Table 6 FIA-MS and HPLC-MS characterization of PPD oxidation products

p-Benzoquinone diimine (BQDI)

Waters Atlantis ACN/ammonium formate pH 7.5

107.06

80 [M-HNC + H]⁺53 [M-2HNC + H]⁺ ≙ [C₄H₄ + H⁺]

HPLC-MS/MS

[49]

Fisher Scientific PepMAP Acclaim C₁₈ (75 μm × 15 cm) ACN/0.05 % TFA

107.06

HPLC-MS/MS

[3]

FIA/NH₄Ac (30:70)

107.06

EC-ESI-TOF-MS

[25]

SBQDIRC

FIA ACN/NH₄Ac (30:70)

108.07 [M]⁺

EC-ESI-TOF-MS

[25]

PPD

Agilent Zorbax SB-C₁₈ (4.6 × 250 mm) methanol/NH₄Ac pH 6.9

109.07

HPLC-MS/MS

[3]

Agilent Zorbax SB-C₁₈ (4.6 × 200 mm) methanol/NH₄Ac pH 6.9

109.07

HPLC-MS

[2]

FIA ACN/NH₄Ac (30:70)

109.07

EC-ESI-TOF-MS

[25]

direct injection

109.07

92.12 [M-NH₃ + H]⁺

MALDI-MS-MS

[78]

Unknown

Waters Xterra MS C₁₈ (4.6 × 150 mm, 5 μm) methanol/NH₄Ac, pH 7.2

137

HPLC-ESI-MS/MS

[8]

Agilent Zorbax SB-C₁₈ (4.6 × 200 mm) methanol/NH₄Ac pH 6.9

137

HPLC-MS

[2]

4-Aminophenyl formamide

Waters X-Bridge Phenyl (2.1 × 150 mm, 3.5 μm) methanol/NH₄Ac, pH 8

137.07

HPLC-ESI-MS

[56]

Dimeric oxidation products

Waters Atlantis ACN/ammonium formate pH 7.5

198

HPLC-MS/MS

[49]

2-(1,4-Benzoquinone diimine)-1,4-benzoquinone diimine

FIA ACN/NH₄Ac (30:70)

211.09

EC-ESI-TOF-MS

[25]

2-(1′,4′-Benzoquinone diimine)-4-aminoaniline

FIA ACN/NH₄Ac (30:70)

213.11

198.10 [M-NH + H]⁺183.09 [M-2NH + H]⁺

EC-ESI-TOF-MS

[25]

Bandrowski’s Base

Waters Atlantis ACN/ammonium formate pH 7.5

319.17

HPLC-MS/MS

[49]

Zorbax SB-C₁₈ (4.6 × 200 mm) methanol/NH₄ Ac pH 6.9

319.17

HPLC-MS

[2]

Zorbax SB-C₁₈ (4.6 × 250 mm) methanol/NH₄Ac pH 6.9

319.17

HPLC-MS/MS

[3]

FIA ACN/NH₄Ac (30:70)

319.17

302.14 [M-NH₃ + H]⁺

EC-ESI-TOF-MS

[25]

160.09 [M + 2H]²⁺

Trimeric compounds

Waters Atlantis ACN/ammonium formate pH 7.5

319

HPLC-MS/MS

[49]

Tetramer (−NH)

FIA ACN/NH₄Ac (30:70)

408.19

EC-ESI-TOF-MS

[25]

Tetramer (+O, −NH)

FIA ACN/NH₄Ac (30:70)

424.18

EC-ESI-TOF-MS

[25]

Pentamer

FIA ACN/NH₄Ac (30:70)

529.25

512.23 [M-NH₃ + H]⁺

EC-ESI-TOF-MS

[25]

265.13 [M + 2H]²⁺