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TB-500

What identity means for this molecule in numbers, how we measure its purity, and whether that method is validated yet. CAS 885340-08-9 Quoted mainly by sellers; not yet checked against the CAS registry.

Identity by mass spectrometry

Identity by LC–MS means every charge state we record lands within 10 parts per million of where the formula says it must. That establishes the formula of the main component; the limits page says what it does not establish. The windows below are that criterion in daltons, at each m/z.

Molecular formula

C₃₈H₆₈N₁₀O₁₄

Monoisotopic mass

888.4916 Da, free peptide

Average mass

889.01 Da, free peptide

Expected charge states of TB-500 in the scan range, with the 10 ppm identity window at each and the spacing of its isotope peaks.
State	m/z	10 ppm, Da	10 ppm, mDa	Isotope spacing, m/z
[M+H]⁺	889.4989	±0.0089	±8.9	1.003
[M+2H]²⁺	445.2531	±0.0045	±4.5	0.501

Scan range 300–2200. The bold state is the one expected to be most abundant. We expect the envelope to centre on the smaller of M/1000 + 1 and the larger of the basic-site count and M/1000, M in daltons; here that is M/1000 + 1 = 1.9. It has 2 basic sites, and a peptide this size rarely carries more charges than that. Two states fall inside the range, and identity rests on both agreeing within 10 ppm.

The last column is the spacing between neighbouring isotope peaks of each ion: the mean step one heavy isotope adds to this composition, 1.0029 Da, divided by the charge. The higher the charge, the closer the peaks; at [M+2H]²⁺ they sit 0.501 m/z apart, one part in 890 of its m/z. Resolving power is m/z over the smallest separation an instrument shows, so the method’s floor of 10 000 at m/z 1000 shows peaks 0.1 m/z apart there, against 0.20 m/z between the isotope peaks of a 5+ ion at that m/z: that is why the 10 ppm criterion is applied only on an instrument of that resolving power or better, and why a unit-resolution instrument, which shows peaks about 1 m/z apart, cannot pick the monoisotopic peak out of any cluster past 1+.

Before you send. Two products are sold as TB-500: the acetylated fragment Ac-LKKTETQ (this row, 888.5 Da monoisotopic) and full-length thymosin β4 (43 residues, C₂₁₂H₃₅₀N₅₆O₇₈S, 4960.4863 Da monoisotopic, average 4963.44 Da, CAS 77591-33-4). Tell us which your label claims; a sample of the protein is identified against the protein’s formula, not this one, and since it is not a row of this table, ask before you ship it.

Expected envelope · computed The charge states a 888 Da peptide should present in ESI+, placed by arithmetic from the formula. Relative intensities are a model. Nothing here is a measurement; the measured spectrum appears on the report.

Method and validation status

Purity is area percent by RP-HPLC–UV 214 nm. Identity is LC–MS (ESI+). The matrix we accept is lyophilised powder.

Status

Validation: Not yet validated
Retention time: not yet measured on this analyte
Limit of quantitation: not yet measured
Reporting threshold: 0.05% area; no limit of quantitation is claimed yet, so a smaller peak may be present and not seen

Not yet validated means the method is written and has not been run on this analyte. The retention time and the limit of quantitation are listed once measured, with the date of the validation that produced them. The scope table shows the status of every analyte.

What the formula tells us to watch for

Deamidation (+0.984 Da) is sought on any sequence with asparagine or glutamine. The sequence has them; where it applies it is confirmed on the chromatogram as a closely eluting peak, before or after the parent, since at charge z the mass shift is 0.984/z m/z, which at 4+ and above overlaps the M+1 isotope.
Truncation products - the sequence short by one or more residues - fall at characteristic mass offsets and are looked for at their expected m/z where the sequence is on file; the certificate lists the impurity masses that were read and whether each was assigned.

Order a test of TB-500

Identity and purity together, $185, in 10 business days or the invoice is cancelled, or the payment refunded, and you still get the results. One sealed container as received.

Order a test How to send a sample

What you get back

A certificate with the chromatogram, every peak, the three injections, the measured spectrum against the windows above, what could not be resolved, a full signature, a hash and a QR that verifies without us. How to read one.