4.5 Minute Analysis of Benzodiazepines in Urine and Whole Blood Using LC/MS/MS and an Ultra Biphenyl Column
A rapid, sensitive method for the routine analysis of benzodiazepines in urine and whole blood was developed using a simple dilute-and-shoot methodology. Partial validation experiments were conducted using fortified urine and blood samples. Linearity was evaluated from 0.1 ng/mL to 1,000 ng/mL. Detection limits ranged from 0.1 ng/mL to 5 ng/mL and quantification limits ranged from 0.5 ng/mL to 10 ng/mL. This method, which uses an Ultra Biphenyl LC column and an API 4000 MS/MS detector, provides a fast 4.5 minute analysis which allows efficient monitoring of a broad range of benzodiazepines at therapeutic levels.
Benzodiazepines are widely used to treat anxiety and sleep disorders such as restless leg syndrome. These drugs are often prescribed in conjunction with pain management medications, due to their ability to relieve the pain caused by stress. Because of their tranquilizing qualities and relative availability, illicit use of benzodiazepines has become more common, and their analysis is now a routine procedure in both clinical and forensic laboratories. While benzodiazepines can be analyzed by either GC/MS or LC/MS/MS, GC/MS methods are more time-consuming and labor-intensive, as sample preparation and derivatization are required. LC/MS/MS methods are often a better choice when higher sample throughput is desired.
The procedure and conditions presented here result in a fast dilute-and-shoot LC/MS/MS chromatographic method for therapeutic levels of a comprehensive list of benzodiazepines in urine and whole blood. While other methods that have been developed for LC/MS/MS range from 10 to 23 minutes, the analysis shown here is complete in 4.5 minutes, allowing more samples to be run per shift.
Various frequently analyzed benzodiazepines were included in this chromatographic method. The compounds analyzed included clonazepam, diazepam, lorazepam, flunitrazepam, triazolam, and their 7-amino, desmethyl, and desalkyl metabolites.
For urine samples, the urine was hydrolyzed prior to fortification by adding 1 mL of a beta-glucuronidase solution from keyhole limpet (Sigma-Aldrich cat.# G8132) to 1 mL of urine and incubating the mixture at 60 °C for 3 hours. The beta-glucuronidase solution was prepared at 5,000 Fishman units/mL in 100 mM ammonium acetate buffer (pH = 5.0). Compounds were spiked directly into the enzymatically-hydrolyzed urine at 11 levels (0.1, 0.5, 1, 5, 10, 25, 50, 100, 200, 500, and 1,000 ng/mL). Then, each sample was diluted 20:1 in mobile phase containing 30 ng/mL of internal standard (5 µL sample + 95 µL mobile phase). After dilution, samples were centrifuged for 10 minutes at 3,000 g to remove any solids remaining in the sample, and the supernatant was removed for analysis.
For blood samples, whole blood was collected offsite and diluted 1:1 with acetonitrile in order to precipitate proteins. After precipitation, the sample was centrifuged for 10 minutes at 3,000 g. Benzodiazepines were spiked into the precipitated whole blood at the same levels specified for urine. Then the fortified samples were diluted 10:1 in mobile phase containing 30 ng/mL internal standard (100 µL sample + 900 µL mobile phase) to yield an overall 20-fold dilution. Samples were then centrifuged for 10 minutes at 3,000 g, and the supernatant was removed for analysis.
All samples were analyzed in triplicate using a Shimadzu UFLCXR HPLC coupled with an AB SCIEX® API 4000 MS/MS operating in positive electrospray mode. A 50 mm x 2.1 mm ID x 5 µm Ultra Biphenyl column (cat.# 9109552) was chosen for analysis as it provides good chromatographic retention of both polar and nonpolar compounds, including the 7-amino metabolites and more nonpolar compounds such as diazepam. Additionally, the short column length allows for a fast analysis.
Precision and accuracy were assessed by comparing back-calculated benzodiazepine concentrations in the calibration solutions with the prepared concentrations. Back-calculated concentrations were determined using a 1/x weighted quadratic calibration curve for each compound.
Results and Discussion
The method developed here allows for fast analysis of a comprehensive list of benzodiazepines and their metabolites using a simple dilute-and-shoot methodology. In addition to the fast sample preparation, this gradient chromatographic method is complete in only 4.5 minutes, allowing for retention of the hydrophilic 7-amino metabolites, as well as timely elution of late eluters like diazepam. Although benzodiazepines are commonly analyzed isocratically, the use of a gradient is beneficial for dilute-and-shoot biological samples. The use of a gradient analysis that varies from low to high organic mobile phase composition ensures that salts, proteins, and fats are eluted from the column during each run. This can extend column lifetime and improve method reproducibility.
Benzodiazepines in Urine
A representative chromatogram of benzodiazepines in dilute-and-shoot urine, along with the chromatographic and MS conditions used for analysis, are shown in Figure 1. Linearity, detection limit, precision, and accuracy data, as well as the expected ion ratios, are presented in Table I.
The limits of detection (LODs) for benzodiazepines in urine ranged from 0.1 ng/mL to 5 ng/mL. The requirement for LOD was a signal-to-noise value greater than 3:1. All limits of quantification (LOQs) were designated as the next calibrator above the LOD, and these levels exhibited a greater than 10:1 signal-to-noise value. R-squared values for all compounds were greater than or equal to 0.9977, demonstrating acceptable linear response across the test range.
Precision was based on relative standard deviations for triplicate injections of each calibrator. The precision range shown in Table I represents the low and high precision values across the calibration range for each analyte. Accuracy was determined using back-calculated values for triplicate injections of the calibrators. The accuracy range shown in Table I represents the low and high accuracy values across the calibration range for each analyte. Ion ratios are average ratios for each MRM over the calibration range.
Note that several compounds (7-aminoclonazepam, clonazepam, alprazolam, diazepam, lorazepam, temazepam, and nordiazepam) were not quantitated in the urine samples. However, data collected during method development and specificity studies indicate that this chromatographic method is suitable for urine analysis with the full list of benzodiazepines included in this application note.
Figure 1: Benzodiazepines in hydrolyzed urine.
Table I: Analytical results for benzodiazepines in hydrolyzed urine.
Benzodiazepines in Whole Blood
This method allows the determination of benzodiazepines in biological matrices from low levels to above therapeutic levels with a fast analysis time of just 4.5 minutes. The data shown here are for samples with a 20-fold dilution factor, if lower LOQs are desired, additional extraction and/or concentration steps may be employed using the same chromatographic method.