Was Lindane Isolated and Recovered from a Biological Matrix Using RP-SPE? If So, How?
One hundred microliters of a methanolic solution containing 5 ng/pL (ppm) lindane was placed in a 1 mL volumetric flask half filled with iso-octane, while 100 pL of the same lindane reference standard was added to approximately 70 mL of distilled deionized water (DDI). One microliter of the former solution containing 500 ng of lindane was injected into a GC, and the resulting peak area served to define a control sample. This laboratory sample represents a 100% recovery of lindane. One microliter of the 1 mL eluent from performing the RP-SPE of the spiked DDI was also injected into the same instrument, and the resulting peak area served to define the spiked recoverу sample. In this study, quadruplicate injections of the control yielded a mean concentration of 400 ppb lindane from interpolation of the least squares calibration curve. Seven replicates of the eluent from the spiked DDI sample were injected, and a mean concentration of 406 ppb lindane was obtained from interpolation of the same calibration curve. Equation (2.57) was used to find a 106% recovery of lindane. RSDs in the % recovery were found by propagating random error between spiked samples and control reference standards as shown in Equations (2.54) and (2.55). A complete result can be given by stating both the accuracy, 106% recovery, and the relative standard deviation of 15.6%. Myometrium samples were then prepared and lindane appeared as expected. This work showed that lindane could easily be isolated and recovered from an aqueous matrix and confirmed the earlier work on lindane isolation and recovery, discussed previously. One would be led to believe that this is a robust sample preparation method for lindane because it can be reproduced with confidence. Thus, a subsequent request for additional sample analyses does not require extensive QC and should merely report the analytical results.
What Does a Sample Analysis Report Using RP-SPE Techniques Look Like?
In addition to a tabular format for the determination of lindane in each of the myometrial tissue samples submitted, a method summary should be included. A one-paragraph method summary serves to inform the reader as to how the samples were handled once they arrived in this analyst’s laboratory. The summary should also provide a brief overview of the sample preparation and a brief description of the determination technique used. The following report illustrates these concepts.
Report on the Quantitative Determination of Lindane in Myometrial Tissue Suspended Cells in Saline
Summary of Method
The entire contents (1 mL) of the sample that was received by the client were refrigerated upon receipt until the sample was prepared for analysis. Upon thawing, the entire contents of each sample were added to a reservoir that contained approximately 70 mL of distilled deionized water. This aqueous solution was passed across a previously conditioned octadecyl-bonded silica sorbent (C|SRPSiO;). The retained analyte was eluted off of the sorbent with two 500 pL aliquots of pesticides-residue- grade iso-octane. The iso-octane eluent was then passed through a second SPE cartridge. This second cartridge was packed with approximately 0.5 g of anhydrous sodium sulfate. The volume of eluent that now contained the recovered analyte was adjusted to a final volume of 1.0 mL using a volumetric flask. Three microliters of this eluent was injected via autosampler into an Autosystem Gas Chromatograph (PerkinElmer) incorporating an electron-capture detector. A 30 m x 0.32 mm capillary GC column containing DB-5 (J&W Scientific) was used to separate the organics in the eluent. This instrument is abbreviated C-GC-ECD to distinguish it from other gas chromatographs in our laboratory. The column was temperature programmed following injection from 200 to 270°C at a rate of 10°C/min. The C-GC-ECD is connected to a 600 Link (PE-Nelson) interface module. This interface, in turn, is connected to a 386 personal computer. This PC uses Turbochrom® (PE-Nelson) software for data acquisition, processing, and control. A method specific for lindane was written, and one peak was identified within a 3% relative time interval (retention time window). A retention time, ?[/?), of 1.8 min was consistently reproduced using autosampler injection.
Calibration
A series of calibration or working standards were prepared from the methanolic stock solution containing lindane. This stock solution was prepared by carefully weighing out pure solid lindane on an analytical balance. These standards were injected into the C-GC-ECD from lowest to highest lindane concentration. The peak at 1.8 min was identified as a reference peak in the Turbochrom software, and a narrow ;[/?] window was defined around the ?[/?] of the apex of the peak. A calibration curve was constructed using a least squares regression algorithm in the software. A correlation coefficient of 0.9990 was obtained.
Sample Analysis
The sequence within which the samples were run after calibration was created by using the Sequence File Editor within Turbochrom. Samples are injected via autosampler according to the instructions in the Sequence File. After the sequence is completed, a Summary File is created and the analytical results are reported within this summary format. In the Summary File, for each sample analyzed, the following is given:
- (a) The sample number
- (b) The concentration of lindane in ppb for 1.0 mL of eluent, interpolated from the external standard mode of instrument calibration
- (c) The retention time for lindane, /[/?], in minutes
- (d) The integrated peak area, in microvolts-seconds.
The reported concentration is that for each eluent and should be multiplied by the eluent volume (in this case, 1.0 mL) to obtain the number of nanograms of lindane found. The number of nanograms found divided by the volume of the aqueous sample used in RP-SPE gives the reported concentration in ppb for lindane. The reported concentration should be divided by the volume of the sample to obtain the reported concentration in ppb for lindane. The reported concentration should also be divided by the percent recovery, expressed as a decimal, in order to find the true and final concentration of lindane in the original sample.
Method Evaluation
Lindane is efficiently recovered from aqueous matrices with percent recoveries between 75 and 100% using RP-SPE. The biological sample closely approximates an aqueous matrix.
