Tsq quantum ultra

Targeted, quantitative analysis was conducted using a Thermo Scientific TSQ Quantum Ultra triple-quadrupole mass spectrometer with a Waters Acquity UPLC separation system and two analytical columns: an Acquity UPLC BEH (Ethylene Bridged Hybrid) Shield RP18 (2.1 mm × 150 mm, 1.7 μm) and an Acquity UPLC BEH C18 (2.1 mm × 100 mm, 1.7 μm). Extraction and quantitation has been previously described (McEachran et al. 2016 (link), 2017a (link)). Two separation and instrument methods, for positive and negative electrospray ionization (ESI), were utilized to maximize identification and quantification capabilities. The separation method used for positive mode ESI data collection utilized water and methanol with 0.05% acetic acid as mobile phases while for negative mode ESI, the mobile phases were water and methanol (McEachran et al. 2016 (link)). Final calculated concentrations (ng/L) and stream discharge measurements were used to calculate the mass load of total targeted CECs downstream of each system using Eq. 1:
$$\text{Mass}\hspace{0.17em}\text{load}\hspace{0.17em}(\text{mg}/{\text{day}}^{-1}\text{) = }\sum \text{CEC}\ast \text{Q}\ast 1/{10}^6$$
where ∑CEC refers to the summed concentration of targeted CECs in downstream samples (in ng/L) and Q is stream discharge at the time of sample collection (in liters/day).

Serine, homoserine, lanthionine and cystathionine – all amino acids produced concurrently with and proxies for
hydrogen sulfide – were measured by LC-MS, similar to our amino acid plus metabolites panel as referenced
[49 (link)]. Tissue homogenate samples were spiked with internal standards
(10 μl of serine, homserine, lanthionine, and cystathionine each at a concentration of 2 μg/ml), then
deproteinized with cold me-thanol followed by centrifugation at 10,000g for 15 min. The supernatant was
immediately derivatized with 6-aminoquinolyl-N-hydro-xysuccinimidyl carbamate according to Waters’ MassTrak kit. An
11-point calibration curve underwent similar derivatization procedure after the addition of internal standards. Both
derivatized standards and samples were analyzed on a triple quadrupole mass spectrometer (Thermo TSQ Quantum Ultra) coupled
with an Ultra Pressure Liquid Chromatography (Waters Acquity) system. Data acquisition was done using select ion monitor
(SRM). The following transitions (m/z) were monitored: 276.25 > 171.04 for serine, 290.2
> 171.04 for homoserine, 275.2 > 171.04 for lanthionine and 282.3 > 171.04 for cystathionine. Concentrations of the
analytes of each unknown were calculated against each respective calibration curve.