Jun.29,2006  6  US 2006/0141632 Al  minutes at room temperature prior to dilution of the resulting  derivatized analyte and mass spectral analysis. The concen› tration of the acidic moiety reagent is decreased by a factor  of as much as 100 when derivatizing smaller quantities.  is diluted into 20 µL of 0.05 M trimethylamine. The  S-acetylmercaptosuccinic anhydride solution (5  µL) is  added and the reaction mixture is vortexed for 30 seconds.  The reaction proceeds for about two minutes at room  temperature and is then oxidized with 10 µL of formic acid  (88%):H$_{2}$ 0$_{2 }$ (30%) prepared at a ratio of 19:1 (v:v). Oxi› dation proceeds for 16 hours at room temperature, and the  sample is dried prior to dilution and mass spectral analysis.  The concentration of the acidic moiety reagent is decreased  by a factor of as much as 100 when derivatizing smaller  quantities.  EXAMPLE 4  EXAMPLE 2  EXAMPLE 5  EXAMPLE 3  [0059]  ASHLGLAR (1  nmol, commercially available  from Sigma Chemical Co., St. Louis Mo.) (SEQ ID NO: 1)  is mixed with 2 µL of 0.02 M sulfoacetic acid, which is  formed by mixing 2 µL  of neat chlorosulfonylacetyl chloride  (commercially available from Aldrich Chemical Co., Mil› waukee, Wis.) with 500 µL of water. The mixture is dried  and then reconstituted in 20 µL oftetrahydrofuran:diisopro› pylethyl amine (4:1 v:v). 0.1 M chlorosulfonylacetyl chlo› ride (2 µL, commercially available from Aldrich Chemical  Co., Milwaukee, Wis.) in dry tetrahydrofuran is added and  the mixture is vortexed for 30 seconds. The derivatization  reaction proceeds for approximately two minutes at ambient  temperature. The derivatized analyte is dried, reconstituted  in 20 µL water and further diluted prior to mass spectral  analysis. Chlorosulfonylacetyl chloride is also a useful  reagent for derivatization of 2D gel isolates, but a modified  synthetic procedure provides more consistent product yields.  The modified procedure is discussed in Example 14.  [0062]  To ASHLGLAR (1 nmol, commercially available  from Sigma Chemical Co., St. Louis, Mo.) (SEQ ID NO: 1)  in 0.1 M trimethylamine (20 µL) is added 2-iminothiolane  (Traut’s reagent, commercially available from Aldrich  Chemical Co., Milwaukee, Wis.) (3 µL, 0.1 Min deionized  water). The reaction proceeds for 5 minutes at room tem› perature. The product is oxidized with 3 µL of formic acid  (88%):H$_{2}$ 0$_{2 }$ (30%) prepared at a ratio of 19:1 (v:v). Oxi› dation proceeds for 5 minutes at room temperature, and the  derivatized analyte is dried prior to mass spectral analysis.  [0058]  [0061]  [0063]  [0060]  [0064]  The polypeptide CDPGYIGSR (commercially  available from Sigma Chemical Co., St. Louis, Mo.) (SEQ  ID NO: 2) is oxidized by mixing 1 to 5 nM of polypeptide  (in 5-20 µL water) with 10 µL of formic acid (88%):H$_{2}$ 0$_{2 }$ (30%) prepared at a ratio of 19:1 (v:v). Oxidation proceeds  for 30 minutes at room temperature, and the derivatized  analyte is dried prior to mass spectral analysis.  S-acetylmercaptosuccinic anhydride ( commercially avail› able from Aldrich Chemical Co., Milwaukee, Wis.) is pre› pared at a concentration of 0.1 M in  dry  tetrahydrofuran  prior to use. ASHLGLAR (1 nmol, commercially available  from Sigma Chemical Co., St. Louis Mo.) (SEQ ID NO: 1)  0  0  110  o=s  /  N-ASHLGLAR  HO  I  H  o  NH  o,,_  Ii  II  --.::: s  ~  I  N-ASHLGLAR  OH  I  H  0  ~~o  HO-S  0  HO,  ~  Jl  y  "-../  ’,-ASHLGLAR  0  H  0  H2N0  )  r-DPGYIGSR  HS  0  H2N/l  N-DPGYIGSR  HO  I  \  H  s  o~~  0 