added dataset dataset_81

raw_data/draft_52580/draft_52580_gradient.tsv

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+t [min]	flow rate [ml/min]	A [%]	B [%]
+0	0.28	99.5	0.5
+4	0.28	30	70
+4.5	0.28	2	98
+5.4	0.28	2	98

raw_data/draft_52580/draft_52580_info.tsv

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+id	url	source	comment	authors	name	missing information	mail
+draft_52580	10.1038/s41586-021-03707-9			Shuo Han, Will Van Treuren, Curt R. Fischer, Bryan D. Merrill, Brian C. DeFelice, Juan M. Sanchez, Steven K. Higginbottom, Leah Guthrie, Lalla A. Fall, Dylan Dodd, Michael A. Fischbach & Justin L. Sonnenburg	dataset_81	Submitted by Fangyuan Sun	

raw_data/draft_52580/draft_52580_metadata.yaml

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+column:
+  name: Waters ACQUITY UPLC BEH C18
+  id: 2.1
+  temperature: 40
+  flowrate: 0.35
+  usp.code: L1
+  length: 100
+  particle.size: '1.7'
+eluent:
+  A:
+    h2o:
+      value: 100
+      unit: '%'
+    meoh:
+      value: 0
+      unit: '%'
+    nh4oh:
+      value: 6.5
+      unit: mM
+  B:
+    h2o:
+      value: 0
+      unit: '%'
+    meoh:
+      value: 100
+      unit: '%'
+    nh4oh:
+      value: 6.5
+      unit: mM
+id: draft_52580