjunction with a highly efficient <2μm particle size column. The 1.9μm Pinnacle® DB Aqueous C18, in a 50 x 2.1mm configuration, is ideally suited for this application.
Using LC/MS/MS technology and Aqueous C18 columns, in combination with gas chromatography, results in the most comprehensive monitoring of pesticide residues. Labs interested in more complete multi-residue analysis of pesticides in food matrices, including difficult polar or thermally unstable compounds, should consider adding LC/MS/MS and Aqueous C18 columns to routine testing procedures. The Aqueous C18 phase is also available on 1.9μm Pinnacle® DB silica for UHPLC platforms.
Acknowledgements
The authors wish to thank the US FDA for their collaboration and recognize the participation of multiple FDA labs in this work.
This abstract is part of Restek application note written by:
Becky Wittrig, Ph.D., Global HPLC Specialist, and André Schreiber, Ph.D., AB SCIEX
For more information about chromatographic conditions, Peak lists for pesticides in positive and negative ion modes and chromatograms, please contact us.
Residual solvents in pharmaceuticals are volatile organic
chemicals that are used in and are produced during the synthesis
of drug substances or can be in excipients used in the
production of drug formulations. These residual volatiles are
remains from processing agents. Many of these volatile organic
chemicals generally can not be completely removed by
standard manufacturing processes or techniques and are left
behind, preferably at low levels. Residual solvent analysis of
bulk drug substance and finished pharmaceutic products is
necessary for a number of reasons. High levels of residual
organic solvents represent a risk to human health because of
their toxicity. Residual organic solvents also play a role in the
physicochemical properties of the bulk drug substance. Crystallinity
of the bulk drug substance can be affected. Differences
in the crystal structure of the bulk drug may lead to
changes in dissolution properties and problems with formulation
of the finished product. Finally, residual organic solvents
can create odor problems and color changes in the finished
product and, thus, can lead to consumer complaints.
Often, the main purpose for residual solvent testing is in its
use as a monitoring check for further drying of bulk pharmaceuticals
or as a final check of a finished product.
In the recent past, guidelines for organic residual solvents
have generally been vague and not up to date. The USP
set official limits in USP XXV (1), but it is far from complete
considering the number of organic solvents actually used
within pharmaceutic manufacturing. The USP lists benzene,
chloroform, 1,4-dioxane, methylene chloride, and 1,1,1-
trichloroethane and has stated limits ranging from 2 to 600
parts per million (ppm). Residual solvent testing beyond loss
on drying (LOD) has been seriously pursued for nearly 20
years, and residual solvent test methods have been published
before that time period (2,3). Internationally, there has been
a demand for the establishment of standard guidelines. The
International Conference on Harmonisation of Technical Requirements
for Registration of Pharmaceuticals for Human
Use (ICH) (4) has made much progress in recent years with
residual solvent guidelines and limits (5). Essentially, this
body has consistently proposed that limits on organic solvents
be set at levels that can be justified by existing safety and
toxicity data. This body has also kept proposed limits within
the level achievable by normal manufacturing processes and
within current analytic capabilities.
Before 1997, the guidelines and regulatory authorities
seemed to be generally behind the actual testing done within
the pharmaceutical industry, but that situation was finally improved
in the United States by the FDA. In 1997, the FDA
issued their guidance “Q3C Impurities: Residual Solvents”
(6,7). This document was designated as a “guidance” rather
than a narrower “guideline,” and it was based on the recommendations
of the ICH (4). The acceptable amounts listed by the FDA guidance were derived only for patient safety considerations.
Residual solvents were classified in three categories
and are listed in Table I. Class 1 solvents are the most
toxic, and those in class 2 are considered a lesser risk. Finally,
class 3 solvents are the lowest risk category. The class 1 solvents
are benzene, carbon tetrachloride, 1,2-dichloroethane,
1,1-dichloroethane and 1,1,1-trichloroethane. The concentration
limits for the first four class 1 solvents listed are between
2 and 8 ppm, and the limit is 1500 ppm for trichloroethane,
which is considered an environmentally hazardous chemical.
Class 1 solvents should be avoided in the manufacturing of
pharmaceuticals. Class 2 solvents should be limited and specifically
tested for in products and have distinct toxicity or
tetraogenicity. The class 3 solvents are considered to have low
toxic potential and include such chemicals as acetic acid and
ethyl acetate. Class 3 solvents require only nonspecific GMPbased
testing and are limited to 5000 ppm or 0.5% (w/w).
THE TYPES OF RESIDUAL SOLVENT ANALYSIS
Residual solvent testing can be conducted by a number
of analytic techniques. Gas chromatograph–based test procedures
are the most popular and are chemically specific for
residual solvents. Gas chromatographic procedures can be
classified into a number of categories; the main three are
direct injection, headspace analysis, and solid-phase microextraction
(SPME). Numerous miscellaneous analytic techniques
exist, including gravimetric analysis [i.e., loss on drying
(LOD)] and some spectrometric and spectroscopic procedures.
All of these residual solvent analysis techniques are
covered in more detail in this review
GAS CHROMATOGRAPHY
The most popular, and the most appropriate, specific solvent
analysis is testing by gas chromatography (GC). GC has
the ability to separate component solvents, thus identifying
them, and it is capable of low detection limits when the appropriate
detector is used. A benchtop mass spectrometer
(MS) can be used for a detector and adds an additional level
of identification capability; this approach is often used in forensic
applications of residual solvent testing in pharmaceuticals
(8). Generally, for known solvent determinations, the
flame ionization detector (FID) is more than adequate for
validated specific residual solvent test methods. The FID was
introduced by McWilliam and Dewar in 1958 (9), and it has
become the most widely used detector for GC because of its
low detection limits, wide linear dynamic range, and general
reliability and utility, especially for trace organic compounds
(10). In a review of residual solvent testing of pharmaceutical
products, Witschi and Doelker (11) reported that more than
80% of the literature citations of gas chromatographic procedures
used the FID. Common detectors used for gas chromatography
and residual solvent testing are shown in Table II
along with general performance characteristics. Capillary GC
columns, which have high resolution and low detection limits,
are used most often for trace organic volatile analysis (10).
This review has been written by: Clayton B’Hymer and published in Pharmaceutical Research journal.
For more information about tables and data of this publication, please contact us.