Agilent solutions to optimize workplace drug testing
By Joan Stevens Agilent Sample Prep Applications Scientist
Many workplace-screening tests for drugs of abuse are done by mass spectrometry (MS) with gas chromatography (GC) or liquid chromatography (LC). At times, you may need to update existing standard operating procedures to achieve lower detection limits, improved linearity in the lower or upper concentration range, calibration range extension, limited sample volume, or to correct frequent replacement of the analytical column. In this article we offer some examples for optimizing forensics sample prep method development.
Better sample prep method development with Agilent Bond Elut Certify
The first step in solid phase extraction (SPE) method development is to understand the characteristics of the target compound. We looked at phencyclidine (PCP), a relatively basic and hydrophobic drug. Ideally, using cation-exchange and hydrophobic interaction would be the best choice for SPE of this drug. Agilent Bond Elut Certify mixed-mode solid phase extraction has a good balance of both hydrophobic and cation-exchange characteristics and is well-suited for PCP analysis. Agilent Bond Elut Certify exhibits a variety of sorbent-analyte interactions so it can be used both for general clean-up and specific extractions for instrumental confirmation of drugs and metabolites.
Figure 3. Calibration curve for THCA spiked into hair samples at 0.002, 0.01, 0.02, 0.05, 0.1, and 0.5 pg/mg of hair.
The conventional SPE workflow consists of conditioning, equilibration, sample loading, washing, elution, evaporation, and reconstitution. The most effective optimization is achieved in the washing and elution steps. During sample loading, compounds of interest bind to the sorbent material, along with interferences. The purpose of the washing step is to remove these interferences. The elution step then recovers the target compound by interrupting the interaction between it and the SPE sorbent. Maximum removal of interference, while maintaining optimal recovery of the target compound, is key to successful method development in SPE. To verify method optimization, every step from sample loading to elution needs to be collected and analyzed by chromatography. Figure 1 shows the sample vials at different stages of the washing and elution process in an investigation of PCP in urine.
The wash 3 vial was visually clear and the chromatogram from wash 3 did not have the target compound peak; hence, wash 3 can be skipped. Eluate 3 did not have a significant amount of PCP, which indicated that eluate 2 and 3 could be combined into a single elution step to save on solvent use and time.
Detecting THC in hair using Agilent 7000B Triple Quadrupole GC/MS
Testing hair has been practiced for over 50 years. Because many drugs are well preserved in hair, it is possible to detect drug use over longer periods compared with other biological matrixes. Workplace programs often include hair testing due to the ease of collection, difficulty of adulteration, and longer detection times.
Marijuana is one of the drugs tested most often in forensic and drug screening applications. The parent compound, tetrahydrocannabinol (THC), is found in higher concentration in hair samples, but detection of the acid metabolite 11-nor-D9-tetrahydrocannabinol-9-carboxylic acid (THCA) is preferred to eliminate the possibility of potential environmental contamination from marijuana smoke.
In this example, we used an Agilent 7890B GC coupled to an Agilent 7000B Triple Quadrupole GC/MS to provide rapid and sensitive detection of a THC metabolite in hair using 2-D GC. The method took advantage of the lower chemical background and higher sensitivity provided by triple quadrupole MS/MS analysis. Backflush was used to increase robustness, and low thermal mass column modules (DB-1ms LTM and DB-17ms LTM) sped the chromatography process, enabling a run time of 7 minutes and a cycle time of 9 minutes. Multiple reaction monitoring MS/MS analysis delivered excellent sensitivity, with an LOD of 0.002 pg/mg and an LOQ of 0.01 pg/mg. The accuracy of quantification was also good, with an R2 of 0.995 from 0.002 to 0.5 pg/mg of hair (Figure 3). Read the Agilent Application Note 5990-7535EN for more details.
Agilent provides complimentary resources and sample prep solutions for drug testing