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. Author manuscript; available in PMC: 2013 Sep 24.

Published in final edited form as: Anal Chem. 2008 Feb 27;80(7):2564–2573. doi: 10.1021/ac702380w

Table 4.

Significant loadings from PCA for both positive ion and negative ion ToF-SIMS data from pure NTA and mixed NTA/OEG monolayers.

PC 1 (60%) positive ion ToF-SIMS data
Positively loaded peaks	15: CH₃⁺ (a); 19: H₃O⁺ (b); 28: C₂H₄⁺ (d);
	29: CHO⁺ (e); 31: CH₃O⁺ (h); 42: C₃H₆⁺ (k);
	43: C₂H₃O⁺ (l); 45: C₂H₅O⁺ (o);
	59: C₃H₇O⁺ (r); 73: C₃H₅O₂⁺ (t);
	87: C₄H₇O₂⁺ (u); 89: C₄H₉O₂⁺ (v);
	133: Cs (w); 225: AuC₂H₄⁺ (x).
Negatively loaded peaks	28: CH₂N⁺ (c); 29: C₂H₅⁺ (f); 30: CH₄N⁺ (g);
	39: C₃H₃⁺ (i); 42: C₂H₄N⁺ (j);
	43: C₂H₅N⁺ (m); 44: C₂H₆N⁺ (n);
	55: C₃H₃O⁺ (p); 57: C₄H₉⁺ (q);
	73: C₄H₁₁N⁺ (s).

PC 1 (70%) negative ion ToF-SIMS data

Positively loaded peaks	13: CH⁻ (a); 17: OH⁻ (c); 25: C₂H⁻ (d);
	33: SH⁻ (f); 41: C₂HO⁻ (h); 43: C₂H₃O⁻ (j);
	59: C₂H₃O₂⁻ (l); 61: C₂H₅O₂⁻ (m); 127: I⁻ (p);
	197: Au⁻ (q); 199: AuH₂⁻ (r)
Negatively loaded peaks	16: O⁻ (b); 26: CN⁻ (e); 35: Cl⁻ (g);
	42: CNO⁻ (i); 45: CHO₂⁻ (k); 80: SO₃⁻ (n);
	97: HSO₄⁻ (O); 230: AuSH⁻ (s)