Introduction Vitamin D measurement has become an important component in clinical assays largely because deficiency is associated with a number of disorders such as rickets, osteomalacia and osteoporosis. When serum concentration falls below 20 ng/mL osteoporosis can result, with normal levels ranging from 20-50 ng/mL. Developments in high pressure fast chromatography LC-MS/MS have now enabled on-line sample preparation methods and analysis times in less than 3 minutes. In these experiments tandem mass spectrometry was used to quantify 25-OH Vitamin D2 / D3 using a kit containing standard compounds and pre-optimised method parameters.

Materials and methods The LCMS-8050 triple quadrupole mass spectrometer was coupled to a Nexera X2 UHPLC system. This was equipped with the switching valve FCV-32AH and configured for sample loading onto the column (pump SPE) and isocratic compound elution (pump MP). Compounds were measured using a commercially available test kit ClinMass® LC-MS/MS Complete Kit for 25-OH-Vitamin D2 / D3, MS7000 (RECIPE Chemicals + Instruments GmbH, Dessauerstraße 3, 80992 München, Germany). Calibrators, control samples, analytical column and mobile phase solvents were provided by the kit. Sample preparation involved taking 50 µL of sample, adding to it 150 µL of precipitant solution (containing internal standard). Following incubation and centrifugation, 10 µL of supernatant was injected for analysis. The LC-MS instrument was equipped with an atmos-pheric pressure chemical ionization source (APCI).

Analytical conditions

UHPLC: Nexera X2 UHPLC Column temperature: 40°C Injection volume: 10 µL Mass spectrometer: LCMS-8050 Source conditions: Nebulizer Gas: 1.5 L/min Interface temperature: 375 °C Desolvation Line: 225 °C Heat Block temperature: 250 °C Drying Gas: Off Interface voltage: 4.5 kV Dwell time: 25 msec Pause time: 3 msec Ionization: APCI, positive mode Scan Type: MRM

Fig. 1 The FCV-32AH six port valve was configured to switch between sample loading (pump SPE) and isocratic sample elution (pump MP). Starting conditions: Pump SPE: 0.1 mL/min Pump MP: 0.5 mL/min FCV: position 1

Time (min) Pump / FCV Action Setting

0.00 FCV position 1 loading 0.00 Pump SPE flow rate 0.1 mL/min 0.00 Pump MP flow rate 0.5 mL/min 0.01 Pump SPE flow rate 5 mL/min 0.75 FCV position 0 elution 0.75 Pump SPE flow rate 5 mL/min 0.85 Pump SPE flow rate 0.1 mL/min 2.15 Pump SPE flow rate 0.1 mL/min 2.20 FCV position 1 conditioning 2.20 Pump SPE position 1 2 mL/min 2.85 Pump SPE flow rate 2 mL/min 2.90 Pump SPE flow rate 0.1 mL/min 3.00 Pump SPE flow rate 0. 1 mL/min 3.00 Pump MP flow rate 0.5 mL/min

Table 1 LC parameters were chosen for rapid compound elution and fast analysis time.

Fig. 2 LC time program during sample loading and elution.

LCMS Analysis of 25-OH Vitamin D2 / D3 in Plasma and Serum by LCMS-8050 using RECIPE ClinMass® LC-MS/MS Complete Kit MS7000 No. SCA_210_010

Dr. Johannes Engl (RECIPE Chemicals + Instruments GmbH), Anja Grüning (Shimadzu Europa GmbH)

Fig. 3 LC-MS separation of 25-OH Vitamin D2 / D3 and deuterated standard in less than three minutes by isocratic chromatography.

Compound Formula MRM1 MRM2 RT

Vitamin D3 T C27H44O 383>257 383>211 2.80

Vitamin D2 T C28H44O 395>209 395>269 2.84

d6-Vitamin D3 I C27H38D6O 389>263 389>211 2.80

Table 2 25-OH-Vit D optimized MRM transitions, retention times (RT). T/I = target or internal standard.

Fig. 4 Calibration curves for 25-OH Vitamin D2 and 25-OH Vitamin D3.

25-OH-Vitamin D2 Control Level I

(16.3 µg/L)

Control Level II

(36.6 µg/L)

25-OH-Vitamin D3

Control Level I

(20.5 µg/L)

Control Level II

(44.3 µg/L)

Conc. Conc.

Conc. Conc.

Control 1 16.631 40.649

Control 1 21.553 48.244

Control 2 16.259 39.991

Control 2 22.094 48.852

Control 3 16.437 39.770

Control 3 20.529 45.402

Control 4 17.802 39.087

Control 4 20.752 45.208

Control 5 17.159 41.588

Control 5 21.786 49.444

Control 6 18.246 41.662

Control 6 21.559 46.223

Control 7 16.450 39.186

Control 7 20.902 47.329

Control 8 16.709 36.783

Control 8 20.876 43.416

Mean 16.962 39.840

Mean 21.256 46.765

SD 0.717 1.576

SD 0.563 2.064

%RSD 4.23 3.96

%RSD 2.65 4.41

Table 3 Reproducibility for 25-OH-Vitamin D2 Table 3 Reproducibility for 25-OH-Vitamin D3

0.0 5.0 10.0 15.0 20.0 25.0 30.0 35.0 40.0 45.0 50.0 55.0 Conc. Ratio0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9Area Ratio

0 10 20 30 40 50 60 Conc. Ratio0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

Area Ratio

25-OH-Vitamin D2 r² = 0.9998232

25-OH-Vitamin D3 r² = 0.9988485

SCA_210_010

Results The rapid elution of vitamin D3 and D2 by isocratic chromatography produced excellent peak shape and accuracy with elution in less than three minutes (Fig. 3). The calibration curve determined in duplicate showed good linearity over a clinically relevant range of 3.94-63.6 µg/L for 25-OH-Vitamin D2 and 9.61-73.4 µg/L for 25-OH-Vitamin D3 (Fig. 4) Two control samples at high and low concentration were analyzed in eightfold to measure analytical reproducibility. The percentage relative standard deviation was typically lower than 5% from these measurements.

Conclusion The application of the clinical ClinMass® Complete Kit, for 25-OH-Vitamin D2/D3 in Plasma and Serum proved easy to implement and showed good sensitivity and linearity in a clinically relevant concentration range.

SCA_210_010