pyrethroid metabolites in general populations, not occupationally exposed, are low,
usually below 1 ng/mL, and therefore advanced methods of sample preparation for
analysis and proper and sensitive apparatus are required. However, even the most
modern and advanced equipment does not ensure reliable results. The laboratory
must follow the principles of good laboratory practice, and the quality assurance
system must necessarily work. Quality control procedure is a prerequisite for
obtaining credible results. Both internal and external quality controls should be
carried out in all laboratories specializing in HBM.
Internal quality control is realized by the purchase or in-house preparation of
appropriate quality control (QC) materials. The QC material should be human
biological material prepared at least at two different levels. The concentration levels
should be adjusted in respect to the expected levels of exposure in studied population. At least one sample of each concentration level should be analyzed in each
analytical batch and the QC results interpreted with the use of quality control charts.
Usually in-house quality control (QC) material is prepared according to generic
procedure: urine is collected from multiple anonymous donors, combined, diluted
with water (1:1 v/v) to reduce endogenous concentrations of the analytes of interest,
and carefully mixed. Urine is filtered and divided into three pools. The first quality
control (QC) pool (low concentration) is spiked with the native standards to yield
low-concentration quality control (LQC) material. The second pool is spiked with
higher amount of native standards to yield the so-called high quality control (HQC)
material. The third pool is not spiked (blank urine) and is used later as a matrix
material for calibration standards and blanks. It is recommended to characterize each
pool by producing a minimum of 20 analytical runs over a period of 20 days.
Obtained results are used then to determine the 95 and 99% control limits by
which the QC sample results in each batch will be evaluated.
External quality control is carried out by analyzing samples obtained from
external laboratories within the intercomparison program. The most well-known
program that has been offering the assessment of the quality of methods for
determination synthetic pyrethroid metabolites for many years is the German external quality control scheme (G-EQUAS,) organized and managed by the Institute and
the Outpatient Clinic for Occupational, Social and Environmental Medicine of the
University of Erlangen-Nuremberg (Erlangen, Germany). Scheme, evaluation, and
certification are based on the German Federal Medical Council (http://www.g-equas.
de/). As part of this program, it is possible to verify the suitability of the method for
the determination of five synthetic metabolites of pyrethroids: DBCA, cis-/transDCCA, 3PBA, and 4F3PBA. The rounds of this program take place two times
a year.
6 Conclusions and Further Research
It seems that at the present time, analytical methods are available covering a fairly
broad spectrum of metabolites with sufficient sensitivity to assess environmental
exposure in global populations. Despite the much simpler sample preparation
76
B. Wielgomas et al.
usually below 1 ng/mL, and therefore advanced methods of sample preparation for
analysis and proper and sensitive apparatus are required. However, even the most
modern and advanced equipment does not ensure reliable results. The laboratory
must follow the principles of good laboratory practice, and the quality assurance
system must necessarily work. Quality control procedure is a prerequisite for
obtaining credible results. Both internal and external quality controls should be
carried out in all laboratories specializing in HBM.
Internal quality control is realized by the purchase or in-house preparation of
appropriate quality control (QC) materials. The QC material should be human
biological material prepared at least at two different levels. The concentration levels
should be adjusted in respect to the expected levels of exposure in studied population. At least one sample of each concentration level should be analyzed in each
analytical batch and the QC results interpreted with the use of quality control charts.
Usually in-house quality control (QC) material is prepared according to generic
procedure: urine is collected from multiple anonymous donors, combined, diluted
with water (1:1 v/v) to reduce endogenous concentrations of the analytes of interest,
and carefully mixed. Urine is filtered and divided into three pools. The first quality
control (QC) pool (low concentration) is spiked with the native standards to yield
low-concentration quality control (LQC) material. The second pool is spiked with
higher amount of native standards to yield the so-called high quality control (HQC)
material. The third pool is not spiked (blank urine) and is used later as a matrix
material for calibration standards and blanks. It is recommended to characterize each
pool by producing a minimum of 20 analytical runs over a period of 20 days.
Obtained results are used then to determine the 95 and 99% control limits by
which the QC sample results in each batch will be evaluated.
External quality control is carried out by analyzing samples obtained from
external laboratories within the intercomparison program. The most well-known
program that has been offering the assessment of the quality of methods for
determination synthetic pyrethroid metabolites for many years is the German external quality control scheme (G-EQUAS,) organized and managed by the Institute and
the Outpatient Clinic for Occupational, Social and Environmental Medicine of the
University of Erlangen-Nuremberg (Erlangen, Germany). Scheme, evaluation, and
certification are based on the German Federal Medical Council (http://www.g-equas.
de/). As part of this program, it is possible to verify the suitability of the method for
the determination of five synthetic metabolites of pyrethroids: DBCA, cis-/transDCCA, 3PBA, and 4F3PBA. The rounds of this program take place two times
a year.
6 Conclusions and Further Research
It seems that at the present time, analytical methods are available covering a fairly
broad spectrum of metabolites with sufficient sensitivity to assess environmental
exposure in global populations. Despite the much simpler sample preparation
76
B. Wielgomas et al.