Quantitative Bioanalysis of Strontium in Human Serum By Inductively Coupled Plasma-Mass Spectrometry

Figures & data

Table 1.  Inductively coupled plasma-mass spectrometry instrument settings.

ICP-MS instrument	Agilent 7700x -ICP-MS
Analyte mass	Strontium (Sr) m/z: 88^†
IS mass	Yttrium (Y) m/z: 89
Plasma gas	Argon
Collision gas	Helium
Recommended parameters	Plasma gas (l/min)	15
	Helium flow (ml/min)	1.5
	Carrier gas (l/min)	0.45
	Make up gas (l/min)	0.69
	Plasma RF power (W)	1550
	Plasma RF matching (V)	1.70
	Sampling depth (mm)	7.5
	S/C temp (˚C)	2
	Extract 1 lens (V)	1.1
	Extract 2 lens (V)	-200
	Omega bias (V)	-75
	Omega lens (V)	9.8
	Cell entrance (V)	-36
	Cell exit (V)	-60
	Deflect (V)	14
	Plate bias (V)	-35
	Energy discrimination (V)	4.5
	OctP Bias (V)	-8.0
	Oct RF (V)	180
	Acquisition mode	Spectrum
	Peak pattern	1
	Replicates	3
	Sweeps/replicate	1000
	Integration time/mass (s)	0.7

† ⁸⁸Sr isotope was monitored because other isotopes (⁸⁴Sr, ⁸⁶ Sr, ⁸⁷Sr) are subject to significant isobaric interference from Krypton (⁸⁴Kr, ⁸⁶Kr present as impurity in Argon) and ⁸⁷Rb from serum [1].

Table 2.  Preparation of quality controls.

QC ID	Volumes used (μl)		Spiked strontium concentration in serum (ng/ml)	Expected strontium concentration in serum (ng/ml)
	10,000 ng/ml stock std (μl)	Matrix, serum (μl)
Low QC	0	1000	0	Observed
Mid QC	8	992	80	80 + low QC result
High QC	15	985	150	150+ low QC result

QC: Quality control.

Table 3.  Analyte response for specificity.

Source lot #	Endogenous analyte (^88Sr) concentration (ng/ml)	Expected analyte (^88Sr) concentration (endogenous+50 ng/ml spike) (ng/ml)	Measured analyte (^88Sr) concentration (ng/ml)	Accuracy (%)
BRH774402	25	75	74	99
BRH774403	22	72	70	98
BRH774404	51	101	100	99
BRH774405	32	82	81	99
BRH774406	22	72	72	101
BRH774407	44	94	90	96
			Mean %accuracy	98.6
			CV (%)	1.5

Table 4.  Accuracy and method precision results (n = 5).

Injection #	LQC (unspiked) (ng/ml)	MQC (80 ng/ml spike) (ng/ml)	HQC (150 ng/ml spike) (ng/ml)
1	40	117	187
2	40	116	182
3	40	118	183
4	43	117	182
5	47	118	185
Mean	42	117	184
%RSD	7.6	0.6	1.2
Mean accuracy (%)	N/A	96.1	95.7

Reference Serum Material: To further ensure the accuracy and validity of the method, freeze dried reference serum material “Seronorm^TM Trace Elements Serum L-2 (Lot#0903107)” was analyzed for strontium (⁸⁸Sr) during validation. One vial was reconstituted with 3 ml of Millipore water, dissolved completely by vortexing gently. A value of 35 ng/ml (average of duplicate injections) was obtained, which is within 4% of the certified value (∼36.3 ng/ml by inductively coupled plasma-sector field mass spectrometry).

Table 5.  Intraday and interday precision results.

Sample type	Intraday precision (%RSD) n = 6	Interday precision (%RSD) n = 9
		Day 1 (n = 3)	Day 2 (n = 3)	Day 3 (n = 3)	Total (n = 9)
LQC (unspiked)	1.5	2.0	1.1	0.5	2.9
MQC (80 ng/ml spike)	0.4	0.5	1.1	2.9	3.2
HQC (150 ng/ml spike)	0.4	0.5	0.9	0.6	2.3

Table 6.  Postpreparative stability results of samples.

Duration	Replicate no.	LQC (unspiked) (ng/ml)	MQC (80 ng/ml spike) (ng/ml)	HQC (150 ng/ml spike) (ng/ml)
Day 1	1	39	119	189
	1	39	118	189
	2	39	118	188
	2	38	118	188
	3	39	118	187
	3	39	118	187
Avg t = 0		38.7	118.2	187.7
Day 2	1	44	122	195
	1	45	122	195
	2	44	127	204
	2	44	127	204
	3	42	127	202
	3	42	127	202
Avg day 2		43.5	125.3	200.2
Day 2 (% of t = 0)		112.3	106.0	106.7
Day 3	1	41	128	197
	1	40	128	198
	2	44	121	196
	2	44	121	196
	3	42	122	199
	3	42	123	198
Avg Day 3		42.0	123.8	197.2
Day 3 (% of t = 0)		108.5	104.7	105.1

Table 7.  Postpreparative stability results of standards.

Duration	Injection no.	25 ng/ml std (ng/ml)	100 ng/ml std (ng/ml)	200 ng/ml std (ng/ml)
Day 1 (t = 0)		26	100	200
Day 2	1	29	106	212
	2	29	106	212
Avg day 2		29.0	105.9	211.9
Day 2 (% of t = 0)		110	105.9	106.0
Day 3	1	26	104	209
	2	26	104	208
Avg Day 3		26.3	104.2	208.4
Day 3 (% of t = 0)		99.8	104.2	104.3

Table 8.  Prepreparative stability results.

Duration	Temperature	Replicate no.	LQC (unspiked) (ng/ml)	MQC (80 ng/ml spike) (ng/ml)	HQC (150 ng/ml spike) (ng/ml)
Day 1	N/A	1	39	117	186
	N/A	2	37	118	188
	N/A	3	38	118	188
Avg day 1			38.2	117.8	187.4
Day 2	Ambient	1	41	128	201
	Ambient	2	41	127	200
	Ambient	3	41	129	200
Avg day 2			41.2	127.8	199.9
Day 2 (% of t = 0)			107.9	108.4	106.7
1 week	≤-20°C	1	39	121	195
	≤-20°C	2	39	123	198
	≤-20°C	3	40	122	199
Avg 1 week (ng/ml)			39.1	121.7	197.3
1 week (% of t = 0)			102.4	103.3	105.3
2 months	≤-20°C	1	42	129	207
	≤-20°C	2	43	130	207
	≤-20°C	3	43	132	207
Avg 2 months (ng/ml)			42.7	130.6	206.8
2 months (% of t = 0)			111.6	110.9	110.3

Table 9.  Endogenous strontium levels observed in healthy human population.

Subject	Age (years)	Gender	Race	Concentration (ng/ml)
1	22	Female	Not Hispanic or Latino White	31
2	23	Male	Not Hispanic or Latino White	19
3	22	Female	Hispanic or Latino White	35
4	40	Male	Not Hispanic or Latino White	47
5	27	Male	Not Hispanic or Latino White	27
6	53	Female	Not Hispanic or Latino White	31
7	27	Male	Not Hispanic or Latino White	32
8	25	Male	Not Hispanic or Latino White	38
9	67	Male	Not Hispanic or Latino White	96
10	49	Female	Not Hispanic or Latino White	24
11	32	Female	Hispanic or Latino White	28
12	54	Male	Not Hispanic or Latino Black or African American	42
13	30	Female	Not Hispanic or Latino Multiple White and Black	31
14	27	Male	Not Hispanic or Latino White	36
15	30	Female	Not Hispanic or Latino White	41
16	23	Female	Not Hispanic or Latino White	24
17	24	Male	Not Hispanic or Latino White	24
18	38	Female	Not Hispanic or Latino White	28
19	28	Male	Hispanic	25
20	36	Male	Black	22
21	50	Male	Black	51
22	49	Female	Hispanic	32
23	21	Female	Hispanic	22
24	26	Female	Caucasian	44

Vandecasteele C , VanhoeH, DamsR, VanballenbergheL, WittoekA, VersieckJ. Determination of strontium in human serum by inductively coupled plasma mass spectrometry and neutron activation analysis: a comparison. Talanta37(8), 819–823 (1990).

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